CONVERSION OF 1-BENZYL-4-AMINOTETRAHYDROPYRIDINE-3-CARBOXYLIC ACID METHYL-ESTER TO ANTITHROMBOTIC PYRIDO[4,3-D]PYRIMIDINE-2,4-DIONES AND TO(2-OXOTETRAHYDROPYRIMIDIN-4-YLIDENE)ACETIC ACID METHYL-ESTERS

,8-tetrahydro-1H-pyrido[4,3-d]pyrimidine-2,4-dione 2, a representative of new antithrombotic compounds with favourable cerebral and peripher al effects has been synthesized from enamine 1 in good yield by two me thods. The thermal fusion of 1 with ureas gave the pyrido[4,3-d]-pyrim idine-2,4-diones 5a, 2 and 5b and unexpectedly the esters 6 and 7. The structure of 6 was deduced from its spectroscopic properties and was proven by ozonolysis to cleavage products 9 and 10 and by oxidative hy drolysis to pyrimidin-2-one 13. The (Z)-configured 6 was converted to (E)-configured 7 by methylation. The products 5a, 5b and 5c were synth esized by independent methods. Hydrogenolysis of 2 led to the secondar y amine 15 which was alkylated to the base of 16.