To a stirred solution of 4-benzyl-2-morpholinecarboxylic acid hydrochloride (intermediate 20, 1.5 g, 5.82 mmol) in N,N-dimethylformamide (10 ml) was added 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluroniumtetrafluoroborate (2.2 g, 6.98 mmol), 1-hydroxybenzotriazole hydrate (236 mg, 1.74 mmol) and N,N-diisopropylethylamine (5.1 ml, 29.1 mmol), and the reaction mixture was stirred at room temperature for 30 minutes. After the addition of N′-hydroxybenzamidine (792 mg, 5.82 mmol), the reaction mixture was stirred at room temperature for one hour, and then heated to 110° C. When the reaction was complete (checked by thin layer chromatography), excess reagent was decomposed by the addition of water and the aqueous layer was extracted with ethyl acetate. The extract was washed with water and brine, dried over magnesium sulfate, and concentrated in vacuo. The resulting residue was purified by column chromatography on silica gel, (eluent; 25% ethyl acetate in hexane) to afford 4-benzyl-2-(3-phenyl-1,2,4-oxadiazol-5-yl)morpholine (intermediate 21, 1.44 g, 77%) as a colorless oil.
