1 H, 13 C and 15 N NMR Studies of Protonation in Imidazo[1,2-α]Pyrimidine and Derivatives
1991; Taylor & Francis; Volume: 24; Issue: 9 Linguagem: Inglês
10.1080/00387019108018176
ISSN1532-2289
AutoresMeng-Long Liu, R. Duncan Farrant, John C. Lindon, Paul Barraclough,
Tópico(s)Structural and Chemical Analysis of Organic and Inorganic Compounds
ResumoAbstract We have studied1 the protonation behaviour of several cardiotonic polyazaheterocycles and recently shown that the 2-arylimidazo[l,2-a]pyrimidine (3a) undergoes protonation at the imidazo nitrogen (Nl). These investigations have utilised the shielding of acarbon nuclei and increases in 13C-1H or 1H-1H couplings that occur on protonation of a heterocyclic nitrogen. We now report unequivocal protonation studies of the parent heterocycle, imidazo[1,2-a]pyrimidine (l), and its 2-aryl derivative (3b) which have allowed the effect of 2-aryl substitution on protonation to be determined. 15N NMR spectroscopy was employed to determine the protonation site of (1) in a titration study with H2SO4. In addition the N-methyl quaternary salts (21, (4) and (5) were prepared and 15N, 13C and 1H chemical shifts measured so as to provide unambiguous substituent effects uncomplicated by possible proton transfers.
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