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Article

A HCl-Mediated, Metal- and Oxidant-Free Photocatalytic Strategy for C3 Arylation of Quinoxalin(on)es with Arylhydrazine

by
Kai Wang
1,
Wenjing Xu
1,
Haoran Qi
1,
Pengfei Zhang
2,
Xian-Ting Cao
1,* and
Guannan Wang
1,*
1
College of Medical Engineering & the Key Laboratory for Medical Functional Nanomaterials, Jining Medical University, Jining 272067, China
2
College of Material, Chemistry and Chemical Engineering, Key Laboratory of Organosilicon Chemistry and Material Technology, Ministry of Education, Hangzhou Normal University, Hangzhou 311121, China
*
Authors to whom correspondence should be addressed.
Catalysts 2022, 12(6), 633; https://doi.org/10.3390/catal12060633
Submission received: 9 May 2022 / Revised: 5 June 2022 / Accepted: 6 June 2022 / Published: 10 June 2022
(This article belongs to the Special Issue Catalyzed C–H Activation and C–X (X= C, O, N, S, Halogen) Formation)
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Abstract

:
A novel and simple HCl-mediated, photocatalytic method for quinoxaline(on)es C3-H arylation with arylhydrazine under transition metal catalyst- and oxidant-free conditions is presented. Various quinoxaline(on)es underwent this transformation smoothly, demonstrating a broad substrate tolerance and providing the corresponding aryl products in moderate to excellent yields. Mechanistic studies indicated that a radical pathway may be involved in this transformation.

1. Introduction

Quinoxalin(one) derivatives have been widely applied in materials, pharmaceuticals, and synthetic chemistry due to their unique physicochemical properties [1,2,3,4,5,6,7,8]. Among others, aryl-substituted quinoxaline(on)es have frequently appeared in natural compounds and pharmaceutical molecules, such as antimicrobials [9,10], antitumor molecules [11,12] and prolyl oligopeptidase inhibitors [13,14,15,16]. Therefore, the development of procedures for arylation has gained increasing attention in synthetic methodology. Traditional methods for the preparation of such compounds include Suzuki cross-coupling and cycloadditions of aryl-1,2-diamines [17,18,19,20].
Over the past few decades, C-H functionalization has become an important tool in organic synthesis, and research on the efficient strategies has been carried out on the preparation of functional quinoxaline(on)es, including C-N bond formation [21,22,23,24,25], C-C formation [26,27,28] and C-S (O) bond formation [29,30,31,32,33,34]. Among others, C3-arylation has been successively achieved employing arylboronic acids, arylamine, aromatic hydrazine and benzene as aryl sources [35,36,37,38,39]. Despite the inspiring progress, expensive and complex catalysts, complicated operations and harsh conditions are usually inevitable, which greatly limited the application of these methods.
Over the past few decades, photoinduced reactions have become an effective method in organic synthesis because of their eco-friendly characteristics [40]. In 2018, Wei and coworkers [41] developed a visible-light-induced protocol C3 arylation of quinoxalinones catalyzed by Eosin Y. The following year, another work of C3 arylation and alkylation of quinoxalinones was reported by Yang and coworkers [42] employing hydrazone-based two-dimensional covalent organic frameworks (2D-COF-1) as catalysts. In 2020, our group [43] declared another visible light-mediated direct C3-H arylation of quinoxalinones with aryl acyl peroxide as the source of aryl (Scheme 1).
Herein, we describe a HCl-mediated, visible-light-induced strategy for the preparation of C3 arylated quinoxaline(on)es with arylhydrazine under catalyst-free conditions, which successfully avoids the use of complex catalysts and expensive aryl sources.

2. Results and Discussion

Initially, N-methylquinoxalin-2(1H)-one (1a) and phenylhydrazine (2a) were chosen as model substrates in the presence of HCl (4.0 equiv) under the illumination of a 25 W blue light-emitting diode (LED) at room temperature for 10 h. The target product (3a) was produced in 80% yield (Table 1, entry 1). Subsequent investigation on the effect of light sources showed that green light gave lower reactivity, and no product could be detected under the irradiation of white light or without light (entries 2–4). Similarly, no desired product was detected with the removal of HCl. Simultaneously, decreasing or increasing the dosage of HCl, the target product yields were 67% and 81%, respectively (entries 5–7). Furthermore, when K2CO3 was used instead of HCl, the yield dropped to 45% (entry 8). Screening of solvents showed that acetonitrile performed in a manner superior to EtOH, DMSO and a mixture of MeCN and H2O (entries 9–11). Simultaneously, no desired product was obtained in H2O (entry 12). Finally, the reaction atmosphere had an obvious effect on the reaction. Specifically, the transformation proceeded smoothly under O2 condition, while it could not take place in N2 atmosphere (entries 13–14).
With the optimized conditions found, the substrate scope of quinoxalinones was tested (Table 2). Substrates containing alkyl, aryl, benzyl and ester groups at N1 position proceeded smoothly and provided the corresponding products (3a–3l) from 45 to 82% yield. Furthermore, substrates bearing alkyl and ester groups (3a–3f) gave better (71 to 88%) yield than the aryl ones (3g, 3h, 63 and 66%). At the same time, quinoxalin-2(1H)-one could also provide the corresponding product (3i) in 59% yields. Likewise, quinoxalinones with methyl and chlorine at C6 and C7 positions (3j, 3k) were examined and the desired products were obtained in 68 and 70% yields. Cyclohexylhydrazine also showed satisfactory reactivity and the target product 3l was obtained in 45% yield.
After that, the arylation reactions of quinoxalines were investigated (Table 3). The effect of the hydrazines substituents on yield revealed the same impact as on quinoxalinones, i.e., that both electron-donating and electron-withdrawing groups are tolerated in this transformation (3m–3q). Simultaneously, quinoxalines with chlorine as well as methyl on C2 position also furnished the corresponding products 3r and 3s in moderate yields, suggesting that steric hindrance had little impact on this reaction. In addition, pyrazine and phthalazine were also tested and the desired products (3t, 3u) were generated in 40% and 53% yield, respectively.
Considering the cheap and available materials, a gram-scale synthesis was carried out to show the preparative value of this reaction (Scheme 2), and the arylated product was isolated in 68% yield. Then, to gain more understanding about the reaction mechanism, several control experiments were performed. Primarily, 4.0 equivs of phenylhydrazine hydrochloride (4a) were used instead of phenylhydrazine with the absence of HCl and no desired product was detected. Next, with the addition of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) and BHT (2,6-di-tert-butyl-4-methylphen-ol) under standard conditions, the reaction was totally suppressed (Scheme 2), indicating that a radical pathway was operating in this transformation.
According to the radical trap experiments and previous reports [44,45,46,47,48], a plausible mechanism was proposed (Scheme 3). In the proposed mechanism, 1a is transformed into the excited intermediate 1a* under the irradiation of blue LEDs. Then, 1a* undergoes an energy transfer (ET) process with triplet oxygen 3O2 to give the higher active singlet oxygen 1O2 along with the regeneration of 1a. [48] Next, a single-electron-transfer (SET) process happens between HCl and 1O2 to provide a chlorine radical and superoxide anion. Next, 2a is oxidized by chlorine radical to provide the radical intermediate (A), which undergoes two steps further oxidization with the participation of chlorine radicals followed by the elimination of nitrogen and formation of the phenyl radical (D). [47,48] After that, (D) attacked the C3 position of 1a to form radical intermediate (E). Finally, the target product 3a, which is also the source for production of 1O2, is formed from (E) by means of a further oxidization [44].

