Unexpected Copper(II) Catalysis: Catalytic Amine Base Promoted β-Borylation of α,β-Unsaturated Carbonyl Compounds in Water

Using bis(pinacolato)diboron, catalytic amounts of Cu(II), and various amine bases in water under atmospheric conditions at rt, acyclic and cyclic α,β-unsaturated ketones and esters are β-borylated in up to 98% yield. Mechanistic investigations using UV-vis spectroscopy, (11)B NMR, and solvent kinetic isotope effect suggest that the role of the amine is not only to coordinate to Cu(II) but also to activate a nucleophilic water molecule to form the reactive sp(2)-sp(3) diboron complex.