Nickel-Catalyzed Difunctionalization of Alkynyl Bromides with Thiosulfonates and N-Arylthio Succinimides: A Convenient Synthesis of 1,2-Thiosulfonylethenes and 1,1-Dithioethenes

Arram Haritha Kumari; Jangam Jagadesh Kumar; Gamidi Rama Krishna; Raju Jannapu Reddy

doi:10.1055/a-1482-2486

Synthesis, Table of Contents

Synthesis 2021; 53(16): 2850-2864
DOI: 10.1055/a-1482-2486

paper

Nickel-Catalyzed Difunctionalization of Alkynyl Bromides with Thiosulfonates and N-Arylthio Succinimides: A Convenient Synthesis of 1,2-Thiosulfonylethenes and 1,1-Dithioethenes

Arram Haritha Kumari

^aDepartment of Chemistry, University College of Science, Osmania University, Hyderabad 500 007, India URL: https://www.rjreddyresearchgroup.com/

,

Jangam Jagadesh Kumar

^aDepartment of Chemistry, University College of Science, Osmania University, Hyderabad 500 007, India URL: https://www.rjreddyresearchgroup.com/

,

Gamidi Rama Krishna

^bX-ray Crystallography, CSIR-National Chemical Laboratory, Pune 411 008, India

,

Raju Jannapu Reddy∗

^aDepartment of Chemistry, University College of Science, Osmania University, Hyderabad 500 007, India URL: https://www.rjreddyresearchgroup.com/

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Abstract

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Key words

alkynyl bromides - atom transfer radical addition (ATRA) - thiosulfonylation - thiosulfonates - vinyl thiosulfones

Stereoselective vicinal difunctionalization of carbon–carbon multiple bonds represents an attractive strategy for the rapid construction of molecular complexity from simple starting materials.[1] Of the many catalytic difunctionalizations, Ni-catalyzed difunctionalization has emerged to introduce two functional groups across an unsaturated carbon–carbon bond in a one-step operation.[2] Atom transfer radical addition (ATRA)[3] has been recognized as a powerful approach for installing two functional groups on the vicinal carbons of a π-system, a process generally known as Kharasch addition.[4] Despite these achievements, installing diverse functional groups on alkynes in a rapid, flexible and efficient manner in order to generate highly substituted alkenes remains a challenging task.

Organosulfur compounds[5] containing sulfone and thioether moieties are attractive compounds in organic synthesis[6] and the pharmaceutical industry.[7] Recently, thiosulfonates (RS–SO₂R¹)[8] [9] [10] have been utilized to install two distinct C–S bonds (sulfenyl and sulfonyl) in alkenes and alkynes through atom transfer thiosulfonylation.[9] [10] Compared to the thiosulfonylation of alkenes,[9] investigations of alkynes and their equivalents are considerably limited, probably due to stereo- and regioselective concerns.[10] In this context, Xu and co-workers developed the first example of the atom transfer thiosulfonylation of alkynes using PhSO₂SR and a combination of an Au/Ru-catalytic system under visible-light irradiation (Scheme [1, a]).[10a] Subsequently, our group employed the Cs₂CO₃-mediated vicinal thiosulfonylation of 1,1-dibromo-1-alkenes with thiosulfonates, leading to a reversal of regioselectivity in the thiosulfonylated products (Scheme [1, b]).[10c] Very recently, the Jia group successfully disclosed the visible-light-driven atom transfer radical addition of aryl alkynes with thiosulfonates under the catalytic influence of Eosin Y to furnish the desired vinyl thiosulfones with the same regioselectivity (Scheme [1, c]).[10d] Regardless of these innovative approaches, the use of expensive reagents and prolonged reaction times were disadvantages in their scale-up synthesis. Therefore, a general, mild and robust vicinal thiosulfonylation using a cheap and readily available catalyst is still desirable. Accordingly, we envisioned that alkynyl bromides would be alternative starting materials for the regioselective construction of two different C–S bonds on the vicinal carbons in a single operation (Scheme [1, d]).

Scheme 1 Representative vicinal thiosulfonylations through atom transfer radical addition (ATRA)

Generally, alkynyl bromides are versatile building blocks, and their chemistry has been widely explored in organic synthesis.[11] As a result, we were interested in investigating the atom transfer thiosulfonylation of alkynyl bromides with thiosulfonates in order to furnish vinyl thiosulfone products whilst delivering the anticipated regioselectivity. In continuation of our interest in organosulfur chemistry[12] and thiosulfonates,[10c] [12c] ^, [12`] [f] [g] [h] [i] we report herein an efficient Ni-catalyzed intermolecular vicinal thiosulfonylation of alkynyl bromides with thiosulfonates under mild conditions. A variety of substrates was explored allowing the synthesis of a wide range of (E)-1,2-thiosulfonylethenes. In addition, the methodology was further applied to the synthesis of 1,1-dithioalkenes in high yields. From a synthetic point of view, the present protocol has also been achieved on gram scale.

Our investigations began with 4-(bromoethynyl)-1,2-dimethoxybenzene (1a) and S-phenyl benzenesulfonothioate (2a) as model substrates (Table [1]). An extensive survey of the reaction conditions was undertaken by investigating different parameters, including the catalyst, solvent, temperature, concentration, etc. (see Table S1 in the Supporting Information). An initial experiment was performed at 90 °C for the thiosulfonylation of 1a with 2a in the presence of Cs₂CO₃, which gave the desired product 3aa in 39% yield (entry 1). Next, the copper-catalyzed thiosulfonylation afforded a slightly improved yield of product 3aa (entries 2 and 3). To our surprise, the NiCl₂·6H₂O-catalyzed vicinal thiosulfonylation proceeded smoothly with 3 equivalents of Cs₂CO₃ in DMF at 90 °C (entries 4–6). The use of 5 mol% of NiCl₂·6H₂O afforded the thiosulfonylated product 3aa in 81% yield with excellent stereoselectivity (entry 6). Inspired by these results, we screened different Ni catalysts, however, none of these proved beneficial in improving the yield of 3aa (entries 7–10). Lowering the amount of Cs₂CO₃, elevating the temperature or performing the reaction under aerobic conditions were unsuccessful in giving better outcomes (entries 11–13). Next, our attention turned to developing a visible-light-induced thiosulfonylation under the influence of an organic dye as the photocatalyst. Gratifyingly, the standard reaction performed with Rose Bengal (RB) (2 mol%) under irradiation with blue LEDs for 16 hours led to the desired product 3aa, albeit in only 61% yield (entry 14). Disappointingly, our subsequent efforts using Rose Bengal, Eosin Y and Eosin B gave 3aa in lower yields compared with the conventional procedure (see Table S2 in the Supporting Information). No reaction was observed in the absence of Cs₂CO₃, thus indicating that the role of Cs₂CO₃ was crucial for this transformation (entry 15).

Table 1 Optimization of the Vicinal Thiosulfonylation Using 1-Bromoalkyne 1a with S-Phenyl Thiosulfonate 2a ^a

Entry	Catalyst (mol%)	Cs₂CO₃	Time	Yield of 3aa ^b	E/Z ^c
1	none	4 equiv	6 h	39%	19:1
2	CuClO₄·6H₂O (20 mol%)	3 equiv	6 h	59%	25:1
3	CuSO₄·5H₂O (20 mol%)	3 equiv	6 h	53%	25:1
4	NiCl₂·6H₂O (20 mol%)	3 equiv	4 h	72%	25:1
5	NiCl₂·6H₂O (10 mol%)	3 equiv	4 h	75%	30:1
6	NiCl₂·6H₂O (5 mol%)	3 equiv	3 h	81%	30:1
7	NiCl₂(PPh₃)₂ (5 mol%)	3 equiv	3 h	71%	30:1
8	Ni(dppp)Cl₂ (5 mol%)	3 equiv	3 h	58%	25:1
9	NiBr₂·6H₂O (5 mol%)	3 equiv	3 h	69%	25:1
10	NiClO₄·6H₂O (5 mol%)	3 equiv	3 h	72%	30:1
11	NiCl₂·6H₂O (5 mol%)	2 equiv	5 h	59%	25:1
12^d	NiCl₂·6H₂O (5 mol%)	3 equiv	5 h	67%	25:1
13^e	NiCl₂·6H₂O (5 mol%)	3 equiv	5 h	55%	20:1
14^f	NiCl₂·6H₂O (5 mol%)	3 equiv	16 h	61%	Nd
15	NiCl₂·6H₂O (5 mol%)	none	24 h	trace	–

^a Unless otherwise specified, all reactions were performed on a 0.2 mmol scale of 1a (1.0 equiv), 2a (1.5 equiv), catalyst (5–20 mol%) and Cs₂CO₃ (2 to 4 equiv) in anhydrous DMF (1 mL) under N₂ at 90 °C.

^b Isolated yield.

^c E/Z mixture based on ¹H NMR analysis; nd = not determined.

^d Reaction at 110 °C.

^e Reaction under an O₂ atmosphere.

^f Irradiation with blue LEDs in the presence of Rose Bengal (2 mol%) at room temperature.

With optimized reaction conditions in hand (see Table [1], entry 6), we next explored the generality of the vicinal thiosulfonylation (Scheme [2]). A series of 1-bromoalkynes (1a–p) employed for 1,2-thiosulfonylation with S-phenyl benzenesulfonothioate (2a) to deliver the corresponding (E)-1,2-thiosulfonylethenes 3(a–o)a in 37–79% yields with excellent stereoselectivities. Notably, the nature and position of the substituent(s) on the benzene ring had little influence on the outcome of the transformation (compare 3ba, 3da and 3ha). The reason behind the observed low selectivity (E/Z = 10:1) of product 3ba was not clear; however, it can be assumed that the strong electron-donating groups (OMe) on the benzene ring might lead to a mixture of isomers. Both 1- and 2-naphthyl-derived 1-bromoalkynes 1i and 1j smoothly afforded the desired products 3ia and 3ja in 69% and 67% yields, respectively. Interestingly, various heteroaryl bearing alkynyl bromides 1k–n were well tolerated, leading to the expected products 3ka–na in good yields and stereoselectivities. The structure and stereochemistry of 3na were further established by single-crystal X-ray analysis (see Figure [1] and the Supporting Information).[13] Moreover, the alkyl-substituted 1-bromoalkynes 1o and 1p were also reacted under the same conditions. Remarkably, the corresponding vinyl thiosulfone 3oa was smoothly obtained in 61% yield, whereas the product 3pa was only formed in a trace amount.

Scheme 2 Substrate scope for vicinal thiosulfonylation using 1a–p and 2a. All reactions were performed on a 0.5 mmol scale of 1a–p (1.0 equiv), 2a (1.5 equiv), NiCl₂·6H₂O (5 mol%) and Cs₂CO₃ (3.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 3 h. Isolated yields are given. E/Z mixture ratios are based on ¹H NMR analysis.

