A mixture of 2,2-dimethyl-6-(5-methyl-1H-pyrazol-4-yl)-2,3-dihydrothieno[3,2-d]pyrimidin-4(1H)-one, 1 M HCl (1.2 mL, 1.2 mmol) and MeOH (4 mL) was stirred at 50° C. for 2 h. Then, the reaction mixture was poured into excess saturated aqueous NaHCO3 and extracted with EtOAc, and the extract was dried over MgSO4, filtered and concentrated under reduced pressure. The residue was mixed with 4,4,4-trifluorobutan-2-one (0.433 g, 3.43 mmol), CSA (7.97 mg, 0.034 mmol), MgSO4 (0.041 g, 0.343 mmol) and DMA (1 mL). The mixture was microwave-irradiated at 140° C. for 1 h. The mixture was poured into saturated aqueous NaHCO3 and extracted with EtOAc, and the extract was dried over MgSO4, filtered and concentrated under reduced pressure. The residue was purified by column chromatography (Purif, silica gel, 95:5 hexane/EtOAc to EtOAc then to 90:10 EtOAc/MeOH). The obtained oil was purified again by column chromatography (Purif, silica gel, 95:5 hexane/EtOAc to EtOAc) to give yellow oil. This oil was dissolved with small amount of EtOAc and poured into heptane (100 mL) with stirring. After 5 min, the precipitate was collected by filtration to afford the title compound (33.5 mg, 30%) as a yellow solid:
