Benign approaches for the microwave-assisted synthesis of quinoxalines

Abstract

Neste trabalho foram usados dois sistemas simples, rápidos (3 min) e versáteis, de transferência de energia de microondas, na ausência de solventes, para a síntese de quinoxalinas (2,3-difenilquinoxalina e seus derivados, 2,3-difenil-4a,5,6,7,8,8a-hexahidroquinoxalina, 2-fenilquinoxalina, piridina-2,3-diamina e 2,3-dihidro-5,6-difenilpirazina). O primeiro método consiste no uso de suportes minerais na reação de 1,2-dicarbonil (benzil) ou α-hidroxicetona (aciloína) com 1,2-diaminas. Entre os suportes minerais, a eficiência da alumina ácida como catalisador foi claramente comprovada (80-86%). Além disso, apresenta um papel importante na oxidação de aciloína ao correspondente sistema 1,2-dicarbonílico. O segundo método consiste no uso de microondas em mistura dos reagentes 1,2-dicarbonil(benzil) e 1,2-diaminas. O excelente rendimento dos produtos (90-97%) e a simples lavagem com água e filtração na ausência de solventes orgânicos fazem desse sistema uma ótima alternativa para a prevenção de poluição, em um processo ambientalmente benigno. Embora os dois métodos tenham sido planejados para evitar passos adicionais de purificação, o último é um processo mais limpo com tratamento reacional mais simples.Two benign, simple, rapid (3 min), solvent-free and versatile microwave energy transfer systems for the synthesis of quinoxalines, i.e. 2,3-diphenylquinoxaline and its derivatives, 2,3-diphenyl-4a,5,6,7,8,8a-hexahydroquinoxaline, and 2-phenylquinoxaline and also pyridine-2,3-diamine and 2,3-dihydro-5,6-diphenylpyrazine have been used. The first approach consists on the use of mineral supports on the reaction of 1,2-dicarbonyl (benzil) or α-hydroxyketone (acyloin) with 1,2-diamines. Among mineral supports, the efficiency of acidic alumina as catalyst was clearly proved (80-86%). Moreover, it has an oxidative role in the tandem oxidation of acyloin to the corresponding 1,2-dicarbonyl. The second approach is the use of polar paste system on the reaction of 1,2-dicarbonyl (benzil) with 1,2-diamines. The excellent products yield (90-97%) and simple washing with water and filtration in the absence of organic solvent makes it an impressive alternative green platform. Although both methods implemented in this study have been designed to circumvent additional purification steps, the latter is cleaner with an easier work-up.

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.…”

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

“…In continuation of our interest on the development of efficient, practical and eco-friendly procedures for the synthesis of condensed benzo[N,N]-heterocyclic compounds, [33][34][35] we herein wish to introduce NH 4 Cl-CH 3 OH as a mild and effective catalyst system for the synthesis of quinoxaline derivatives. In general, this method affords the products in excellent yields and avoids the problems associated with catalyst cost, handling and safety.…”

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

“…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.…”