Construction of [6-5-5-6-6] Pentacyclic Skeleton via a Phosphine-Catalyzed Domino Reaction and Mechanism Study.

A novel phosphine-promoted domino reaction between thioaurone or aurone derivatives and MBH carbonate is described. A wide range of [6-5-5-6-6] pentacyclic compounds was prepared efficiently. Interestingly, the stereoselectivity was affected by the sulfur or oxygen atom in the substrates. Moreover, the reaction mechanism was explored by density functional calculations, which identified the 1,4-hydrogen-shift step to be the selectivity-determining step.