To a solution of 1-t-butoxycarbonyl-4-hydroxypiperidine (3.32 g), 2-chloro-4-nitrophenol (2.36 g) and triphenylphosphine (5.11 g) in dichloromethane (60 ml) was added dropwise diethyl azodicarboxylate (3.1 ml) in an ice bath and the mixture was stirred at room temperature for 18 hours. The reaction mixture was concentrated in vacuo. The residue was purified by chromatography on a silica gel column using hexane/ethyl acetate=5/2 as an eluant to give the desired compound (3.90 g, yield 76%) as a pale yellow solid.