3. Materials and Methods

All the chemicals were obtained commercially and used without any prior purification. 1H NMR and 13C NMR spectra were recorded on a Bruker Avance II 400 spectrometer (Swiss Brüker, Hangzhou, China). All products were isolated by short chromatography on a silica gel (200–300 mesh) column using petroleum ether (60–90 °C) and ethyl acetate, unless otherwise noted. All compounds were characterized by 1H NMR, and 13C NMR which are consistent with those reported in the literature (Supplementary Materials).
General procedure for synthesis of3: A mixture of the 1 (0.2 mmol), 2 (1.5 equiv, HCl (4.0 equiv) in CH3CN (2.0 mL) was placed in a Schlenk tube under the irradiation of 25 W blue LED in air atmosphere for 10 h. Then, the mixture was concentrated under vacuum after filtration. The product 3 was purified by silica gel column flash chromatography using PE/AcOEt (40:1) as an eluent.
Procedure for gram scale synthesis of 3a: A mixture of the 1a (1.12 g, 7 mmol), 2a (1.5 equiv), HCl (4.0 equiv) in CH3CN (30.0 mL) was placed in a 50 mL round bottom under the irradiation of 25 W blue LED in air atmosphere for 10 h. Then, the mixture was concentrated under vacuum after filtration. The product 3 was purified by silica gel column flash chromatography using PE/AcOEt (40:1) as an eluent.
Methyl-3-phenylquinoxalin-2(1H)-one (3a)
Yellow solid, obtained in 80% yield, m.p. 135–137 °C. 1H NMR (400 MHz, CDCl3) δ 8.44–8.23 (m, 2H), 7.97 (d, J = 8.0 Hz, 1H), 7.63–7.56 (m, 1H), 7.51 (d, J = 3.6 Hz, 3H), 7.38 (dd, J = 19.8, 8.4 Hz, 2H), 3.79 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.75, 154.19, 136.13, 133.42, 133.15, 130.50, 130.34, 129.59 (2C), 128.10 (2C), 123.74, 113.60, 29.32.
3-(4-Chlorophenyl)-1-methylquinoxalin-2(1H)-one (3b)
Yellow solid, obtained in 74% yield, m.p. 173–175 °C. 1H NMR (400 MHz, CDCl3) δ 8.38 (d, J = 8.1 Hz, 2H), 7.95 (d, J = 8.0 Hz, 2H), 7.60 (t, J = 7.9 Hz, 1H), 7.47 (d, J = 8.4 Hz, 3H), 3.78 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.62, 152.59, 136.58, 134.50, 133.42, 133.04, 131.05 (2C), 130.58, 130.54, 128.29 (2C), 123.86, 113.64, 29.33.
Methyl-3-(p-tolyl)quinoxalin-2(1H)-one (3c)
Yellow solid, obtained in 82% isolated yield, m.p. 156–158 °C. 1H NMR (400 MHz, CDCl3) δ 8.25 (d, J = 8.2 Hz, 2H), 7.92 (d, J = 8.0 Hz, 1H), 7.54 (t, J = 7.8 Hz, 1H), 7.35 (t, J = 7.6 Hz, 1H), 7.33–7.30 (m, 3H), 3.76 (s, 3H), 2.42 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.81, 154.02, 140.63, 133.40, 133.35, 133.20, 130.37, 130.03, 129.58 (2C), 128.83 (2C), 123.65, 113.53, 29.28, 21.54.
3-(4-(Tert-butyl)phenyl)-1-methylquinoxalin-2(1H)-one (3d)
Yellow oil, obtained in 77% yield. 1H NMR (400 MHz, CDCl3) δ 8.27 (d, J = 8.6 Hz, 2H), 7.96 (dd, J = 8.0, 1.5 Hz, 1H), 7.60–7.51 (m, 3H), 7.41–7.33 (m, 2H), 3.79 (s, 3H), 1.39 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 154.67, 154.06, 153.51, 133.24, 133.20, 133.10, 130.25, 129.91, 129.18 (2C), 124.99 (2C), 123.51, 113.40, 34.74, 31.10 (3C), 29.14.
3-(3-Fluorophenyl)-1-methylquinoxalin-2(1H)-one (3e)
1H NMR (400 MHz, CDCl3) δ 8.20 (d, J = 7.9 Hz, 1H), 8.15–8.11 (m, 1H), 7.95 (d, J = 8.0 Hz, 1H), 7.61 (t, J = 7.1 Hz, 1H),7.49–7.45 (m, 1H), 7.40 (t, J = 7.6 Hz, 1H), 7.36 (d, J = 8.4 Hz, 1H), 7.22–7.17 (m, 1H), 3.79 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 163.74 (d, J = 243.0 Hz), 154.54, 152.47, 152.44, 138.09 (d, J = 8.0 Hz), 133.41, 132.90, 130.82 (d, J = 21.0 Hz), 129.62 (d, J = 8.0 Hz), 125.37 (d, J = 3.0 Hz), 123.95, 117.40 (d, J = 21.0 Hz), 116.69 (d, J = 24.0 Hz), 113.71, 29.40.
Ethyl 2-(2-oxo-3-(p-tolyl)quinoxalin-1(2H)-yl)acetate (3f)
Yellow solid, obtained in 76% yield, m.p. 159–161 °C. 1H NMR (400 MHz, CDCl3) δ 8.25 (d, J = 8.2 Hz, 2H), 7.98–7.93 (m, 1H), 7.55–7.49 (m, 1H), 7.39–7.34 (m, 1H), 7.28 (t, J = 8.1 Hz, 2H), 7.09 (d, J = 8.4 Hz, 1H), 5.09 (s, 2H), 4.26 (q, J = 7.1 Hz, 2H), 2.42 (s, 3H), 1.28 (t, J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 167.09, 154.18, 153.58, 140.67, 133.04, 132.80, 132.24, 130.47, 130.04, 129.37 (2C), 128.68 (2C), 123.82, 112.80, 61.91, 43.59, 21.38, 13.97.
Phenyl-3-(p-tolyl)quinoxalin-2(1H)-one (3g)
Yellow solid, obtained in 66% yield, m.p. 192–193 °C. 1H NMR (400 MHz, CDCl3) δ 8.33 (d, J = 8.3 Hz, 2H), 7.98 (dd, J = 6.1, 3.4 Hz, 1H), 7.67–7.61 (m, 2H), 7.60–7.55 (m, 1H), 7.36–7.33 (m, 4H), 7.28 (d, J = 8.1 Hz, 2H), 6.68 (dd, J = 6.2, 3.4 Hz, 1H), 2.42 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.57, 154.31, 140.83, 136.12, 134.03, 132.98, 132.95, 130.29 (2C), 129.87, 129.65, 129.63 (2C), 129.37, 128.79 (2C), 128.27 (2C), 123.84, 115.30, 21.53.
Benzyl-3-(p-tolyl)quinoxalin-2(1H)-one (3h)
Yellow solid, obtained in 63% yield, m.p. 145–146 °C. 1H NMR (400 MHz, DMSO-d6) δ 8.17 (d, J = 8.0 Hz, 2H), 7.82 (d, J = 7.8 Hz, 1H), 7.46 (t, J = 7.8 Hz, 1H), 7.38 (d, J = 8.4 Hz, 1H), 7.32–7.15 (m, 8H), 5.50 (s, 2H), 2.32 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δ 154.59, 153.46, 140.60, 136.36, 133.54, 133.00, 132.73, 130.80, 130.17, 129.86 (2C), 129.15 (2C), 128.93 (2C), 127.74, 127.28 (2C), 124.17, 115.43, 45.53, 21.50.
3-(4-Fluorophenyl)quinoxalin-2(1H)-one (3i)
