Vinylogous Nicholas reactions in the synthesis of bi- and tricyclic cycloheptynedicobalt complexes

The Lewis acid mediated intramolecular Nicholas reactions of allylic acetate enyne-Co₂(CO)₆ complexes afford cycloheptenyne-Co₂(CO)₆ complexes in three manifestations. Electron rich aryl substituted alkyne complexes give tricyclic 6,7,x-benzocycloheptenyne complexes, with x = 5, 6, or 7. Allylsilane substituted complexes afford exo methylene bicyclic x,7-cycloheptenyne complexes (x = 6,7). The allyl acetate function may also be replaced by a benzylic acetate, to afford dibenzocycloheptyne-Co₂(CO)₆ complexes. Following reductive complexation, the methodology may be applied to the synthesis of the icetexane diterpene carbon framework.