2-Pyridyl-3-arylaminoisoxazol-5(2H)-ones, rearranged under flash-vacuum-pyrolysis (FVP) conditions accompanied by elimination of carbon dioxide to give imidazo[1,2-a]pyridines in high to excellent yields (85-95 %). ... 4-MeC6H4)2 with triethylamine in ethanol give imidazo annulated compounds (2, Ar: 4-BrC6H4 (84 %), 4-MeC6H4 (75 %) as net products (Scheme-I). ... 2-Pyridyl-3-arylaminoisoxazol -5(2H)-ones, rearranged under flash-vacuum-pyrolysis (FVP) conditions accompanied by ...