[From routine acylation towards stable sigma-complexes of pyrimidine: carbon protonation of the pyrimdine-ring]

It is well known, that the ring nitrogen of pyrimidine possesses basic property, electron donating groups increase basicity. According to literature data published so far pyrimidines protonate at the ring nitrogen. The present paper gives brief account of the C(5) carbon-protonation observed among triaminopyrimidine derivatives, which in some cases results in stable sigma-complexes. Steric and electronic effects responsible for carbon-protonation are investigated in simple C(5) substituted 2,4,6-triaminopyrimidine derivatives. We show new stable sigma-complexes in the triaminopyrimidine series. The paper summarizes, in Hungarian, our recently published results (J. Amer. Chem. Soc., 125, 2535-2540, 2003) as well as our new results presented in the symposium ,,Gyógyszerkémiai Gyógyszertechnológiai Szimpózium 2003".