Synthesis of Functionalized 9-Substituted Fluorene Derivatives via Boron Trifluoride Catalysed Reaction of Coplanar 9-(Phenylethynyl)-9H-fluoren-9-ols, Aryl Aminoamides and N-Bromosuccinimide

Abstract

A boron trifluoride catalysed reaction of coplanar 9-(phenyl­ethynyl)-9H-fluoren-9-ols with various 2-aminobenzamides affords a number of highly functionalized, conjugated (Z)-2-((2-(9H-fluoren-9-ylidene)-1-phenylethylidene)amino) benzamides in excellent yield. The reaction in the presence of N-bromosuccinimide affords (E)-5-bromo-2-((2-bromo-2-(9H-fluoren-9-ylidene)-1-phenylethylidene)amino)benz­amides in very good yields. The scope of the reaction is demonstrated by selecting N-aryl substituted 2-aminobenzamides and aminosulfonamides as reaction partners. The structures of representative compounds were established by single-crystal XRD analysis. Based on the structure of the products, a plausible mechanism via formation of allene carbocation intermediates is proposed.

Key words

aryl aminoamides - propargylic alcohol - N-bromosuccin­imide - BF₃·OEt₂ - fluorene - allene

Fluorene-based compounds have been widely investigated because of their wide range of applications as organic materials,[1] semiconductors,[2] optoelectronics,[3] organic dyes,[4] photoconductors[5] as well as their applications in solar cells,[6] fuel cells,[7] and materials science[8] as indicated in Figure [1]. Their highly fluorescent nature has enabled fluorene derivatives to be used in bright and efficient displays.[9]

Figure 1 Selected materials and bioactive molecules based on the 9-substituted fluorene core structure

The presence of two benzylic acidic hydrogens at the C-9 position of fluorene activates them towards alkylation under basic conditions. Compounds with a fluorene motif such as NPC 16570 and NPC 17923 have been used as anti-inflammatory agents and inhibitors of leukocytes in inflamed tissue,[10] and also exhibit anticancer activity as well as cardiac and bone marrow toxicity.[11] Propargylic alcohols and their derivatives are useful precursors in organic synthesis.[12] Propargylic alcohols react with metal salts, iodine, and Lewis acids,[13] and they undergo nucleophilic substitution reactions via allene carbocation or propargyl cation species. In these situations, the allene intermediate shows diverse reactivity as well as selectivity.[14] Aryl aminoamides have been used as starting materials for the preparation of heterocyclic compounds and aryl amino amide appended carbocycles.[15] We have utilised fluorenone for the synthesis of spirofluorene-based fluorescent molecules[16] and we have recently reported the reaction of fluorene-9-propargylic alcohols with isatin imines for the preparation of blue emissive compounds via highly stable propargylic cation intermediates.[17] The reactions of aryl substituted propargylic alcohols with several nucleophiles such as sulfonamides,[19] nitroso compounds,[20] acetamides,[21] tosylhydrazines,[12] and imines[22] have been investigated by various research groups, to provide highly functionalized products through allenyl cation intermediates.[23] It should be noted that the two aryl groups in the diaryl substituted phenyl propargylic alcohols are conformationally orthogonal and decisive in the formation, stability, and reactivity of either carbocation or allenyl intermediate.[24] On the other hand, when the aryl groups are coplanar or nonplanar, the formation, stability, and reactivity of the reactive intermediate can be modified and provide products via the most stable intermediate. To our knowledge, the reaction of coplanar 9-(phenylethynyl)-9H-fluoren-9-ols with amino amides has not been reported. Thus, we have explored the reaction of rigid and coplanar diaryl substituted fluorene propargylic alcohols with substituted benzamides and sulfonamides.

In contrast to previous reports that coplanar fluorene propargylic alcohols with isatin imine nucleophiles affords products via the propargylic cation, herein we report the reaction with nucleophiles having labile amine protons, the reactivity being found to be reversed to afford products via an allenyl cation. The preliminary results of the study are presented in this manuscript.

Initially, a reaction between 1 equivalent of fluorenone propargylic alcohol 1a [25] in dichloromethane and 1 equivalent of 2-aminobenzamide (2a) and 0.1 equivalents of BF₃·Et₂O at room temperature for 10 minutes afforded (Z)-2-((2-(9H-fluoren-9-ylidene)-1-phenylethylidene)amino)benzamide (3a) in 65% yield (Scheme [1], Table [1], entry 1). The structure of 3a was established by FTIR, ¹H NMR, ¹³C NMR, DEPT-135 and HRMS analyses.

Scheme 1 Synthesis of compound 3a

To improve the yield and to optimize the reaction conditions for the synthesis of compound 3a, a study was carried out, varying reaction parameters such as relative quantities and nature of the acid catalyst, solvent and reaction time. Thus, performing the reaction using 0.3 equivalent of BF₃·Et₂O led to the yield of the product 3a being improved to 92% and was ultimately found to be optimal (Table [1], entry 2). Reactions using 0.5 equivalent of catalyst slightly decreased the yield to 89% (entry 3). Catalysts such as p-TsOH, FeCl₃, and AlCl₃, led to either decreased yields or no reaction (entries 4–7). Hence, BF₃·Et₂O was found to be the most suitable catalyst. Other solvents such as acetonitrile, methanol, and toluene did not improve the yield (entries 8–10). Hence, dichloromethane was found to be the most suitable solvent. An experiment without a Lewis acid catalyst failed to provide any product (entry 11).

Table 1 Optimization of Synthesis of Compound 3a

Entry	Catalyst	Solvent	Catalyst (equiv)	Time (min)	Yield of 3a (%)a
1	BF3·OEt2	DCM	0.1	10	65
2	BF3·OEt2	DCM	0.3	5	92b
3	BF3·OEt2	DCM	0.5	5	89
4	p-TsOH	DCM	0.3	30	40
5	FeCl3	DCM	0.3	30	40
6	AlCl3	DCM	0.3	30	no reaction
7	InBr3	DCM	0.3	7	80
8	BF3·OEt2	MeCN	0.8	0.5	decomposition
9	BF3·OEt2	MeOH	0.8	30	10
10	BF3·OEt2	toluene	0.8	5	no reaction
11	–	DCM		300	no reaction

^a Isolated yield after column purification.

