To a mixture of 4-chloro-6-(4,4-dimethylcyclohexyl)-2-methylthieno[2,3-d]pyrimidine (1.0 g), tributyl(1-ethoxyvinyl)stannane (1.16 mL), and toluene (10.8 mL) was added Pd(PPh3)4 (392 mg), followed by heating to reflux for 5 hours. The reaction mixture was left to be cooled to room temperature, and to the reaction mixture were added a saturated aqueous NH4Cl solution, followed by extraction with EtOAc. The organic layer was washed sequentially with water and brine, dried over MgSO4, and then concentrated under reduced pressure to obtain a crude product (1.12 g) containing 6-(4,4-dimethylcyclohexyl)-4-(1-ethoxyvinyl)-2-methylthieno[2,3-d]pyrimidine. To this crude product were added EtOH (9.0 mL) and 1 M hydrochloric acid (10.2 mL) at room temperature, followed by stirring at 50° C. overnight. The reaction mixture was left to be cooled and concentrated under reduced pressure. To the residue was added water, followed by extraction with EtOAc. The organic layer was washed with brine, dried over MgSO4, and then concentrated under reduced pressure. The residue was purified by silica gel column to obtain 1-[6-(4,4-dimethylcyclohexyl)-2-methylthieno[2,3-d]pyrimidin-4-yl]ethanone (820 mg).
