259809-79-5

259809-78-4

259809-79-5

Method I - Step c: Synthesis of tert-butyl 2-(methylsulfonyl)-7,8-dihydropyrido[4,3-d]pyrimidine-6(5H)-carboxylate [2-12]. Tert-butyl 2-(methylthio)-7,8-dihydropyrido[4,3-d]pyrimidine-6(5H)-carboxylate (7.38 g, 26.26 mmol) was dissolved in 50 mL of dichloromethane, and 3-chloroperoxybenzoic acid (75%, 12.5 g, 54.50 mmol) was slowly added at 0 °C. The reaction mixture was stirred at room temperature for 12 hours. Subsequently, saturated sodium bicarbonate solution (10 mL) and saturated sodium thiosulfate solution (10 mL) were added and stirring was continued for 2 hours at room temperature. The organic layer was separated and concentrated under reduced pressure. Purification by silica gel column chromatography (petroleum ether: ethyl acetate = 3:1) afforded a white solid product (5.5 g, 66.9% yield).1H NMR (400 MHz, CDCl3) δ 8.63 (s, 1H), 4.70 (s, 2H), 3.79 (t, J = 5.9 Hz, 2H), 3.33 (s, 3H), 3.09 (t, J = 5.8 Hz, 2H). 5.8 Hz, 2H), 1.49 (s, 9H).