^b Optimized conditions.

Figure 2 Various propargyl alcohols 1a–c and aryl aminoamides 2a–k

Having the optimized conditions in hand, the scope of the reaction was investigated by using a number of propargylic alcohols 1a–d and aryl aminoamides 2a–g (Figure [2]). Under the optimized conditions, all reactions proceeded well to afford the corresponding products 3a–m in excellent yields (Table [2], Figure [3]). To demonstrate the diversity of the amino derivatives in the reaction, 2-aminobenzenesulfonamide 2b was reacted with propargyl alcohol 1a to provide the sulfonamide derivative 3b in 90% yield (entry 2). Reaction of propargylic alcohol 1a with 5-iodobenzamide 2c yielded product 3c in 91% yield (entry 3). In a further exploration of various benzamides, substituted aminoamides 2d–f were chosen to react with 1a to afford products 3d–f in good yields (entries 4–6). Substituted aminoamides 2d–f were prepared from isatoic anhydride and aryl amines in water at room temperature.[26] The structure and relative stereochemistry of the representative compound 3e was confirmed by single-crystal XRD analysis (Figure [4]).[27]

Figure 3 Synthesized compounds 3a–m

Figure 4 ORTEP diagram of compound 3e (CCDC-1967615)[27]

To study the reactivity of fluorene propargylic alcohols bearing electron-donating groups, substrate 1b was reacted with substituted amino amides 2d–f to provide compounds 3g–i in moderate to good yields (Table [2], entries 7–9). Alcohol 1b, on reaction with dimethyl substituted amino amide 2g, afforded product 3j in low yield (entry 10). Furthermore, reaction of alcohol 1c with amino amides 2d–e proceeded smoothly to afford the respective products 3k and 3l (entries 11 and 12). To study the effect of substitution on the fluorenone ring, propargylic alcohol 1d was reacted with 2e, furnishing product 3m in 72% yield (entry 13).

Table 2 Reaction Scope^a

Entry	Substrate	Aminoamide	Product (Yield, %)b
1	1a	2a	3a (92)
2	1a	2b	3b (90)
3	1a	2c	3c (91)
4	1a	2d	3d (89)
5	1a	2e	3e (90)
6	1a	2f	3f (88)
7	1b	2d	3g (87)
8	1b	2e	3h (91)
9	1b	2f	3i (88)
10	1b	2g	3j (75)
11	1c	2d	3k (84)
12	1c	2e	3l (83)
13	1d	2e	3m (69)
14	1a	2h	decomposition
15	1a	2i	decomposition
16	1a	2j	decomposition
17	1a	2k	decomposition

^a Reaction conditions: BF₃·Et₂O (0.3 equiv), CH₂Cl₂, 5 min. r.t.

^b Isolated yield after column purification.

It is worth noting that the reaction of alcohol 1a with meta-substituted aminobenzamide 2h and para-substituted aminobenzamide 2i failed to provide the expected product. Thus, the reaction occurs only with ortho-amino arylamides, possibly due to hydrogen bonding. On the other hand, we also wished to test the reaction with arylamines such as aniline 2j and aliphatic amines such as isopropylamine 2k with alcohol 1a. However, both reactions failed to provide the desired product and decomposed.

Based on the structure of the products formed and on literature reports,[17] a plausible mechanism for the formation of product 3 is proposed in Scheme [2]. Accordingly, initial reaction of the fluorene derived propargylic alcohol 1 with BF₃ [12e] [18] generates the propargyl cation/allenic carbocation intermediate A. Subsequent nucleophilic attack of the lone pair of electrons of the amine group of arylaminoamide 2 onto the allenic carbocation A provides allene substituted product B. Subsequent skeletal rearrangement of B leads to product 3.

Scheme 2 Plausible mechanism for the formation of compound 3

To explore the scope of the reaction further and to diversify the products with halogen derivatives, the reaction shown in Scheme [3] in the presence of N-bromosuccinimide (NBS) was proposed. Thus, the reaction was carried out with 1 equiv of fluorenone derived propargylic alcohol 1a in dichloromethane, 1 equiv of 2-aminobenzamide 2a, 1 equiv of NBS, and 0.3 equiv amount of BF₃·Et₂O at room temperature for 5 minutes to afford the dibromination product, namely, (E)-5-bromo-2-((2-bromo-2-(9H-fluoren-9-ylidene)-1-phenylethylidene)amino)benzamide (4a) in good yield (60%; Scheme [3]). The structure and relative stereochemistry of compound 4a was confirmed by single-crystal XRD analysis (Figure [5]).[27]

Scheme 3 Synthesis of compound 4a

Figure 5 ORTEP diagram of compound 4a (CCDC-1957144)[27]

Under the optimized conditions, the scope of the reaction in the presence of NBS was demonstrated by using various propargylic alcohols 1a and 1b and aryl benzamides 2a, sulfonamide 2b and iodo-substituted aryl benzamide 2c to produce products 4a–d in 60–75% yields (Figure [6]). The structure of all the new compounds was established by spectroscopic analyses.[28]

Figure 6 Synthesized compounds 4a–d

Based on the products and on literature precedents,[17] ^, [19] [20] [21] [22] a possible mechanism for the formation of compound 4 is shown in Scheme [4]. The allenic carbocation intermediate A with aminobenzamide 2 forms allene intermediate B. Meanwhile, in the presence of BF₃·OEt₂, NBS is activated and eliminates a bromine cation. Due to the electron-donating nature of nitrogen, the electron-rich internal carbon atom of allene intermediate B reacts with the bromine cation to form intermediate C. Elimination of a proton from intermediate C followed by aromatic electrophilic bromination forms the observed compound 4.

