FeCl3-catalyzed cyclization of α-sulfonamido-allenes with aldehydes--the substituent effect.

FeCl(3)-catalyzed aza-Prins-cyclization reaction of α-sulfonamido-allenes with aldehydes afforded 1,2,3,6-tetrahydropyridine or 2,5-dihydro-1H-pyrrole derivatives efficiently and highly selectively. The different regioselectivity is probably caused by the stabilizing effect of the phenyl group on the positively charged allylic intermediate.