Enantioselective Synthesis of Dihydropyrazolo[3,4-b]pyridin-6-ones via N-Heterocyclic Carbene Catalyzed [3+3] Cycloaddition of a-Bromoenals with 5-Aminopyrazoles

An N-heterocyclic carbene (NHC) catalyzed asymmetric [3+3] annulation of alpha-bromoenals with 5-aminopyrazoles is described. Using the established methodology, a structurally diverse set of high value dihydropyrazolo[3,4-b]pyridine-6-ones were efficiently constructed in high yields (up to 99%) with excellent enantioselectivities (up to > 99%). The easily available starting materials, broad substrate scope, mild reaction conditions, excellent yield and enantioselectivity make this strategy attractive for the asymmetric construction of pyrazolo-fused pyridone derivatives.