Asymmetric Total Synthesis of Brasiliquinones B and C via Oxidative Cyclization of a Hydroquinone-Silyl Enol Ether Hybrid.

The asymmetric total synthesis of angucycline antibiotics ()-brasiliquinones B and C was accomplished. The benz[]anthraquinone core was constructed via oxidative cyclization of a hydroquinone-silyl enol ether hybrid. The resultant pentacyclic acetal was converted to the silyl enol ether, which was treated with Pd(II)/O to afford brasiliquinone C, after multistep conversion including dehydrogenation, desilylation and deacetalization, and hydroquinone oxidation. The ()-configuration of natural brasiliquinones was confirmed based on the stereochemical correlation with the synthetic products.