Scheme 4 Plausible mechanism for the formation of compound 4

In conclusion, we have developed a procedure for the synthesis of (Z)-2-((2-(9H-fluoren-9-ylidene)-1-phenyl-ethylidene)amino)benzamides via BF₃-mediated reaction of coplanar 9-(phenylethynyl)-9H-fluoren-9-ols with various 2-aminobenzamides.[28] Reaction in the presence of NBS afforded­ (E)-5-bromo-2-((2-bromo-2-(9H-fluoren-9-ylidene)-1-ethenylethylidene)amino)benzamides. A plausible mechanism for the formation of products via an allene carbocation intermediate is proposed. The structure of representative compounds has been established by single-crystal XRD analysis.

Acknowledgment

P.S. thanks the Director, CSIR-CLRI for providing infrastructure facilities. The authors thank SAIF-IITM for single-crystal XRD analysis and CSIR-IICB, Kolkata for HRMS data. This research work was carried out as a part of a Ph.D. degree registered at the University of Madras.

• References and Notes

• 1 Oda M, Nothofer HG, Scherf U, Šunjić V, Richter D, Regenstein W, Neher D. Macromolecules 2002; 35: 6792
• 2 Scherf U, List EJ. Adv. Mater. 2002; 7: 477
• 3 Belfield KD, Yao S, Bondar MV. Adv. Polym. Sci. 2008; 213: 97
• 4 Baheti A, Thomas KJ, Lee CP, Li CT, Ho KC. J. Mater. Chem. A 2014; 2: 5766
• 5 Takaaki IS, Takashi RT, Eiji K. (Numazu. Ricoh Company, Ltd., Tokyo, Japan) US Patent US005702855A, 1997
• 6 Thomas KJ, Venkateswararao A, Lee CP, Ho KC. Dyes Pigm. 2015; 123: 154
• 7 Miyatake K, Bae B, Watanabe M. Polym. Chem. 2011; 2: 1919
• 8 Liao YL, Hung WY, Hou TH, Lin CY, Wong KT. Chem. Mater. 2007; 19: 6350
• 9 Tao SL, Peng ZK, Zhang XH, Wang PF, Lee CS, Lee ST. Adv. Funct. Mater. 2005; 15: 1716
• 10 Perumattam J, Shao C, Confer WL. Synthesis 1994; 1182
• 11 Morgan LR, Thangaraj K, LeBlanc B, Rodgers A, Wolford LT, Hooper CL, Jursic BS. J. Med. Chem. 2003; 46: 4552
• 12a Liu W, Wang H, Zhao H, Li B, Chen S. Synlett 2015; 26: 2170
• 12b Bauer EB. Synthesis 2012; 44: 1131
• 12c Engel DA, Dudley GB. Org. Biomol. Chem. 2009; 7: 4149
• 12d Swaminathan S, Narayanan KV. Chem. Rev. 1971; 5: 429
• 12e Roy R, Saha S. RSC Adv. 2018; 8: 31129
• 13a Qian H, Huang D, Bi Y, Yan G. Adv. Synth. Catal. 2019; 361: 3240
• 13b Zhang L, Fang G, Kumar RK, Bi X. Synthesis 2015; 47: 2317
• 13c Cadierno V, Crochet P, Gimeno J. Synlett 2008; 8: 1105
• 14 Yu S, Ma S. Angew. Chem. Int. Ed. 2012; 51: 3074
• 15 Novanna M, Kannadasan S, Shanmugam P. Tetrahedron Lett. 2019; 60: 201
• 16 Meerakrishna RS, Periyaraja S, Shanmugam P. Eur. J. Org. Chem. 2016; 4516
• 17 Athira M, Meerakrishna RS, Shanmugam P. New J. Chem. 2020; 44: 6652
• 18a Yuan H, Zheng Y, Zhang J. J. Org. Chem. 2016; 5: 1989
• 18b Shao Y, Zhu K, Qin Z, Li E, Li Y. J. Org. Chem. 2013; 78: 5731
• 19 Zhu Y, Yin G, Hong D, Lu P, Wang Y. Org. Lett. 2011; 13: 1024
• 20 Muthusamy S, Balasubramani A, Suresh E. Adv. Synth. Catal. 2017; 359: 786
• 21 Liu Y, Barry BD, Yu H, Liu J, Liao P, Bi X. Org. Lett. 2013; 15: 2608
• 22 Muthusamy S, Balasubramani A, Suresh E. Adv. Synth. Catal. 2019; 361: 702
• 23 Wei LL, Xiong H, Hsung RP. Acc. Chem. Res. 2003; 36: 773
• 24 Roy R, Saha S. RSC Adv. 2018; 8: 31129
• 25 Chen S, Yuan F, Zhao H, Li B. Res. Chem. Intermed. 2013; 39: 2391
• 26 Bahadorikhalili S, Mahdavi M, Ma’mani L, Shafiee A, Mahdavi H, Akbarzadeh T. New J. Chem. 2018; 42: 5499
• 27 CCDC-1967615 (3e) and CCDC-1957144 (4a) contain the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.
