Some Observations on the Mechanism of Diorganocuprate 1,4-Addition Reactions with α,β-Unsaturated Ketones: Effects of Diethyl Ether in Reactions of Butylcoppers in Toluene

Mixtures of butyllithium and copper iodide prepared in toluene react with α,β-unsaturated ketones predominantly in a 1,2-fashion. Addition of 2 equiv of diethyl ether to the system results in a dramatic preference for the 1,4-product, as found normally with diorganocuprates in ethereal solvents. These results are in accordance with the theoretical predictions that a suitable ligand is required to facilitate the stabilization of a formally copper(III) reaction intermediate on the 1,4-addition mechanistic pathway.