GENERAL METHOD: 2-hydroxyacetophenone 4a (1.0 g, 7.4 mmol), acetohydroxamic acid (0.83 g, 11.0 mmol), acetonitrile (3 ml) and concentrated sulfuric acid (0.2 ml) were added to a 10 ml pressure tube. The mixture was heated in a microwave reactor (CEM Discover, 360W, 80°C, 25 psi) for 8 min. After completion of the reaction, the mixture was diluted with ethyl acetate (3 ml) and saturated sodium bicarbonate solution (5 ml) was added dropwise to neutralize it. Subsequently, the mixture was extracted with ethyl acetate (2 x 10 ml). The organic layers were combined, washed with saturated sodium chloride solution and dried with anhydrous sodium sulfate. After concentration under reduced pressure, the mixture was purified by conventional column chromatography (silica gel 60-120 mesh, eluent ethyl acetate/hexane: 1:9) to afford benzoxazole 5a (0.67 g, 70%) as a yellow oil and 2-hydroxyacetophenone oxime 6a (68 mg, 6%, melting point 104-107°C) as a white powder.
