2-cyanoethyl 4-(4-cyano-2-methoxyphenyl)-5-ethoxy-2,8-dimethyl-1,4-dihydro-1,6-naphthyridine-3-carboxylate is prepared by the reaction of 2-Cyanoethyl 4-(4-cyano-2-methoxyphenyl)-2,8-dimethyl-5-oxo-1,4,5,6-tetrahydro-1,6-naphthyridine-3-carboxylate and Triethyl orthoacetate. The specific synthesis steps are as follows:
2-Cyanoethyl 4-(4-cyano-2-methoxyphenol)-5-ethoxy-2,8-dimethyl-1,4-dihydro-1,6-naphthyridine-3-carboxylate (XI) 2.142 kg (5.3 mol) of 2-cyanoethyl 4-(4-cyano-2-methoxyphenyl)-2,8-dimethyl-5-oxo-1,4,5,6-tetrahydro-1,6-naphthyridine-3-carboxylate (X) and 2.35 kg (14.5 mol) of triethyl orthoacetate are dissolved in 3.21 kg of NMP (1-methyl-2-pyrrolidone) and 157.5 g of concentrated sulphuric acid are added. The mixture is heated at 115° C. for 1.5 hours and then cooled to 50° C. At 50° C., 2.2 l of water are added dropwise over 30 minutes. After completion of the addition, the mixture is seeded with 10 g of the title compound (XI) and a further 4.4 l of water are added dropwise over 30 minutes at 50° C. The mixture is cooled to 0° C. (gradient, 2 hours) and then stirred at 0° C. for two hours. The product is filtered off, washed twice with 4 l each time of water and dried at 50° C. under vacuum. Yield: 2180.7 g (95.1% of theory) of a pale yellow solid. -Pos=93,Num=8 247 H-0:h-00351 248 248 248 248 248 248 --3:p-00352 248 --3:p-00353 --00-00-00-0-1-00 -710189200HPLC method B: RT ca. 10.2 min.
