Stereoselective synthesis of N,N-acetals by cyclization of an N-acyliminium ion through interaction with an N-sulfonyl group

A new method for the stereoselective synthesis of five- and six-membered bicyclic N,N-acetals with trans configuration was developed using N-acyliminium ion cyclization. The N-sulfonyl substituted compounds were effectively cyclized to give the corresponding acetals in high yields and stereoselectivities, suggesting that the intramolecular interaction between the iminium and the sulfonyl group plays a key role in the cyclization.