Total Synthesis of Maoecrystal P: Application of a Strained Bicyclic Synthon.

A new strategy was devised for the total synthesis of highly oxidized ent-kauranoids. A highly regio- and diastereoselective intermolecular Diels-Alder cycloaddition involving a diene embedded in a substituted bicyclo[4.1.0] skeleton was used to assemble all carbon centers but C17 of the target molecule at an early stage of the synthesis. Subsequent synthetic steps, including redox manipulations, SmI2 -mediated cyclization, and isomerization reactions, afforded the antitumor natural product maoecrystal P.