Trapping of Zwitterionic Intermediates by Isatins and Imines: Synthesis of Benzoxazines Bearing a C4-Quaternary Stereocenter

Benzoxazines bearing a C4-quaternary stereocenter have been accomplished via the rhodium-catalyzed electrophilic trapping of zwitterionic intermediates by isatins and imines, respectively. The key intermediates of the strategy are proposed to generate from the reaction of donor–acceptor rhodium carbenes with secondary amides. Usage of chiral BINOL-phosphoric acid co-catalyst resulted in enrichment of enantioselectivity in the trapping process with imines.