Dihydropyrimidines and related structures. I. N 2 ‐substituted 2‐pyrimidinamines and dihydro‐2‐pyrimidinamines by reaction of phenylbutenones and monosubstituted guanidines

The reactions of monosubstituted guanidines 2 with phenylbutenones 7 and 10 exclusively yield N 2 ‐substituted 2‐pyrimidinamines 8 and 9 . The structure of the reaction products is proved and their differing stability is discussed. Action of methyl‐ and benzylguanidine respectively ( 2b, c ) on 4‐phenyl‐3‐buten‐2‐one ( 7 ) and of 2c on l‐phenyl‐2‐buten‐1‐one ( 10 ) under atmospheric oxygen affords aromatic N 2 ‐substituted 2‐pyrimidinamines 9b and c . The dihydropyrimidines 8b and c, probable intermediates of the reactions, could not be isolated. In contrast, heating of arylguanidines 2d , e with 7 leads to stable dihydropyrimidinarnines 8d and e, which can be isolated as bases. Addition of methanol to 8d yields 6‐methoxy‐2‐pyrimidinamine 11d , boiling of 8d in DMF affords 9d . Under nitrogen, guanidine adds to 7 to yield aminopyrimidinol 13a , which is transformed by heating in benzene into pyrimidine 9a . The low stability of 8a‐c is attributed to their strong basicity, the greater stability of 8d and e to their lower basicity. The structural formulae of 8d , e and 9b‐d and their salts respectively were established partly ( 8e ) by nmr and partly ( 9b‐d ) by comparison of the corresponding picrates with authentic samples [17].