General procedure for the synthesis of tert-butyl 4-chloro-5,8-dihydropyrido[3,4-d]pyrimidine-7(8H)-carboxylate from tert-butyl 4-hydroxy-5,6-dihydropyrido[3,4-d]pyrimidine-7(8H)-carboxylate: to a solution of intermediate 1 (1.26 g, 5.02 mmol) in ethylene dichloride (DCE, 36 mL), sequentially added triphenylphosphine (PPh3, 2.69 g, 10.05 mmol) and carbon tetrachloride (CCl4, 1.46 mL, 15.07 mmol). The reaction mixture was heated to 70 °C and maintained for 2.5 hours. After completion of the reaction, the mixture was concentrated under reduced pressure and purified by silica gel (SiO2) column chromatography with ethyl acetate/hexane as eluent to afford the target compound as a light yellow solid (1.20 g, 88% yield). The mass spectrometry (ESI) calculated value of C12H16ClN3O2 was 269.09, and the measured value m/z 270.1 [M + H]+.1H NMR (400 MHz, CDCl3) δ: 8.79 (s, 1H), 4.65 (br s, 2H), 3.80-3.68 (m, 2H), 2.93-2.82 (m, 2H), 1.49 ( s, 9H).
![tert-butyl 4-oxo-3,4,5,6-tetrahydropyrido[3,4-d]pyriMidine-7(8H)-carboxylate](/CAS/GIF/1142188-60-0.gif)
![4-chloro-5,8-dihydro-6H-pyrido[3,4-d]pyriMidine-7-carboxylic acid tert-butyl ester](/CAS/20180808/GIF/1053656-57-7.gif)