• 28 Synthesis of Compounds 3a–m; General Procedure: To a stirred solution of propargylic alcohol derivative of fluorenone 1 (0.35 mmol, 1equiv) and aminobenzamide 2 (0.35 mmol, 1 equiv) in dichloromethane (5 mL) was added BF₃·OEt₂ (0.1 mmol, 0.3 equiv). The resulting reaction mixture was stirred at room temperature for 5 minutes. After the completion of the reaction (monitored by TLC), the reaction mixture was diluted with dichloromethane, washed with distilled water and saturated brine. The combined organic layers were dried over anhydrous Na₂SO₄, filtered, and the solvent was evaporated under reduced pressure. The crude mixture was purified by silica gel column chromatography (eluent: hexane/EtOAc) to afford the corresponding compounds 3a–m in good yields. Synthesis of Compounds 4a–d; General Procedure: To a solution of propargylic alcohol 1 (0.35 mmol, 1 equiv) and aminobenzamide 2 (0.35 mmol, 1 equiv) in dichloromethane (5 mL) was added NBS (0.4 mmol, 1.2 equiv) followed by BF₃·Et₂O (0.1 mmol, 0.3 equiv) and the reaction mixture was stirred at room temperature. After the completion of the reaction (monitored by TLC), the reaction mixture was diluted with dichloromethane, washed with distilled water and saturated brine. The combined organic layer was dried over anhydrous Na₂SO₄, filtered, and the solvent was evaporated under reduced pressure. The crude mixture was purified by silica gel column chromatography (eluent: hexane/EtOAc) to afford the corresponding compounds 4a–d in good yields. (Z)-2-((2-(9H-Fluoren-9-ylidene)-1-phenylethylidene)amino)benzamide (3a): Yield: 92%; yellow solid; R_f (30% EtOAc–Hexane): 0.45. FTIR (KBr): 3293, 3057, 2922, 2852, 1914, 1810, 1656, 1611, 1487, 1447, 1378, 1289, 1267, 1236, 1158, 1107, 1016, 943, 836, 747, 730, 697, 622 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 8.25 (s, 1 H), 8.13 (dd, J = 7.5, 1.8 Hz, 1 H), 7.98–7.95 (m, 2 H), 7.58–7.53 (m, 2 H), 7.47 (d, J = 7.6 Hz, 1 H), 7.43 (d, J = 7.3 Hz, 1 H), 7.35 (t, J = 7.5 Hz, 2 H), 7.29 (t, J = 7.1 Hz, 1 H), 7.21–7.15 (m, 2 H), 7.10 (ddd, J = 7.5, 4.8, 1.7 Hz, 3 H), 6.92 (t, J = 7.2 Hz, 1 H), 6.85 (s, 1 H), 6.73 (dd, J = 7.6, 1.3 Hz, 1 H), 6.07 (s, 1 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 119.1, 119.9, 120, 120.9, 121.1, 124.7, 125.7, 127.4, 127.5, 128.7, 129.2, 129.6, 129.7, 131.4, 132, 135.5, 137.3, 137.7, 139.9, 141.7, 142.7, 148.6, 166.9, 168.6. HRMS (ESI): m/z [M + H] calcd for C₂₈H₂₁N₂O: 401.1653; found: 401.1652.(Z)-2-((2-(9H-Fluoren-9-ylidene)-1-phenylethylidene)amino)benzenesulfonamide (3b): Yield: 90%; yellow solid; R_f (30% EtOAc–Hexane): 0.47. FTIR (KBr): 3360, 3268, 2923, 1918, 1643, 1604, 1587, 1535, 1445, 1401, 1344, 1276, 1254, 1209, 1171, 1128, 1070, 1024, 942, 857, 833, 807, 772, 730, 689, 620 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 8.06–8.03 (m, 2 H), 8.00 (dd, J = 7.9, 1.4 Hz, 1 H), 7.66 (dd, J = 7.5, 0.8 Hz, 2 H), 7.57 (d, J = 7.6 Hz, 1 H), 7.53–7.48 (m, 1 H), 7.44–7.37 (m, 3 H), 7.32 (ddd, J = 10.2, 8.2, 1.3 Hz, 2 H), 7.27 (dd, J = 2.6, 1.3 Hz, 1 H), 7.25–7.22 (m, 2 H), 7.18–7.14 (m, 1 H), 7.03 (td, J = 7.6, 1.1 Hz, 1 H), 6.97 (s, 1 H), 6.77 (dd, J = 7.9, 1.0 Hz, 1 H), 5.34 (s, 2 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 119.7, 119.9, 120.1, 120.9, 121.5, 124.6, 125.9, 127, 127.4, 127.6, 128.8, 129.2, 129.6, 129.7, 132.3, 132.8, 133.6, 135.8, 137, 137.7, 139.9, 141.9, 142.4, 148.2, 169.5. HRMS (ESI): m/z [M + H] calcd for C₂₇H₂₁N₂O₂S: 437.1323; found: 437.1323.