Synthesis of the benzophenone fragment of balanol via an intramolecular cyclization event

Studies are reported on the use of either a 7-exo radical cyclization or an intramolecular Heck reaction as the key step for the construction of the benzophenone fragment of the PKC inhibitor, balanol. Whereas, the former approach was unsuccessful, the Heck reaction proved to be viable for the coupling of two fully functionalized aryl subunits affording regioselectively a biaryl seven-membered lactone with an exocyclic alkene as the major component, in contrast to the competing eight-membered ring lactone. Hydrolysis of the lactone followed by oxidative cleavage of the alkene with ruthenium tetraoxide completed this short synthesis of the benzophenone unit.