Palladium-Catalyzed Direct Acylation: One-Pot Relay Synthesis of Anthraquinones

Basuli Suchand; Gedu Satyanarayana

doi:10.1055/s-0037-1610296

Synthesis, Inhaltsverzeichnis

Synthesis 2019; 51(03): 769-779
DOI: 10.1055/s-0037-1610296

paper

Palladium-Catalyzed Direct Acylation: One-Pot Relay Synthesis of Anthraquinones

Basuli Suchand

,

Gedu Satyanarayana *

Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi 502 285, Sangareddy, Telangana, India eMail: gvsatya@iith.ac.in

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Abstract

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Key words

anthraquinone - catalysis - acylation - one-pot - Friedel–Crafts acylation

Anthraquinones are essential chemical compounds and are prominent in pharmaceutical and materials chemistry.[1] A wide range of natural products constitute anthraquinone structural motif, manifesting interesting biological features.[2] These anthraquinone-based natural products are significant constituents in lichens, bacteria, fungi, enzymes, and higher plants. Also, anthraquinones are present in vitamins, pigments, etc.[3] They exhibit anticancer, antitumor, antineoplastic, antibacterial, anti-HIV, and antitrypanosomal activities.[4] For example, mitoxantrone (5), ametantrone (6), and doxorubicin (7) exhibit potent antitumor activities and have been utilized in medical care as powerful anticancer agents for the treatment of various leukemia and lymphomas (Figure [1]).[5] Moreover, anthraquinone derivatives are industrially utilized as versatile dyeing agents for coloring synthetic and natural fibers, such as wool, silk, cotton, polyester, and polyamide.[6] In addition, these compounds have outstanding photo-oxidant properties, enabling them to absorb UV-A radiation. Further, anthraquinones are capable of cleaving protein molecules upon photoirradiation.[7] Anthraquinone derivatives also serve as useful precursors for the synthesis of organic semiconductors and electronic devices.[8]

Figure 1 Representative examples of bioactive anthraquinones

The anthraquinones have been the target of synthetic chemists to accomplish various chemical strategies.[9] [10] As a result, numerous synthetic routes as well as their industrial applications have been exclusively examined. Anthraquinones are extensively synthesized on the industrial level as dye reagents. The diverse scope for anthraquinone derivatives includes Friedel–Crafts acylation reaction of phthalic anhydride with various substituted arenes,[9a] oxidation of anthracenes or hydroxyanthracenes,[9h] reaction of isobenzofuran and chromium carbenes,[9e] Lewis acid catalyzed or thermal Diels–Alder reactions and aromatization sequences,[9b] [g] [i] Diels–Alder reaction catalyzed by zinc iodide followed by Friedel–Crafts reaction,[9j] cyclization reactions of polyketides,[9c] [d] and copper-catalyzed intramolecular enyne cyclization.[9f] The cyclization reaction between reduced 1,4-naphthoquinone and ortho-phthalaldehyde,[10b] and intramolecular dehydro Diels–Alder approach[10a] also belong to further routes towards anthraquinones. Apart from these advantages, most of these synthetic routes display a number of limitations, such as multiple reaction steps and the use of expensive catalysts.

Therefore, still, there is a room to develop simple, mild, and efficient strategies, which enable the synthesis of a range of anthraquinone derivatives. In this regard, we felt that sequential one-pot transformation would serve as an ideal protocol. Sequential one-pot methods render the construction of more than one bond and yield the products with reasonable complexity. Also, in comparison to stepwise methods, such protocols could contribute to some extent in saving time and reducing the amount of waste generated. Furthermore, these processes cut down the mundane task of isolating and purifying the intermediate product(s). In particular, transition-metal-catalyzed coupling reactions are very significant in the construction of carbon–carbon and carbon–heteroatom bonds.[11] Therefore, we presumed that the synthesis of anthraquinones can be executed by means of a one-pot method, through transition-metal-catalyzed acylation and intramolecular Friedel–Crafts acylation. In this context, we have established direct acylation using benchtop aldehydes as non-toxic acylating agents, under palladium catalysis.[12] Unlike earlier reports, the present protocol deals with [Pd]-catalyzed direct coupling (acylation) of iodoarenes with unactivated aldehydes.[13a] [e] Based on this concept of direct acylation, recently, we have demonstrated one-pot formation of indenones, lactams, and phthalzines.[13] Inspired by these results, herein, we describe an efficient sequential one-pot protocol, for the synthesis of various anthraquinones starting from commercially available ortho-iodobenzoates and aldehydes.

We intended that anthraquinones 3 could be achieved from ortho-keto esters 4 by employing intramolecular Friedel–Crafts acylation. The required ortho-keto esters 4 would be accomplished from ortho-iodomethylbenzoates 1 via [Pd]-catalyzed acylations as shown in Scheme [1].

