Step 1: Preparation of 4-hydroxybenzaldehyde oxime; 4-hydroxybenzaldehyde (5 g, 40.94 mmol) was dissolved in ethanol (100 ml). To this solution, hydroxylamine hydrochloride (4.3 g, 61.41 mmol) and pyridine (9.9 ml, 122.82 mmol) were added sequentially. The reaction mixture was heated to reflux for 1 hour. After completion of the reaction, the mixture was concentrated under reduced pressure and subsequently extracted with ether. The organic phases were combined, washed with saturated brine and dried with anhydrous magnesium sulfate. The dried organic solution was concentrated under reduced pressure and purified by column chromatography (eluent ratio: ethyl acetate:hexane = 1:2) to afford the target compound 4-hydroxybenzaldehyde oxime (5.9 g, 100% yield).1H NMR (CDCl3, 200 MHz) δ 9.23 (s, 1H), 8.15 (brs, 1H), 7.82 (s, 1H), 7.22 (d, J = 8.8Hz, 2H), 6.63 (d, J = 8.8Hz, 2H).