Yellow solid, obtained in 59% yield, m.p. 182–184 °C. 1H NMR (400 MHz, DMSO-d6) δ 12.54 (s, 1H), 8.43–8.32 (m, 2H), 7.78 (d, J = 8.0 Hz, 1H), 7.53–7.45 (m, 1H), 7.32–7.23 (m, 4H). 13C NMR (100 MHz, DMSO-d6) δ 165.03 (d, J = 246.0 Hz), 155.01, 153.26, 132.55 (2C) (d, JC-F = 3.0 Hz), 132.49 (2C) (d, J = 10.0 Hz), 132.15, 132.06, 130.75, 129.16, 123.86, 115.56, 115.36(d, JC-F = 21.0 Hz).
1,6,7-Trimethyl-3-(p-tolyl)quinoxalin-2(1H)-one (3j)
Yellow solid, obtained in 71% yield, m.p. 193–195 °C. 1H NMR (400 MHz, CDCl3) δ 8.22 (d, J = 8.2 Hz, 2H), 7.66 (s, 1H), 7.27 (d, J = 8.4 Hz, 2H), 7.06 (s, 1H), 3.72 (s, 3H), 2.41 (s, 6H), 2.35 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.82, 152.75, 140.21, 140.00, 133.59, 132.59, 131.54, 131.28, 130.31, 129.39 (2C), 128.77 (2C), 114.11, 29.18, 21.54, 20.67, 19.26.
6,7-Dichloro-1-methyl-3-(p-tolyl)quinoxalin-2(1H)-one (3k)
Yellow solid, obtained in 70% yield, m.p. 187–189 °C. 1H NMR (400 MHz, CDCl3) δ 8.23 (d, J = 8.0 Hz, 2H), 7.98 (s, 1H), 7.38 (s, 1H), 7.29 (s, 2H), 3.69 (s, 3H), 2.43 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.83, 154.13, 141.42, 133.89, 132.58, 132.54, 132.14, 130.87, 129.60 (2C), 128.91 (2C), 127.36, 114.99, 29.53, 21.59.
3-Cyclohexyl-1-methylquinoxalin-2(1H)-one (3l)
White solid, obtained in 45% yield, m.p. 110–113 °C. 1H NMR (400 MHz, CDCl3) δ 7.85 (d, J = 7.9 Hz, 1H), 7.51 (t, J = 7.3 Hz, 1H), 7.35–7.27 (m, 2H), 3.70 (s, 3H), 3.38–3.31 (m, 1H), 1.97–1.85 (m, 4H), 1.78–1.75 (d, J = 12.6 Hz, 1H), 1.63–1.41 (m, 4H), 1.37–1.29 (m, 1H). 13C NMR (100 MHz, CDCl3) δ 164.32, 154.57, 132.89, 132.86, 129.77, 129.42, 123.43, 113.48, 40.80, 30.54 (2C), 29.09, 26.33 (2C), 26.17.
2-(4-Chlorophenyl)quinoxaline (3m)
White solid, obtained in 47% yield, m.p. 128–130 °C. 1H NMR (400 MHz, CDCl3) δ 9.29 (s, 1H), 8.17–8.11 (m, 4H), 7.83–7.72 (m, 2H), 7.58–7.49 (m, 2H). 13C NMR (100 MHz, CDCl3) δ 150.59, 142.86, 142.24, 141.68, 136.60, 135.20, 130.47, 129.78, 129.61, 129.41 (2C), 129.18, 128.78 (2C).
2-(p-Tolyl)quinoxaline (3n)
White solid, obtained in 52% yield, m.p. 88–90 °C. 1H NMR (400 MHz, CDCl3) δ 9.32 (s, 1H), 8.19–8.07 (m, 4H), 7.84–7.71 (m, 2H), 7.38 (d, J = 8.0 Hz, 2H), 2.46 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 151.97, 143.45, 142.42, 141.51, 140.67, 134.05, 130.38, 130.05 (2C), 129.64, 129.48, 129.20, 127.56 (2C), 21.60.
2-(4-Methoxyphenyl)quinoxaline (3o)
Yellow solid, obtained in 56% yield, m.p. 103–105 °C. 1H NMR (400 MHz, CDCl3) δ 9.29 (s, 1H), 8.21–8.15 (m, 2H), 8.13–8.08 (m, 2H), 7.79–7.69 (m, 2H), 7.11–7.05 (m, 2H), 3.90 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 161.59, 151.57, 143.21, 142.42, 141.28, 130.37, 129.50, 129.37, 129.24, 129.17, 129.13 (2C), 114.72 (2C), 55.59.
2-(2-Bromophenyl)quinoxaline (3p)
Yellow solid, obtained in 42% yield, m.p. 120–121 °C. 1H NMR (400 MHz, CDCl3) δ 9.21 (s, 1H), 8.23–8.17 (m, 2H), 7.85 (dt, J = 6.4, 3.5 Hz, 2H), 7.77 (dd, J = 8.0, 1.2 Hz, 1H), 7.70 (dd, J = 7.6, 1.7 Hz, 1H), 7.53 (td, J = 7.5, 1.2 Hz, 1.0Hz, 1H), 7.42–7.37 (m, 1H). 13C NMR (100 MHz, CDCl3) δ 153.64, 146.13, 142.13, 141.38, 138.55, 133.46, 131.90, 130.92, 130.31, 130.16, 129.64, 129.28, 128.02, 122.02.
2-(Naphthalen-2-yl)quinoxaline (3q)
Yellow solid, obtained in 51% yield, m.p. 148–150 °C. 1H NMR (400 MHz, CDCl3) δ 9.47 (s, 1H), 8.65 (s, 1H), 8.36 (dd, J = 8.6, 1.8 Hz, 1H), 8.20 (dd, J = 8.1, 1.7 Hz, 1H), 8.14 (dd, J = 8.1, 1.7 Hz, 1H), 8.01 (dd, J = 9.0, 5.0 Hz, 2H), 7.93–7.87 (m, 1H), 7.83–7.72 (m, 2H), 7.59–7.53 (m, 2H). 13C NMR (100 MHz, CDCl3) δ 152.32, 144.15, 143.02, 142.20, 134.78, 134.70, 134.03, 130.99, 130.27, 130.22, 129.80, 129.69, 129.56, 128.46, 128.13, 127.95, 127.34, 125.13.
2-Chloro-3-(p-tolyl)quinoxaline (3r)
White solid, obtained in 66% yield, m.p. 126–128 °C. 1H NMR (400 MHz, CDCl3) δ 8.18–8.11 (m, 1H), 8.08–8.02 (m, 1H), 7.81–7.75 (m, 4H), 7.35 (d, J = 7.9 Hz, 2H), 2.46 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 152.98, 146.21, 140.98, 140.84, 140.01, 133.83, 130.68, 130.39, 129.57 (2C), 129.15, 129.01 (2C), 128.06, 21.46.
2-Methyl-3-(p-tolyl)quinoxaline (3s)
White solid, obtained in 58% yield, m.p. 56–57 °C. 1H NMR (400 MHz, CDCl3) δ 8.14–8.02 (m, 2H), 7.77–7.68 (m, 2H), 7.56 (d, J = 8.2 Hz, 2H), 7.34 (d, J = 7.8 Hz, 2H), 2.80 (s, 3H), 2.45 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.97, 152.57, 141.02, 140.93, 139.05, 136.03, 129.64, 129.24 (2C), 129.20, 129.17, 128.87 (2C), 128.15, 24.42, 21.39.
2,3-Dimethyl-5-(p-tolyl)pyrazine (3t)
Yellow solid, obtained in 51% yield, m.p. 110–112 °C. 1H NMR (400 MHz, CDCl3) δ 8.68 (s, 1H), 7.88 (d, J = 8.3 Hz, 2H), 7.29 (d, J = 7.9 Hz, 2H), 2.61 (s, 3H), 2.58 (s, 3H), 2.41 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 151.65, 150.04, 149.42, 139.25, 137.98, 133.94, 129.61 (2C), 126.49 (2C), 22.26, 21.71, 21.31.
1-(p-Tolyl)phthalazine (3u)
Yellow solid, obtained in 53% isolated yield, m.p. 97–99 °C. 1H NMR (400 MHz, CDCl3) δ 9.50 (s, 1H), 8.09 (d, J = 8.3 Hz, 1H), 8.00 (d, J = 7.6 Hz, 1H), 7.92–7.82 (m, 2H), 7.65 (d, J = 8.1 Hz, 2H), 7.37 (d, J = 7.8 Hz, 2H), 2.46 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 13C NMR (101 MHz, CDCl3) δ 159.79, 150.29, 139.37, 133.05, 132.44, 132.06, 129.86 (2C), 129.18 (2C), 126.97, 126.52, 126.18, 125.34, 21.34.

