To a solution of 3-benzyloxycarbonyl-3-azabicyclo[3.2.0]heptane-1-carboxylic acid (2.60 mmol) in tertiary butanol (15 ml) were added 0.474 ml (3.4 mmol) of triethylamine and 0.733 ml (3.4 mmol) of diphenylphosphorylazide, followed by 9 hours of stirring at 70° C. After cooling to room temperature, the reaction solution was poured into saturated sodium bicarbonate and extracted with ethyl acetate. The organic layer was washed with water and saturated brine and dried over anhydrous sodium sulfate. After evaporation of the solvent, the resulting residue was purified by a silica gel column chromatography (n-hexane:ethyl acetate=4:1) to give 642.2 mg (1.78 mmol, 68.4% for 2 steps from Reference Example B-7) of the title compound.
