NH4Cl-CH3OH: an efficient, acid- and metal-free catalyst system for the synthesis of quinoxalines

Abstract

A condensação direta de benzeno-1,2-diaminas (4-R-Ph-(NH 2 ) 2 , onde R = H, Me, Cl e NO 2 ) e 1,2-dicarbonil (R'-CO-CO-R', onde R' = Ph, 4-MeO-Ph e Me) foi realizada com excelentes rendimentos (95-100%) usando (NH 4 Cl-CH 3 OH) como sistema catalítico brando, eficiente, de boa relação custo-benefício, fácil obtenção, isento de ácido e de metal e ambientalmente amigável, a temperatura ambiente. O procedimento pode ser realizado para diversas quinoxalinas e a natureza do grupo funcional no anel aromático das 1,2-diaminas exerce uma forte influência no tempo e rendimento da reação. A eficiência da condensação pode ser regulada também pela quantidade de catalisador e tempo de reação.The direct condensation of various benzene-1,2-diamines [4-R-Ph-(NH 2 ) 2 , where R = H, Me, Cl and NO 2 ] and 1,2-dicarbonyl compounds (R'-CO-CO-R', where R' = Ph, 4-MeO-Ph and Me) has been successfully achieved mostly in excellent yields (95-100%) using (NH 4 Cl-CH 3 OH) as a mild, efficient, cost-effective, readily available, acid-free, metal-free and eco-friendly catalyst system at room temperature. The procedure can be performed for a broad scope of quinoxalines, however, the nature of the functional group on the aromatic ring of 1,2-diamine exerts a strong influence on the time and the reaction yield. The condensation efficiency could be further regulated by the amount of catalyst and reaction time.

Silica-Supported Antimony(III) Chloride as Highly Effective and Reusable Heterogeneous Catalyst for the Synthesis of Quinoxalines

“…As a part of our continued interest in the development of highly expedient methods for the synthesis of heterocyclic compounds [26][27][28][29], we herein report a facile and efficient synthetic strategy for quinoxaline derivatives in excellent yield using SbCl 3 /SiO 2 in methanol as benign solvent [30]. Despite the use of few solid heterogeneous catalysts in literature [20,22,23,25], silica-supported heterogeneous Lewis acid catalysts, like SbCl 3 /SiO 2 , have not yet been explored with regard to the preparation of quinoxalines.…”

Ammonium chloride; as a mild and efficient catalyst for the synthesis of some 2-arylbenzothiazoles and bisbenzothiazole derivatives

“…Ammonium chloride (NH4Cl) is a very inexpensive, eco-friendly and easily available catalyst; it has been reported as catalyst for synthesis of various organic compounds. It has effectively promoted Claisen rearrangement [28], Biginelli synthesis of 3,4-dihydropyrimidinones [29], the thia-michael addition reaction [30], the one-pot synthesis of diindolymethanes [31], and the synthesis of Quinoxalines [32].…”

“…The aim of this study is to utilize an eco-friendly NH4Cl-CH3OH system for the synthesis of 2-arylbenzothiazoles at ambient temperature using ammonium chloride as catalyst and methanol as the benign reaction medium in medicinal chemistry [32]. In order to investigate the optimal conditions for these reactions, we start by examining the influence of the reaction time and the solvent effect at room temperature.…”

Heterogeneous SnCl2/SiO2versus Homogeneous SnCl2Acid Catalysis in the Benzo[N,N]-heterocyclic Condensation

“…[36][37][38][39][43][44] The regioselectivity for 4-substituted 1,2-diaminobenzenes on treatment with phenylglyoxal in the presence of SnCl 2 /SiO 2 was also investigated (Table 5, entries [17][18][19][20]. With the exception of 2,3-diaminopyridine, which showed very high selectivity to cis-regioisomer 1t, [45][46] the condensation of other 4-substituted 1,2-diaminobenzenes with phenylglyoxal resulted in a mixture of regioisomers 1q-1s, in favor of trans-regioisomers [47][48][49] ( Fig.…”

“…Therefore, development of an efficient and environmentally benign method is still required. As part of our continuous efforts to develop eco-friendly catalytic processes, [36][37][38][39][40][41] herein, we introduce SnCl 2 /SiO 2 as a novel heterogeneous catalyst for the acid-catalyzed reactions, e.g. benzo[N,N]-heterocyclic condensation.…”