Phenylboronic acid (417 mg), tetrakis(triphenylphosphine)palladium (132 mg), toluene (10 mL), 1,4-dioxane (5 mL), and a 2 mol/L aqueous solution of sodium carbonate (10 mL) were added to 5-[3,5-bis(trifluoromethyl)benzyl]-7-iodo6-oxo-2,3,4,5-tetrahydro-6H-pyrido[2,3-b][1,5]oxazocine (compound of Reference Example 3; 1.00 g). While heated, the mixture was stirred for 7 hours under a stream of argon gas. The reaction mixture was diluted with ethyl acetate, and the diluted mixture was washed with a 2 mol/L aqueous solution of sodium carbonate, and was then dried on anhydrous sodium sulfate. The solvent was removed by distillation to obtain a residue, and then the residue was recrystallized from isopropanol to obtain 5-[3,5-bis(trifluoromethyl)benzyl]-6-oxo-7-phenyl-2,3,4,5-tetrahydro-6H-pyrido[2,3-b][1,5]oxazocine (729 mg, 80%).
