[2.2]Paracyclophane-based carbene–copper catalyst tuned by transannular electronic effects for asymmetric boration

Abstract

A series of planar chiral carbene–copper complexes based on the [2.2]paracyclophane backbone with a pseudo-ortho substitution pattern have been synthesized and applied to asymmetric β-boration of α,β-unsaturated esters. As a result, transannular electronic effects of the substituent of the chiral catalyst have significant influence on the catalytic performance. A variety of chiral β-hydroxyl esters were obtained in excellent enantioselectivities (up to 97% ee) and yields (up to 99%).