Figure 1 ORTEP representation of compound 3na (CCDC 2061705)

Encouraged by these results, we sought to evaluate the scope of various thiosulfonates (2b–m) with (bromoethynyl)benzene (1e) (Scheme [3]). Different symmetrical and unsymmetrical thiosulfonates smoothly participated in the vicinal thiosulfonylation to deliver the anticipated (E)-1,2-thiosulfonylethenes in satisfactory yields. Symmetrical aryl and heteroaryl thiosulfonates 2b–f reacted with 1e with no adverse effect on the outcome. Disappointingly, the unsymmetrical thiosulfonates 2g–j significantly influenced the stereoselectivity, albeit thiosulfonylated products 3eg, 3eh, 3ei and 3ej were obtained in satisfactory yields. To our surprise, the 2-pyridyl-derived thiosulfonates 2k and 2l afforded the corresponding products 3ek and 3el in satisfactory yields, predominantly as the E-isomers. Unfortunately, S-benzyl thiosulfonate 2m was found to be unsuitable as a substrate for this transformation. Next, (iodoethynyl)benzene (1e′) was reacted with different thiosulfonates (2a,b,d) to generate the corresponding products 3e′(a,b,d) in modest yields. The less reactive (chloroethynyl)benzene (1e′′) reacted sluggishly with 2a to form the desired product.

Scheme 3 Substrate scope for vicinal thiosulfonylation. All reactions were performed on a 0.5 mmol scale of 1e, 1e′ or 1e′′ (1.0 equiv), 2a–m (1.5 equiv), NiCl₂·6H₂O (5 mol%) and Cs₂CO₃ (3.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 3 h. Isolated yields are given. E/Z mixture ratios are based on ¹H NMR analysis.

Moreover, the scope of the vicinal thiosulfonylation reaction could be extended to construct representative classes of thiosulfonylated products (Scheme [4]). Several aryl- and heteroaryl-derived alkynyl bromide substrates were readily reacted with 2b to form the corresponding products 3(a–c,i,j,k,m,n)b in reasonably good yields. Similarly, the heteroaryl-derived thiosulfonates 2f and 2k furnished thiosulfonylated products 3af, 3ak, 3kf and 3kl in acceptable yields. Additionally, the naphthyl-containing thiosulfonates 2e and 2n gave the corresponding α-heteroaryl-substituted vinyl sulfones 3ke, 3ne and 3nn in moderate yields. It is worth noting that these multifunctional vinyl (thio)sulfones are potentially valuable compounds in organic and medical chemistry.[14] Interestingly, the thiophene-based vinyl sulfones 3af and 3kf are promising structural scaffolds in advanced functional materials.[15]

Scheme 4 Substrate scope for vicinal thiosulfonylation. All reactions were performed a 0.5 mmol scale of 1 (1.0 equiv), 2 (1.5 equiv), NiCl₂·6H₂O (5 mol%) and Cs₂CO₃ (3.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 3 h. Isolated yields are given. E/Z mixture ratios are based on ¹H NMR analysis.

Moreover, the protocol was also extended to Se-phenyl benzeneselenosulfonate (2o) under the optimized conditions. As presented in Scheme [5], the reaction of 1e with 2o did not afford the anticipated product 3eo. Instead, the unexpected β-keto selenosulfone 4 was obtained in 49% yield. Further, the structure of 4 was ambiguously confirmed by single-crystal X-ray analysis (Figure [2] and the Supporting Information).[13]

Scheme 5 Synthesis of β-keto selenosulfone 4 using 1e and 2o

Figure 2 ORTEP representation of compound 4 (CCDC 2061706)

Next, the robustness of vicinal thiosulfonylation was further examined by using dihaloalkene substrates 5a–h, which were previously unexplored.[10c] Indeed, the Cs₂CO₃-mediated 1,2-thiosulfonylation afforded fruitful results compared to the present Ni-catalyzed standard conditions (Scheme [6]). Thus, N-Ts/N-Boc-indole-derived dibromoalkenes 5a and 5b were studied and were found to smoothly react with different thiosulfonates (2a,b,e,n) in the presence of Cs₂CO₃ (4 equiv) to deliver the expected thiosulfones 3(m,n)a,b,e,n in good yields. Disappointingly, N-Ms/N-Ns-indole-, 3-chloroquinoline- and imidazopyridine-derived dibromoolefins 5c–f were either degraded or reacted sluggishly under the same conditions (see the Supporting Information). Similarly, dichloroalkene 5g and difluoroalkene 5h were also challenging substrates for this protocol.

Scheme 6 Substrate scope for vicinal thiosulfonylation. All reactions were performed on a 0.5 mmol scale of 5 (1.0 equiv), 2 (1.5 equiv) and Cs₂CO₃ (4.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 4 h. Isolated yields are given. E/Z mixture ratios are based on ¹H NMR analysis. ^a Reaction using NiCl₂·6H₂O (5 mol%). Ms: methanesulfonyl; Ns: nosyl (4-O₂NC₆H₄SO₂).

To understand the generality of the vicinal difunctionalization, we turned our attention to more valuable substrates 6a–e in order to install diverse substituents on the products (Scheme [7]). In this direction, we performed the vicinal amidosulfonylation of 1a with N-phenylthio succinamide (6a) under the optimized conditions. Unfortunately, we did not obtain the expected amido-sulfonylated product; instead a 1,1-dithiolated-alkene was observed. Yang and co-workers[16] had previously developed the synthesis of 1,1-dithio-1-alkenes using 1,1-dibromoalkenes with thiols in the presence of DBU. It is worth mentioning that our protocol has the advantage of using bench-stable and odorless sulfenylating reagents 6a and 6b instead of thiols. Using 2.5 equivalents of 6a, the yield of 7aa (85%) significantly improved under similar conditions (Scheme [7]). With fine-tuned reaction conditions in hand, we probed the scope of 1-bromoalkynes 1a,e,g,j,k,l and N-arylthio succinimides 6a and 6b to provide the corresponding 1,1-dithioalkenes 7(a,e,g,k)a,b, 7ja and 7lb in 69–88% yields. However, the cyclopropyl-derived 1,1-dithio-1-alkene 7pb was detected in only a trace amount. This protocol was also applied to other sulfenylating agents (6c–e) under the same conditions but failed to give the desired products.

Scheme 7 Substrate scope for the 1,1-dithiolation of 1 with N-arylthio succinamides 6a and 6b. All reactions were performed on a 0.5 mmol scale of 1 (1.0 equiv), 6a,b (2.5 equiv), NiCl₂·6H₂O (5 mol%) and Cs₂CO₃ (3.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 2 h. Isolated yields are given.

Reactions were next carried out on gram scale under the optimized conditions to highlight the efficacy of the 1,2-thiosulfonylation process. As shown in Scheme [8], reactions of (bromoethynyl)benzene (1e) with S-aryl arylsulfonothioates 2a,b were performed on 5 mmol scale to produce 3ea in 68% (1.19 g) and 3eb in 57% (1.08 g) yields; thus the protocol proved to be scalable with only a minor deviation in the outcome. Developing a sequential one-pot operation offers attractive insights into a step-economic perspective, thereby avoiding the separation of intermediates.[17] Accordingly, a successive bromination with NBS followed by vicinal thiosulfonylation of phenylacetylene with 2a was performed on 10 mmol scale to give 3ea in 45% (1.58 g) yield.

Scheme 8 Gram-scale vicinal thiosulfonylation reactions

Scheme 9 Control experiments

Control experiments were performed on the 1,2-thiosulfonylation under the standard conditions to gain insights into the reaction mechanism (Scheme [9]). The reaction of 2a with phenylacetylene gave the desired product 3ea in <10% yield (Scheme [9, a]). In contrast, the reaction of 2a with 3-phenylpropiolic acid (8) formed alkynyl thioether 9,[18] whilst the use of TMS-derived phenylacetylene 10 afforded a mixture of products along with 9 (Schemes 9, b and c). Additionally, thioalkyne 9 failed to react with 2a under the same conditions (Scheme [9, d]). Moreover, the standard reaction was performed in the presence of radical scavengers. Using BHT (4 equiv), the desired product 3ea was formed in only 14% yield (Scheme [9, e]). Furthermore, the reaction was almost totally inhibited in the presence of TEMPO (4 equiv), with only a trace amount of 3ea being detected (Scheme [9, f]). Overall, these results indicate that the thiosulfonylation process possibly involves a radical pathway.

Based on the above results and literature precedent,[10] ^, [19] [20] [21] a plausible mechanism has been proposed for this transformation (Scheme [10]). The thermal homolytic cleavage of thiosulfonate 2a can generate a thiyl radical[19] and a sulfonyl radical species (Scheme [10, a]).[20] Firstly, Ni(II) is reduced to Ni(0), which can react with 1e to form the alkynyl-Ni species A.[2a] The sulfenyl radical would react with A to form transient alkenyl radical B,[10d] which can then react with the sulfonyl radical to give intermediate C. Alternately, the radical B can undergo oxidation with the sulfonyl radical to generate alkenyl cation D and a sulfonyl anion. Reaction with the sulfonyl anion subsequently produces intermediate C. Finally, hydrogen may be abstracted from DMF[21] to produce the desired product 3ea and the Ni catalyst is regenerated to continue the catalytic process. Additionally, the transition-state model E can explain the steric repulsion between the sulfone and the thioether, which may form the Z-isomer as a minor product. The mechanism for the formation of 1,1-dithioalkenes 7 is still not clear.[16] However, a tentative mechanism has been proposed in the Supporting Information based on experimental results.

Scheme 10 A plausible mechanism for the vicinal thiosulfonylation

In summary, we have successfully demonstrated the Ni-catalyzed vicinal thiosulfonylation of alkynyl bromides with thiosulfonates in the presence of Cs₂CO₃ under mild reaction conditions. The atom transfer radical addition (ATRA) protocol has been utilized to efficiently generate a series of (E)-1,2-thiosulfonylethenes in good to high yields and with high levels of stereoselectivity. Substantial variation of both the alkynyl bromides and thiosulfonates demonstrates the broad functional group tolerance and compatibility of the process. Indole-derived 1,1-bromoalkenes have also been employed as valuable substrates for the stereoselective synthesis of vinyl thiosulfones. In addition, the methodology has been further extended to the 1,1-dithiolation of alkynyl bromides with N-arylthio succinimides to furnish 1,1-dithio-1-alkenes in high yields. The protocol is also amenable to large-scale synthesis, which is quite challenging when using other thiosulfonylation methods. A step-economic, sequential one-pot bromination and thiosulfonylation approach has been achieved on gram scale, which offers an additional benefit to the described process. Finally, a plausible mechanism has been presented to rationalize the experimental outcome.

