Under argon gas, 7-[4-(4-fluorobenzoyl)benzyl]-4-methoxy-5-methyl-2-methylthio-7H-pyrrolo[2,3-d]pyrimidine (6.75 g) was dissolved in dioxane (45 ml) followed by addition of 4,4'-thiobis(6-t-butyl-m-cresol) (75 mg). Then, 0.5N-hydrochloric acid (12 ml) was added and the mixture was stirred at 105° C for 23 hours. Thereafter, 0.5N-hydrochloric acid (12 ml) was further added and the mixture was stirred at the same temperature as above for 22 hours. Then, 1N-hydrochloric acid (3 ml) and dioxane (6 ml) were added and the mixture was further stirred at the same temperature for 24 hours. This reaction mixture was allowed to stand at room temperature and the resulting crystals were collected by filtration, rinsed with methanol, DME, and ether, and finally dried to provide the title compound (5.35 g).