(Z)-2-((2-(9H-Fluoren-9-ylidene)-1-phenylethylidene)amino)-5-iodobenzamide (3c): Yield: 91%; yellow solid; R_f (30% EtOAc–Hexane): 0.50. FTIR (KBr): 3413, 3339, 3149, 2971, 2924, 1670, 1608, 1575, 1495, 1447, 1404, 1350, 1294, 1256, 1211, 1159, 1095, 1018, 951, 918, 862, 813, 780, 733, 698, 663 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 8.46 (d, J = 2.1 Hz, 1 H), 8.19 (s, 1 H), 7.99–7.94 (m, 2 H), 7.57 (dd, J = 11.0, 7.6 Hz, 2 H), 7.51 (d, J = 7.6 Hz, 1 H), 7.48–7.39 (m, 2 H), 7.34 (ddd, J = 10.7, 8.3, 4.3 Hz, 3 H), 7.22 (ddd, J = 7.6, 4.3, 0.9 Hz, 2 H), 7.06 (d, J = 7.7 Hz, 1 H), 6.91 (td, J = 7.7, 0.9 Hz, 1 H), 6.82 (s, 1 H), 6.48 (d, J = 8.4 Hz, 1 H), 5.74 (s, 1 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 89.9, 118.5, 120.0, 120.4, 121.2, 122.8, 125.8, 126.7, 127.5, 127.7, 128.8, 129.3, 129.9, 129.4, 132.4, 135.4, 137.2, 137.6, 140.1, 140.2, 140.7, 141.9, 143.2, 148.1, 166.9, 167.5. HRMS (ESI): m/z [M + H] calcd for C₂₈H₂₀IN₂O: 527.0620; found: 527.0619.(Z)-2-((2-(9H-Fluoren-9-ylidene)-1-phenylethylidene)amino)-N-phenylbenzamide (3d): Yield: 89%; yellow crystals; R_f (10% EtOAc–Hexane): 0.49. FTIR (KBr): 3418, 3114, 3058, 1915, 1710, 1662, 1595, 1537, 1494, 1445, 1401, 1315, 1279, 1249, 1157, 1124, 882, 752, 730, 694, 620 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.75 (s, 1 H), 8.25–8.20 (m, 1 H), 8.05–8.01 (m, 2 H), 7.52 (dd, J = 12.3, 7.5 Hz, 2 H), 7.47–7.36 (m, 6 H), 7.26 (dd, J = 7.5, 0.8 Hz, 1 H), 7.17 (d, J = 2.3 Hz, 1 H), 7.15–7.11 (m, 5 H), 7.08–7.06 (m, 1 H), 6.96–6.92 (m, 1 H), 6.90 (s, 1 H), 6.81–6.76 (m, 2 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 118.8, 120.0, 120.1, 121.0, 121.2, 123.9, 125.9, 126.1, 126.3, 127.4, 127.6, 128.9, 129.0, 129.2, 129.8, 131.6, 131.8, 132.4, 135.4, 137.4, 137.7, 138.7, 140.1, 141.8, 143.1, 147.7, 164.3, 167.3. HRMS (ESI): m/z [M + H] calcd for C₃₄H₂₅N₂O: 477.1966; found: 477.1970.(Z)-2-((2-(9H-Fluoren-9-ylidene)-1-phenylethylidene)amino)-N-(3-bromophenyl)benzamide (3e): Yield: 90%; yellow crystals; R_f (15% EtOAc–Hexane): 0.45. FTIR (KBr): 3649, 3051, 3012, 2971, 2922, 2363, 1942, 1913, 1665, 1589, 1523, 1476, 1446, 1417, 1285, 1249, 1159, 1126, 1064, 994, 956, 913, 877, 768, 726, 697, 674, 621 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.98 (s, 1 H), 8.24–8.21 (m, 1 H), 8.05–8.02 (m, 2 H), 7.57 (d, J = 2.0 Hz, 1 H), 7.54 (d, J = 4.5 Hz, 1 H), 7.53–7.47 (m, 3 H), 7.42 (d, J = 7.2 Hz, 3 H), 7.32–7.28 (m, 1 H), 7.20–7.16 (m, 3 H), 7.15 (d, J = 1.9 Hz, 1 H), 7.06 (d, J = 7.8 Hz, 2 H), 7.00 (t, J = 8.0 Hz, 1 H), 6.90 (s, 1 H), 6.84–6.79 (m, 2 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 118.3, 118.6, 120.0, 120.1, 121.1, 121.2, 122.6, 122.8, 125.8, 125.9, 126.5, 126.7, 127.4, 127.6, 128.8, 129.4, 129.8, 129.9, 130.3, 131.6, 132.1, 132.6, 135.4, 137.4, 137.7, 140.0, 140.1, 141.8, 143.5, 147.6, 164.3, 167.4. HRMS (ESI): m/z [M + 2] calcd for C₃₄H₂₄BrN₂O: 557.1072; found: 557.1060.(Z)-2-((2-(9H-fluoren-9-ylidene)-1-phenylethylidene)amino)-N-(p-toluenesulfonyl)benzamide (3f): Yield: 88%; yellow solid; R_f (15% EtOAc–Hexane): 0.49. FTIR (KBr): 3009, 2919, 1911, 1652, 1593, 1564, 1527, 1446, 1404, 1345, 1314, 1280, 1248, 1177, 1124, 1090, 1019, 881, 849, 812, 767, 729, 696, 621 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.70 (s, 1 H), 8.23 (dd, J = 6.0, 3.5 Hz, 1 H), 8.06–8.03 (m, 2 H), 7.57–7.52 (m, 2 H), 7.48 (t, J = 7.7 Hz, 2 H), 7.39 (d, J = 7.2 Hz, 2 H), 7.31 (dd, J = 14.2, 7.8 Hz, 3 H), 7.20–7.14 (m, 4 H), 7.09 (d, J = 7.8 Hz, 1 H), 6.97 (d, J = 8.3 Hz, 2 H), 6.91 (s, 1 H), 6.81 (ddd, J = 11.9, 6.6, 2.4 Hz, 2 H), 2.20 (s, 3 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 20.9, 118.9, 119.9, 120.0, 120.1, 120.9, 121.2, 125.9, 126.1, 126.3, 127.4, 127.6, 128.9, 129.2, 129.5, 129.7, 129.8, 131.5, 131.8, 132.4, 133.4, 135.5, 136.1, 137.4, 137.8, 140.1, 141.8, 143.1, 147.7, 164.1, 167.1. HRMS (ESI): m/z [M + H] calcd for C₃₅H₂₇N₂O: 491.2123; found: 491.2122.