902576-09-4

General procedure for the synthesis of 2-(methylthio)pyrido[4,3-d]pyrimidin-5(6H)-ones from ethyl 4-((E)-2-(dimethylamino)vinyl)-2-(methylthio)pyrimidine-5-carboxylate: ethyl 4-((E)-2-(dimethylamino)vinyl)-2-(methylthio)pyrimidine-5-carboxylate (13.5 g, 50.5 mmol) and NH4OAc (38.9 g, 505 mmol) were dissolved in DMF (250 mL) and the reaction mixture was stirred under reflux conditions for about 4 days. Upon completion of the reaction, the mixture was concentrated, the residue was dissolved in trichloromethane (TCM), washed with water, and the organic phase was dried, filtered and concentrated. The product was purified by crystallization from ethanol to afford 2-(methylthio)pyrido[4,3-d]pyrimidin-5(6H)-one (7.60 g, 39.4 mmol, 78% yield) as a colorless solid.

[1] Patent: WO2010/63352, 2010, A1. Location in patent: Page/Page column 89
[2] Patent: US2013/225589, 2013, A1. Location in patent: Paragraph 0439
[3] Patent: WO2014/23385, 2014, A1. Location in patent: Page/Page column 73; 76; 77