Organocatalyzed asymmetric cascade Mannich/cyclization of 3-isothiocyanato oxindoles with cyclic ketimines for the synthesis of polycyclic spiro-thioimidazolidine-oxindoles

Abstract

The first diastereo- and enantioselective cascade Mannich/cyclization reaction of 3-isothiocyanato oxindoles with cyclic ketimines has been successfully developed. By using chiral bifunctional organocatalysts, a range of structurally diverse chiral polycyclic spiro-thioimidazolidine-oxindoles, bearing two contiguous tetrasubstituted stereocenters, could be obtained in excellent yields (up to 99%) with good diastereo- and enantioselectivities (up to >20:1 dr and 94.5:5.5 er) under mild reaction conditions.