All reagents were purchased from Sigma-Aldrich, TCI, Alfa Aesar, SDFine, SRL, Spectrochem and AVRA chemicals, and were used without further purification unless otherwise stated. Solvents were dried over activated 4 Å molecular sieves for all reactions carried out under an inert atmosphere. The progress of reactions was monitored by thin-layer chromatography (TLC) using Silica gel 60 F254 plates. Visualization of samples was achieved by a combination of ultraviolet light (254 nm) and staining with potassium permanganate solution, iodine or p-anisaldehyde. Flash column chromatography was performed using SRL silica gel (100–200 mesh) as the stationary phase. Melting points were measured in open capillaries using a DBK digital melting point apparatus and are uncorrected. ¹H and ¹³C NMR spectra were recorded using a Bruker AVIII 400 spectrometer (¹H: 400 MHz; ¹³C: 101 MHz) at 300 K. Chemical shifts (δ) are given in ppm relative to TMS and the coupling constants (J) are quoted in Hz. For spectra recorded in CDCl₃, the signals at δ 7.26 (due to residual CHCl₃) and at δ 77.16 (the resonance of CDCl₃) were used as internal references. ¹H NMR spectral data are reported as follows: chemical shift (multiplicity, coupling constant, integration). The following abbreviations are used for multiplicities: s (singlet), d (doublet), t (triplet), q (quartet), dd (doublet of doublets), td (triplet of doublets), quin (quintet), sept (septet), m (multiplet). All NMR spectra were processed using MestReNova version 6.0.2(v). High-resolution mass spectrometry (HRMS) was performed using a Thermo scientific ExactiveTM Orbitrap mass spectrometer or Q STAR XL Hybrid MS/MS spectrometer by employing ESI-TOF techniques. Spectra were obtained using a lock-mass to adjust the calibrated mass scale.

XRD experiments were performed by measuring the X-ray intensity data on a Bruker SMART APEX III single-crystal X-ray CCD diffractometer using graphite-monochromated radiation (Mo-Kα = 0.71073) at low temperature (100 K). The X-ray generator was operated at 50 kV and 30 mA. A preliminary set of cell constants and an orientation matrix were calculated from a total of 36 frames. The optimized strategy used for data collection consisted of different sets of ϕ and ω scans with 0.5° steps ϕ/ω. Data were collected with a timeframe of 10 seconds for all the components by keeping the sample-to-detector distance fixed at 40 cm. All the data are corrected for Lorentzian, polarization and absorption effects using SAINT and SADABS (Bruker, 2016). SHELX-97 was used for structure solution and full-matrix least-squares refinement on F2 with anisotropic displacement parameters for non-H atoms. Hydrogen atoms associated with carbon atoms were fixed in geometrically constrained positions. The hydrogen atoms associated with oxygen and nitrogen atoms were included in the located positions. ORTEP diagrams were generated by using the X-Seed software package (version 2.0).

(E)-1,2-Thiosulfonylethenes; General Procedure 1 (GP1)

A heat-gun-dried Schlenk tube was charged with alkynyl bromide 1a–p (0.5 mmol, 1.0 equiv), thiosulfonate 2a–o (0.75 mmol, 1.5 equiv), NiCl₂·6H₂O (5.9 mg, 0.025 mmol, 0.05 equiv) and Cs₂CO₃ (1.5 mmol, 3.0 equiv) in DMF (2.5 mL). The reaction mixture was stirred at 90 °C for 3 h under N₂. The progress was monitored by TLC (until the reaction appeared to be complete or was not proceeding any further). The mixture was quenched by the addition of H₂O (10 mL) followed by extraction with EtOAc (3 × 10 mL). The combined organic layers were washed with brine (2 × 10 mL), dried over anhydrous Na₂SO₄, and the solvent was removed under reduced pressure. The resulting residue was subjected to flash chromatography (silica gel, 100–200 mesh, eluting with 8% to 10% EtOAc/PE) to afford the corresponding (E)-1,2-thiosulfonylethene.

(E)-[2-(3,4-Dimethoxyphenyl)-2-(phenylsulfonyl)vinyl](phenyl)sulfane (3aa)

Following GP1 using 4-(bromoethynyl)-1,2-dimethoxybenzene (1a) (120.5 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3aa as a colorless solid (162.9 mg, 79%, >30:1 mixture of E/Z isomers).

Mp 94–96 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.11 (s, 1 H), 7.64 (dd, J = 8.4, 1.2 Hz, 2 H), 7.53 (tt, J = 7.4, 1.2 Hz, 1 H), 7.50–7.47 (m, 2 H), 7.43–7.37 (m, 5 H), 6.81 (d, J = 8.2 Hz, 1 H), 6.77–6.73 (m, 2 H), 3.88 (s, 3 H), 3.78 (s, 3 H).

These data are consistent with literature values.[10c]

(E)-Phenyl[2-(phenylsulfonyl)-2-(3,4,5-trimethoxyphenyl)vinyl]sulfane (3ba)

Following GP1 using 5-(bromoethynyl)-1,2,3-trimethoxybenzene (1b) (135.5 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ba as a colorless solid (170.4 mg, 77%, >10:1 mixture of E/Z isomers).

Mp 142–144 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.11 (s, 1 H), 7.68 (d, J = 7.6 Hz, 2 H), 7.54 (t, J = 7.5 Hz, 1 H), 7.48 (d, J = 6.0 Hz, 2 H), 7.45–7.37 (m, 5 H), 6.38 (s, 2 H), 3.85 (s, 3 H), 3.72 (s, 6 H).

These data are consistent with literature values.[10c]

(E)-[2-(4-Methoxyphenyl)-2-(phenylsulfonyl)vinyl](phenyl)sulfane (3ca)

Following GP1 using 1-(bromoethynyl)-4-methoxybenzene (1c) (105.0 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ca as a colorless solid (132.0 mg, 69%, >30:1 mixture of E/Z isomers).

Mp 96–97 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.14 (s, 1 H), 7.65 (dd, J = 8.4, 1.2 Hz, 2 H), 7.53 (tt, J = 7.4, 1.2 Hz, 1 H), 7.49–7.46 (m, 2 H), 7.43–7.37 (m, 5 H), 7.24 (t, J = 7.9 Hz, 1 H), 6.92–6.88 (m, 1 H), 6.78–6.75 (m, 2 H), 3.74 (s, 3 H).

These data are consistent with literature values.[10c]

(E)-[2-(3-Methoxyphenyl)-2-(phenylsulfonyl)vinyl](phenyl)sulfane (3da)

Following GP1 using 1-(bromoethynyl)-3-methoxybenzene (1d) (105.5 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3da as a yellow viscous liquid (126.2 mg, 66%, >30:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 8.14 (s, 1 H), 7.66 (dd, J = 8.4, 1.2 Hz, 2 H), 7.53 (tt, J = 7.4, 1.2 Hz, 1 H), 7.49–7.46 (m, 2 H), 7.43–7.37 (m, 5 H), 7.22 (d, J = 8.0 Hz, 1 H), 6.92–6.89 (m, 1 H), 6.78–6.74 (m, 2 H), 3.73 (s, 3 H).

These data are consistent with literature values.[10c]

(E)-Phenyl[2-phenyl-2-(phenylsulfonyl)vinyl]sulfane (3ea)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 8% EtOAc/PE) yielded the title compound 3ea as a colorless solid (132.0 mg, 75%, >30:1 mixture of E/Z isomers).

Mp 91–93 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.15 (s, 1 H), 7.63 (dd, J = 8.3, 1.1 Hz, 2 H), 7.53 (t, J = 7.4 Hz, 1 H), 7.49–7.46 (m, 2 H), 7.42–7.33 (m, 8 H), 7.21 (dd, J = 7.9, 1.6 Hz, 2 H).

¹³C NMR (101 MHz, CDCl₃): δ = 144.2, 139.4, 136.1, 133.2, 132.9, 131.3 (2 C), 130.7, 130.3 (2 C), 129.7 (2 C), 129.6, 128.9, 128.8 (3 C), 128.3.

These data are consistent with literature values.[10c]

(E)-Phenyl[2-(phenylsulfonyl)-2-(p-tolyl)vinyl]sulfane (3fa)

Following GP1 using 1-(bromoethynyl)-4-methylbenzene (1f) (97.5 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3fa as a colorless solid (130.1 mg, 71%, >30:1 mixture of E/Z isomers).

Mp 135–137 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.11 (s, 1 H), 7.63 (dd, J = 8.4, 1.2 Hz, 2 H), 7.53 (tt, J = 7.4, 1.2 Hz, 1 H), 7.49–7.46 (m, 2 H), 7.43–7.36 (m, 5 H), 7.14 (d, J = 8.0 Hz, 2 H), 7.09 (d, J = 8.2 Hz, 2 H), 2.35 (s, 3 H).

These data are consistent with literature values.[10c]

(E)-[2-(4-Isopropylphenyl)-2-(phenylsulfonyl)vinyl](phenyl)sulfane (3ga)

Following GP1 using 1-(bromoethynyl)-4-isopropylbenzene (1g) (111.5 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ga as a colorless solid (128.2 mg, 65%, >30:1 mixture of E/Z isomers).

Mp 140–142 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.12 (s, 1 H), 7.63 (dd, J = 8.4, 1.2 Hz, 2 H), 7.54 (tt, J = 7.4, 1.2 Hz, 1 H), 7.49–7.46 (m, 2 H), 7.42–7.36 (m, 5 H), 7.19 (d, J = 8.2 Hz, 2 H), 7.12 (d, J = 8.3 Hz, 2 H), 2.89 (sept, J = 6.9 Hz, 1 H), 1.24 (d, J = 6.9 Hz, 6 H).

¹³C NMR (101 MHz, CDCl₃): δ = 150.3, 143.9, 139.6, 136.2, 133.1, 133.0, 131.3 (2 C), 130.1 (2 C), 129.7 (2 C), 128.9 (2 C), 128.7, 128.3 (2 C), 127.9, 126.9 (2 C), 34.0, 23.9 (2 C).

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₃H₂₃O₂S₂: 395.1139; found: 395.1140.

(E)-[2-(2-Chlorophenyl)-2-(phenylsulfonyl)vinyl](phenyl)sulfane (3ha)

Following GP1 using 1-(bromoethynyl)-2-chlorobenzene (1h) (107.7 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ha as a colorless solid (119.9 mg, 62%, >30:1 mixture of E/Z isomers).

Mp 100–102 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.19 (s, 1 H), 7.60 (d, J = 8.5 Hz, 2 H), 7.56 (tt, J = 7.4, 1.2 Hz, 1 H), 7.49–7.46 (m, 2 H), 7.42 (d, J = 7.7 Hz, 2 H), 7.39–7.36 (m, 5 H), 7.33–7.31 (m, 2 H).

¹³C NMR (101 MHz, CDCl₃): δ = 146.0, 138.9, 134.9, 133.4, 133.2, 132.9, 132.5, 131.4 (2 C), 131.1, 129.8, 129.7 (2 C), 129.1, 129.0 (2 C), 128.9, 128.7 (2 C), 127.1.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₀H₁₅ClNaO₂S₂: 409.0100; found: 409.0095.

