157327-41-8

869198-95-8

1-Boc-3-[(dimethylamino)methylene]-4-oxopiperidine (7.64 g, 30.04 mmol) was used as starting material and dissolved in methanol (190 mL). To this solution, guanidine carbonate (21.65 g, 120.16 mmol) and sodium acetate trihydrate (32.70 g, 240.32 mmol) were added sequentially. The reaction mixture was heated to reflux and the reaction was continued for 17 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure. The residue was diluted with water and mixed by vortexing for several minutes. The undissolved white solid was collected and washed sequentially with water and a small amount of cold ethyl acetate to give the final pyrido[4,3-d]pyrimidine-6(5H)-carboxylic acid, 2-amino-7-1,8-dihydro-1,1-dimethylethyl ester (4.10 g, 55% yield).