Flash-vacuum-pyrolysis (F.V.P) of the 4-acetyl-3-(4-substitutedphenylamino) -2-(benzoxazol-2-yl)-isoxazol-5-(2H)-ones (4) at 900oC and 0.4 mm Hg has been investigated and net product, 1-(2-(4-substitutedphenylamino)-imidazo-[2,1-b]-benzoxazol-3-yl)-ethanone in high to excellent yields (80-85%).
