A mixture containing 4.08 (0.02 mole) of 6-methyl-4-oxo-4H-pyrido[1.2-a]pyrimidine-3-carboxylic acid and 3.1 ml (0.022 mol) of triethylamine in 120 ml of chloroform is cooled below -10° C. by ice-salt. A solution of 2.52 ml (0.026 mol) of methyl chloroformate in 10 ml of chloroform is dropped to the above mixture at -15° C. during 10 minutes. After stirring for 5 minutes, 3.33 g (0.022 mol) of 1-adamantanamine dissolved in 20 ml of chloroform are dropped to the above solution at -15 0° C. during 15 minutes. The reaction mixture is stirred below -10° C. for 1 hour, then allowed to stand overnight under cooling by ice. For working up, the reaction mixture is washed 3 times with 70 ml of 5% sodium hydrogen carbonate solution each, then 3 times with 70 ml of water each. The organic phase is dried over anhydrous sodium sulfate, filtered and evaporated to yield 4.4 g (65.2%) of the named product as pale yellow crystals after recrystallization from ethanol, m.p.: 190°-193° C.