(Z)-2-((2-(9H-Fluoren-9-ylidene)-1-(p-toluenesulfonyl)ethylidene)amino)-N-phenylbenzamide (3g): Yield: 87%; yellow solid; R_f (15% EtOAc–Hexane): 0.49. FTIR (KBr): 3566, 3057, 2921, 2852, 2364, 1718, 1666, 1597, 1561, 1538, 1495, 1446, 1315, 1280, 1247, 1178, 1121, 1036, 824, 776, 753, 730, 692, 621 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.82 (s, 1 H), 8.22 (dd, J = 6.0, 3.5 Hz, 2 H), 7.94 (d, J = 8.2 Hz, 2 H), 7.54 (dd, J = 11.8, 7.5 Hz, 2 H), 7.48 (dd, J = 7.4, 2.4 Hz, 3 H), 7.31–7.27 (m, 1 H), 7.20–7.15 (m, 6 H), 7.14–7.10 (m, 3 H), 6.96 (t, J = 7.4 Hz, 1 H), 6.90 (s, 1 H), 6.84–6.76 (m, 2 H), 2.35 (s, 3 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 21.8, 119.2, 119.9, 120.0, 120.1, 121.1, 123.9, 125.9, 126.0, 126.1, 127.5, 127.6, 128.9, 129.0, 129.7, 129.8, 130.0, 131.5, 131.9, 134.6, 135.5, 137.7, 138.7, 140.0, 141.7, 142.9, 143.1, 147.8, 164.4, 167.1. HRMS (ESI): m/z [M + H] calcd for C₃₅H₂₇N₂O: 491.2123; found: 491.2123.(Z)-2-((2-(9H-Fluoren-9-ylidene)-1-(p-toluenesulfonyl)ethylidene)amino)-N-(3-bromophenyl)benzamide (3h): Yield: 91%; yellow solid; R_f (15% EtOAc–Hexane): 0.49. FTIR (KBr): 3772, 3050, 3009, 2922, 2852, 1938, 1661, 1589, 1553, 1418, 1351, 1313, 1300, 1286, 1251, 1224, 1180, 1158, 1043, 773, 724, 695, 625 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 11.04 (s, 1 H), 8.23–8.20 (m, 1 H), 7.93 (d, J = 8.2 Hz, 2 H), 7.57–7.52 (m, 3 H), 7.49–7.47 (m, 2 H), 7.29 (td, J = 7.5, 0.9 Hz, 1 H), 7.24–7.19 (m, 3 H), 7.17 (s, 1 H), 7.16–7.13 (m, 2 H), 7.10 (s, 1 H), 7.07 (dd, J = 6.5, 1.6 Hz, 1 H), 7.01 (d, J = 7.9 Hz, 1 H), 6.89 (s, 1 H), 6.85–6.80 (m, 2 H), 2.35 (s, 3 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 21.8, 118.4, 118.8, 120.0, 120.1, 121.1, 121.2, 122.6, 122.8, 125.8, 126.0, 126.3, 126.7, 127.4, 127.6, 128.8, 129.8, 129.9, 130.2, 130.4, 131.4, 131.5, 132.1, 134.8, 135.5, 137.8, 140.1, 141.8, 143.2, 143.4, 143.7, 164.4, 167.2. HRMS (ESI): m/z [M + 2] calcd for C₃₅H₂₆BrN₂O: 571.1206; found: 571.1213.(Z)-2-((2-(9H-Fluoren-9-ylidene)-1-(p-toluenesulfonyl)ethylidene)amino)-N-(p-toluenesulfonyl)benzamide (3i): Yield: 88%; yellow solid; R_f (15% EtOAc–Hexane): 0.49. FTIR (KBr): 3465, 3361, 3271, 3171, 3040, 2917, 2854, 2363, 1920, 1715, 1658, 1539, 1512, 1473, 1446, 1405, 1319, 1281, 1246, 1176, 1128, 1089, 1039, 1014, 983, 938, 895, 851, 815, 777, 728, 693, 664, 621 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.75 (s, 1 H), 8.22 (dd, J = 5.9, 3.6 Hz, 1 H), 7.93 (d, J = 8.2 Hz, 2 H), 7.54 (dd, J = 11.7, 7.5 Hz, 2 H), 7.47 (d, J = 7.6 Hz, 1 H), 7.36 (d, J = 8.4 Hz, 2 H), 7.28 (dd, J = 10.9, 4.0 Hz, 1 H), 7.18 (d, J = 8.7 Hz, 2 H), 7.11 (dd, J = 6.1, 3.3 Hz, 3 H), 6.98 (d, J = 8.2 Hz, 2 H), 6.90 (s, 1 H), 6.84–6.79 (m, 1 H), 6.77 (dd, J = 5.9, 3.2 Hz, 1 H), 2.34 (s, 3 H), 2.20 (s, 3 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 21.0, 21.8, 119.3, 119.9, 120.0, 121.0, 121.1, 125.9, 126.0, 127.4, 127.5, 128.9, 129.5, 129.7, 130.0, 131.4, 131.7, 133.4, 135.5, 136.2, 137.7, 140.0, 141.7, 142.8, 143.0, 147.8, 164.2, 170.0. HRMS (ESI): m/z [M + H] calcd for C₃₆H₂₉N₂O: 505.2279; found: 505.2273.(Z)-2-((2-(9H-Fluoren-9-ylidene)-1-(p-toluenesulfonyl)ethylidene)amino)-N-(3,5-dimethylphenyl)benzamide (3j): Yield: 75%; yellow solid; R_f (15% EtOAc–Hexane): 0.49. FTIR (KBr): 3163, 3057, 2961, 3919, 2850, 2359, 1910, 1717, 1658, 1594, 1558, 1537, 1502, 1469, 1446, 1405, 1313, 1280, 1252, 1176, 1130, 1092, 1043, 937, 880, 862, 826, 777, 728, 695, 662, 620 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.84 (s, 1 H), 8.32 (dd, J = 5.9, 3.6 Hz, 1 H), 8.03 (d, J = 8.2 Hz, 1 H), 7.64 (dd, J = 11.5, 7.5 Hz, 2 H), 7.57 (d, J = 7.6 Hz, 1 H), 7.42–7.36 (m, 2 H), 7.30–7.26 (m, 4 H), 7.22 (dd, J = 6.7, 3.1 Hz, 3 H), 7.18 (s, 1 H), 7.03 (d, J = 8.2 Hz, 1 H), 6.98 (s, 1 H), 6.93 (td, J = 7.7, 0.9 Hz, 1 H), 6.86 (dd, J = 5.9, 3.2 Hz, 1 H), 2.44 (s, 3 H), 2.20 (s, 3 H), 2.15 (s, 3 