Tf2O‑Mediated Cyclization of α‑Acyl-β-(2-aminopyridinyl)acrylamides: Access to N‑Substituted 4H‑Pyrido[1,2‑a]pyrimidin-4-imines

A facile and efficient direct synthesis of N-substituted 4H-pyrido­[1,2-a]­pyrimidin-4-imines is developed from α-acyl-β-(2-aminopyridinyl)­acrylamides mediated by triflic anhydride (Tf2O) in the presence of 2-chloropyridine. This amide activation protocol features mild reaction conditions, simple execution, excellent yields, and high chemoselectivity, and is also applied to the synthesis of substituted 4H-pyrido­[1,2-a]­pyrimidin-4-ones via a practical one-pot procedure.