Asymmetric Synthesis of 2,3-Dihydrofurans via Squaramide Catalyzed Michael-Alkylation Reaction

A highly stereoselective methodology was developed to construct dihydrofurans. In the presence of a bifunctional squaramide catalyst, the Michael addition/cyclization between cyclohexane- 1,3-dione and α-bromonitroalkenes occurred smoothly to provide the desired dihydrofurans with high to excellent yields (90-94%) and good to high enantioselectivities (80-94% ee). This catalytic protocol was compatible with a range of structurally distinct α-bromonitroalkenes.