Asymmetric synthesis of chiral pyrazolo[3,4- b ]pyridin-6-ones under carbene catalysis.

A structurally diverse set of chiral pyrazolo[3,4- b ]pyridin-6-ones was efficiently prepared in excellent yields with excellent enantioselectivities via N-heterocyclic carbene-catalyzed oxidative [3 + 3] annulation of enals with pyrazol-5-amines. The reaction features mild reaction conditions, a broad substrate scope, and easy scale-up.