Mechanistic understanding of domino cyclization between gem-dialkylthio vinylallenes and benzylamine towards economic synthesis: a computational study

Abstract

DFT investigations are carried out to improve the domino cyclization between gem-dialkylthio vinylallenes and benzylamine. Economic reaction approaches were explored, namely, this reaction can occur under organic solvent-free conditions either catalyzed by trace water or self-catalyzed by BnNH₂. Three types of reactions (DMSO-assisted, trace water-catalyzed, and self-catalyzed by BnNH₂) shared the same reaction mechanism with the nucleophilic attack of BnNH₂ on the allenic carbon of thioamide intermediate Re. For trace water-catalyzed reaction another mechanism was also found that is the BnNH₂ attacks the carbonyl carbon of the conformational isomer of Re. Among the investigated mechanisms, the trace water-catalyzed one is suggested to be the most efficient and convenient synthetic method for pyrroles. Our calculated results were further confirmed by the experimental observation, which opens a new strategy for the synthesis of pyrroles.