8-(3,4-difluorophenyl)-7,8-dihydro-1H-pyrano[3,4-e][1,3]oxazine-2.4(3H,5H)-dione 、
ammonium hydroxide 以to give 8-(3,4-difluorophenyl)-7,8-dihydro-1H-pyrano[4,3-d]pyrimidine-2,4(3H,5H)-dione (Intermediate Y(4))的产率得到8-(3,4-difluorophenyl)-7,8-dihydro-1H-pyrano[4,3-d]pyrimidine-2,4(3H,5H)-dione