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

An efficient method has been developed for the synthesis of uniquely substituted pyrazolo[1,5-]pyridine and pyrido[1,2-]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 -amino-2-iminopyridines. The proposed tentative mechanism involves formal acetic acid-promoted oxidative C(sp)-C(sp) dehydrogenative coupling followed by dehydrative cyclization under a catalyst-free condition within high atom economy processes.