Scheme 1 Anticipated retrosynthetic route of anthraquinones 3

In order to evaluate our protocol for the preparation of anthraquinones, we initiated the synthetic investigations by choosing methyl 2-iodobenzoate (1a) and aldehyde 2a as the model substrates. It has already been established that TBHP (tert-butyl hydroperoxide) in decane is as effective as TBHP in H₂O for carrying out acylation reaction in the presence of [Pd]-catalyst.[13a] Therefore, it was anticipated that the desired second reaction step (intramolecular Friedel–Crafts acylation) may be feasible in decane as inert solvent and would avoid the aid of any other solvent. Thus, the acylation reaction was carried out by subjecting ortho-iodoester 1a with aldehyde 2a using our previously reported conditions [i.e., Pd(OAc)₂ (5 mol%), Ag₂O (1.2 equiv), TBHP in decane (5 equiv), 120 °C, 14 h].[13a] After confirming the formation of acylation product 4aa by TLC, the subsequent acid-mediated Friedel–Crafts type cyclization was explored under various conditions (Table [1]). Thus, the reaction mixture containing 4aa was reacted with concentrated H₂SO₄ (10.0 equiv) at room temperature for 3 hours. Unfortunately, no progress was observed and only the acylated product 4aa was isolated in 67% yield (Table [1], entry 1). Addition of DCE as second solvent along with the acid to the reaction mixture of 4aa did not show any progress (entry 2). Even AlCl₃ and TfOH could not promote the reaction, respectively (entries 3, 4). On the other hand, acylation reaction was performed in TBHP/H₂O and subsequently, the acylated product 4aa, was treated with concentrated H₂SO₄ at room temperature for 5 hours (entry 5). This attempt was also futile to furnish the product 3aa. Gratifyingly, trace amounts of anthraquinone 3aa and more amounts of transesterification products were observed when the cyclization was conducted in EtOH as solvent at 65 °C for 10 hours (entry 6). Formation of transesterification product could be attributed to the nucleophilic nature of EtOH. This preliminary progress encouraged us to search for more efficient conditions for this transformation. With the increased amount of acid and at slightly elevated temperature (75 °C) for 12 hours, the product 3aa was formed in 10% yield (entry 7). Replacing EtOH with non-nucleophilic and inert solvent (DCE) and with increased amount of concentrated H₂SO₄ (0.5 mL) at 60 °C for 3 hours, afforded the desired anthraquinone product 3aa in 55% yield (entry 8). Interestingly, further increasing the amount of acid, from 0.5 mL to 1.0 mL, increased the overall yield of the product 3aa to 62% (entry 9). However, no progress was observed when the reaction was conducted at room temperature (entry 10), while further increasing the amount of acid decreased the product 3aa yield to 46% (entry 11). This might be due to decomposition of product 3aa with excess amount of strong acid. Acylation in TBHP/decane and subsequent acid-mediated cyclization without additional solvent at 60 °C for 2 hours, gave 3aa in 42% yield (entry 12). On the other hand, by the addition of solvent DCE for the cyclization step, the product 3aa was accomplished in 50% yield (entry 13).

Table 1 Screening Conditions for One-Pot Synthesis of Anthraquinone 3aa via the Keto Ester 4aa ^a

Entry	TBHP (5 equiv)	Acid (equiv or mL)	Solvent (2.0 mL)	Temp (°C)	Time (h)	Yield (%)^b 3aa	Yield (%)^b 4aa
1	TBHP/decane	H₂SO₄ (10.0)	–^c	r.t.	3	–^d	67
2	TBHP/decane	H₂SO₄ (10.0)	DCE	r.t.	3	–^d	65
3	TBHP/decane	AlCl₃ (5.0)	DCE	r.t.	5	–^d	62
4	TBHP/decane	TfOH (10.0)	DCE	r.t.	3	–^d	60
5	TBHP/H₂O	H₂SO₄ (10.0)		r.t.	5	–^d	65
6	TBHP/H₂O	H₂SO₄ (10.0)	EtOH	65	6	trace (3aa) + transesterification	–^e
7	TBHP/H₂O	H₂SO₄ (0.5 mL)	EtOH	75	12	10% (3aa) + transesterification	–^e
8	TBHP/H₂O	H₂SO₄ (0.5 mL)	DCE	60	3	55	–^e
9	TBHP/H₂O	H₂SO₄ (1.0 mL)	DCE	60	2	62	–^e
10	TBHP/H₂O	H₂SO₄ (1.0 mL)	DCE	r.t.	5	–^d	55
11	TBHP/H₂O	H₂SO₄ (2.0 mL)	DCE	60	1.5	46	–^e
12	TBHP/decane	H₂SO₄ (1.0 mL)	–^c	60	2	42	–^e
13	TBHP/decane	H₂SO₄ (1.0 mL)	DCE	60	2	50	–^e

^a Reaction was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2a (217.0 mg, 1.6 mmol).

^b Chromatographically isolated yields of pure compounds.

^c No second solvent was used.

^d No 3aa was formed.

^e No 4aa remained.

With the above optimized conditions (Table [1], entry 9), next, it was sought to investigate the scope of the method by exploring the reaction between methyl 2-iodobenzoate (1a) and other benzaldehydes 2. Gratifyingly, the process was feasible and furnished the desired anthraquinone products 3aa–ak (Scheme [2]). The reaction was smooth with electron-releasing substituents on the aromatic ring of benzaldehydes 2a–d, 2j, and 2k (OMe, OEt, and -OCH₂O-). Remarkably, the protocol was also compatible with benzaldehydes 2f–i possessing free hydroxyl group (Scheme [2], 3af–ai). Significantly, the efficiency of the reaction was not impeded by ortho-substituents on the benzaldehyde moiety 2h (3ah). Notably, the reaction was also competent with highly electron-rich benzaldehyde 2k (i.e., trimethoxybenzaldehyde 3ak). However, it is worth noticing that in the case of para-methoxybenzaldehyde (2l), the expected product 3al was not formed. No progress of the desired cyclized product formation was observed even after 10 hours, however, with excess amount of concentrated H₂SO₄ (3.0 mL), complete decomposition of the reaction mixture took place. This may be attributed to the fact that the electron-releasing methoxy group is in meta relation to the reacting carbon of that aromatic ring and hence, could not promote the second acylation step. Notably, this observation is in good agreement to that of earlier report published by Hilt et al.[9j]

Scheme 2 Scope of the method for one-pot synthesis of anthraquinone 3aa–ak. Isolated yields of chromatographically pure products 3aa–ak are given. Product 3ai was not formed.

