A quinine-squaramide catalyzed enantioselective vinylogous Mannich reaction between benzothiazolimines and γ-butenolides for efficient preparation of chiral N-benzothiazole butyrolactones

Abstract

A highly effective and enantioselective vinylogous Mannich reaction between benzothiazolimines and γ-butenolides catalyzed by a quinine based squaramide has been disclosed. A series of chiral benzothiazole amines containing a γ,γ-disubstituted butanolide scaffold bearing an adjacent chiral stereocenter have been successfully obtained in good to excellent yields (up to 91%) with excellent enantioselectivities (up to >99% ee) and diastereoselectivities (>20 : 1 dr) with broad substrate generality under mild conditions. The new scaffold integrated with both chiral benzothiazolimine and γ-butenolide moieties may provide a possibility for the development of new pharmaceutical entities.