To a solution of [3-(propoxymethyl)-1,2,4-oxadiazol-5-yl]methanol (250 mg, compound D22) and CBr4 (620 mg) in DCM (5 ml) are added triphenylphosphine (490 mg) and the reaction mixture is stirred for 15 min at RT. This solution is added to a stirred suspension of tert-butyl 4-(2,4-dioxo-6-phenyl-1,4-dihydrothieno[3,2-d]pyrimidin-3(2H)-yl)piperidine-1-carboxylate (0.5 g; compound B50) and potassium carbonate (323 mg) in DMF and the reaction mixture is stirred for 3 h at 65° C. Afterwards the solvent is removed under vacuo, the resulting residue is treated with EtOAc/cyclohexane (1:1) and the suspension is filtered. The filtrate is purified by flash chromatography (silica gel, eluent EtOAc/cyclohexane 1:1) and the product fraction are washed with diethylether to give the title compound as a solid.
