Acetic Acid → tert-butyl 11-chloro-6-oxo-3,4,7,11b-tetrahydro-2H-pyrido[3,2-e]pyrimido[1,2-c]pyrimidine-1(6H)-carboxylate

tert-Butyl (4-chloro-3-formylpyridin-2-yl)carbamate (1.2 g, 4.67 mmol), tert-butyl (3-amino-propyl)carbamate (855 mg, 4.91 mmol), and AcOH (0.28 g, 4.67 mmol) were suspended in toluene (50 mL), and stirred overnight at room temperature. The reaction mixture was concentrated. The crude intermediate was dissolved in NMP (8 mL) in a 40 mL sealed tube, and stirred for 30 min. at 160 ° C. The reaction mixture was cooled, and the resulting precipitate was filtered, washed with MeOH, and dried under vacuum. LC-MS (M+H=339, obsd.=339).