23.6 g of 3-ethoxycarbonyl-7-methyl-4-oxo-6,7,8,9-tetrahydro-4Hpyrido[
1,2a]pyrimidine and 10.0 g of glyoxylic acid monohydrate are reacted
and the obtained 3-ethoxycarbonyl-7-methyl-9-carboxy(hydroxymethyl)-4-
oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2a]pyrimidine is heated in 150 ml ethanol
under stirring for 3 h. After cooling the crystals are filtered off and
recrystallized from ethanol. Thus 3-ethoxycarbonyl-7-methyl-9-
(carboxymethylene)-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2a]pyrimidine
melting point 110°-112°C, is obtained (yield: 51%).
55.6 g of 3-ethoxycarbonyl-9-(carboxymethylene)-4-oxo-6,7,8,9-tetrahydro-
4H-pyrido[1,2a]pyrimidine are hydrogenated in 500 ml of ethanol in the
presence of 20.0 g of 9% by weight Pd/C catalyst containing metal. When 1
mole of hydrogen has been used up, the catalyst is removed from the reaction
mixture by filtration and the solution is evaporated under reduced pressure.
The 3-ethoxycarbonyl-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-9-
acetic acid is obtained (yield: 57%), melting point 156°-157°C (recrystallized
from ethanol).
