Regio-, Enantio-Controlled Cascade Oxa-Michael Addition of Hydroxyl Amine: Synthesis of Dihydro-1,2-Oxazines

Abstract

Herein, we disclose a cinchona-alkaloid-based squaramide-catalyzed intermolecular oxa-Michael cascade addition cyclization of N-protected hydroxyl amine to formyl-tethered Michael acceptors toward the synthesis of enantioenriched 1,2-oxazine scaffolds. Generally, good yield (up to 78%), good to excellent enantiomeric ratio (up to 98:2 er), and excellent regioselectivity (>19:1) were observed. Furthermore, the scalability of this methodology and a successful demonstration of postsynthetic transformations have been accomplished.