Copper-catalyzed conjugate addition of in situ formed alkyl boranes to α,β-unsaturated ketones

Abstract

Conjugate addition of in situ formed organometallic reagents to α,β-unsaturated carbonyl compounds provides an efficient way to generate new C–C bonds. We show optimization of the copper-catalyzed conjugate addition of alkylboranes, which were formed directly in the reaction mixture by hydroboration of alkenes. We have improved the reaction conditions by employing “greener”, less hygroscopic, and higher boiling solvent, 2-methyltetrahydrofuran. We have also broadened the scope of the reaction. Furthermore, chiral ferrocenyl carbene ligands were assessed in the enantioselective version of the transformation with medium enantioselectivity 67:33 e.r.