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 19.3, 19.8, 21.7, 117.4, 119.1, 119.9, 120.0, 120.9, 121.2, 121.3, 125.9, 126.0, 126.1, 127.5, 127.6, 128.9, 129.7, 129.9, 130.0, 131.4, 131.7, 132.1, 134.8, 135.6, 136.5, 1370, 137.8, 140.0, 141.7, 142.9, 142.9, 147.7, 134.1, 166.9. HRMS (ESI): m/z [M + H] calcd for C₃₇H₃₁N₂O: 519.2436; found: 519.2438. (Z)-2-((1-(4-Bromophenyl)-2-(9H-fluoren-9-ylidene)ethylidene) amino)-N-phenylbenzamide (3k): Yield: 84%; yellow solid; R_f (10% EtOAc–Hexane): 0.47. FTIR (KBr): 3645, 3052, 3010, 2970, 2932, 2363, 1942, 1913, 1665, 1589, 1523, 1476, 1446, 1417, 1285, 1249, 1159, 1126, 1064, 994, 956, 877, 768, 726, 674, 623 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.55 (s, 1 H), 8.25–8.21 (m, 1 H), 7.93–7.91 (m, 2 H), 7.58–7.53 (m, 4 H), 7.49–7.42 (m, 3 H), 7.33–7.29 (m, 1 H), 7.21 (dd, J = 10.8, 4.3 Hz, 4 H), 7.18 (d, J = 0.8 Hz, 1 H), 7.17 (dd, J = 2.5, 1.0 Hz, 1 H), 7.05 (d, J = 7.7 Hz, 1 H), 6.99 (dd, J = 10.0, 3.7 Hz, 1 H), 6.88–6.85 (m, 2 H), 6.80–6.78 (m, 1 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 118.2, 120.0, 120.1, 120.2, 120.9, 121.2, 124.1, 125.8, 126.5, 127.3, 127.6, 127.7, 129.2, 130.0, 130.1, 130.2, 131.6, 132.0, 132.6, 135.3, 136.3, 137.6, 138.6, 140.1, 141.9, 143.6, 147.5, 164.2, 166.4. HRMS (ESI): m/z [M + 2] calcd for C₃₄H₂₄BrN₂O: 557.1052; found: 557.1053.(Z)-N-(3-Bromophenyl)-2-((1-(4-bromophenyl)-2-(9H-fluoren-9-ylidene)ethylidene)amino)benzamide (3l): Yield: 83%; yellow solid; R_f (15% EtOAc–Hexane): 0.48. FTIR (KBr): 3060, 2923, 2850, 1668, 1589, 1531, 1478, 1445, 1417, 1304, 1284, 1247, 1171, 1121, 1072, 1007, 859, 835, 774, 727, 680, 621 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.78 (s, 1 H), 8.24–8.21 (m, 1 H), 7.92–7.89 (m, 2 H), 7.56 (t, J = 5.5 Hz, 4 H), 7.52 (dd, J = 6.9, 5.0 Hz, 2 H), 7.47 (d, J = 7.6 Hz, 1 H), 7.44–7.41 (m, 1 H), 7.30 (dt, J = 7.5, 3.7 Hz, 1 H), 7.23–7.20 (m, 1 H), 7.18 (s, 2 H), 7.09 (dd, J = 6.6, 1.8 Hz, 1 H), 7.06–7.03 (m, 2 H), 6.87 (dd, J = 7.6, 1.0 Hz, 1 H), 6.85 (s, 1 H), 6.82–6.80 (m, 1 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 117.9, 118.2, 120.1, 120.3, 121.0, 121.3, 122.7, 122.8, 125.8, 125.9, 126.7, 126.9, 127.5, 127.9, 127.7, 130.1, 130.2, 130.3, 130.5, 131.6, 132.2, 132.7, 135.2, 136.4, 137.6, 139.8, 140.1, 141.9, 143.9, 147.4, 164.2, 166.5. HRMS (ESI): m/z [M + 4] calcd for C₃₄H₂₃Br₂N₂O: 637.0177; found: 637.1037.(Z)-N-(3-Bromophenyl)-2-((2-(2,7-dibromo-9H-fluoren-9-ylidene)-1-phenylethylidene)amino)benzamide (3m): Yield: 69%; yellow solid; R_f (15% EtOAc–Hexane): 0.49. FTIR (KBr): 3056, 2919, 2849, 1734, 1671, 1589, 1533, 1476, 1447, 1422, 1307, 1251, 1063, 1003, 952, 879, 810, 773, 696 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 10.97 (s, 1 H), 8.30–8.26 (m, 1 H), 8.00–7.97 (m, 2 H), 7.62 (d, J = 1.4 Hz, 1 H), 7.58–7.54 (m, 2 H), 7.49 (d, J = 7.8 Hz, 2 H), 7.43 (d, J = 1.4 Hz, 1 H), 7.41–7.35 (m, 3 H), 7.31 (dd, J = 8.1, 1.5 Hz, 1 H), 7.24–7.21 (m, 2 H), 7.14 (d, J = 1.4 Hz, 1 H), 7.06 (dd, J = 6.8, 1.6 Hz, 1 H), 7.01 (d, J = 8.0 Hz, 1 H), 6.98 (s, 1 H), 6.83–6.79 (m, 1 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 118.4, 121.1, 121.2, 121.3, 121.4, 121.5, 121.9, 122.6, 122.9, 124.6, 126.1, 126.8, 127.0, 128.7, 129.2, 129.6, 130.2, 131.9, 132.1, 133.0, 136.7, 137.2, 137.9, 139.3, 139.7, 140.0, 141.3, 147.0, 164.0, 166.1. HRMS (ESI): m/z [M + 6] calcd for C₃₄H₂₁Br₃N₂O: 716.9222; found: 716.9244.