A stereoselective synthesis of symmetrical and unsymmetrical bibenzo[e][1,3]oxazine-2,2′-dione derivatives induced by low-valent titanium reagent

A series of symmetrical and unsymmetrical bibenzo[e][1,3]oxazine-2,2′-dione derivatives were synthesized by the reaction of various o-hydroxy Schiff bases and triphosgene induced by low-valent titanium reagent (TiCl4/Sm). A variety of substrates can participate in the process with good yields. The present method provides a useful preparation of 3,3′,4,4′-tetrahydro-4,4′-bibenzo[e][1,3]oxazine-2,2′-dione derivatives, which cannot be prepared otherwise. The mechanistic course of the reaction suggests the involvement of reduction, coupling, and cyclization by one-pot.