Diastereoselective Spirocyclization of Benzoxazines with Nitroalkenes via Rhodium-Catalyzed C-H Functionalization/Annulation Cascade under Mild Conditions.

A Rh(III)-catalyzed [3 + 2] annulation of benzoxazines with nitroolefins that proceeds via redox-neutral C-H functionalization has been demonstrated, leading to the novel class of spirocycles in a single step. The construction of three continuous stereogenic centers has been achieved starting from easily accessible achiral substrates in an atom-efficient manner under mild reaction conditions. A broad range of pharmaceutically relevant nitro substituted spirocyclic 2,3-dihydro-1,4-benzoxazine derivatives has been synthesized in good to excellent yields with high diastereoselectivity.