Highly Enantio- and Diastereoselective Brassard Type Hetero-Diels−Alder Approach to 5-Methyl-Containing α,β-Unsaturated δ-Lactones

Two efficient new chiral copper (II) Schiff base complexes were developed for the highly enantio- and
diastereoselective HDA reaction of Brassard type diene 1b with aldehydes, to afford the corresponding
5-methyl-containing α,β-unsaturated δ-lactone derivatives in moderate yields, high enantioselectivities
(up to 99% ee) and excellent diastereoselectivities (up to 99:1 anti/syn). On the basis of the absolute
configuration of 4a−4j disclosed by X-ray diffraction and CD analysis, a possible transition-state model
for the enantio- and diastereoselective catalytic reaction has been proposed.