Bismuth(iii) triflate promoted intramolecular hydroamination of unactivated alkenyl sulfonamides in the preparation of pyrrolidines

Abstract

Bi(OTf)₃·nH₂O was found to be an efficient promoter of the cyclisative hydroamination of unactivated alkenyl sulfonamides, giving rise to the N-protected 2-methyl pyrrolidines in good to excellent yields (up to 95%). Based on control experiments, a joint Lewis acid–Brønsted acid catalysis might be in operation, or triflic acid itself, generated in situ by hydrolysis of metal triflate, could be the true hydroamination catalyst.