Pyrimidine 4- amino-5-cyano-2-methyl-, ring

Lappin s publication, 1,8-naphthyridine (72 R = NH2) was obtained under similar conditions from the 6-amino derivative of 70 by Adams et al.127 The special behavior of the 6-substituted derivatives of 70 was ascribed by Lappin126 to the steric hindrance effect of the 6-substituent. Some later results,29 128 however, contradicted Lappin s concept. On vacuum distillation of the 2-(6-methyl-2-pyridylaminomethylene)acetoacetate and -cyano-acetate, Antaki did not obtain the 1,8-naphthyridines but instead the 3-substituted 6-methyl-4-oxo-4H-pyrido[l,2-a]pyrimidines.29 By the thermal ring closure of 70 (R = 5-CONH2) Richardson and McCarty128 obtained a product described as a 1,8-naphthyridine of type 72. 

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