4. Conclusions

In conclusion, we present a practical HCl-mediated, photocatalytic metal- and oxidant-free protocol for C3 selective arylation of quinoxaline(on)es employing arylhydrazine hydrochlorides as aryl reagent, which exhibits highly efficient and broad functional group tolerance. Various quinoxaline(on)es and arylhydrazines react smoothly in this transformation and provide the corresponding aryl-substituted products in moderate to excellent yields.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal12060633/s1, Figure S1: 1H NMR Spectra of Compound 3a; Figure S2: 13C NMR Spectra of Compound 3a; Figure S3: 1H NMR Spectra of Compound 3b; Figure S4: 13C NMR Spectra of Compound 3b; Figure S5: 1H NMR Spectra of Compound 3c; Figure S6: 13C NMR Spectra of Compound 3c; Figure S7: 1H NMR Spectra of Compound 3d; Figure S8: 13C NMR Spectra of Compound 3d; Figure S9: 1H NMR Spectra of Compound 3e; Figure S10: 13C NMR Spectra of Compound 3e; Figure S11: 1H NMR Spectra of Compound 3f; Figure S12: 13C NMR Spectra of Compound 3f; Figure S13: 1H NMR Spectra of Compound 3g; Figure S14: 13C NMR Spectra of Compound 3g; Figure S15: 1H NMR Spectra of Compound 3h; Figure S16: 13C NMR Spectra of Compound 3h; Figure S17: 1H NMR Spectra of Compound 3i; Figure S18: 13C NMR Spectra of Compound 3i; Figure S19: 1H NMR Spectra of Compound 3j; Figure S20: 13C NMR Spectra of Compound 3j; Figure S21: 1H NMR Spectra of Compound 3k; Figure S22: 13C NMR Spectra of Compound 3k; Figure S23: 1H NMR Spectra of Compound 3l; Figure S24: 13C NMR Spectra of Compound 3l; Figure S25: 1H NMR Spectra of Compound 3m; Figure S26: 13C NMR Spectra of Compound 3m; Figure S27: 1H NMR Spectra of Compound 3n; Figure S28: 13C NMR Spectra of Compound 3n; Figure S29: 1H NMR Spectra of Compound 3o; Figure S30: 13C NMR Spectra of Compound 3o; Figure S31: 1H NMR Spectra of Compound 3p; Figure S32: 13C NMR Spectra of Compound 3p; Figure S33: 1H NMR Spectra of Compound 3q; Figure S34: 13C NMR Spectra of Compound 3q; Figure S35: 1H NMR Spectra of Compound 3r; Figure S36: 13C NMR Spectra of Compound 3r; Figure S37: 1H NMR Spectra of Compound 3s; Figure S38: 13C NMR Spectra of Compound 3s; Figure S39: 1H NMR Spectra of Compound 3t; Figure S40: 13C NMR Spectra of Compound 3t; Figure S41: 1H NMR Spectra of Compound 3u; Figure S42: 13C NMR Spectra of Compound 3u.

