Ring strain is the driving force for numerous ring-opening reactions of 3- and 4-membered heterocycles. By comparison, 5-membered heterocycles lack this thermodynamic driving force. As a result, only a few methods exist for the ring-opening of unactivated 5-membered heterocycles using transition metal catalysts. We report a novel strategy for the asymmetric ring-opening of 2,5-dihydrofurans with dichloroalkenes utilizing an earth-abundant cobalt catalyst. We propose that the dichloroalkenes form reactive vinylidene intermediates with the chiral (iPrPybox)CoBr2 catalyst, followed by a [2+2] cycloaddition with the heterocyclic alkene. This complex could potentially undergo a β-H elimination, form cyclopropanes via a direct reductive elimination, or undergo the desired β-O elimination. We optimized our catalytic system to selectively perform the β-O elimination. The resulting 5-membered metallacycle can transmetallate with Zn and subsequently give rise to homoallylic alcohols, upon quenching, with high diastereoselectivity and enantioselectivity. Additionally, the organozinc intermediate can be trapped in situ by various electrophiles for further derivatizations.

Enantioselective cobalt-catalyzed ring-opening of unstrained heterocyclic alkenes

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