Cyclocondensation of acylketene S,N- and N,N-acetals with maleic anhydride and maleimide: a facile one-step synthesis of pyrano [3,4-c]pyrrole, pyrrolo [3,4-c]pyridine and condensed pyrrole derivatives

Abstract

The acylketene S,N-acetals 1a-c react with maleic anhydride (2) in refluxing acetonitrile to give the corresponding 3-pyrrolin-2-one-3-acetic acid derivatives 3a-c in good yields. Condensation of S,N-acetals 1a-j and 2 in presence of acetic anhydride directly afforded the corresponding 2-substituted-3-methylthio-4-aryl (or methyl)-1,6-dioxo- 2,3-dihydropyrano[3,4-c]pyrroles 4 a-j in excellent yields. The reaction of cyclic S,N- (5a-c) and N,N- (5d-f) acetals with 2 in refluxing acetonitrile gave the corresponding pyrrolo[2,1-b]thiazole (6a-c) and pyrrolo[1,2-a]imidazole (6d-f) derivatives, respectively, in good yields. Similarly, the condensation of S,N-acetals 1a and 1d with maleimide directly yielded the respective pyrrolo[3,4-c]pyridine derivatives 9a and 9b, while the corresponding pyrrolinone-3-acetamide derivatives 8a and 8b were obtained under similar conditions, when the reaction time was reduced.