Enantioselective Construction of All-Carbon Quaternary Centers by Branch-Selective Pd-Catalyzed Allyl Allyi Cross-Coupling

The Pd-catalyzed cross-coupling of racemic tertiary allylic carbonates and allylboronates is described. This reaction generates all-carbon quaternary centers in a highly regioselective and enantioselective fashion. The outcome of these reactions is consistent with a process that proceeds by way of 3,3'-reductive elimination of bis(eta(1)-allyl)palladium intermediates. Strategies for distinguishing the product alkenes and application to the synthesis of (+)-alpha-cuparenone are also described.