To a solution of tert-butyl (7RS)-7-(3,4-dichlorophenyl)-7-(hydroxymethyl)-1,4-oxazepane-4-carboxylate (2 g), phthalimide (0.86 g) and triphenylphosphine (4.17 g) in THF (40 ml) was added dropwise a solution (2.2 M, 7.2 ml) of diethyl azodicarboxylate in toluene at 0° C., and the mixture was stirred at 0° C. for 30 min, and then for 6 hr while warming to room temperature. To the reaction mixture were added phthalimide (0.43 g) and a solution (2.2 M, 3.6 mL) of diethyl azodicarboxylate in toluene, and the mixture was stirred at room temperature for 14 hr. The reaction mixture was diluted with water, and the mixture was extracted with ethyl acetate. The obtained extract was washed with brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography (ethyl acetate/hexane) and silica gel column chromatography (NH, ethyl acetate/hexane) to give the title compound (1.49 g).