Furthermore, to demonstrate the applicability of the present protocol, next, we turned our attention to check the scope of the method by means of iodoester precursors 1. Therefore, the reaction was performed between various methyl 2-iodobenzoates 1b–d and benzaldehydes 2a–j. Gratifyingly, the reaction was also found suitable and furnished the products 3ba–da (Scheme [3]). As anticipated, the reaction was successful with methyl substituted ortho-iodoester 1b with benzaldehydes 2a–j (Scheme [3], 3ba–bj). To our delight, this protocol was also found smooth to methyl 2-iodobenzoates 1c and 1d bearing electron-deactivating F and Br functional groups (Scheme [3], 3ca–da). Notably, anthraquinones 3ca–ci with bromo-substituent are of particular importance, as they can be further derivatized by means transition-metal-catalyzed coupling reactions.

Scheme 3 Scope of one-pot synthesis of anthraquinone 3ba–da. Isolated yields of chromatographically pure products 3ba–da are given.

In conclusion, a sequential one-pot relay process has been developed for the synthesis of diverse anthraquinones. The overall process involves a sequential dual acylation via [Pd]-catalyzed intermolecular acylation and acid mediated intramolecular Friedel–Crafts acylation. The key reaction of the coupling was [Pd]-catalyzed direct acylation between ortho-iodoesters and aromatic aldehydes. Simple bench-top benzaldehydes served as nontoxic acylating surrogates.

IR spectra were recorded on a FTIR spectrophotometer. ¹H NMR spectra were recorded on 400 MHz spectrometer at 295 K in CDCl₃; chemical shifts (δ ppm) and coupling constants (Hz) are reported in standard fashion with reference to either internal standard TMS (δ_H = 0.00) or CHCl₃ (δ_H = 7.25). ¹³C NMR spectra were recorded on 100 MHz spectrometer at r.t. in CDCl₃; chemical shifts (δ ppm) are reported relative to CHCl₃ [δ_C = 77.00 (central line of triplet)]. In the ¹³C NMR spectra, the nature of carbons (C, CH, CH₂, and CH₃) was determined by recording the DEPT-135 spectra. In the ¹H NMR, standard abbreviations were used throughout to denote the multiplicity of the signals. High-resolution mass spectra (HRMS) were recorded on Q-TOF electron spray ionization (ESI) mode and atmospheric pressure chemical ionization (APCI) modes. Melting points were determined on an electrothermal melting point apparatus and are uncorrected.

All small scale reactions were carried out using Schlenk tube. Reactions were monitored by TLC on silica gel using a combination of hexane and EtOAc as eluents. Reactions were generally run under argon or N₂ atmosphere. Solvents were distilled prior to use; petroleum ether (PE) with a boiling range of 60–80 °C was used. Acme’s silica gel (60–120 mesh) was used for column chromatography (approximately 20 g per one gram of crude material).

Aldehydes 2a–k and ortho-iodoesters 1a–d are commercially available.

Anthraquinones 3; General Procedure

This kind of general experimental procedure is based on our already published procedure.[13]

The general procedure (GP) was carried out with ortho-iodoester 1a–d (105.0–136.0 mg, 0.40 mmol) and aldehyde 2a–k (195.0–313.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) allowing the reaction mixture to stir at 120 °C for 12–20 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a–d had completely reacted. Then the reaction mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 5 min to 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the products 3 (57.0–86.0 mg, 55–69%). The products 3aa, 3ac, 3ai, 3aj, 3ak, 3ba, 3bc, 3be, and 3bj are reported in the literature.[9]

2-Methoxyanthracene-9,10-dione (3aa)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2a (217.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol %), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the reaction mixture was removed from the oil bath and allowed to reach r.t.. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3aa; yield: 59.0 mg (62%); yellow solid, m.p. 194–196 °C; R_f (1a) = 1.0, R_f (3aa) = 0.30 (PE/EtOAc 95:05), UV detection.

¹H NMR (CDCl₃, 400 MHz): δ =8.32–8.20 (m, 3 H, ArH), 7.84–7.72 (m, 2 H, ArH), 7.69 (d, J = 2.4 Hz, 1 H, ArH), 7.24 (dd, J = 8.8, 2.4 Hz, 1 H, ArH), 3.97 (s, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ =183.2 (s, C=O), 182.1 (s, C=O), 164.3 (s, ArC), 135.6 (s, ArC), 134.1 (d, ArCH), 133.6 (s, ArC), 133.6 (d, ArCH), 133.5 (s, ArC), 129.7 (d, ArCH), 127.0 (s, ArC), 127.1 (d, 2 C, ArCH), 121.1 (d, ArCH), 109.9 (d, ArCH), 55.9 (q, CH₃).

2-Ethoxyanthracene-9,10-dione (3ab)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2b (240.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 12 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the reaction mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 1.5 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ab; yield: 66.0 mg (65%); orange viscous liquid; R_f (1a) = 1.0, R_f ( 3ab) = 0.30 (PE/EtOAc 95:05), UV detection.

IR (MIR-ATR): 3071, 2941, 1712, 1683, 1611, 1465, 1287, 1099, 1006, 926, 705 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 8.26–8.22 (m, 3 H, ArH), 8.20 (d, J = 8.8 Hz, 1 H, ArH), 7.75–7.22 (m, 2 H, ArH), 7.20 (dd, J = 8.5, 2.6 Hz, 1 H, ArH), 4.18 (q, J = 6.8 Hz, 2 H), 1.46 (t, J = 6.8 Hz, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ =183.2 (s, C=O), 182.1 (s, C=O), 163.7 (s, ArC), 135.5 (s, ArC), 134.1 (d, ArCH), 133.6 (s, ArC), 133.6 (d, ArCH), 133.5 (s, ArC), 129.7 (d, ArCH), 127.0 (d, 2 C, ArCH), 126.8 (s, ArC), 121.4 (d, ArCH), 110.4 (d, ArCH), 64.3 (t, CH₂), 14.6 (q, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₆H₁₃O₃]⁺: 253.0859; found: 253.0859.