(E)-5-Bromo-2-((2-bromo-2(9H-fluoren-9-ylidene)-1-phenyl ethylidene)amino)benzamide (4a): Yield: 60%; yellow solid; R_f (15% EtOAc–Hexane): 0.43. FTIR (KBr): 3400, 3059, 1664, 1604, 1576, 1462, 1447, 1408, 1344, 1315, 1263, 1204, 1181, 1096, 1056, 1024, 936, 851, 811, 779, 730, 691, 649, 620 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 8.52 (d, J = 7.9 Hz, 1 H), 8.23 (d, J = 2.3 Hz, 1 H), 7.98 (dd, J = 5.3, 3.3 Hz, 2 H), 7.87 (s, 1 H), 7.61 (d, J = 7.2 Hz, 1 H), 7.56 (d, J = 7.5 Hz, 1 H), 7.50–7.46 (m, 1 H), 7.39 (ddd, J = 9.6, 7.0, 4.0 Hz, 3 H), 7.31 (d, J = 7.9 Hz, 1 H), 7.25 (ddd, J = 7.3, 6.8, 3.8 Hz, 2 H), 7.17 (dd, J = 6.4, 2.1 Hz, 1 H), 6.98 (td, J = 7.8, 1.1 Hz, 1 H), 6.62 (d, J = 8.5 Hz, 1 H), 6.05 (s, 1 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 113.1, 119.3, 119.9, 120.0, 120.6, 124.4, 126.4, 126.6, 127.6, 127.9, 128.6, 129.5, 129.6, 130.4, 132.7, 134.1, 134.2, 134.9, 136.2, 136.3, 139.9, 140.3, 141.5, 146.2, 165.6, 166.6. HRMS (ESI): m/z [M + 4] calcd for C₂₈H₁₉Br₂N₂O: 560.9864; found: 560.9847.(E)-2-((2-Bromo-2-(9H-fluoren-9-ylidene)-1-(p-toluenesulfonyl) ethylidene)amino)benzamide (4b): Yield: 75%; yellow solid; R_f (15% EtOAc–Hexane): 0.45. FTIR (KBr): 3608, 3440, 3341, 3159, 3059, 2919, 2852, 1670, 1563, 1492, 1471, 1445, 1374, 1290, 1267, 1204, 1181, 1113, 1059, 1019, 977, 926, 834, 777, 727, 660, 624 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 8.51 (d, J = 7.9 Hz, 1 H), 8.11–8.07 (m, 1 H), 7.96 (s, 1 H), 7.88 (d, J = 8.3 Hz, 2 H), 7.61–7.53 (m, 2 H), 7.39–7.33 (m, 2 H), 7.26–7.18 (m, 4 H), 7.06 (dd, J = 5.9, 3.5 Hz, 2 H), 7.01–6.97 (m, 1 H), 6.74–6.71 (m, 1 H), 5.95 (s, 1 H), 2.33 (s, 3 H); ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 21.7, 114.2, 119.0, 119.9, 120.0, 124.7, 125.7, 126.4, 127.6, 128.0, 128.7, 129.5, 130.2, 130.3, 131.4, 131.8, 132.2, 136.5, 136.6, 139.6, 140.3, 141.5, 143.4, 147.5, 164.9, 168.3. HRMS (ESI): m/z [M + 2] calcd for C₂₉H₂₂BrN₂O: 495.0995; found: 495.1180.(E)-2-((2-Bromo-2-(9H-fluoren-9-ylidene)-1-phenyl­ethylidene)amino)benzenesulfonamide (4c): Yield: 73%; yellow solid; R_f (15% EtOAc–Hexane): 0.44. FTIR (KBr): 3358, 3260, 2920, 1915, 1641, 1611, 1530, 1444, 1344, 1276, 1254, 1209, 1171, 1128, 1070, 1024, 942, 857, 832, 807, 772, 689, 620 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 8.58 (d, J = 7.9 Hz, 1 H), 7.98–7.93 (m, 3 H), 7.66 (d, J = 7.6 Hz, 1 H), 7.61 (d, J = 7.5 Hz, 1 H), 7.45–7.39 (m, 3 H), 7.38–7.35 (m, 2 H), 7.29–7.24 (m, 2 H), 7.16–7.11 (m, 2 H), 7.00 (td, J = 7.9, 1.0 Hz, 1 H), 6.90–6.87 (m, 1 H), 5.39 (s, 2 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 21.0, 21.8, 119.3, 120.0, 121.0, 121.1, 125.9, 126.0, 127.4, 127.5, 128.9, 129.5, 129.7, 129.8, 131.4, 131.7, 133.4, 134.6, 135.5, 136.2, 137.7, 140.0, 141.7, 142.8, 143.0, 147.8, 164.2, 166.9. HRMS (ESI): m/z [M + 2] calcd for C₂₇H₂₀BrN₂O₂S: 517.0408; found: 517.0420.(E)-2-((2-Bromo-2-(9H-fluoren-9-ylidene)-1-phenyl­ethylidene)amino)-5-iodobenzamide (4d): Yield: 72%; yellow solid; R_f (15% EtOAc–Hexane): 0.43. FTIR (KBr): 3370, 3327, 3145, 3063, 2921, 2774, 2252, 1959, 1903, 1811, 1669, 1596, 1565, 1445, 1404, 1347, 1314, 1260, 1202, 1152, 1087, 1052, 1022, 935, 904, 872, 845, 801, 774, 727, 688, 645, 622 cm^–1. ¹H NMR (400 MHz, CDCl₃/TMS): δ = 8.52 (d, J = 7.9 Hz, 1 H), 8.40 (d, J = 2.1 Hz, 1 H), 7.99–7.96 (m, 2 H), 7.84 (d, J = 2.6 Hz, 1 H), 7.60 (d, J = 7.5 Hz, 1 H), 7.56–7.54 (m, 1 H), 7.47–7.44 (m, 1 H), 7.41–7.33 (m, 5 H), 7.30 (d, J = 7.9 Hz, 1 H), 7.27–7.19 (m, 2 H), 6.97 (td, J = 7.8, 1.1 Hz, 1 H), 6.49–6.46 (m, 1 H). ¹³C NMR (CDCl₃/TMS, 100.6 MHz): δ = 90.1, 113.2, 120.0, 120.1, 120.9, 124.5, 126.5, 126.6, 127.7, 128.0, 128.8, 129.6, 129.7, 130.5, 132.9, 134.2, 136.3, 136.4, 139.9, 140.1, 140.4, 140.9, 141.6, 146.9, 165.6, 166.8. HRMS (ESI): m/z [M + 2] calcd for C₂₈H₁₉BrIN₂O: 606.9705; found: 606.9719.

Publication History

Received: 16 May 2020

Accepted after revision: 03 January 2021

Article published online:
25 January 2021