Synthesis and application of a dual chiral [2.2]paracyclophane-based N-heterocyclic carbene in enantioselective ß-boration of acyclic enones.

ABSTRACT

An enantioselective conjugate addition of boron to α,ß-unsaturated ketones catalysed by either a N-heterocyclic carbene or a copper-carbene complex generated in situ from a new chiral bicyclic triazolium based on [2.2]paracyclophane is presented. The dual chiral carbene-copper catalyst has significant advantages over its carbene counterpart as an organocatalyst in asymmetric ß-boration of acyclic enones, giving a variety of chiral ß-boryl ketones in good yields and enantioselectivities. This is a successful example of employing the same N-heterocyclic carbene in one catalytic reaction as both an organocatalyst and a ligand for transition metal catalysis.