Enantioselective Cu-Catalyzed Hetero-Diels-Alder Synthesis of δ-Lactones

Abstract

Two new chiral copper(II) Schiff base complexes have been shown to catalyze the hetero-Diels-Alder reaction of Brassard dienes with a variety of aldehydes to give 5-methyl-α,β-unsaturated δ-lactones in moderate yields but with excellent diastereo- and enantioselectivity. A series of aromatic and heteroaromatic aldehydes bearing electron-withdrawing and -donating groups were employed. Other chiral tridentate Schiff base ligands, Lewis acids and conditions were tested with less effective results.