Cobalt Mediated [2 + 2 + 2]‐Cycloadditions: Stereospecific Intramolecular Reactions of Enediynes to Tricyclic Dienes Bearing Angular Methyl Groups

Enediynes such as (1), prepared by the Wittig reaction, can be converted into tricycles such as (2) via a simultaneous triple ring-closure reaction by irradiating in the presence of (C5H5)(CO)2Co. The ligands—which can in part be viewed as model compounds for vitamin D precursors—can be liberated by oxidative demetalation.