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Part-IISynthesis of Pyrimidinesthe nucleophilic attack by the amidine nitrogen on the amide carbonyl group (path ‘a’) orthrough the nucleophilic attack of the amide nitrogen on the amidine carbon (path ‘b’)(Scheme 7).OOaR 1+ RCNR 2 NH 2NH 2Sdry HClNH 2R 1R 2 SNbNH 229RbaR 2R 1SONHNHRNH 2R 2R 1H 2 NSOHNHNR-NH 2-NH 2OR 2R 1SIN NHRScheme 7The fact that the reaction of o-amino-N-methylcarboxamide 10b with acetonitrile leads tothe exclusive formation of 3-N-unsubstitutedthienopyrimidin-4(3H)-one and not to 3-Nmethyltheinopyrimidin-4-oneindicates that the reaction with the amides, presumablyproceeds by the pathway ‘a’ involving the loss of NH 3 from the amide function. 28OO+NHCH 3 CNdry HClNHS10bNH 2S+ONNSN254