Stereocontrolled Construction of Tetrahydro­pyrano­[2,3‑c]pyrazole Scaffold via an Organocatalyzed Formal [3 + 3] Annulation

A bifunctional squaramide catalyzed enantioselective formal [3 + 3] annulation reaction with pyrazolin-5-ones and nitroallylic acetates has been developed. Densely substituted tetrahydro­pyrano­[2,3-c]­pyrazoles with two adjacent stereogenic centers are obtained in a highly stereocontrolled manner. Representative transformation of the annulation product to a biologically important fused dihydroisoquinoline is achieved without any appreciable loss in the diastereo- and enantioselectivity.