Ring Enlargement of Enantiopure 1,2-Oxazines to 1,2-Oxazepine Derivatives and Their Palladium-Catalyzed Couplings

Phase-transfer-catalyzed cyclopropanation of enantiopure 1,2-oxazine derivatives anti-1a,b or syn-1 followed by solvolysis of the resulting geminal dibromocyclopropane intermediates afforded the expected ring-expanded products, namely 1,2-oxazepines anti-3a,b or syn-3. These heterocycles could be further substituted by use of their bromoalkenyl group employing palladium-catalyzed coupling reactions, which smoothly led to new enantiopure 1,2-oxazepine derivatives anti-4-anti-8.