2,3-Dimethoxyanthracene-9,10-dione (3ac)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2c (265.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ac; yield: 73.0 mg (68%); orange solid, m.p. 230–233 °; R_f (1a) = 1.0, R_f (3ac) = 0.40 (PE/EtOAc 85:15), UV detection.

¹H NMR (CDCl₃, 400 MHz): δ = 8.25 (dd, J = 5.8, 3.4 Hz, 2 H, ArH), 7.75 (dd, J = 5.8, 3.4 Hz, 2 H, ArH), 7.79 (s, 2 H, ArH), 4.05 (s, 6 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.5 (s, 2 C, C=O), 153.8 (s, 2 C, ArC), 133.7 (d, 2 C, ArCH), 133.5 (s, 2 C, ArC), 128.4 (s, 2 C, ArC), 127.0 (d, 2 C, ArCH), 108.3 (d, 2 C, ArCH), 56.5 (q, 2 C, CH₃).

2-Ethoxy-3-methoxyanthracene-9,10-dione (3ad)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2d (288.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 18 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ad; yield: 64.0 mg (57%); yellow solid, m.p. 242–245 °C; R_f (1a) = 1.0, R_f (3ad) = 0.30 (PE/EtOAc 95:05), UV detection.

IR (MIR-ATR): 3074, 1704, 1680, 1635, 1620, 1590, 1570, 1504, 1475, 1363, 1301, 1257, 1160, 963, 843 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 8.27–8.24 (m, 2 H, ArH), 7.74 (dd, J = 5.8, 3.4 Hz, 2 H, ArH), 7.70 (d, J = 5.8 Hz, 2 H, ArH), 4.30 (q, J = 7.0 Hz, 2 H), 4.05 (s, 3 H), 1.54 (t, J = 7.0 Hz, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.6 (s, C=O), 182.5 (s, C=O), 154.0 (s, ArC), 153.3 (s, ArC), 133.7 (d, 2 C, ArCH), 133.6 (s, 2 C, ArC), 128.4 (s, ArC), 128.2 (s, ArC), 127.0 (d, 2 C, ArCH), 109.1 (d, ArCH), 108.5 (d, ArCH), 65.0 (t, CH₂), 56.5 (q, CH₃) 14.5 (q, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₇H₁₅O₄]⁺: 283.0965; found: 283.0964.

2,3-Diethoxyanthracene-9,10-dione (3ae)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2e (310.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ae; yield: 75.0 mg (63%); yellow solid, m.p. 247–248 °C; R_f (1a) = 1.0, R_f (3ae) = 0.30 (PE/EtOAc 85:15), UV detection.

IR (MIR-ATR): 3062, 1710, 1682, 1639, 1622, 1591, 1582, 1500, 1471, 1367, 1311, 1253, 1170, 903, 743 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 8.24 (dd, J = 5.8, 3.4 Hz, 2 H, ArH), 7.73 (dd, J = 5.8, 3.4 Hz, 2 H, ArH), 7.70 (s, 2 H, ArH), 4.29 (q, J = 6.8 Hz, 4 H), 1.53 (t, J = 6.8 Hz, 6 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.6 (s, 2 C, C=O), 153.4 (s, 2 C, ArC), 133.7 (d, 2 C, ArCH), 133.6 (d, 2 C, ArCH), 128.2 (s, 2 C, ArC), 126.9 (d, 2 C, ArCH), 109.3 (d, 2 C, ArCH), 65.0 (t, 2 C, CH₂), 14.5 (q, 2 C, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₈H₁₇O₄]⁺: 297.1121; found: 297.1125.

2-Hydroxy-3-methoxyanthracene-9,10-dione (3af)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2f (243.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 20 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 5 min. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3af; yield: 56.0 mg (55%); red solid, m.p. 252–254 °C; R_f (1a) = 1.0, R_f (3af) = 0.30 (PE/EtOAc 80:20), UV detection.

IR (MIR-ATR): 3065, 1710, 1682, 1631, 1627, 1587, 1560, 1501, 1476, 1392, 1343, 1311, 1282, 1236, 1152, 943, 812 cm^–1.

¹H NMR (DMSO-d ₆, 400 MHz): δ = 10.76 (s, 1 H, Ar–OH), 8.15–8.10 (m, 2 H, ArH), 7.86–7.84 (m, 2 H, ArH), 7.59 (s, 1 H, ArH), 7.52 (s, 1 H, ArH), 3.96 (s, 3 H).

¹³C NMR (DMSO-d ₆, 100 MHz): δ = 181.8 (s, C=O), 181.4 (s, C=O), 152.8 (s, ArC), 152.5 (s, ArC), 134.1 (d, ArCH), 134.0 (d, ArCH), 133.1 (s, ArC), 133.0 (s, ArC), 128.0 (s, ArC), 126.5 (s, ArC), 126.5 (d, ArCH), 126.4 (d, ArCH), 112.4 (d, ArCH), 108.8 (d, ArCH), 56.0 (q, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₅H₁₁O₄]⁺: 255.0652; found: 255.0648.

2-Hydroxy-3-methoxyanthracene-9,10-dione (3ag)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2g (243.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 19 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 10 min. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ag; yield: 59.0 mg (58%); red solid, m.p. 252–254 °C; R_f (1a) = 1.0, R_f (3ag) = 0.30 (PE/EtOAc 80:20), UV detection.

This product is identical with the product 3af obtained from 1a and 2f.

IR (MIR-ATR): 3070, 1701, 1688, 1642, 1619, 1583, 15750, 1507, 1415, 1358, 1311, 1248, 1205, 918, 803 cm^–1.

¹H NMR (DMSO-d ₆, 400 MHz): δ = 10.76 (s, 1 H, Ar–OH), 8.15–8.10 (m, 2 H, ArH), 7.86–7.84 (m, 2 H, ArH), 7.59 (s, 1 H, ArH), 7.52 (s, 1 H, ArH), 3.96 (s, 3 H).

