Density functional computations of enantioselective alkynylation of aldehyde catalyzed by chiral zinc(II)-complexes.

The enantioselective alkynylation of aldehyde catalyzed by chiral zinc(II)-complexes was studied by means of the density functional theory (DFT). All the structures were optimized completely at the B3LYP/6-31G(d,p) level. To obtain more exact energies, single-point energy calculations at B3LYP/6-31+G(d,p) level were carried out on the B3LYP/6-31G(d,p) geometries. As shown, this enantioselective alkynylation was endothermic. The chirality-determining step for the alkynylation was the formation of the catalyst-ethanol complexes and the transition states for this step involved a six-membered ring. The dominant products predicted theoretically were of (R)-chirality, in good agreement with experiment. [Structure: see text].