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 medi ated 4+3 cycloadditions with allylsilanes, incorporating halide from the Le wis acid to give halocycloheptynes 3, 6, 7. A phenyl group may be incorpora ted in place of the halogen (to give 8) by use of benzene as solvent and wi th B(C6F5)(3) as the Lewis acid; chlorobenzene and toluene also participate in the process.