¹³C NMR (DMSO-d ₆, 100 MHz): δ = 181.8 (s, C=O), 181,4 (s, C=O), 152.8 (s, ArC), 152.5 (s, ArC), 134.1 (d, ArCH), 134.0 (d, ArCH), 133.1 (s, ArC), 133.0 (s, ArC), 128.0 (s, ArC), 126.5 (s, ArC), 126.5 (d, ArCH), 126.4 (d, ArCH), 112.4 (d, ArCH), 108.8 (d, ArCH), 56.0 (q, CH₃).

HR-MS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₅H₁₁O₄]⁺: 255.0652; found: 255.0648.

1-Hydroxy-2-methoxyanthracene-9,10-dione (3ah)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2h (243.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 18 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 20 min. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ah; yield: 57.0 mg (56%); red solid, m.p. 238–242 °C; R_f (1a) = 1.0, R_f (3ah) = 0.60 (PE/EtOAc 80:20), UV detection.

IR (MIR-ATR): 3070, 1701, 1688, 1642, 1619, 1583, 15750, 1507, 1415, 1358, 1311, 1248, 1205, 918, 803 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 13.03 (s, 1 H, Ar–OH), 8.31–8.26 (m, 2 H, ArH), 7.86 (d, J = 8.8 Hz, 1 H, ArH), 7.80–7.77 (m, 2 H, ArH), 7.17 (d, J = 8.3 Hz, 1 H, ArH), 4.01 (s, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 189.2 (s, C=O), 181.5 (s, C=O), 154.0 (s, ArC), 152.8 (s, ArC), 134.8 (d, ArCH), 134.1 (s, ArC), 133.8 (d, ArCH), 133.3 (s, ArC), 127.4 (d, ArCH), 126.9 (d, ArCH), 125.3 (s, ArC), 121.1 (d, ArCH), 116.1 (s, ArC), 115.8 (d, ArCH), 56.4 (q, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₅H₁₁O₄]⁺: 255.0652; found: 255.0639.

2-Hydroxyanthracene-9,10-dione (3ai)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2i (195.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ai; yield: 62.0 mg (69%); red solid, m.p. 306–308 °C; R_f (1a) = 1.0, R_f (3ai) = 0.30 (PE/EtOAc 75:25), UV detection.

¹H NMR (DMSO-d ₆, 400 MHz): δ = 11.03 (br s, 1 H, Ar–OH), 8.17–8.14 (m, 2 H, ArH), 8.08 (d, J = 8.8 Hz, 1 H, ArH), 7.90–7.86 (m, 2 H, ArH), 7.49 (d, J = 2.9 Hz, 1 H, ArH), 7.24 (dd, J = 8.8, 2.9 Hz, 1 H, ArH).

¹³C NMR (DMSO-d ₆, 100 MHz): δ = 182.7 (s, C=O), 181.2 (s, C=O), 163.1 (s, ArC), 135.2 (s, ArC), 134.6 (d, ArCH), 134.0 (d, ArCH), 133.2 (s, ArC), 133.1 (s, ArC), 129.9 (d, ArCH), 126.7 (d, ArCH), 126.6 (d, ArCH), 125.2 (s, ArC), 121.6 (d, ArCH), 112.2 (d, ArCH).

Anthra[2,3-d][1,3]dioxole-5,10-dione (3aj)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2j (240.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 17 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 1.5 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3aj; yield: 64.0 mg (63%); yellow viscous liquid; R_f (1a) = 1.0, R_f (3aj) = 0.30 (PE/EtOAc 90:10), UV detection.

¹H NMR (CDCl₃, 400 MHz): δ = 8.32–8.20 (m, 2 H, ArH), 7.80–7.50 (m, 2 H, Ar–H), 7.66 (s, 2 H, ArH), 6.15 (s, 2 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.0 (s, 2 C, C=O), 152.6 (s, 2 C, ArC), 133.8 (d, 2 C, ArCH), 133.3 (s, 2 C, ArC), 130.8 (s, 2 C, ArC), 127.1 (d, 2 C, ArCH), 106.4 (d, 2 C, ArCH), 102.6 (t, CH₂).

1,2,3-Trimethoxyanthracene-9,10-dione (3ak)

GP was carried out with ortho-iodoester 1a (105.0 mg, 0.40 mmol) and aldehyde 2k (313.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ak; yield: 73.0 mg (61%); red solid, m.p. 165–167 °C; R_f (1a) = 1.0, R_f (3ak) = 0.30 (PE/EtOAc 70:30), UV detection.

¹H NMR (CDCl₃, 400 MHz): δ = 8.25 (dd, J = 7.8, 1.7 Hz, 1 H, ArH), 8.22 (dd, J = 7.8, 2.4 Hz, 1 H, ArH), 7.77 (ddd, J = 7.8, 7.8, 2.4 Hz, 1 H, ArH), 7.73 (ddd, J = 7.8, 7.8, 1.7 Hz, 1 H, ArH), 7.67 (s, 1 H, ArH), 4.03 (s, 3 H), 3.99 (s, 3 H), 3.98 (s, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.7 (s, C=O), 181.5 (s, C=O), 157.5 (s, ArC), 154.8 (s, ArC), 148.4 (s, ArC), 134.9 (s, ArC), 134.1 (d, ArCH), 133.1 (d, ArCH), 132.5 (s, ArC), 130.8 (s, ArC), 127.0 (d, ArCH), 126.6 (d, ArCH), 121.3 (s, ArC), 106.4 (d, ArCH), 61.6 (q, CH₃), 61.3 (q, CH₃), 56.4 (q, CH₃).

2-Methoxy-6-methylanthracene-9,10-dione (3ba)

GP was carried out with ortho-iodoester 1b (110.0 mg, 0.40 mmol) and aldehyde 2a (217.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ba; yield: 65.0 mg (64%); yellow solid, m.p. 192–194 °C; R_f (1a) = 1.0, R_f (3ba) = 0.30 (PE/EtOAc 95:05), UV detection.

