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

The Lewis acid mediated intramolecular Nicholas reactions of allylic acetate enyne-Co-2(CO)(6) complexes afford cycloheptenyne-Co-2(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-Co-2(CO)(6) complexes. Following reductive complexation, the methodology may be applied to the synthesis of the icetexane diterpene carbon framework.