Monothioacetalization of acetals catalyzed by dicyanoketene acetals

A type of capto-dative olefin, dicyanoketene acetal such as dicyanoketene dimethyl acetal and ethylene acetal is introduced to be a novel type of π-acid catalyst for the monothioacetalization of acetals as well as the corresponding α,β-unsaturated systems. Particularly, the catalytic activity of dicyanoketene ethylene acetal was found to be superior to that of tetracyanoethylene and highly chemoselective in the crossover reaction of a ketone-, aldehyde-acetal, an alcohol THP-, and MOM-ether providing a ketone monothioacetal favorably.