Synthetic Strategy for Pyrazolo[1,5‑a]pyridine and Pyrido[1,2‑b]indazole Derivatives through AcOH and O2‑Promoted Cross-dehydrogenative Coupling Reactions between 1,3-Dicarbonyl Compounds and N‑Amino-2-iminopyridines

An efficient method has been developed for the synthesis of uniquely substituted pyrazolo­[1,5-a]­pyridine and pyrido­[1,2-b]­indazole derivatives, which involves acetic acid and molecular oxygen promoted cross-dehydrogenative coupling reactions of respective β-ketoesters and β-diketones (like ethyl acetoacetate, ethyl benzoylacetate, methyl propionylacetate, acetylacetone, dimedone, 1,3-cyclohexanedione, and 1,3-cyclopentanedione) with N-amino-2-iminopyridines. The proposed tentative mechanism involves formal acetic acid-promoted oxidative C­(sp3)–C­(sp2) dehydrogenative coupling followed by dehydrative cyclization under a catalyst-free condition within high atom economy processes.