Highly Diastereo- and Enantioselective Synthesis of Spiro-tetrahydrofuran-pyrazolones via Organocatalytic Cascade Reaction between γ-Hydroxyenones and Unsaturated Pyrazolones

The first diastereo- and enantioselective synthesis of spiro-tetrahydrofuran-pyrazolones is reported via organocatalytic asymmetric cascade oxa-Michael/Michael reaction between γ-hydroxyenones and unsaturated pyrazolones. Bifunctional squaramide catalyst was found to be effective for this reaction. With 10 mol % of catalyst, excellent results were attained for a variety of spiropyrazolones under mild reaction conditions.