Formal total synthesis of the PKC inhibitor, balanol: preparation of the fully protected benzophenone fragment

The synthesis of a perbenzylated derivative of balanolʹs highly functionalized benzophenone fragment is reported employing a regioselective Heck reaction as the key step for the connection of the two aromatic rings. The intermediate 7-membered lactone obtained, is subsequently opened and then subjected to an oxidative degradation, resulting in a short synthesis of the benzophenone unit. As the benzophenone has previously been successfully carried through to the synthesis of balanol, our work constitutes a formal total synthesis of this natural product. Attempts were also made to provide other direct entries to this fragment via a Heck-like coupling onto an aryl aldehyde or a SmI2-promoted ketyl radical cyclization.