Enantioselective Synthesis of 3,4-Dihydropyran Derivatives via Organocatalytic Michael Reaction of α,β-Unsaturated Enones

A simple chiral diamine catalyst (1a) was
successfully
applied in the asymmetric Michael reaction between cyclic dimedone
and α,β-unsaturated ketones. Both acyclic enones with
aryl or alkyl β-substituents and cyclic enones were tolerated
well in the reaction. The desired adducts were obtained in high yields
(up to 98%) with excellent enantioselectivities (up to 97% ee). The
additives were found to increase the reactivity dramatically. The
biologically active 2,4-disubstituted polyhydroquinoline scaffold
was conveniently prepared through an ammoniation from the generated
3,4-dihydropyran product.