Abstract
The solution structure of mixed aggregate derived from lithium ester enolate, chiral diether ligand and lithium amide was investigated by low-temperature NMR. Although chiral diether ligand alone was not efficient to activate the lithium ester enolate in the asymmetric Michael reaction, in the presence of both of chiral ligand and lithium amide the Michael addition product was obtained in good yield with good enantioselectivity. The formation of the ternary complex reagent of lithium ester enolate–chiral ligand–lithium amide was suspected in the equimolar mixture of these reagents by low-temperature 1H, 13C NMR spectroscopies. By using [6Li, 15N]-LDA, two sets of doublet peaks were appeared in 6Li NMR of 1:1:1 mixture of enolate–ligand–LDA, which also indicates the formation of the ternary complex reagent.
