Cobalt( I )‐Mediated Intramolecular [2+2+2] Cocyclizations of (Methylenecyclopropyl)diynes as an Easy Access to Cyclopropanated Oligocycles

Enediynes with methylenecyclopropane moieties attached either through the three‐membered ring or the double bond smoothly underwent cobalt‐mediated [2+2+2] cocyclizations to give cyclopropane‐fused and spirocyclopropanated cobalt‐complexed tricyclo[7.3.0.0 2,6 ]dodeca‐1,6‐dienes (1,2,3,3a,4,6,7,8‐octahydro‐ as ‐indacenes) under relatively mild conditions in yields ranging from 31 to 94 % (6 examples). Electron‐withdrawing substituents at the acetylenic terminus of the precursor are essential for a successful oligocyclization. While diphenyloxyphosphinyl‐substituted enediynes provided tricyclo[7.3.0.0 2,6 ]dodeca‐1,6‐diene complexes as mixtures of two diastereomers in high yields, the analogous methoxycarbonyl‐substituted precursors gave only one diastereomer. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)