Conjugate reduction of .alpha.,.beta.-unsaturated carbonyl compounds by catecholborane

α,β-Unsaturated ketones which can readily adopt an s-cis conformation undergo conjugate reduction by catecholborane at room temperature. α,β-Unsaturated imides, esters, and amides are unreactive under the same conditions. However, catalytic quantities of Rh(PPh 3 ) 3 Cl greatly accelerate the 1,4-addition process, effecting conjugate reduction of these substrates by catecholborane at -20°C. The resulting boron enolates may be reacted with electrophiles to provide functionalized products