Reaction Pathway of Conjugate Addition of Lithium Organozincates to s-trans-Enones

Density functional theory (DFT) calculations were performed to understand the reaction mechanism of organozincates in 1,4-addition to methyl vinyl ketone (MVK). Examination of the addition of Me 3 ZnLi to MVK as compared with that of (MeLi) 2 showed that the precise transition state structures critically determine the reaction selectivity for α,β-unsaturated carbonyl compounds. In the case of organozincates, the 1,4-addition proceeds smoothly through an open form TS, whereas alkyllithiums favor 1,2-addition through a closed TS. This 1,4-addition mechanism of Zn-ates does not involve an electron transfer process and is different from the reaction of organocuprates, in which oxidation/reduction of the copper atom occurs.