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.