3-(3,4-difluorophenyl)dihydro-2H-pyran-4(3H)-one 、
N-(氯甲酰)异氰酸酯 以to give 8-(3,4-difluorophenyl)-7,8-dihydropyrano[3,4-e][1,3]oxazine-2,4(3H,5H)-dione (Intermediate Y(3))的产率得到8-(3,4-difluorophenyl)-7,8-dihydro-1H-pyrano[3,4-e][1,3]oxazine-2.4(3H,5H)-dione