Chiral Bifunctional Thiosquaramides as Organocatalysts in the Synthesis of Enantioenriched 3,3-Disubstituted Oxindoles

Abstract

Four novel chiral bifunctional thiosquaramides have been prepared from cyclopentyl dithiosquarates and diamines derived from natural l‐Valine and l‐tert‐Leucine. The novel thiosquaramides have been tested as organocatalyst in the nitro‐Michael addition of 3‐substituted oxindoles to different β‐aryl‐substituted nitroalkenes. The reaction occurred easily in high yields and excellent stereoselectivities, showing that the novel organocatalysts are much more effective than their thioureas and squaramides homologs.