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

摘要

Zinc and copper are neighbors in the periodic table, so that Zn-(II) and Cu(I) have isoelectronic states, and consequently, their organometallic complexes have many similarities in reactivity. For instance, their ate complexes, lithium triorganozincates R_.3Zn(II)-Li and lithium diorganocuprates R._2Cu(I)Li, react smoothly and selectively with alpha,beta-unsaturated carbonyl compounds to undergo 1,4-addition reactions, and hence both can be classified as "soft" reagents (Figure l). However, this similarity is essentially superficial because the group 11 metal is a transition metal element and the group 12 metal belongs to the main group. Thus, it is of interest to investigate the true reason for the origin of the 1,4-addition selectivity ("soft" nucleophilicity) of organozincate reagents.5 Here, we report a theoretical/computational study, using density functional theory, of the pathway and mechanism of the selectivity of 1,4-addition of Me_3ZnLi to alpha,beta-unsaturated carbonyl compounds, using s-trans methyl vinyl ketone (MVK (1)) as the simplest model for acyclic and cyclic enones.