(E)-[2-(Naphthalen-1-yl)-2-(phenylsulfonyl)vinyl](phenyl)sulfane (3ia)

Following GP1 using 1-(bromoethynyl)naphthalene (1i) (115.5 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ia as a colorless solid (138.9 mg, 69%, >30:1 mixture of E/Z isomers).

Mp 69–71 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.31 (s, 1 H), 7.79 (d, J = 8.2 Hz, 1 H), 7.73 (d, J = 8.1 Hz, 1 H), 7.47 (d, J = 7.5 Hz, 2 H), 7.42 (d, J = 8.4 Hz, 1 H), 7.35–7.31 (m, 5 H), 7.27–7.19 (m, 6 H), 7.12 (d, J = 6.9 Hz, 1 H).

These data are consistent with literature values.[10c]

(E)-[2-(Naphthalen-2-yl)-2-(phenylsulfonyl)vinyl](phenyl)sulfane (3ja)

Following GP1 using 2-(bromoethynyl)naphthalene (1j) (173.3 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ja as a yellow liquid (134.8 mg, 67%, >30:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 8.22 (s, 1 H), 7.84–7.77 (m, 3 H), 7.73 (s, 1 H), 7.64 (d, J = 7.4 Hz, 2 H), 7.53–7.48 (m, 5 H), 7.41–7.34 (m, 5 H), 7.30 (dd, J = 8.5, 1.5 Hz, 1 H).

These data are consistent with literature values.[10c]

(E)-2-[1-(Phenylsulfonyl)-2-(phenylthio)vinyl]thiophene (3ka)

Following GP1 using 2-(bromoethynyl)thiophene (1k) (93.5 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ka as a light yellow solid (111.1 mg, 62%, >30:1 mixture of E/Z isomers).

Mp 99–100 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.20 (s, 1 H), 7.74 (d, J = 7.2 Hz, 2 H), 7.55–7.50 (m, 3 H), 7.45–7.40 (m, 6 H), 7.20 (dd, J = 3.7, 1.2 Hz, 1 H), 7.04–7.02 (m, 1 H).

These data are consistent with literature values.[10c]

(E)-2-(1-(Phenylsulfonyl)-2-(phenylthio)vinyl)furan (3la)

Following GP1 using 2-(bromoethynyl)furan (1l) (85.4 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3la as a colorless solid (63.3 mg, 37%, >30:1 mixture of E/Z isomers).

Mp 101–103°C.

¹H NMR (400 MHz, CDCl₃): δ = 8.07 (s, 1 H), 7.87 (d, J = 7.3 Hz, 2 H), 7.60–7.52 (m, 3 H), 7.50–7.38 (m, 6 H), 6.83 (d, J = 3.5 Hz, 1 H), 6.43 (dd, J = 3.5, 1.8 Hz, 1 H).

These data are consistent with literature values.[10c]

(E)-2-[1-(Phenylsulfonyl)-2-(phenylthio)vinyl]-1-tosyl-1H-indole (3ma)

Following GP1 using 2-(bromoethynyl)-1-tosyl-1H-indole (1m) (187.1 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ma as a colorless solid (161.0 mg, 59%, >30:1 mixture of E/Z isomers).

Mp 140–142 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.30 (s, 1 H), 7.95 (d, J = 8.4 Hz, 1 H), 7.74 (d, J = 8.4 Hz, 2 H), 7.54 (s, 1 H), 7.52 (dd, J = 8.4, 1.2 Hz, 2 H), 7.47–7.42 (m, 3 H), 7.39 (dd, J = 5.1, 2.0 Hz, 2 H), 7.31–7.26 (m, 3 H), 7.24 (m, 3 H), 7.25–7.21 (d, J = 7.4 Hz, 1 H), 7.14 (t, J = 7.9 Hz, 1 H), 2.38 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 146.6, 145.4, 139.1, 135.1, 134.7, 133.3, 132.5, 131.4 (2 C), 130.1 (2 C), 129.8 (2 C), 129.0, 128.9 (2 C), 128.5, 128.2 (2 C), 128.1, 127.8, 127.1 (2 C), 125.3, 123.6, 120.7, 113.8, 112.0, 21.8.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₉H₂₄NO₄S₃: 546.0867; found: 546.0863.

(E)-tert-Butyl 2-[1-(Phenylsulfonyl)-2-(phenylthio)vinyl]-1H-indole-1-carboxylate (3na)

Following GP1 using tert-butyl 2-(bromoethynyl)-1H-indole-1-carboxylate (1n) (160.1 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3na as a brown solid (130.3 mg, 53%, >30:1 mixture of E/Z isomers).

Mp 115–117 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.32 (s, 1 H), 7.70 (d, J = 8.5 Hz, 2 H), 7.58 (s, 1 H), 7.49–7.45 (m, 3 H), 7.41–7.33 (m, 6 H), 7.31–7.26 (m, 1 H), 7.13–7.05 (m, 2 H), 1.67 (s, 9 H).

¹³C NMR (101 MHz, CDCl₃): δ = 149.3, 146.2, 139.5, 135.1, 133.2, 132.7, 131.3 (2 C), 129.7 (2 C), 129.0 (2 C), 128.8, 128.2 (2 C), 127.9, 127.7, 127.3, 124.9, 122.9, 120.0, 115.4, 110.0, 84.6, 28.3 (3 C).

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₇H₂₅NNaO₄S₂: 514.1123; found: 514.1117.

(E)-Phenyl[4-phenyl-2-(phenylsulfonyl)but-1-en-1-yl]sulfane (3oa)

Following GP1 using (4-bromobut-3-yn-1-yl)benzene (1o) (104.9 mg, 0.5 mmol), S-phenyl benzenesulfonothioate (2a) (187.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3oa as a colorless liquid (116.0 mg, 61%, >30:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 8.10–8.04 (m, 2 H), 7.67 (tt, J = 7.4, 1.2 Hz, 1 H), 7.58 (t, J = 7.6 Hz, 2 H), 7.32–7.28 (m, 3 H), 7.26–7.20 (m, 3 H), 7.19–7.16 (m, 2 H), 7.01 (d, J = 6.6 Hz, 2 H), 6.66 (s, 1 H), 2.77 (t, J = 7.3 Hz, 2 H), 2.63 (t, J = 7.4 Hz, 2 H).

¹³C NMR (101 MHz, CDCl₃): δ = 143.0, 140.9, 140.1, 135.9, 133.8, 132.2, 131.0 (2 C), 129.4 (2 C), 129.3 (2 C), 128.9 (2 C), 128.6 (2 C), 128.3, 127.6 (2 C), 126.3, 35.2, 34.4.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₂H₂₀NaO₂S₂: 403.0802; found: 403.0797.

(E)-(2-Phenyl-2-tosylvinyl)(p-tolyl)sulfane (3eb)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-p-tolyl 4-methylbenzenesulfonothioate (2b) (208.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3eb as a colorless solid (121.8 mg, 64%, >30:1 mixture of E/Z isomers).

Mp 178–180 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.07 (s, 1 H), 7.49 (d, J = 8.2 Hz, 2 H), 7.37–7.33 (m, 5 H), 7.22–7.17 (m, 6 H), 2.38 (s, 3 H), 2.37 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 144.5, 144.0, 139.1, 136.5, 135.8, 131.6 (2 C), 130.9, 130.42 (2 C), 130.35 (2 C), 129.6 (2 C), 129.43, 129.38, 128.7 (2 C), 128.3 (2 C), 21.7, 21.3.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₂H₂₀NaO₂S₂: 403.0802; found: 403.0797.

These data are consistent with literature values.[10d]

(E)-(4-Fluorophenyl){2-[(4-fluorophenyl)sulfonyl]-2-phenylvinyl}sulfane (3ec)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-(4-fluorophenyl) 4-fluorobenzenesulfonothioate (2c) (143.1 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ec as a colorless solid (112.6 mg, 58%, >30:1 mixture of E/Z isomers).

Mp 98–100 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.01 (s, 1 H), 7.63–7.58 (m, 2 H), 7.48–7.44 (m, 2 H), 7.39–7.33 (m, 3 H), 7.20 (dd, J = 7.9, 1.6 Hz, 2 H), 7.12–7.04 (m, 4 H).

¹³C NMR (101 MHz, CDCl₃): δ = 165.5 (d, J = 255.9 Hz), 163.4 (d, J = 264.1 Hz), 144.5, 136.0, 135.3 (d, J = 3.2 Hz), 134.0 (d, J = 8.5 Hz, 2 C), 131.1 (d, J = 9.5 Hz, 2 C), 130.3 (d, J = 6.3 Hz, 3 C), 129.8 (2 C), 128.9 (3 C), 127.8 (d, J = 3.5 Hz), 116.99 (d, J = 22.2 Hz), 116.26 (d, J = 22.6 Hz).

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₀H₁₄F₂NaO₂S₂: 411.0301; found: 411.0295.

(E)-(4-Bromophenyl){2-[(4-bromophenyl)sulfonyl)]-2-phenylvinyl}sulfane (3ed)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-(4-bromophenyl) 4-bromobenzenesulfonothioate (2d) (306.1 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ed as a colorless solid (137.7 mg, 54%, >30:1 mixture of E/Z isomers).

Mp 188–190 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.04 (s, 1 H), 7.54–7.50 (m, 4 H), 7.44 (d, J = 8.7 Hz, 2 H), 7.39–7.31 (m, 5 H), 7.20 (dd, J = 7.9, 1.5 Hz, 2 H).

¹³C NMR (101 MHz, CDCl₃): δ = 143.7, 138.3, 136.3, 132.9 (2 C), 132.8 (2 C), 132.3 (2 C), 131.8, 130.3 (2 C), 130.2, 129.9, 129.8 (2 C), 129.0 (2 C), 128.6, 123.3.

HRMS (ESI-TOF): m/z [M + K]⁺ calcd for C₂₀H₁₄Br₂KO₂S₂: 546.8439; found: 546.8433.

(E)-Naphthalen-2-yl[2-(naphthalen-2-ylsulfonyl)-2-phenylvinyl]sulfane (3ee)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-naphthalen-1-yl naphthalene-1-sulfonothioate (2e) (175.2 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ee as a yellow solid (140.3 mg, 62%, >30:1 mixture of E/Z isomers).

Mp 150–152 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.31 (s, 1 H), 8.20 (s, 1 H), 7.98 (s, 1 H), 7.89–7.82 (m, 6 H), 7.65–7.59 (m, 2 H), 7.58–7.54 (m, 4 H), 7.37–7.30 (m, 3 H), 7.24 (dd, J = 8.1, 1.6 Hz, 2 H).

