Base induced cycloaddition of ethyl/methyl isocyanoacetate with 2-(methylsulfonyl)-3-(het)arylquinoxalines: a new pathway to access ethyl/methyl 4-(het)arylimidazo[1,5-a]quinoxaline-3-carboxylates

Abstract

We herein report the DBU induced dipolar cycloaddition of ethyl/methyl isocyanoacetate with 2-(methylsulfonyl)-3-(het)arylquinoxalines which afford ethyl/methyl 4-(het)arylimidazo[1,5-a]quinoxaline-3-carboxylates in 80–95 % yields. The required 2-(methylsulfonyl)-3-(het)arylquinoxalines were synthesized by the oxidation of 2-(methylsulfanyl)-3-(het)arylquinoxalines by m-CPBA. These reactions were compatible in the presence of various aryl/heteroaryl groups. The plausible mechanism of formation of products is also presented. This protocol avoids the need of expensive transition metal catalysts and overcome limitations such as formation of regioisomeric mixture of products, elevated temperatures and long reaction times.