摘要：

The kinetics of the reaction of several α,β-unsaturated ketones with excess lithium dimethylcuprate in the presence and absence of lithium iodide was studied by stopped-flow ultraviolet spectroscopy in diethyl ether solution at 25.0°C, by measuring the rate of disappearence of a spectroscopically observable intermediate. Under these conditions, the conjugate additions are first order in ketone but exhibit a more complex dependence upon cuprate concentration. The rates of reaction of aryl-substituted 1-phenyl-3-methyl-2-buten-1-ones and β-aryl-substituted chalcones with (CH3)2CuLi were also measured, and the rate and equilibrium constants for these reactions were correlated separately with Hammett σ constants. The rates of reaction of mesityl oxide and isophorone were also studied by stopped-flow infrared spectroscopy. Rapid scanning experiments in which reacting solutions of several enones were scanned over the carbonyl double-bond region of the infrared spectrum revealed the presence of an intermediate. These results are consistent with a mechanism in which the reactants are in equilibrium with an intermediate complex, which may unimolecularly rearrange to form a trialkylcopper(III) species with copper bonded to the β-carbon of the lithium enolate, followed by a reductive elimination process involving the copper ligands to form the β-methyllithium enolate product and methylcopper.

展开