Triethylamine → 8-Cyclopentyl-2-methylsulfanyl-5-oxo-5,8-dihydro-pyrido[2,3-d]pyrimidine-6-carboxylic acid ethyl ester

Bromine (0.13 g, 0.82 mmol) was added to a solution of 8-Cyclopentyl-2-methylsulfanyl-5-oxo-5,6,7,8-tetrahydro-pyrido[2,3-d]pyrimidine-6-carboxylic acid ethyl ester (0.34 g, 0.82 mmol) in DCM (5 mL). After 15 min, the solution was concentrated and the crude residue was redissolved in DCM (5 mL) and triethylamine (0.16 mL, 0.24 mmol) was added. After 15 h, the reaction mixture was partitioned between water and DCM, the organic layer was separated, dried (MgSO4) and concentrated to provide the title compound. Mass Spectrum (LCMS, ESI pos.) Calcd. For C16H19N3O3S: 333.11, found: (M+H) 334.1.