alkyne complexes, cobalt, ring closure, Lewis acids, nucleophiles
Butyne-1,4-diether hexacarbonyldicobalt complexes 1 undergo Lewis acid mediated 4+3 cycloadditions with allylsilanes, incorporating halide from the Lewis acid to give halocycloheptynes 3, 6, 7. A phenyl group may be incorporated in place of the halogen (to give 8) by use of benzene as solvent and with B(C6F5)(3) as the Lewis acid; chlorobenzene and toluene also participate in the process.
Lu, Yafan and Green, James R.. (2001). Tandem 4+3 cycloaddition/nucleophilic trapping reactions of butyne-1,4-diether dicobalt hexacarbonyl complexes. Synlett (2), 0243-0247.