Diastereoselective synthesis of cyclopentanoids: applications to the construction of the ABCD tetracyclic core of retigeranic acid A.

A concise and efficient approach for the construction of the tetracyclic carbon skeleton of retigeranic acid A is described. The key transformations include a novel Rh-catalyzed [3+2] cycloaddition of enyol to afford cyclopentanoid E, bearing two contiguous quaternary stereocenters at the bridgehead positions, and an intramolecular Pauson-Khand reaction to construct the advanced tetracyclic core structure of retigeranic acid A.