To a solution of 1-t-butoxycarbonyl-4-hydroxypiperidine (3.62 g), 2-methyl-4-nitrophenol (2.55 g) and triphenylphosphine (5.25 g) in dichloromethane (100 ml), diethyl azodicarboxylate (3.2 ml) was added dropwise with stirring under ice-cooling, and the resulting mixture was stirred at room temperature overnight and then evaporated in vacuo. The residue obtained was purified by chromatography on a silica gel column using dichloromethane as the eluent to afford the title compound (4.07 g) containing impurities as a pale yellow oil.
