Stereospecific Construction of Contiguous Quaternary All-Carbon Centers by Oxidative Ring Contraction.

Oxidative ring contraction of cyclic α-formyl ketones was facilitated by the action of H2 O2 under operationally simple and environmentally benign reaction conditions. The process was highly regioselective and enables stereospecific construction of contiguous quaternary all-carbon centers from stereodefined all-substituted all-cyclic ketones. The asymmetric syntheses of (+)-cuparene and (+)-tochuinyl acetate were also successively achieved by taking advantage of this novel protocol.