Enantioselective Construction of 5‐6‐5 Tricyclic Lactone Framework Bearing a Quaternary Bridgehead Carbon via Rh‐Catalyzed Asymmetric [2+2+2] Cycloaddition of Enediynes
Herein, we report a Rh-catalyzed asymmetric [2+2+2] cycloaddition of ene-yne-yne enediynes to generate enantio-enriched tricyclic cyclohexadienes bearing a quaternary bridgehead carbon. We found that the Rh-Phanephos complex is an appropriate catalyst for the cycloaddition of enediynes bearing an unsubstituted propiolate terminus, whereas Rh-biaryl bisphosphine catalysts, which have been widely used