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.