¹H NMR (CDCl₃, 400 MHz): δ = 8.15 (d, J = 8.3 Hz, 1 H, ArH), 8.09 (d, J = 7.8 Hz, 1 H, ArH), 7.99 (s, 1 H, ArH), 7.63 (d, J = 2.4 Hz, 1 H, ArH), 7.49 (dd, J = 7.8, 1.2 Hz, 1 H, ArH), 7.18 (dd, J = 8.3, 2.4 Hz, 1 H, ArH), 3.93 (s, 3 H), 2.47 (s, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.9 (s, C=O), 182.2 (s, C=O), 164.2 (s, ArC), 145.2 (s, ArC), 135.5 (s, ArC), 134.3 (d, ArCH), 133.4 (s, ArC), 131.2 (s, ArC), 129.5 (d, ArCH), 127.3 (d, ArCH), 127.2 (d, ArCH), 127.0 (s, ArC), 120.8 (d, ArCH), 109.8 (d, ArCH), 55.6 (q, CH₃), 21.8 (q, CH₃).

2-Ethoxy-6-methylanthracene-9,10-dione (3bb)

GP was carried out with ortho-iodoester 1b (110.0 mg, 0.40 mmol) and aldehyde 2b (240.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1b had completely reacted. Then the reaction mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3bb; yield: 66.0 mg (62%); red solid, m.p. 210–213 °C; R_f (1b) = 1.0, R_f (3bb) = 0.30 (PE/EtOAc 95:05), UV detection.

IR (MIR-ATR): 3080, 1705, 1690, 1639, 1621, 1580, 15751, 1517, 1408, 1361, 1310, 1249, 1215, 908, 813 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 8.17 (d, J = 8.8 Hz, 1 H, ArH), 8.11 (d, J = 7.8 Hz, 1 H, ArH), 8.03 (s, 1 H, ArH), 7.63 (d, J = 2.9 Hz, 1 H, ArH), 7.50 (dd, J = 7.8, 0.9 Hz, 1 H, ArH), 7.18 (dd, J = 8.8, 2.6 Hz, 1 H, ArH), 4.18 (q, J = 7.0 Hz, 2 H), 2.49 (s, 3 H), 1.46 (t, J = 7.0 Hz, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 183.0 (s, C=O), 182.3 (s, C=O), 163.6 (s, ArC), 145.2 (s, ArC), 135.6 (s, ArC), 134.3 (d, ArCH), 133.5 (s, ArC), 131.3 (s, ArC), 129.6 (d, ArCH), 127.4 (d, ArCH), 127.3 (d, ArCH), 126.9 (s, ArC), 121.2 (d, ArCH), 110.3 (d, ArCH), 64.3 (t, CH₂), 21.9 (q, CH₃), 14.6 (q, CH₃).

HR-MS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₇H₁₅O₃]⁺: 267.1016; found: 267.1017.

2,3-Dimethoxy-6-methylanthracene-9,10-dione (3bc)

GP was carried out with ortho-iodoester 1b (110.0 mg, 0.40 mmol) and aldehyde 2c (265.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 17 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1b had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 30 min. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3bc; yield: 75.0 mg (66%); yellow viscous liquid; R_f (1b) = 1.0, R_f (3bc) = 0.30 (PE/EtOAc 85:15), UV detection.

¹H NMR (CDCl₃, 400 MHz): δ = 8.11 (d, J = 7.8 Hz, 1 H, ArH), 8.01 (s, 1 H, ArH), 7.65 (s, 1 H, ArH), 7.64 (s, 1 H, ArH), 7.51 (dd, J = 7.8, 0.9 Hz, 1 H, ArH), 4.03 (s, 6 H), 2.49 (s, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.7 (s, C=O), 182.3 (s, C=O), 153.7 (s, ArC), 153.6 (s, ArC), 144.7 (s, ArC), 134.4 (d, ArCH), 133.4 (s, ArC), 131.3 (s, ArC), 128.5 (s, ArC), 128.4 (s, ArC), 127.8 (d, ArCH), 127.2 (d, ArCH), 108.3 (d, ArCH), 108.2 (d, ArCH), 56.5 (q, 2 C, CH₃), 21.8 (q, CH₃).

2,3-Diethoxy-6-methylanthracene-9,10-dione (3be)

GP was carried out with ortho-iodoester 1b (110.0 mg, 0.40 mmol) and aldehyde 2e (310.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol %), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 18 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1b had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 30 min. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3be; yield: 76.0 mg (61%); yellow viscous liquid; R_f (1b) = 1.0, R_f (3be) = 0.30 (PE/EtOAc 95:05), UV detection.

¹H NMR (CDCl₃, 400 MHz): δ = 8.13 (d, J = 7.8 Hz, 1 H, ArH), 8.03 (s, 1 H, ArH), 7.67 (s, 2 H, ArH), 7.52 (dd, J = 7.8, 1.9 Hz, 1 H, ArH), 4.28 (q, J = 7.0 Hz, 2 × 2 H), 2.50 (s, 3 H), 1.52 (t, J = 7.0 Hz, 2 × 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.9 (s, C=O), 182.5 (s, C=O), 153.3 (s, ArC), 153.2 (s, ArC), 144.7 (s, ArC), 134.4 (d, ArCH), 133.5 (s, ArC), 131.4 (s, ArC), 128.3 (s, ArC), 128.2 (s, ArC), 127.3 (d, ArCH), 127.1 (d, ArCH), 109.3 (d, ArCH), 109.2 (d, ArCH), 64.9 (t, 2 C, 2 × CH₂), 21.8 (q, CH₃), 14.5 (q, 2 C, 2 × CH₃).

