tert-Butyl 4-hydroxy-2-(trifluoromethyl)-5,6-dihydropyrido[3,4-d]pyrimidine-7(8H)-carboxylate (5.12 g, 16.05 mmol) was combined with triphenylphosphine (8.42 g, 32.1 mmol) and stirred in dichloroethane (160 mL) at ambient temperature for 15 minutes, and then carbon tetrachloride (7.41 g, 48.1 mmol) was added. The reaction was stirred at 70° C. for 3 hours, cooled to room temperature, and concentrated in vacuo. The crude residue was purified by flash chromatography on silica gel (elution gradient from 0% to 3% methanol/DCM) to afford the title compound as a clear oil (5.22 g, 86% yield). MS (ESI) m/e (M−H)−=336.3.
