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

Bi(OTf)(3)center dot nH(2)O 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-Bronsted acid catalysis might be in operation, or triflic acid itself, generated in situ by hydrolysis of metal triflate, could be the true hydroamination catalyst.