Author Contributions

Conceptualization, K.W.; writing—original draft preparation, K.W., W.X., and H.Q.; writing—review and editing, K.W. and W.X.; Writing—review and editing, P.Z. and X.-T.C.; Supervision, G.W.; project administration, P.Z., X.-T.C. and G.W.; funding acquisition, P.Z., X.-T.C. and G.W. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Innovation Team Fund of Jining Medical College (No. 102425001), the Doctoral Scientific Research Foundation of Jining Medical University (No. 6001/600763002) and the “Ten-thousand Talents Plan” of Zhejiang Province (2019R51012).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. TenBrink, R.E.; Im, W.B.; Sethy, V.H.; Tang, A.H.; Carter, D.B. Antagonist, Partial Agonist, and Full Agonist Imidazo[1,5-a]quinoxaline Amides and Carbamates Acting through the GABAA/Benzodiazepine Receptor. J. Med. Chem. 1994, 37, 758–768. [Google Scholar] [CrossRef] [PubMed]
  2. Badran, M.M.; Abouzid, K.A.M.; Hussein, M.H.M. Synthesis of Certain Substituted Quinoxalines as Antimicrobial Agents (Part II). Arch. Pharmacal. Res. 2003, 26, 107–113. [Google Scholar] [CrossRef] [PubMed]
  3. Weïwer, M.; Spoonamore, J.; Wei, J.; Guichard, B.; Ross, N.T.; Masson, K.; Silkworth, W.; Dandapani, S.; Palmer, M.; Scherer, C.A.; et al. A Potent and Selective Quinoxalinone-Based STK33 Inhibitor Does Not Show Synthetic Lethality in KRAS-Dependent Cells. ACS Med. Chem. Lett. 2012, 3, 1034–1038. [Google Scholar] [CrossRef] [PubMed]
  4. Chen, D.; Bao, W. An Efficient Domino Synthesis of Quinoxalin-2(1H)-ones via an SNAr/Coupling/Demesylation Reaction Catalyzed by Copper(I) as Key Step. Adv. Synth. Catal. 2010, 352, 955–960. [Google Scholar] [CrossRef]
  5. Wen, J.; Wei, W.; Xue, S.; Yang, D.; Lou, Y.; Gao, C.; Wang, H. Metal-Free Oxidative Spirocyclization of Alkynes with Sulfonylhydrazides Leading to 3-Sulfonated Azaspiro[4,5]trienones. J. Org. Chem. 2015, 80, 4966–4972. [Google Scholar] [CrossRef] [PubMed]
  6. Xie, L.-Y.; Qu, J.; Peng, S.; Liu, K.-J.; Wang, Z.; Ding, M.-H.; Wang, Y.; Cao, Z.; He, W.-M. Selectfluor-mediated Regioselective Nucleophilic Functionalization of N-heterocycles under Metal- and Base-free Conditions. Green Chem. 2018, 20, 760–764. [Google Scholar] [CrossRef]
  7. Quinn, J.; Guo, C.; Ko, L.; Sun, B.; He, Y.; Li, Y. Pyrazino[2,3-g]quinoxaline-2,7-dione Based π-conjugated Polymers with Affinity Towards Acids and Semiconductor Performance in Organic Thin Film Transistors. RSC Adv. 2016, 6, 22043–22501. [Google Scholar] [CrossRef]
  8. Jeon, S.O.; Lee, J.Y. Comparison of Symmetric and Asymmetric Bipolar type high Triplet Energy host Materials for Deep Blue Phosphorescent Organic Light-emitting Diodes. J. Mater. Chem. 2012, 22, 7239–7244. [Google Scholar] [CrossRef]
  9. El-Hawash, S.A.M.; Habib, N.S.; Kassem, M.A. Synthesis of Some New Quinoxalines and 1,2,4-Triazolo[4,3-a]-quinoxalines for Evaluation of in vitro Antitumor and Antimicrobial Activities. Arch. Pharm. Chem. Life Sci. 2006, 339, 564–571. [Google Scholar] [CrossRef]
  10. Parhi, A.K.; Zhang, Y.; Saionz, K.W.; Pradhan, P.; Kaul, M.; Trivedi, K.; Pilch, D.S.; LaVoie, E.J. Antibacterial activity of quinoxalines, quinazolines, and 1,5-naphthyridines. Bioorg. Med. Chem. Lett. 2013, 23, 4968–4974. [Google Scholar] [CrossRef]
  11. Rodrigues, F.A.R.; Bomfim, I.D.S.; Cavalcanti, B.C.; Pessoa, C.D.Ó.; Wardell, J.L.; Wardell, S.M.S.V.; Pinheiro, A.C.; Kaiser, C.R.; Nogueira, T.C.M.; Low, J.N.; et al. Design, Synthesis and Biological Evaluation of (E)-2-(2-arylhydrazinyl)quinoxalines, a Promising and Potent New Class of Anticancer Agents. Bioorg. Med. Chem. Lett. 2014, 24, 934–939. [Google Scholar] [CrossRef] [PubMed]
  12. Newahie, A.M.S.E.; Ismail, N.S.M.; Ella, D.A.A.E.; Abouzid, K.A.M. Quinoxaline-Based Scaffolds Targeting Tyrosine Kinases and Their Potential Anticancer Activity. Arch. Pharm. Chem. Life Sci. 2016, 349, 309–326. [Google Scholar] [CrossRef] [PubMed]
