Transannular [4 + 2] Cycloaddition Reactions of Cobalt-Complexed Macrocyclic Dienynes

The first transannular [4 + 2] cycloaddition reactions of macrocyclic dicobalt hexacarbonyl–dienyne complexes were demonstrated. Complexes were conveniently prepared through palladium­(II)-catalyzed intramolecular oxidative cyclization of bis­(vinylboronate esters) followed by complexation with dicobalt octacarbonyl. Transannular [4 + 2] cycloaddition reactions of the complexes occurred at lower temperatures and shorter times than transannular Diels–Alder reactions of metal-free dienynes. Intermolecular control reactions confirmed the effect of cobalt complexation on [4 + 2] cycloaddition reactions of unactivated alkynes and dienes