Asymmetric Boration of para-Quinone Methides Catalyzed by N-Heterocyclic Carbene

The first carbene-catalyzed enantioselective 1,6-conjugate addition of boron to para-quinone methides was achieved by using the commercially available chiral triazolium and bis(pinacolato)diboron. The main features of this reaction include mild conditions, broad scope of substrates, excellent functional group tolerance, as well as good yield and enantioselectivity. Notably, in the absence of any transition metals, the reaction proceeded very well even with 0.1 mol% of catalyst loading without obvious erosion of yield and enantioselectivity, albeit longer reaction time was required.

Automated summary

The first carbene-catalyzed enantioselective 1,6-conjugate addition of boron to para-quinone methides was achieved using a commercially available chiral triazolium and bis(pinacolato)diboron. This reaction features mild conditions, broad substrate scope, excellent functional group tolerance, and good yield and enantioselectivity. Remarkably, even in the absence of any transition metals, the reaction proceeded well with just 0.1 mol% of catalyst loading without significant loss of yield and enantioselectivity, although longer reaction time was required.