Kinetics and mechanism of the conjugate addition of lithium dimethylcuprate to .alpha.,.beta.-unsaturated ketones

Wherefore Art Thou Copper? Structures and Reaction Mechanisms of Organocuprate Clusters in Organic Chemistry

“…Important kinetic studies by Krauss and Smith for Me 2 CuLi and a variety of ketones revealed the kinetic expressions shown in Equation (13), which are first order for both the organocuprate dimer and the enone. [165] This rate expression is consistent with the reaction scheme shown in Equation (14) (14) rate-determining step copper ± olefin coordinations [177] forms the product via the intermediate(s). A lithium ± carbonyl complex also forms but is a dead-end intermediate.…”

“…Nakamura and S. Mori 2) Qualitative correlation of the apparent rate of 1,4-addition with the reduction potential of the enone [161] was later proven by quantitative kinetic studies by Krauss and Smith to be only superficial. [165] 3) b-Cyclopropyl a,b-unsaturated ketones, such as the one shown in Equation (12), often give a ring-opened product, which was taken as strong evidence for radical anion formation by SET. [166] An elegant study by Casey and Cesa with deuterium-labeled substrate indicated stereospecificity of the cyclopropane ring opening that denies the radical mechanism [Eq.…”

“…Experiments have shown that the enone/ lithium complex (top left of Scheme 11) is a dead-end species. [165,179] The intermediate CPop is the ªb-cuprio ketoneº intermediate that has been widely debated in the mechanistic discussions of conjugate addition (compare with Equations (13) and (16)). On the basis of the Nakamura ± Morokuma theoretical analysis, one can now consider three limiting structures for CPop that are shown in the lower box in Scheme 11.…”

On the Role of PIII Ligands in the Conjugate Addition of Diorganozinc Derivatives to Enones

“…As soon as the addition was complete, a 50 mL sample was taken from the reaction mixture and treated with water (1 mL) and diethyl ether (0.5 mL). Additional aliquots were taken after 2,4,6,8,10,15,20,30,45,60,80, 100, 120, 150 and 180 min and treated likewise. The ethereal phases were examined by GC.…”

“…[8] However, in spite of the importance of this promising catalytic process, very few mechanistic studies have been undertaken to elucidate its mechanism. In the related area of the conjugate addition of Gilman cuprates [9] early kinetic studies by Krauss and Smith [10] and subsequent NMR studies by Ullenius and Smith [11] clearly pointed to a mechanism, where an intermediate formed in equilibrium with the starting material goes through an irreversible step to give the conjugate adduct. Further support came from mechanistic studies by Krause, who identified such an intermediate, followed by elegant investigations on kinetic isotope effects by Singleton.…”