¹³C NMR (101 MHz, CDCl₃): δ = 144.3, 136.33, 136.31, 135.1, 133.7, 132.9, 132.1, 130.7, 130.5, 130.4 (2 C), 130.03, 130.00, 129.65, 129.62, 129.5, 129.22, 129.16, 128.9 (2 C), 128.1, 128.02, 127.99, 127.8, 127.6, 127.3, 127.2, 123.2.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd for C₂₈H₂₄NO₂S₂: 470.1248; found: 470.1248.

(E)-2-{[2-Phenyl-2-(thiophen-2-ylsulfonyl)vinyl]thio}thiophene (3ef)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-thiophen-2-yl thiophene-2-sulfonothioate (2f) (131.2 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ef as a yellow solid (94.7 mg, 52%, >30:1 mixture of E/Z isomers).

Mp 116–118 °C.

¹H NMR (400 MHz, CDCl₃): δ = 7.92 (s, 1 H), 7.59 (dd, J = 5.0, 1.3 Hz, 1 H), 7.47 (dd, J = 5.4, 1.2 Hz, 1 H), 7.41–7.36 (m, 3 H), 7.32 (dd, J = 3.8, 1.3 Hz, 1 H), 7.29–7.26 (m, 2 H), 7.25 (dd, J = 3.6, 1.2 Hz, 1 H), 7.06–7.03 (m, 1 H), 6.99 (dd, J = 4.9, 3.8 Hz, 1 H).

¹³C NMR (101 MHz, CDCl₃): δ = 145.5, 140.3, 136.1, 135.4, 134.4, 134.1, 131.4, 130.3 (2 C), 130.1, 129.9, 129.2, 128.9 (2 C), 128.2, 127.6.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₁₆H₁₂NaO₂S₄: 386.9618; found: 386.9613.

(E)-Phenyl(2-phenyl-2-tosylvinyl)sulfane (3eg)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-phenyl 4-methylbenzenesulfonothioate (2g) (198.3 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3eg as a colorless solid (124.6 mg, 68%, >5:1 mixture of E/Z isomers).

Mp 118–120 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.11 (s, 1 H), 7.52–7.45 (m, 4 H), 7.39–7.34 (m, 6 H), 7.23–7.18 (m, 4 H), 2.38 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 144.1, 143.6, 136.4, 132.9, 131.6, 131.2 (2 C), 130.8, 130.3 (2 C), 129.7 (2 C), 129.6 (2 C), 129.5, 128.9, 128.7 (2 C), 128.3 (2 C), 21.7.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd for C₂₁H₂₂NO₂S₂: 384.1092; found: 384.1087.

These data are consistent with literature values.[10d]

(E)-(4-Methoxyphenyl)(2-phenyl-2-tosylvinyl)sulfane (3eh)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-(4-methoxyphenyl)-4-methylbenzenesulfonothioate (2h) (220.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3eh as a colorless solid (113.0 mg, 57%, >6:1 mixture of E/Z isomers).

Mp 175–172 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.00 (s, 1 H), 7.48 (d, J = 8.3 Hz, 2 H), 7.41 (d, J = 8.9 Hz, 2 H), 7.36–7.31 (m, 3 H), 7.22–7.17 (m, 4 H), 6.91 (d, J = 8.9 Hz, 2 H), 3.83 (s, 3 H), 2.38 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 160.5, 145.5, 144.0, 136.6, 135.3, 134.0 (2 C), 132.8, 130.9, 130.4 (2 C), 129.6, 129.4, 128.7, 128.3 (2 C), 123.3, 115.3 (2 C), 114.7, 55.7, 21.7.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd for C₂₂H₂₄NO₃S₂: 414.1198; found: 414.1195.

These data are consistent with literature values.[10d]

(E)-(4-Fluorophenyl)[2-phenyl-2-(phenylsulfonyl)vinyl]sulfane (3ei)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-(4-fluorophenyl) benzenesulfonothioate (2i) (201.2 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ei as a yellow solid (100.0 mg, 54%, >30:1 mixture of E/Z isomers).

Mp 115–117 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.02 (s, 1 H), 7.61 (d, J = 9.3 Hz, 2 H), 7.53 (t, J = 7.5 Hz, 1 H), 7.48–7.44 (m, 2 H), 7.42–7.31 (m, 5 H), 7.21–7.17 (m, 2 H), 7.11–7.06 (m, 2 H).

¹³C NMR (101 MHz, CDCl₃): δ = 163.2 (d, J = 250.0 Hz), 144.4 (d, J = 20.8 Hz), 139.2, 136.2, 134.05 (d, J = 4.5 Hz), 133.96 (d, J = 4.4 Hz), 131.1 (d, J = 9.5 Hz), 130.5, 130.3 (2 C), 129.8, 129.6, 128.9 (2 C), 128.8 (2 C), 128.3 (2 C), 116.9 (d, J = 22.2 Hz), 116.3 (d, J = 22.6 Hz).

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₀H₁₅FNaO₂S₂: 393.0395; found: 393.0395.

(E)-(4-Methoxyphenyl)[2-phenyl-2-(phenylsulfonyl)vinyl]sulfane (3ej)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-(4-methoxyphenyl) benzenesulfonothioate (2j) (210.3 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ej as a yellow liquid (97.5 mg, 51%, >15:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 8.03 (s, 1 H), 7.61 (d, J = 7.2 Hz, 2 H), 7.52 (t, J = 7.4 Hz, 1 H), 7.43–7.39 (m, 4 H), 7.37–7.31 (m, 3 H), 7.20 (dd, J = 7.9, 1.6 Hz, 2 H), 6.91 (d, J = 8.8 Hz, 2 H), 3.83 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 160.5, 146.1, 139.5, 135.0, 134.0 (2 C), 133.2, 130.7, 130.4 (2 C), 129.5, 128.9 (2 C), 128.8 (2 C), 128.3 (2 C), 123.2, 115.3 (2 C), 55.6.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₁H₁₉O₂S₂: 383.0776; found: 383.0769.

(E)-2-{[2-Phenyl-2-(phenylsulfonyl)vinyl]thio}pyridine (3ek)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-pyridin-2-yl benzenesulfonothioate (2k) (188.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ek as a yellow liquid (93.6 mg, 53%, >30:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 9.14 (s, 1 H), 8.61–8.58 (m, 1 H), 7.67 (dd, J = 8.4, 1.2 Hz, 2 H), 7.58 (td, J = 7.9, 1.8 Hz, 1 H), 7.52 (tt, J = 7.4, 1.2 Hz, 1 H), 7.42–7.32 (m, 5 H), 7.19–7.14 (m, 4 H).

¹³C NMR (101 MHz, CDCl₃): δ = 153.4, 150.3, 139.4, 138.9, 137.1, 136.7, 133.2, 131.4, 130.2 (2 C), 129.5, 128.9 (2 C), 128.8 (2 C), 128.4 (2 C), 123.1, 121.8.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₁₉H₁₅NNaO₂S₂: 376.0442; found: 376.0437.

(E)-2-[(2-Phenyl-1-tosylvinyl)thio]pyridine (3el)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), S-pyridin-2-yl 4-methylbenzenesulfonothioate (2l) (199.0 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3el as a colorless liquid (93.7 mg, 51%, >30:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 9.10 (s, 1 H), 8.60–6.58 (m, 1 H), 7.59 (dd, J = 7.5, 1.9 Hz, 1 H), 7.56–7.52 (m, 2 H), 7.37–7.31 (m, 3 H), 7.20–7.15 (m, 6 H), 2.38 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 153.6, 150.3, 144.1, 138.3, 137.1, 137.0, 136.5, 131.6, 130.3 (2 C), 129.6 (2 C), 129.5, 128.8 (2 C), 128.5 (2 C), 123.1, 121.8, 21.8.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₀H₁₈NO₂S₂: 368.0773; found: 368.0767.

These data are consistent with literature values.[10d]

(E)-[2-(3,4-Dimethoxyphenyl)-2-tosylvinyl](p-tolyl)sulfane (3ab)

Following GP1 using 4-(bromoethynyl)-1,2-dimethoxybenzene (1a) (120.5 mg, 0.5 mmol), S-p-tolyl 4-methylbenzenesulfonothioate (2b) (208.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ab as a white solid (158.6 mg, 72%, >30:1 mixture of E/Z isomers).

Mp 126–127 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.03 (s, 1 H), 7.51 (d, J = 8.3 Hz, 2 H), 7.36 (d, J = 8.1 Hz, 2 H), 7.20–7.16 (m, 4 H), 6.82–6.76 (m, 2 H), 6.75 (s, 1 H), 3.87 (s, 3 H), 3.78 (s, 3 H), 2.37 (s, 3 H), 2.36 (s, 3 H).

These data are consistent with literature values.[10d]

(E)-p-Tolyl[2-tosyl-2-(3,4,5-trimethoxyphenyl)vinyl]sulfane (3bb)

Following GP1 using 5-(bromoethynyl)-1,2,3-trimethoxybenzene (1b) (135.5 mg, 0.5 mmol), S-p-tolyl 4-methylbenzenesulfonothioate (2b) (208.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3bb as a colorless solid (148.2 mg, 63%, >5:1 mixture of E/Z isomers).

Mp 167–169 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.04 (s, 1 H), 7.54 (d, J = 8.3 Hz, 2 H), 7.36 (d, J = 8.1 Hz, 2 H), 7.22–7.17 (m, 4 H), 7.11 (s, 1 H), 6.40 (s, 1 H), 3.85 (s, 3 H), 3.73 (s, 6 H), 2.38 (s, 3 H), 2.37 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 153.2, 144.3, 144.1, 139.1, 138.8, 136.6, 135.6, 131.5 (2 C), 130.4 (2 C), 130.3, 129.5 (2 C), 129.4, 128.4 (2 C), 125.9, 107.3, 106.9, 61.0, 56.2 (2 C), 21.6, 21.3.

These data are consistent with literature values.[10c]

(E)-[2-(4-Methoxyphenyl)-2-tosylvinyl](p-tolyl)sulfane (3cb)

Following GP1 using 1-(bromoethynyl)-4-ethoxybenzene (1c) (105.0 mg, 0.5 mmol), S-p-tolyl 4-methylbenzenesulfonothioate (2b) (208.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3cb as a colorless solid (137.5 mg, 67%, >30:1 mixture of E/Z isomers).

Mp 92–94 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.06 (s, 1 H), 7.52 (d, J = 8.3 Hz, 2 H), 7.36 (d, J = 8.1 Hz, 2 H), 7.25–7.21 (m, 1 H), 7.21–7.18 (m, 4 H), 6.91–6.88 (m, 1 H), 6.78–6.75 (m, 2 H), 3.75 (s, 3 H), 2.38 (s, 3 H), 2.37 (s, 3 H).