7-Methylanthra[2,3-d][1,3]dioxole-5,10-dione (3bj)

GP was carried out with ortho-iodoester 1b (110.0 mg, 0.40 mmol) and aldehyde 2j (240.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 17 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1a had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 1 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3bj; yield: 64.0 mg (60%); redish viscous liquid; R_f (1b) = 1.0, R_f (3bj) = 0.30 (PE/EtOAc 90:10), UV detection.

¹H NMR (CDCl₃, 400 MHz): δ = 8.14 (d, J = 7.8 Hz, 1 H, ArH), 8.04 (s, 1 H, ArH), 7.65 (s, 2 H, ArH), 7.54 (d, J = 7.8 Hz, 1 H, ArH), 6.15 (s, 2 H, ArH), 2.50 (s, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.3 (s, C=O), 181.9 (s, C=O), 152.6 (s, ArC), 152.5 (s, ArC), 144.9 (s, ArC), 134.6 (d, ArCH), 133.2 (s, ArC), 131.1 (s, ArC), 130.9 (s, ArC), 130.8 (s, ArC), 127.4 (d, ArCH), 127.3 (d, ArCH), 106.3 (d, 2 C, ArCH), 102.6 (t, CH₂), 21.9 (q, CH₃).

2-Bromo-6-methoxyanthracene-9,10-dione (3ca)

GP was carried out with ortho-iodoester 1c (136.0 mg, 0.40 mmol) and aldehyde 2a (217.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 17 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1c had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ca; yield: 79.0 mg (62%); yellow solid, m.p. 212–215 °C; R_f (1c) = 1.0, R_f ( 3ca) = 0.30 (PE/EtOAc 95:05), UV detection.

IR (MIR-ATR): 3056, 2938, 1710, 1687, 1612, 1460, 1280, 1081, 914, 705 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 8.40 (d, J = 1.9 Hz, 1 H, ArH), 8.23 (d, J = 8.8 Hz, 1 H, ArH), 8.12 (d, J = 8.3 Hz, 1 H, ArH), 8.86 (dd, J = 8.3, 2.4 Hz, 1 H, ArH), 7.70 (d, J = 2.4 Hz, 1 H, ArH), 7.28–7.26 (m, 1 H, ArH), 3.98 (s, 3 H, OCH₃).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.5 (s, C=O), 180.9 (s, C=O), 164.6 (s, ArC), 136.7 (d, ArCH), 135.4 (s, ArC), 134.7 (s, ArC), 132.1 (s, ArC), 130.2 (d, ArCH), 129.9 (d, ArCH), 129.8 (s, ArC), 128.9 (d, ArCH), 126.7 (s, ArC), 121.3 (d, ArCH), 110.1 (d, ArCH), 56.0 (q, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₅H₁₀ ⁷⁹BrO₃]⁺: 316.9808; found; 316.9806; m/z [M + H]⁺ calcd for [C₁₅H₁₀ ⁸¹BrO₃]⁺: 318.9789; found: 318.9789.

2-Bromo-6-ethoxyanthracene-9,10-dione (3cb)

GP was carried out with ortho-iodoester 1c (136.0 mg, 0.40 mmol) and aldehyde 2b (240.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1c had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3cb; yield: 86.0 mg (65%); red solid, m.p. 202–203 °C; R_f (1c) = 1.0, R_f (3cb) = 0.30 (PE/EtOAc 95:05), UV detection.

IR (MIR-ATR): 3070, 1709, 1691, 1645, 1599, 1580, 15751, 1506, 1410, 1357, 1310, 1245, 1215, 940, 813 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 8.40 (d, J = 1.9 Hz, 1 H, ArH), 8.22 (d, J = 8.3 Hz, 1 H, ArH), 8.12 (d, J = 8.3 Hz, 1 H, ArH), 8.86 (dd, J = 8.0, 2.2 Hz, 1 H, ArH), 7.67 (d, J = 2.9 Hz, 1 H, ArH), 7.26–7.23 (m, 1 H, ArH), 4.21 (q, J = 7.0 Hz, 2 H), 1.48 (t, J = 7.0 Hz, 3 H).

¹³C NMR (CDCl₃, 100 MHz): δ = 182.5 (s, C=O), 180.9 (s, C=O), 164.0 (s, ArC), 136.6 (d, ArCH), 135.4 (s, ArC), 134.8 (s, ArC), 132.2 (s, ArC), 130.2 (d, ArCH), 129.9 (d, ArCH), 129.7 (s, ArC), 128.9 (d, ArCH), 126.5 (s, ArC), 121.6 (d, ArCH), 110.6 (d, ArCH), 64.5 (t, CH₂), 14.6 (q, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₆H₁₂ ⁷⁹BrO₃]⁺: 330.9964; found: 330.9988; m/z [M + H]⁺ calcd for [C₁₆H₁₂ ⁸¹BrO₃]⁺: 332.9946; found: 332.9958.

6-Bromo-2,3-dimethoxyanthracene-9,10-dione (3cc)

GP was carried out with ortho-iodoester 1c (136.0 mg, 0.40 mmol) and aldehyde 2c (265.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1c had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3cc; yield: 85.0 mg (61%); yellow viscous liquid; R_f (1c) = 1.0, R_f (3cc) = 0.30 (PE/EtOAc 80:20), UV detection.

IR (MIR-ATR): 3074, 1709, 1691, 1640, 1620, 1576, 15751, 1517, 1416, 1363, 1313, 1244, 1213, 928, 834 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 8.36 (d, J = 2.4 Hz, 1 H, ArH), 8.09 (d, J = 8.3 Hz, 1 H, ArH), 7.84 (dd, J = 8.3, 1.9 Hz, 1 H, ArH), 7.67 (s, 1 H, ArH), 7.66 (s, 1 H, ArH), 4.05 (s, 6 H, OCH₃).

