Phosphine-Catalyzed Domino Reaction of Thioaurones and Allenoate: Synthesis of Benzothiophene-Fused Dioxabicyclo[3.3.1]nonane Derivatives.

The reaction of thioaurone derivatives with allenoate catalyzed by tris(4-methoxyphenyl)phosphane (P(4-MeOCH)) resulted in a domino annulation reaction to produce a benzothiophene-fused bridged bicyclic ring, with 40-91% yields. The advantages of the methodology include diastereoselective formation of a bridged bicyclic ring in a single step, very mild reaction conditions, and success resulting from a broad functional group. The proposed mechanism was tested and supported by DFT calculations.