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 Me3ZnLi to MVK as compared with that of (MeLi)(2) showed that the precise transition state structures critically determine the reaction selectivity for alpha,beta-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.