  13. Kánai, K.; Arányi, P.; Böcskei, Z.; Ferenczy, G.; Harmat, V.; Simon, K.; Bátori, S.; Náray-Szabó, G.; Hermecz, I. Prolyl Oligopeptidase Inhibition by N-Acyl-pro-pyrrolidine-type Molecules. J. Med. Chem. 2008, 51, 7514–7522. [Google Scholar] [CrossRef] [PubMed]
  14. Qin, X.; Hao, X.; Han, H.; Zhu, S.; Yang, Y.; Wu, B.; Hussain, S.; Parveen, S.; Jing, C.; Ma, B.; et al. Design and Synthesis of Potent and Multifunctional Aldose Reductase Inhibitors Based on Quinoxalinones. J. Med. Chem. 2015, 58, 1254–1267. [Google Scholar] [CrossRef]
  15. Viswanadham, K.K.D.R.; Reddy, M.P.; Sathyanarayana, P.; Ravi, O.; Kant, R.; Bathula, S.R. Iodine-mediated oxidative annulation for one-pot synthesis of pyrazines and quinoxalines using a multipathway coupled domino strategy. Chem. Commun. 2014, 50, 13517–13520. [Google Scholar] [CrossRef]
  16. Hazarika, D.; Phukan, P. Metal Free Synthesis of Quinoxalines from Alkynes via a Cascade Process using TsNBr2. Tetrahedron 2017, 73, 1374–1379. [Google Scholar] [CrossRef]
  17. Xu, Y.; Huang, X.; Lv, G.; Lai, R.; Lv, S.; Li, J.; Hai, L.; Wu, Y. Iridium-Catalyzed Carbenoid Insertion of Sulfoxonium Ylides for Synthesis of Quinoxalines and β-Keto Thioethers in Water. Eur. J. Org. Chem. 2020, 2020, 4635–4638. [Google Scholar] [CrossRef]
  18. Gulevskaya, A.V.; Burov, O.N.; Pozharskii, A.F.; Kletskii, M.E.; Korbukova, I.N. Oxidative Alkylamination of Azinones as a Direct route to Aminoazinones: Study of some Condensed Diazinones. Tetrahedron 2008, 64, 696–707. [Google Scholar] [CrossRef]
  19. Li, Y.; Gao, M.; Wang, L.; Cui, X. Copper-catalysed Oxidative Amination of Quinoxalin-2(1H)-ones with Aliphatic Amines. Org. Biomol. Chem. 2016, 14, 8428–8432. [Google Scholar] [CrossRef]
  20. Gupta, A.; Deshmukh, M.S.; Jain, N. Iodine-Catalyzed C–N Bond Formation: Synthesis of 3-Aminoquinoxalinones under Ambient Conditions. J. Org. Chem. 2017, 82, 4784–4792. [Google Scholar] [CrossRef]
  21. Wei, W.; Wang, L.; Bao, P.; Shao, Y.; Yue, H.; Yang, D.; Yang, X.; Zhao, X.; Wang, H. Metal-Free C(sp2)–H/N–H Cross-Dehydrogenative Coupling of Quinoxalinones with Aliphatic Amines under Visible-Light Photoredox Catalysis. Org. Lett. 2018, 20, 7125–7130. [Google Scholar] [CrossRef] [PubMed]
  22. Yuan, J.; Fu, J.; Yin, J.; Dong, Z.; Xiao, Y.; Mao, P.; Qu, L. Transition-metal-free Direct C-3 Alkylation of Quinoxalin-2(1H)-ones with Ethers. Org. Chem. Front. 2018, 5, 2820–2828. [Google Scholar] [CrossRef]
  23. Sun, A.C.; McClain, E.J.J.; Beatty, W.; Stephenson, C.R.J. Visible Light-Mediated Decarboxylative Alkylation of Pharmaceutically Relevant Heterocycles. Org. Lett. 2018, 20, 3487–3490. [Google Scholar] [CrossRef] [PubMed]
  24. Xue, W.X.; Su, Y.P.; Wang, K.-H.; Zhang, R.; Feng, Y.W.; Cao, L.D.; Huang, D.F.; Hu, Y. Visible-light induced Decarboxylative Alkylation of Quinoxalin-2(1H)-ones at the C3-position. Org. Biomol. Chem. 2019, 17, 6654–6661. [Google Scholar] [CrossRef]
  25. Xu, J.; He, L.; Liang, C.F.; Yue, X.G.; Ouyang, Y.N.; Zhang, P.F. Multicomponent Bifunctionalization of Methyl Ketones Enabled by Heterogeneous Catalysis and Solar Photocatalysis in Water. ACS Sustain. Chem. Eng. 2021, 9, 13663–13671. [Google Scholar] [CrossRef]
  26. Niu, K.K.; Hao, Y.K.; Song, L.Y.; Liu, Y.X.; Wang, Q.M. Electro-oxidative C–H Alkylation of Quinoxalin-2(1H)-ones with Organoboron Compounds. Green Chem. 2021, 23, 302–306. [Google Scholar] [CrossRef]
  27. Xie, L.Y.; Chen, Y.L.; Qin, L.; Wen, Y.; Xie, J.W.; Tan, J.X.; Huang, Y.; Cao, Z.; He, W.M. Visible-light-promoted Direct C–H/S–H Cross-coupling of Quinoxalin-2(1H)-ones with Thiols Leading to 3-sulfenylated Quinoxalin-2(1H)-ones in air. Org. Chem. Front. 2019, 6, 3950–3955. [Google Scholar] [CrossRef]
  28. Xie, L.Y.; Liu, Y.S.; Ding, H.R.; Gong, S.F.; Tan, J.X.; He, J.Y.; Cao, Z.; He, W.M. C(sp2)–H/O–H Cross-dehydrogenative Coupling of Quinoxalin-2(1H)-ones with Alcohols under Visible-light Photoredox Catalysis. Chin. J. Catal. 2020, 41, 1168–1173. [Google Scholar] [CrossRef]
