Enantioselective Synthesis Of Fused Dihydropyranones Via Squaramide-catalyzed Michael Addition/lactonization Cascade Reaction

A highly enantioselective(49-99% ee)Michael addition/lactonization cascade process has been developed to construct 3,4-dihydropyran-2-one in the presence of a quinine-based bifunctional squaramide.Various ?,?-unsaturated N-acyl heterocycles were well tolerated and afforded 3,4-dihydropyran-2-ones in moderate to excellent isolated yields(50-99%).Moreover,a single squaramide was sufficient to promote this enantioselective transformation,and no additional additive was required in comparison with previous protocol.Superior reactivity and enantiopurity were obtained via our established protocol when compared with those previous organocatlytic protocols.Both cyclic and acyclic ?-diketones were well compatible with this catalytic protocol.The enantioenriched dihydropyranones generated via this domino process are synthetically versatile materials.Chemoselective reduction of ester motif worked properly under mild reaction conditions to give rise to oxadecalinones.The reactivity of these acceptors depended closely on electron-withdrawing character and leaving ability of the heteroaromatic residues beside the carbonyl groups.