Skeletal Editing of Isoxazoles to Pyrimidines via O‑to-CN Transmutation.

Heterocyclic scaffolds are highly valued in medicinal chemistry due to their structural rigidity, tunable electronic properties, and functional versatility. The direct interconversion of heterocyclic cores via skeletal editing provides rapid access to structurally diverse bioactive molecules. Herein, we report a Ru-catalyzed ring expansion strategy that converts isoxazoles into pyrimidines via O-to-CN transmutation. The transformation employs readily available nitriles as the CN source and proceeds via ruthenium-catalyzed N-O bond cleavage to generate an enaminone intermediate, followed by nucleophilic addition and cyclization. This protocol accommodates a broad range of functional groups and enables the late-stage modification of complex pharmaceuticals, including receptor modulators and anticancer agents. This skeletal editing strategy expands the synthetic toolbox for medicinal chemistry and scaffold diversification.