¹³C NMR (CDCl₃, 100 MHz): δ = 181.7 (s, C=O), 181.2 (s, C=O), 154.1 (s, ArC), 154.0 (s, ArC), 136.7 (d, ArCH), 134.6 (s, ArC), 132.1 (s, ArC), 129.9 (d, ArCH), 129.2 (s, ArC), 128.7 (d, ArCH), 128.2 (s, ArC), 128.1 (s, ArC), 108.4 (d, 2 × CH, ArCH), 56.6 (q, 2 C, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₆H₁₂ ⁷⁹BrO₄]⁺: 346.9913; found: 346.9900; m/z [M + H]⁺ calcd for [C₁₆H₁₂ ⁸¹BrO₄]⁺: 348.9895; found: 348.9891.

7-Bromo-1-hydroxyanthracene-9,10-dione (3ci)

GP was carried out with ortho-iodoester 1c (136.0 mg, 0.40 mmol) and aldehyde 2i (195.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowing the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1c had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3ci; yield: 71.0 mg (59%); red solid, m.p. 227–230 °C; R_f (1c) = 1.0, R_f (3ci) = 0.30 (PE/EtOAc 80:20), UV detection.

IR (MIR-ATR): 3061, 2937, 1711, 1692, 1618, 1469, 1285, 1181, 911, 715 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ =12.41 (s, 1 H, Ar–OH), 8.41 (d, J = 1.9 Hz, 1 H, ArH), 8.14 (d, J = 8.3 Hz, 1 H, ArH), 7.91 (dd, J = 8.3, 1.9 Hz, 1 H, ArH), 7.81 (dd, J = 7.5, 1.2 Hz, 1 H, ArH), 7.69 (dd, J = 8.3, 8.3 Hz, 1 H, ArH), 7.31 (dd, J = 8.3, 0.9 Hz, 1 H, ArH).

¹³C NMR (CDCl₃, 100 MHz): δ =187.4 (s, C=O), 181.6 (s, C=O), 162.6 (s, ArC), 137.7 (d, ArCH), 137.1 (d, ArCH), 134.3 (s, ArC), 133.2 (s, ArC), 132.2 (s, ArC), 129.9 (d, ArCH), 129.8 (s, ArC), 129.1 (d, ArCH), 124.6 (d, ArCH), 119.8 (d, ArCH), 115.9 (s, ArC).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₄H₈ ⁷⁹BrO₃]⁺: 302.9651; found: 302.9662; [M + H]⁺ calcd for [C₁₄H₈ ⁸¹BrO₃]⁺: 304.9632; found: 304.9648.

2-Fluoro-6-methoxyanthracene-9,10-dione (3da)

GP was carried out with ortho-iodoester 1d (112.0 mg, 0.40 mmol) and aldehyde 2a (217.0 mg, 1.6 mmol) in the presence of Pd(OAc)₂ (5.0 mg, 5 mol%), Ag₂O (111.3 mg, 0.48 mmol), and TBHP (257.1 mg, 2.0 mmol) by allowinng the reaction mixture to stir at 120 °C for 14 h. Progress of the reaction was monitored by TLC until the ortho-iodoester 1d had completely reacted. Then the mixture was removed from the oil bath and allowed to reach r.t. DCE (2 mL) and concd H₂SO₄ (1.0 mL) were added and the mixture was stirred at 60 °C for 2 h. Progress of the product formation was monitored by TLC until the reaction was complete. The mixture was quenched by the addition of aq NaHCO₃ and then extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were washed with brine, dried (Na₂SO₄), and filtered. Evaporation of the solvent under reduced pressure and purification of the crude material by silica gel column chromatography (PE/EtOAc) furnished the product 3da; yield: 65.0 mg (63%); yellow viscous liquid; R_f (1d) = 1.0, R_f (3da) = 0.30 (PE/EtOAc 95:05), UV detection.

IR (MIR-ATR): 3071, 2928, 1711, 1689, 1622, 1462, 1285, 1181, 914, 705 cm^–1.

¹H NMR (CDCl₃, 400 MHz): δ = 8.30 (dd, J = 8.5, 5.1 Hz, 1 H, ArH), 8.22 (d, J = 8.8 Hz, 1 H, ArH), 7.90 (dd, J = 8.8, 2.4 Hz, 1 H, ArH), 7.70 (d, J = 2.4 Hz, 1 H, ArH), 7.43–7.38 (m, 1 H, ArH), 7.26–7.23 (m, 1 H, ArH), 3.97 (s, 3 H, OCH₃).

¹³C NMR (CDCl₃, 100 MHz): δ = 181.9 (s, C=O), 180.9 (s, C=O), 166.4 (s, ArC_F, J _C,F = 260 Hz), 164.6 (s, ArC), 136.5 (s, ArC, J _C,F = 8.7 Hz), 135.5 (s, ArC), 130.5 (d, J _C,F = 8.8 Hz, ArCH), 130.2 (s, J _C,F = 2.9 Hz, ArC), 129.9 (d, ArCH), 127.0 (s, ArC), 121.1 (d, ArCH), 120.9 (d, J _C,F = 22.9 Hz, ArCH), 113.8 (d, J _C,F = 22.7 Hz, ArCH), 110.2 (d, ArCH), 56.0 (q, CH₃).

HRMS (ESI⁺): m/z [M + H]⁺ calcd for [C₁₅H₁₀FO₃]⁺: 257.0608; found: 257.0606.

Referenzen

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Abbildungen

Figure 1 Representative examples of bioactive anthraquinones

Scheme 1 Anticipated retrosynthetic route of anthraquinones 3

Scheme 2 Scope of the method for one-pot synthesis of anthraquinone 3aa–ak. Isolated yields of chromatographically pure products 3aa–ak are given. Product 3ai was not formed.

Scheme 3 Scope of one-pot synthesis of anthraquinone 3ba–da. Isolated yields of chromatographically pure products 3ba–da are given.

Zusatzmaterial

Supporting Information