Synthesis of imidazo[1,2-a]pyridines: "water-mediated" hydroamination and silver-catalyzed aminooxygenation.

Aqueous syntheses of methylimidazo[1,2-a]pyridines without any deliberate addition of catalyst are reported. Imidazo[1,2-a]pyrazine and imidazo[2,1-a]isoquinoline were also obtained in good yields under similar conditions. With acetonitrile as solvent, Ag-catalyzed intramolecular aminooxygenation produced imidazo[1,2-a]pyridine-3-carbaldehydes in moderate to good yields.