One‐Pot Synthesis of Naphtho[1′,2′:4,5]imidazo[1,2‐a]pyridin‐5‐yl(aryl)methanones through Sequential Sonogashira Coupling/Alkyne–Carbonyl Metathesis
An efficient one-pot route for the construction of naphtho[1′,2′:4,5]imidazo[1,2-a]pyridin-5-yl(aryl)methanones and 5-phenylnaphtho[1′,2′:4,5]imidazo[1,2-a]pyridines by sequential Sonogashira coupling reaction followed by trifluoroacetic acid promoted alkyne-carbonyl metathesis (ACM) has been developed. 2-(2-Bromophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde preferentially underwent ACM with phenyl acetylenes, whereas intramolecular hydroarylation reaction was the common pathway in the absence of a carbonyl moiety at the C-3 position under similar conditions. This protocol is compatible with a wide variety of functional groups and delivered corresponding naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines in good to excellent yields.