  29. Xu, X.; Xia, C.C.; Li, X.; Sun, J.; Hao, L.Q. Visible-light-induced aerobic C3–H Fluoroalkoxylation of Quinoxalin-2(1H)-ones with Fluoroalkyl Alcohols. RSC Adv. 2020, 10, 2016–2026. [Google Scholar] [CrossRef] [Green Version]
  30. Carrër, A.; Brion, J.D.; Alami, M.; Messaoudi, S. Assisted Tandem Palladium(II)/Palladium(0)-Catalyzed C- and N-Arylations of Quinoxalin-2(1 H)-ones in Water. Adv. Synth. Catal. 2014, 356, 3821–3830. [Google Scholar] [CrossRef]
  31. Paul, S.; Khanal, H.D.; Clinton, C.D.; Kim, S.H.; Lee., Y.R. Pd(TFA)2-catalyzed Direct Arylation of Quinoxalinones with Arenes. Org. Chem. Front. 2019, 6, 231–235. [Google Scholar] [CrossRef]
  32. Paul, S.; Ha, J.H.; Park, G.E.; Lee, Y.R. Transition Metal-Free Iodosobenzene-Promoted Direct Oxidative 3-Arylation of Quinoxalin-2(H)-ones with Arylhydrazines. Adv. Synth. Catal. 2017, 359, 1515–1521. [Google Scholar] [CrossRef]
  33. Yin, K.; Zhang, R.H. Transition-Metal-Free Direct C–H Arylation of Quinoxalin-2(1H)-ones with Diaryliodonium Salts at Room Temperature. Org. Lett. 2017, 19, 1530–1533. [Google Scholar] [CrossRef] [PubMed]
  34. Yuan, J.W.; Liu, S.N.; Qu, L.B. Transition Metal-Free Direct C-3 Arylation of Quinoxalin-2(1H)-ones with Arylamines under Mild Conditions. Adv. Synth. Catal. 2017, 359, 4197–4207. [Google Scholar] [CrossRef]
  35. Song, S.J.; Shi, X.J.; Zhu, Y.S.; Ren, Q.L.; Zhou, P.; Zhou, J.D.; Li, J.J. Electrochemical Oxidative C–H Arylation of Quinoxalin(on)es with Arylhydrazine Hydrochlorides under Mild Conditions. J. Org. Chem. 2022, 87, 4764–4776. [Google Scholar] [CrossRef]
  36. Liu, K.-J.; Wang, Z.; Lu, L.-H.; Chen, J.-Y.; Zeng, F.; Lin, Y.-W.; Cao, Z.; Yu, X.Y.; He, W.-M. Synergistic Cooperative Effect of CF3SO2Na and Bis(2-butoxyethyl)ether Towards Selective Oxygenation of Sulfides with Molecular Oxygen under Visible-light Irradiation. Green Chem. 2021, 23, 496–500. [Google Scholar] [CrossRef]
  37. Zhu, X.J.; Liu, Y.; Liu, C.; Yang, H.; Fu, J.H. Light and Oxygen-enabled Sodium Trifluoromethanesulfinate-mediated Selective Oxidation of C–H Bonds. Green Chem. 2020, 22, 4357–4363. [Google Scholar] [CrossRef]
  38. Prier, C.K.; Rankic, D.A.; MacMillan, D.W.C. Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis. Chem. Rev. 2013, 113, 5322–5363. [Google Scholar] [CrossRef] [Green Version]
  39. Narayanam, J.M.R.; Stephenson, C.R.J. Visible Light Photoredox Catalysis: Applications in Organic Synthesis. Chem. Soc. Rev. 2011, 40, 102–113. [Google Scholar] [CrossRef]
  40. Chatterjee, T.; Iqbal, N.; You, Y.; Cho, E.J. Controlled Fluoroalkylation Reactions by Visible-Light Photoredox Catalysis. Acc. Chem. Res. 2016, 49, 2284–2294. [Google Scholar] [CrossRef]
  41. Wang, L.L.; Bao, P.L.; Liu, W.W.; Liu, S.T.; Hu, C.S.; Yue, H.L.; Yang, D.S.; Wei, W. Direct C-H 3-Arylation of Quinoxalin-2(H)-ones with Aryl Diazonium Salts under Visible-Light Irradiation. Chin. J. Org. Chem. 2018, 38, 3189–3196. [Google Scholar] [CrossRef]
  42. Tian, M.; Liu, S.; Bu, X.; Yu, J.P.; Yang, X. Covalent Organic Frameworks: A Sustainable Photocatalyst toward Visible-Light-Accelerated C3 Arylation and Alkylation of Quinoxalin-2(1H)-ones. Chem. Eur. J. 2020, 26, 369–373. [Google Scholar] [CrossRef] [PubMed]
  43. Xu, J.; Zhang, H.; Zhao, J.; Ni, Z.; Zhang, P.F.; Shi, B.F.; Li, W.M. Photocatalyst-, Metal- and Additive-free, Direct C–H Arylation of Quinoxalin-2(1H)-ones with Aryl Acyl Peroxides Induced by Visible Light. Org. Chem. Front. 2020, 7, 4031–4042. [Google Scholar] [CrossRef]
  44. Wang, J.Y.; Sun, B.; Zhang, L.; Xu, T.W.; Xie, Y.Y.; Jin, C. Visible-Light-Induced Trifluoromethylation of Quinoxalin-2(1H)-Ones under Photocatalyst-Free Conditions. Asian J. Org. Chem. 2019, 8, 1942–1946. [Google Scholar] [CrossRef]
  45. Sun, K.; Xiao, F.; Yu, B.; He, W.-M. Photo-/electrocatalytic Functionalization of Quinoxalin-2(1H)-ones. Chin. J. Catal. 2021, 42, 1921–1943. [Google Scholar] [CrossRef]
  46. Xie, L.-Y.; Bai, Y.-S.; Xu, X.-Q.; Peng, X.; Tang, H.-S.; Huang, Y.; Lin, Y.-W.; Cao, Z.; He, W.-M. Visible-light-induced Decarboxylative Acylation of Quinoxalin-2(1H)-ones with α-oxo Carboxylic Acids under Metal-, Strong Oxidant- and External Photocatalyst-free Conditions. Green Chem. 2020, 22, 1720–1725. [Google Scholar] [CrossRef]