These data are consistent with literature values.[13] [14]

(E)-[2-(Naphthalen-1-yl)-2-tosylvinyl](p-tolyl)sulfane (3ib)

Following GP1 using 1-(bromoethynyl)-1-naphthaene (1i) (115.5 mg, 0.5 mmol), S-p-tolyl 4-methylbenzenesulfonothioate (2b) (208.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ib as a colorless solid (127.0 mg, 59%, >30:1 mixture of E/Z isomers).

Mp 104–106 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.32 (s, 1 H), 7.88 (d, J = 8.3 Hz, 1 H), 7.83 (d, J = 8.1 Hz, 1 H), 7.56 (d, J = 8.4 Hz, 1 H), 7.45–7.40 (m, 4 H), 7.35–7.30 (m, 3 H), 7.18–7.16 (m, 3 H), 7.10 (d, J = 8.0 Hz, 2 H), 2.36 (s, 3 H), 2.33 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 146.3, 144.1, 139.0, 136.0, 134.3, 133.7, 131.5 (2 C), 131.1, 130.4 (2 C), 130.2, 129.52, 129.49 (2 C), 129.2, 128.6 (2 C), 128.5, 128.0, 126.7, 126.2, 125.3, 125.1, 21.7, 21.3.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd for C₂₆H₂₆NO₂S₂: 448.1405; found: 448.1399.

These data are consistent with literature values.[10d]

(E)-[2-(Naphthalen-2-yl)-2-tosylvinyl](p-tolyl)sulfane (3jb)

Following GP1 using 1-(bromoethynyl)-2-naphthaene (1j) (156.0 mg, 0.5 mmol), S-(4-tolyl) 4-methylbenzenesulfonothioate (2b) (208.79 mg, 0.75 mmol) and Cs₂CO₃ (651.6 mg, 2 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3jb as a yellow solid (124.8 mg, 58%, >30:1 mixture of E/Z isomers).

Mp 180–182 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.15 (s, 1 H), 7.84–7.76 (m, 3 H), 7.74 (s, 1 H), 7.53–7.46 (m, 4 H), 7.37 (d, J = 8.1 Hz, 2 H), 7.31 (dd, J = 8.5, 1.7 Hz, 1 H), 7.17 (dd, J = 15.6, 8.0 Hz, 4 H), 2.37 (s, 3 H), 2.36 (s, 3 H).

These data are consistent with literature values.[10d]

(E)-2-[2-(p-Tolylthio)-1-tosylvinyl]thiophene (3kb)

Following GP1 using 2-(bromoethynyl)thiophene (1k) (93.5 mg, 0.5 mmol), S-p-tolyl 4-methylbenzenesulfonothioate (2b) (208.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3kb as a colorless solid (106.3 mg, 55%, >30:1 mixture of E/Z isomers).

Mp 128–130 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.13 (s, 1 H), 7.60 (d, J = 8.3 Hz, 2 H), 7.41–7.38 (m, 3 H), 7.22–7.18 (m, 5 H), 7.03 (dd, J = 5.1, 3.7 Hz, 1 H), 2.38 (s, 3 H), 2.38 (s, 3 H).

These data are consistent with literature values.[10c] [d]

(E)-2-[2-(p-Tolylthio)-1-tosylvinyl]-1-tosyl-1H-indole (3mb)

Following GP1 using 2-(bromoethynyl)-1-tosyl-1H-indole (1m) (187.1 mg, 0.5 mmol), S-p-tolyl 4-methylbenzenesulfonothioate (2b) (208.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3mb as a colorless solid (146.3 mg, 51%, >12:1 mixture of E/Z isomers).

Mp 135–138 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.23 (s, 1 H), 7.94 (d, J = 8.3 Hz, 1 H), 7.87–7.80 (m, 1 H), 7.74 (d, J = 8.3 Hz, 2 H), 7.52 (s, 1 H), 7.40 (d, J = 8.2 Hz, 2 H), 7.34–7.29 (m, 4 H), 7.24 (s, 1 H), 7.19–7.16 (m, 3 H), 7.04 (d, J = 7.9 Hz, 2 H), 2.37 (s, 6 H), 2.33 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 147.0, 145.4, 144.1, 139.3, 136.2, 135.1, 134.7, 134.0, 131.7 (2 C), 130.5 (2 C), 130.1 (2 C), 129.5 (2 C), 129.0, 128.6, 128.2 (2 C), 127.7, 127.1 (2 C), 125.2, 123.6, 121.0, 113.7, 112.3, 21.8, 21.7, 21.3.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₃₁H₂₇NNaO₄S₃: 596.0995; found: 596.1000.

(E)-tert-Butyl 2-[2-(p-Tolylthio)-1-tosylvinyl]-1H-indole-1-carboxylate (3nb)

Following GP1 using tert-butyl 2-(bromoethynyl)-1H-indole-1-carboxylate (1n) (160.1 mg, 0.5 mmol), S-p-tolyl 4-methylbenzenesulfonothioate (2b) (208.8 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3nb as a yellow solid (137.7 mg, 53%, >30:1 mixture of E/Z isomers).

Mp 130–132 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.25 (s, 1 H), 7.59–7.55 (m, 3 H), 7.35 (d, J = 8.1 Hz, 2 H), 7.32–7.28 (m, 1 H), 7.21–7.14 (m, 4 H), 7.14–7.09 (m, 3 H), 2.37 (s, 3 H), 2.33 (s, 3 H), 1.67 (s, 9 H).

¹³C NMR (101 MHz, CDCl₃): δ = 149.3, 146.4, 144.1, 139.1, 136.7, 131.6 (2 C), 130.4 (2 C), 129.7, 129.6 (2 C), 129.3, 128.5, 128.3 (2 C), 127.7, 125.6, 124.8, 122.8, 120.2, 115.4, 110.2, 84.5, 28.3 (3 C), 21.7, 21.3.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₉H₂₉NNaO₄S₂: 542.1436; found: 542.1432.

(E)-2-{[2-(3,4-Dimethoxyphenyl)-2-(thiophen-2-ylsulfonyl)vinyl]thio}thiophene (3af)

Following GP1 using 4-(bromoethynyl)-1,2-dimethoxybenzene (1a) (120.5 mg, 0.5 mmol), S-thiophen-2-yl thiophene-2-sulfonothioate (2f) (131.2 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3af as a brown liquid (118.9 mg, 56%, >5:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 7.89 (s, 1 H), 7.59 (dd, J = 5.0, 1.3 Hz, 1 H), 7.47 (dd, J = 5.4, 1.3 Hz, 1 H), 7.35 (dd, J = 3.8, 1.3 Hz, 1 H), 7.24 (dd, J = 3.6, 1.3 Hz, 1 H), 7.04 (dd, J = 5.4, 3.6 Hz, 1 H), 6.99 (dd, J = 4.9, 3.8 Hz, 1 H), 6.84 (d, J = 1.1 Hz, 2 H), 6.81 (s, 1 H), 3.89 (s, 3 H), 3.82 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 150.2, 149.0, 145.2, 140.4, 135.9, 135.3, 134.3, 134.0, 131.4, 129.4, 128.2, 127.6, 123.3, 122.1, 112.8, 111.1, 56.1, 55.9.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd for C₁₈H₂₀NO₄S₄: 442.0275; found: 442.0269.

(E)-2-{[2-(3,4-Dimethoxyphenyl)-2-(phenylsulfonyl)vinyl]thio}pyridine (3ak)

Following GP1 using 4-(bromoethynyl)-1,2-dimethoxybenzene (1a) (120.5 mg, 0.5 mmol), S-pyridin-2-yl benzenesulfonothioate (2k) (188.5 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ak as a yellow liquid (109.6 mg, 53%, >7:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 9.09 (s, 1 H), 8.60–8.57 (m, 1 H), 7.69 (d, J = 7.2 Hz, 2 H), 7.58 (td, J = 7.9, 1.8 Hz, 1 H), 7.52 (tt, J = 7.4, 1.2 Hz, 1 H), 7.40 (t, J = 7.7 Hz, 2 H), 7.19 (d, J = 8.0 Hz, 1 H), 7.17–7.13 (m, 1 H), 6.80 (d, J = 8.3 Hz, 1 H), 6.73 (dd, J = 8.2, 2.0 Hz, 1 H), 6.68 (d, J = 1.9 Hz, 1 H), 3.87 (s, 3 H), 3.74 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 153.6, 150.3, 149.9, 148.9, 139.5, 138.7, 137.1, 136.5, 133.1, 128.9 (2 C), 128.5 (2 C), 123.5, 123.2, 123.1, 121.8, 112.8, 111.0, 56.0, 55.9.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₁H₁₉NNaO₄S₂: 436.0653; found: 436.0648.

(E)-2-{[2-(Thiophen-2-yl)-2-(thiophen-2-ylsulfonyl)vinyl]thio}thiophene (3kf)

Following GP1 using 2-(bromoethynyl)thiophene (1k) (93.5 mg, 0.5 mmol), S-thiophen-2-yl thiophene-2-sulfonothioate (2f) (131.2 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 8% EtOAc/PE) yielded the title compound 3kf as a brown solid (88.9 mg, 48%, >30:1 mixture of E/Z isomers).

Mp 120–122 °C.

¹H NMR (400 MHz, CDCl₃): δ = 7.99 (s, 1 H), 7.60 (dd, J = 5.0, 1.3 Hz, 1 H), 7.49 (dd, J = 5.4, 1.3 Hz, 1 H), 7.47 (d, J = 1.1 Hz, 1 H), 7.45 (td, J = 1.6 Hz, 1 H), 7.30–7.26 (m, 2 H), 7.07 (td, J = 5.4, 3.6 Hz, 2 H), 7.02 (dd, J = 5.0, 3.8 Hz, 1 H).

¹³C NMR (101 MHz, CDCl₃): δ = 146.8, 140.2, 135.5, 134.4, 134.2, 133.4, 131.6, 131.1, 129.9, 129.5, 129.1, 128.3, 127.6, 127.4.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd for C₁₄H₁₄NO₂S₅: 387.9628; found: 387.9623.

(E)-2-{[2-(Thiophen-2-yl)-2-tosylvinyl]thio}pyridine (3kl)

Following GP1 using 2-(bromoethynyl)thiophene (1k) (93.5 mg, 0.5 mmol), S-pyridin-2-yl benzenesulfonothioate (2l) (199.0 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 8% EtOAc/PE) yielded the title compound 3kl as a yellow liquid (85.9 mg, 46%, >30:1 mixture of E/Z isomers).

¹H NMR (400 MHz, CDCl₃): δ = 9.21 (s, 1 H), 8.61–8.58 (m, 1 H), 7.65 (d, J = 8.3 Hz, 2 H), 7.63–7.59 (m, 2 H), 7.40 (dd, J = 5.1, 1.2 Hz, 1 H), 7.24 (d, J = 8.0 Hz, 1 H), 7.21 (d, J = 8.6 Hz, 2 H), 7.17 (dd, J = 3.6, 1.2 Hz, 1 H), 7.02 (dd, J = 5.1, 3.7 Hz, 1 H), 2.37 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 153.2, 150.3, 149.6, 144.2, 139.5, 137.5, 137.2, 136.4, 130.5, 129.6, 128.6, 128.3, 127.2, 123.2, 122.0, 121.2, 119.8, 21.7.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₁₈H₁₆NO₂S₃: 374.0343; found: 374.0331.

