A unified strategy to ent-kauranoid natural products: total syntheses of (-)-trichorabdal A and (-)-longikaurin E.

The first total syntheses of (-)-trichorabdal A and (-)-longikaurin E are reported. A unified synthetic strategy is employed that relies on a Pd-mediated oxidative cyclization of a silyl ketene acetal to generate an all-carbon quaternary center and build the bicyclo[3.2.1]octane framework. These studies, taken together with our previous synthesis of (-)-maoecrystal Z, demonstrate that three architecturally distinct ent-kauranoids can be prepared from a common spirolactone intermediate.