  47. Zhang, Y.-Z.; Mo, Z.-Y.; Wang, H.-S.; Wen, X.-A.; Tang, H.-T.; Pan, Y.-M. Electrochemically Enabled Chemoselective Sulfonylation and Hydrazination of Indoles. Green Chem. 2019, 21, 3807–3811. [Google Scholar] [CrossRef]
  48. Niu, K.K.; Shi, X.D.; Ding, L.; Liu, Y.X.; Song, H.J.; Wang, Q.M. HCl-Catalyzed Aerobic Oxidation of Alkylarenes to Carbonyls. ChemSusChem 2022, 15, e202102326. [Google Scholar] [CrossRef]
Catalysts 12 00633 sch001 550
Scheme 1. Photocatalytic direct C3 arylation of quinoxalinones. Previous work on photoinduced C3 arylation (a) [41], (b) [42], (c) [43].
Scheme 1. Photocatalytic direct C3 arylation of quinoxalinones. Previous work on photoinduced C3 arylation (a) [41], (b) [42], (c) [43].
Catalysts 12 00633 sch001
Catalysts 12 00633 sch002 550
Scheme 2. Gram-scale synthesis and mechanistic studies.
Scheme 2. Gram-scale synthesis and mechanistic studies.
Catalysts 12 00633 sch002
Catalysts 12 00633 sch003 550
Scheme 3. Proposed mechanism.
Scheme 3. Proposed mechanism.
Catalysts 12 00633 sch003
Table
Table 1. Optimization of the reaction conditions a,b.
Table 1. Optimization of the reaction conditions a,b.
Catalysts 12 00633 i001
EntryVariation from Given ConditionsYields (%)
1none80
2green LED instead of blue LEDtrace
3white LED instead of blue LED43
4without light0
5without HCl0
63.0 equivs of HCl used67
75.0 equivs of HCl used81
8K2CO3 instead of HCl45
9EtOH instead of MeCN61
10DMSO instead of MeCN56
11MeCN/H2O (v/v = 1:1) instead of MeCN47
12H2O instead of MeCNtrace
13Reaction was performed under O283
14Reaction was performed under N20
a Reaction conditions: 1 (0.2 mmol), 2 (1.5 equiv), HCl (4.0 equiv), MeCN (2.0 mL), blue LED (25 W), rt, in air, 10 h. b Isolated yields.
Table
Table 2. Substrate scope of quinoxalinones a,b.
Table 2. Substrate scope of quinoxalinones a,b.
Catalysts 12 00633 i002
Catalysts 12 00633 i003 Catalysts 12 00633 i004 Catalysts 12 00633 i005
Catalysts 12 00633 i006 Catalysts 12 00633 i007 Catalysts 12 00633 i008
Catalysts 12 00633 i009 Catalysts 12 00633 i010 Catalysts 12 00633 i011
Catalysts 12 00633 i012 Catalysts 12 00633 i013 Catalysts 12 00633 i014
a Reaction conditions: 1 (0.2 mmol), 2 (1.5 equiv), HCl (4.0 equiv), MeCN (2.0 mL), blue. LED (25 W), rt, in air, 10 h. b Isolated yields.
Table
Table 3. Substrate scope of quinoxalines a,b.
Table 3. Substrate scope of quinoxalines a,b.
Catalysts 12 00633 i015
Catalysts 12 00633 i016 Catalysts 12 00633 i017 Catalysts 12 00633 i018
Catalysts 12 00633 i019 Catalysts 12 00633 i020 Catalysts 12 00633 i021
a Reaction conditions: 1 (0.2 mmol), 2 (1.5 equiv), HCl (4.0 equiv), MeCN (2.0 mL), blue LED (25 W), rt, in air, 10 h. b Isolated yields.
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Wang, K.; Xu, W.; Qi, H.; Zhang, P.; Cao, X.-T.; Wang, G. A HCl-Mediated, Metal- and Oxidant-Free Photocatalytic Strategy for C3 Arylation of Quinoxalin(on)es with Arylhydrazine. Catalysts 2022, 12, 633. https://doi.org/10.3390/catal12060633

AMA Style

Wang K, Xu W, Qi H, Zhang P, Cao X-T, Wang G. A HCl-Mediated, Metal- and Oxidant-Free Photocatalytic Strategy for C3 Arylation of Quinoxalin(on)es with Arylhydrazine. Catalysts. 2022; 12(6):633. https://doi.org/10.3390/catal12060633

Chicago/Turabian Style

Wang, Kai, Wenjing Xu, Haoran Qi, Pengfei Zhang, Xian-Ting Cao, and Guannan Wang. 2022. "A HCl-Mediated, Metal- and Oxidant-Free Photocatalytic Strategy for C3 Arylation of Quinoxalin(on)es with Arylhydrazine" Catalysts 12, no. 6: 633. https://doi.org/10.3390/catal12060633

APA Style

Wang, K., Xu, W., Qi, H., Zhang, P., Cao, X.-T., & Wang, G. (2022). A HCl-Mediated, Metal- and Oxidant-Free Photocatalytic Strategy for C3 Arylation of Quinoxalin(on)es with Arylhydrazine. Catalysts, 12(6), 633. https://doi.org/10.3390/catal12060633

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