(E)-2-[1-(Naphthalen-2-ylsulfonyl)-2-(naphthalen-2-ylthio)vinyl]thiophene (3ke)

Following GP1 using 2-(bromoethynyl)thiophene (1k) (93.5 mg, 0.5 mmol), S-naphthalen-1-yl naphthalene-1-sulfonothioate (2e) (175.2 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ke as a light yellow solid (112.3 mg, 49%, >30:1 mixture of E/Z isomers).

Mp 150–152 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.38 (s, 1 H), 8.35 (s, 1 H), 8.03 (s, 1 H), 7.92–7.85 (m, 6 H), 7.69 (dd, J = 8.7, 1.8 Hz, 1 H), 7.65–7.61 (m, 1 H), 7.59–7.55 (m, 4 H), 7.41 (dd, J = 5.1, 1.1 Hz, 1 H), 7.24 (dd, J = 3.7, 1.1 Hz, 1 H), 7.02 (dd, J = 5.1, 3.7 Hz, 1 H).

These data are consistent with literature values.[10c]

tert-Butyl (E)-2-[1-(Naphthalen-2-ylsulfonyl)-2-(naphthalen-2-ylthio)vinyl]-1H-indole-1-carboxylate (3ne)

Following GP1 using tert-butyl 2-(bromoethynyl)-1H-indole-1-carboxylate (1n) (160.1 mg, 0.5 mmol), S-naphthalen-2-yl naphthalene-2-sulfonothioate (2e) (175.2 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3ne as a yellow solid (145.0 mg, 49%, >30:1 mixture of E/Z isomers).

Mp 99–101 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.49 (s, 1 H), 8.30 (d, J = 1.5 Hz, 1 H), 7.97 (d, J = 1.6 Hz, 1 H), 7.89–7.81 (m, 7 H), 7.69 (dd, J = 8.7, 1.8 Hz, 1 H), 7.63–7.58 (m, 1 H), 7.56–7.52 (m, 6 H), 7.17 (d, J = 7.8 Hz, 1 H), 7.07 (t, J = 7.5 Hz, 1 H), 1.59 (s, 9 H).

¹³C NMR (101 MHz, CDCl₃): δ = 149.2, 146.2, 136.4, 135.1, 133.6, 133.0, 132.1, 130.6, 130.5, 130.0, 129.8, 129.6, 129.5, 129.3, 129.1, 129.0, 128.1, 128.03, 127.99 (2 C), 127.8, 127.5, 127.33, 127.28, 127.2, 125.0, 123.1, 122.9, 120.1, 115.5, 110.1, 84.5, 28.2 (3 C).

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₃₅H₂₉NNaO₄S₂: 614.1436; found: 614.1436.

tert-Butyl (E)-2-[1-(naphthalen-1-ylsulfonyl)-2-(naphthalen-1-ylthio)vinyl]-1H-indole-1-carboxylate (3nn)

Following GP1 using tert-butyl 2-(bromoethynyl)-1H-indole-1-carboxylate (1n) (160.1 mg, 0.5 mmol), S-naphthalen-1-yl naphthalene-1-sulfonothioate (2n) (175.2 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 10% EtOAc/PE) yielded the title compound 3nn as a colorless solid (139.0 mg, 47%, >30:1 mixture of E/Z isomers).

Mp 106–108 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.49 (s, 1 H), 8.30 (s, 1 H), 8.13 (d, J = 8.3 Hz, 1 H), 7.97 (s, 1 H), 7.89–7.81 (m, 6 H), 7.70 (dd, J = 8.7, 1.8 Hz, 1 H), 7.64–7.57 (m, 2 H), 7.57–7.50 (m, 5 H), 7.17 (d, J = 7.8 Hz, 1 H), 7.07 (t, J = 7.5 Hz, 1 H), 1.59 (s, 9 H).

¹³C NMR (101 MHz, CDCl₃): δ = 149.2, 146.2, 136.3, 135.1, 133.6, 133.0, 132.1, 130.5, 130.0, 129.8, 129.6, 129.5, 129.3, 129.1, 129.0, 128.2, 128.1, 128.0 (2 C), 127.9, 127.8, 127.5, 127.33, 127.29, 127.2, 125.0, 123.1, 123.0, 120.1, 115.5, 110.1, 84.5, 28.2 (3 C).

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₃₅H₂₉NNaO₄S₂: 614.1436; found: 614.1432.

(S)-1-Phenyl-2-(phenylselanyl)-2-(phenylsulfonyl)ethanone (4)

Following GP1 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), Se-phenyl benzenesulfonoselenoate (2o) (222.9 mg, 0.75 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 3 h. Purification by flash column chromatography (silica gel, 8% EtOAc/PE) yielded the title compound 4 as a yellow solid (101.6 mg, 49%).

Mp 100–102 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.02 (dd, J = 8.4, 1.1 Hz, 2 H), 7.76 (dd, J = 8.4, 1.1 Hz, 2 H), 7.63 (t, J = 7.5 Hz, 1 H), 7.59–7.50 (m, 5 H), 7.42–7.38 (m, 2 H), 7.35 (d, J = 7.4 Hz, 1 H), 7.28–7.24 (m, 2 H), 5.79 (s, 1 H).

¹³C NMR (101 MHz, CDCl₃): δ = 189.5, 137.1, 135.9 (2 C), 135.1, 134.4, 134.3, 130.7 (2 C), 129.8, 129.6 (2 C), 129.0 (2 C), 128.9 (2 C), 128.8 (2 C), 127.7, 68.2.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd for C₂₀H₂₀NO₃SSe: 434.0329; found: 434.0315.

1,1-Disulfenylethenes; General Procedure 2 (GP2)

A heat-gun-dried Schlenk tube was charged 1-bromoalkene 1(a,e,f,g,j,k,l) (0.5 mmol, 1.0 equiv), N-arylthiosuccinamide 6a,b (1.25 mmol, 2.5 equiv), NiCl₂·6H₂O (0.025 mmol, 0.05 equiv) and Cs₂CO₃ (1.5 mmol, 3.0 equiv) in DMF (2.5 mL). The reaction mixture was stirred at 90 °C for 3 h. The progress was monitored by TLC (until the reaction appeared to be complete or was not proceeding any further). The mixture was quenched by the addition of H₂O (10 mL) followed by extraction with EtOAc (3 × 20 mL). The combined organic layers was washed with brine (2 × 20 mL), dried over anhydrous Na₂SO₄, and the solvent was removed under reduced pressure. The resulting residue was subjected to flash chromatography (silica gel, 100–200 mesh, eluting with 5% EtOAc/PE) to afford the corresponding 1,1-disulfenylethene.

[2-(3,4-Dimethoxyphenyl)ethene-1,1-diyl]bis(phenylsulfane) (7aa)

Following GP2 using 4-(bromoethynyl)-1,2-dimethoxybenzene (1a) (120.5 mg, 0.5 mmol), 1-(phenylthio)pyrrolidine-2,5-dione (6a) (259.1 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7aa as a colorless solid (161.7 mg, 85%).

Mp 92–94 °C.

¹H NMR (400 MHz, CDCl₃): δ = 7.52–7.49 (m, 2 H), 7.36 (t, J = 7.3 Hz, 2 H), 7.32–7.28 (m, 1 H), 7.27–7.24 (m, 2 H), 7.18 (t, J = 7.6 Hz, 2 H), 7.14–7.09 (m, 3 H), 7.07 (d, J = 2.2 Hz, 1 H), 6.74 (d, J = 8.4 Hz, 1 H), 3.83 (s, 3 H), 3.80 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 147.7, 147.6, 134.4, 133.7, 132.7, 130.7, 129.4 (2 C), 128.7, 128.2 (2 C), 128.0, 127.8 (2 C), 127.5, 126.4, 125.0, 118.4, 109.8, 109.1, 54.8 (2).

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₂H₂₁O₂S₂: 381.0983; found: 381.0982.

[2-(3,4-Dimethoxyphenyl)ethene-1,1-diyl]bis(p-tolylsulfane) (7ab)

Following GP2 using 4-(bromoethynyl)-1,2-dimethoxybenzene (1a) (120.5 mg, 0.5 mmol), 1-(p-tolylthio)pyrrolidine-2,5-dione (6b) (276.6 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7ab as a colorless solid (179.7 mg, 88%).

Mp 78–80 °C.

¹H NMR (400 MHz, CDCl₃): δ = 7.40 (d, J = 8.1 Hz, 2 H), 7.19–7.14 (m, 4 H), 7.10 (dd, J = 8.3, 2.2 Hz, 1 H), 7.06 (d, J = 2.1 Hz, 1 H), 7.02 (s, 1 H), 6.99 (d, J = 8.0 Hz, 2 H), 6.73 (d, J = 8.4 Hz, 1 H), 3.83 (s, 3 H), 3.80 (s, 3 H), 2.36 (s, 3 H), 2.25 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 148.70, 148.68, 137.7, 136.0, 134.1, 132.02, 131.98, 131.2, 130.9 (2 C), 130.1 (2 C), 129.8, 129.7 (2 C), 129.0 (2 C), 119.5, 110.9, 110.3, 55.9 (2 C), 21.2, 21.1.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₄H₂₅O₂S₂: 409.1296; found: 409.1281.

(2-Phenylethene-1,1-diyl)bis(phenylsulfane) (7ea)

Following GP2 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), 1-(phenylthio)pyrrolidine-2,5-dione (6a) (259.1 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7ea as a yellow liquid (137.8 mg, 86%).

¹H NMR (400 MHz, CDCl₃): δ = 7.59–7.54 (m, 2 H), 7.52–7.47 (m, 2 H), 7.39–7.34 (m, 2 H), 7.30 (tt, J = 7.2, 1.3 Hz, 1 H), 7.27–7.22 (m, 5 H), 7.21–7.16 (m, 3 H), 7.08 (tt, J = 7.2, 1.2 Hz, 1 H).

¹³C NMR (101 MHz, CDCl₃): δ = 138.9, 136.7, 135.3, 134.8, 130.7 (2 C), 129.4 (3 C), 129.0 (2 C), 128.5 (2 C), 128.3 (2 C), 127.75, 127.70, 126.9 (2 C), 126.0.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₀H₁₇S₂: 321.0772; found: 321.0784.

(2-Phenylethene-1,1-diyl)bis(p-tolylsulfane) (7eb)

Following GP2 using (bromoethynyl)benzene (1e) (90.5 mg, 0.5 mmol), 1-(p-tolylthio)pyrrolidine-2,5-dione (6b) (276.6 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7eb as a colorless solid (139.4 mg, 80%).

