Tandem 4 + 3 Cycloaddition/Nucleophilic Trapping Reactions of Butyne-1,4-diether Dicobalt Hexacarbonyl Complexes

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.