Chromium(0)-promoted multicomponent cycloaddition of tethered diynes with cyclic trienes: application to the total synthesis of 9-epi-pentalenic acid.

An efficient protecting group controlled regioselective chromium(0)-mediated three-component higher order cycloaddition of tethered diynes with cyclic trienes that generates five rings and six stereogenic centers in one step is described. Following a sequence of reactions featuring a chemoselective Baeyer-Villiger rearrangement and a regioselective cyclopropane hydrogenolysis, the total synthesis of 9-epi-pentalenic acid was achieved. Copyright 2004 American Chemical Society