Mp 76–78 °C.

¹H NMR (400 MHz, CDCl₃): δ = 7.57–7.54 (m, 2 H), 7.41 (d, J = 8.1 Hz, 2 H), 7.27–7.23 (m, 2 H), 7.20–7.15 (m, 6 H), 7.01 (d, J = 8.0 Hz, 2 H), 2.37 (s, 3 H), 2.24 (s, 3 H).

These data are consistent with literature values.[16]

[2-(4-Isopropylphenyl)ethene-1,1-diyl]bis(phenylsulfane) (7ga)

Following GP2 using 1-(bromoethynyl)-4-isopropylbenzene (1g) (111.5 mg, 0.5 mmol), 1-(phenylthio)pyrrolidine-2,5-dione (6a) (259.1 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7ga as a colorless liquid (137.7 mg, 76%).

¹H NMR (400 MHz, CDCl₃): δ = 7.52–7.47 (m, 4 H), 7.35 (t, J = 7.3 Hz, 2 H), 7.31–7.25 (m, 4 H), 7.19 (t, J = 7.7 Hz, 2 H), 7.13–7.07 (m, 3 H), 2.85 (sept, J = 6.9 Hz, 1 H), 1.20 (d, J = 6.9 Hz, 6 H).

¹³C NMR (101 MHz, CDCl₃): δ = 148.6, 136.5, 136.2, 135.5, 135.1, 130.6 (2 C), 129.4 (2 C), 129.2, 129.0 (2 C), 128.0 (2 C), 127.6, 126.7 (2 C), 126.6 (2 C), 125.8, 33.8, 24.0 (2 C).

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₃H₂₃S₂: 363.1241; found: 363.1228.

[2-(4-Isopropylphenyl)ethene-1,1-diyl]bis(p-tolylsulfane) (7gb)

Following GP2 using 1-(bromoethynyl)-4-isopropylbenzene (1g) (111.5 mg, 0.5 mmol), 1-(p-tolylthio)pyrrolidine-2,5-dione (6b) (276.6 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7gb as a colorless liquid (154.2 mg, 79%).

¹H NMR(400 MHz, CDCl₃): δ = 7.48 (d, J = 8.4 Hz, 2 H), 7.39 (d, J = 8.1 Hz, 2 H), 7.19–7.15 (m, 5 H), 7.10 (d, J = 8.2 Hz, 2 H), 7.01 (d, J = 8.0 Hz, 2 H), 2.85 (sept, J = 6.9 Hz, 1 H), 2.36 (s, 3 H), 2.25 (s, 3 H), 1.20 (d, J = 6.9 Hz, 6 H).

¹³C NMR (101 MHz, CDCl₃): δ = 148.4, 137.7, 136.72, 136.70, 135.7, 132.0, 131.5, 131.0 (2 C), 130.1 (2 C), 129.8 (2 C), 128.9, 128.3 (2 C), 126.7 (2 C), 126.6 (2 C), 33.8, 24.0 (2 C), 21.2, 21.1.

These data are consistent with literature values.[15]

[2-(Naphthalen-2-yl)ethene-1,1-diyl]bis(phenylsulfane) (7ja)

Following GP2 using 2-(bromoethynyl)naphthalene (1j) (173.3 mg, 0.5 mmol), 1-(phenylthio)pyrrolidine-2,5-dione (6a) (259.1 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7ja as a colorless solid (150.0 mg, 81%).

Mp 88–90 °C.

¹H NMR (400 MHz, CDCl₃): δ = 8.06 (s, 1 H), 7.80–7.75 (m, 2 H), 7.72 (d, J = 1.6 Hz, 2 H), 7.58–7.54 (m, 2 H), 7.45–7.37 (m, 5 H), 7.36–7.30 (m, 3 H), 7.18 (t, J = 7.6 Hz, 2 H), 7.07 (tt, J = 7.2, 1.2 Hz, 1 H).

¹³C NMR (101 MHz, CDCl₃): δ = 137.5, 136.2, 135.3, 134.8, 133.4, 132.9, 130.8 (2 C), 129.5 (2 C), 129.2, 129.0 (2 C), 128.33, 128.27 (2 C), 128.2, 127.8, 127.6, 126.4, 126.17, 126.04, 125.96, 124.7.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₄H₁₉S₂: 371.0928; found: 371.0913.

2-[2,2-Bis(phenylthio)vinyl]thiophene (7ka)

Following GP2 using 2-(bromoethynyl)thiophene (1k) (93.5 mg, 0.5 mmol), 1-(phenylthio)pyrrolidine-2,5-dione (6a) (259.1 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7ka as a yellow liquid (115.9 mg, 71%).

¹H NMR (400 MHz, CDCl₃): δ = 7.44–7.41 (m, 2 H), 7.33–7.28 (m, 3 H), 7.27–7.25 (m, 3 H), 7.18 (t, J = 7.6 Hz, 2 H), 7.11–7.07 (m, 2 H), 7.05 (dd, J = 5.1, 1.1 Hz, 1 H), 6.82 (dd, J = 5.1, 3.7 Hz, 1 H).

¹³C NMR (101 MHz, CDCl₃): δ = 144.2, 135.9, 134.9, 134.8, 130.7 (2 C), 129.5 (2 C), 129.1 (2 C), 128.1 (2 C), 127.8, 127.7, 126.2, 125.0, 124.8, 122.9.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₁₈H₁₅S₃: 327.0336; found: 327.0322.

2-[2,2-Bis(p-tolylthio)vinyl]thiophene (7kb)

Following GP2 using 2-(bromoethynyl)thiophene (1k) (93.5 mg, 0.5 mmol), 1-(p-tolylthio)pyrrolidine-2,5-dione (6b) (276.6 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7kb as a yellow solid (132.9 mg, 75%).

Mp 78–80 °C.

¹H NMR (400 MHz, CDCl₃): δ = 7.40 (d, J = 8.1 Hz, 2 H), 7.27–7.25 (m, 3 H), 7.19 (d, J = 7.9 Hz, 2 H), 7.14 (dd, J = 3.7, 1.2 Hz, 1 H), 7.11 (dd, J = 5.1, 1.2 Hz, 1 H), 7.07 (d, J = 7.9 Hz, 2 H), 6.89 (dd, J = 5.1, 3.7 Hz, 1 H), 2.38 (s, 3 H), 2.30 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 144.4, 138.0, 136.3, 136.2, 131.4, 131.2, 131.1 (2 C), 130.2 (2 C), 129.9 (2 C), 128.5 (2 C), 127.6, 124.8, 124.6, 122.7, 21.2, 21.1.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₀H₁₉S₃: 355.0649; found: 355.0636.

2-[2,2-Bis(p-tolylthio)vinyl]furan (7lb)

Following GP2 using 2-(bromoethynyl)furan (1l) (85.5 mg, 0.5 mmol), 1-(p-tolylthio)pyrrolidine-2,5-dione (6b) (276.6 mg, 1.25 mmol), NiCl₂·6H₂O (5.9 mg, 0.025 mmol) and Cs₂CO₃ (487.3 mg, 1.5 mmol) for 2 h. Purification by flash column chromatography (silica gel, 5% EtOAc/PE) yielded the title compound 7lb as a brown liquid (116.7 mg, 69%).

¹H NMR (400 MHz, CDCl₃): δ = 7.47 (s, 1 H), 7.39 (d, J = 8.1 Hz, 2 H), 7.30 (d, J = 1.7 Hz, 1 H), 7.24 (d, J = 8.2 Hz, 2 H), 7.17 (d, J = 7.9 Hz, 2 H), 7.07 (d, J = 8.0 Hz, 2 H), 6.36 (d, J = 3.3 Hz, 1 H), 6.30 (dd, J = 3.4, 1.8 Hz, 1 H), 2.36 (s, 3 H), 2.29 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 153.3, 142.4, 137.9, 136.5, 136.1, 131.41, 131.39, 131.1 (2 C), 130.1 (2 C), 129.9 (2 C), 128.2 (2 C), 118.0, 111.7, 107.6, 21.3, 21.2.

HRMS (ESI-TOF): m/z [M + H]⁺ calcd for C₂₀H₁₉OS₂: 339.0877; found: 339.0867.

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Figures

Scheme 1 Representative vicinal thiosulfonylations through atom transfer radical addition (ATRA)

Scheme 2 Substrate scope for vicinal thiosulfonylation using 1a–p and 2a. All reactions were performed on a 0.5 mmol scale of 1a–p (1.0 equiv), 2a (1.5 equiv), NiCl₂·6H₂O (5 mol%) and Cs₂CO₃ (3.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 3 h. Isolated yields are given. E/Z mixture ratios are based on ¹H NMR analysis.

Figure 1 ORTEP representation of compound 3na (CCDC 2061705)

Scheme 3 Substrate scope for vicinal thiosulfonylation. All reactions were performed on a 0.5 mmol scale of 1e, 1e′ or 1e′′ (1.0 equiv), 2a–m (1.5 equiv), NiCl₂·6H₂O (5 mol%) and Cs₂CO₃ (3.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 3 h. Isolated yields are given. E/Z mixture ratios are based on ¹H NMR analysis.

Scheme 4 Substrate scope for vicinal thiosulfonylation. All reactions were performed a 0.5 mmol scale of 1 (1.0 equiv), 2 (1.5 equiv), NiCl₂·6H₂O (5 mol%) and Cs₂CO₃ (3.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 3 h. Isolated yields are given. E/Z mixture ratios are based on ¹H NMR analysis.

Scheme 5 Synthesis of β-keto selenosulfone 4 using 1e and 2o

Figure 2 ORTEP representation of compound 4 (CCDC 2061706)

Scheme 6 Substrate scope for vicinal thiosulfonylation. All reactions were performed on a 0.5 mmol scale of 5 (1.0 equiv), 2 (1.5 equiv) and Cs₂CO₃ (4.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 4 h. Isolated yields are given. E/Z mixture ratios are based on ¹H NMR analysis. ^a Reaction using NiCl₂·6H₂O (5 mol%). Ms: methanesulfonyl; Ns: nosyl (4-O₂NC₆H₄SO₂).

Scheme 7 Substrate scope for the 1,1-dithiolation of 1 with N-arylthio succinamides 6a and 6b. All reactions were performed on a 0.5 mmol scale of 1 (1.0 equiv), 6a,b (2.5 equiv), NiCl₂·6H₂O (5 mol%) and Cs₂CO₃ (3.0 equiv) in anhydrous DMF (2.5 mL) under N₂ at 90 °C for 2 h. Isolated yields are given.

Scheme 8 Gram-scale vicinal thiosulfonylation reactions

Scheme 9 Control experiments

Scheme 10 A plausible mechanism for the vicinal thiosulfonylation

Supplementary Material

Supporting Information