Straightforward approach to 5-substituted 7H-imidazo[2,1-b][1,3]thiazines via cyclization of 2-alkynylthioimidazoles

Abstract

Electrophile-initiated nucleophilic cyclization of 2-alkynylthiobenzimidazoles is a useful tool for synthesizing new heterocyclic systems. However, halogen-initiated cyclization demonstrates poor selectivity between electrophilic addition and substitution reactions using other imidazole analogues. In this research, several different coinage-metal catalysts were employed to broaden the scope of 7H-imidazo[2,1-b][1,3]thiazines in atom-economic manner. Selective 6-endo-dig pathway reactions were achieved in good to excellent yields using various 2-alkynylthioimidazoles with AuCl as a catalyst in DCE/DCM.