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.