Divergent access to polycyclic spiro- and fused- N ,O-ketals through Bi(OTf) 3 -catalyzed [4+2]-annulation of cyclic N -sulfonyl ketimines and alkynols.

Bismuth(III) triflate-catalyzed [4+2]-annulation of cyclic N -sulfonyl ketimines (derived from saccharin) and alkynyl alcohols (4-pentyn-1-ols and 5-hexyn-1-ols) has been reported. This cascade annulation provides a diverse array of polycyclic spiro-and-fused N , O -ketals with excellent substrate scope, good isolated yields, and diastereoselectivities under mild reaction conditions.