Three-Component Coupling of Aldehydes, 2‑Aminopyridines, and Diazo Esters via Rhodium(III)-Catalyzed Imidoyl C–H Activation: Synthesis of Pyrido[1,2‑a]pyrimidin-4-ones

Imines formed in situ from 2-aminopyridines and aldehydes undergo Rh­(III)-catalyzed imidoyl C–H activation and coupling with diazo esters to give pyrido­[1,2-a]­pyrimidin-4-ones. Aromatic and enolizable aliphatic aldehydes were both effective substrates, and a broad range of functional groups were incorporated at different sites on the heterocyclic products. In addition, methoxy and dimethylamino functionalities could be directly installed on the pyrimidine ring by employing trimethyl orthoformate or N,N-dimethylformamide dimethyl acetal in place of the aldehyde, respectively.