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Part-IISynthesis of Pyrimidines+RCNdry HClNH 2NNNNNNNH 212h 18NRInterestingly, when mono arylcyanamides were reacted with thiophene o-aminonitrilesunder the influence of dry HCl gas, a mixture of two products was obtained. The majorproduct was 2-amino-3-aryl-4-iminothieno[2,3-d]pyrimidine 20, while the minor productwas 2-amino-3-arylthieno[2,3-d]pyrimidin-4-one 23 (Scheme 5).The proposed reaction mechanism envisages the possibility of the formation of threeisomeric 2,4-diamoaminothieno[2,3-d]pyrimidines 20-22 through the alternate modes ofcyclization of the guanidine intermediate 19 and Dimroth rearrangement of one of theisomers to the third isomer. However, the structural proof to the actual products wasgiven through the unequivocal synthesis of three isomeric 2,4-diamoaminothieno[2,3-d]pyrimidines (Table 30) as well as, the 2-amino-3-arylthieno[2,3-d]pyrimidin-4-one(Table 27 and 29). 60,61 Compound 23 is infact the antifact of the reaction, arising throughthe hydrolysis of 20 during the workup.248