super(1)H, super(13)C and super(15)N NMR spectral analysis of substituted 1,2,3,4-tetrahydro-pyrido[1,2-a]pyrimidines

The NMR spectroscopic data of a series of thirty-four 3-acylpyrido[1,2-a]pyrimidinium salts are analyzed, which were prepared as either perchlorates or chlorides. Methyl group substituted 3-aroyltetrahydropyrido[1,2-a]pyrimidines with the methyl substituent in positions 6, 8 and 9 as well as both in positions 6 and 8 were investigated bearing various aroyl substituents. Unequivocal assignment of all resonances was achieved via two-dimensional super(1)H, super(1)H-COSY measurements, super(1)H, super(13)C and super(1)H, super(15)N HSQC as well as HMBC experiments, and important diagnostic CH and NH couplings in the heteroaromatic ring system are evaluated. The influence of the methyl substituents was analyzed on the proton, carbon and nitrogen shifts. A significant effect of the counter ion on some chemical shifts of the nuclei under discussion of the pyridopyrimidines is found, allowing the indirect detection of the anion, which is confirmed by direct measurement of the super(35)Cl nucleus of the perchlorates. Copyright [copy 2013 John Wiley & Sons, Ltd. The super(1)H, super(13)C and super(15)N NMR spectroscopic data of a series of thirty-four 3-acylpyrido[1,2-a]pyrimidinium salts are analyzed, which were prepared as either perchlorates or chlorides They contain methyl substituent(s) in positions 6, 8 and 9 as well as both in positions 6 and 8. Important CH and NH long range couplings and significant differences of the chemical shifts depending on either the position of the methyl group or the counter ion were evaluated.