Studies of dihydropyridines by X-ray diffraction and solid state 13C NMR

Fourteen dimethyl 4-aryl-2,6-dimethyl-1,4-dihydropyridine-3,5- dicarboxylates (DHPs) were evaluated by means of single crystal X-ray diffraction in order to investigate the effects of the structure in the crystals on the solid state 13C NMR chemical shifts. These include the analysis of three DHPs containing two molecules per asymmetric unit. The chiral rotamer unit generated by the s-cisls-trans orientation of the carbonyl groups, as well as by rotation of the 4-phenyl ring out of the bisecting plane containing the N1, C4, C7 atoms, resulted in a significant magnetic non-equivalence for the C2-CH3/C6-CH3 and the COOCH 3 pairs of signals. The solid state 13C NMR data reveal that the substitution pattern of the phenyl ring has a marked effect on the extent to which the signals of the carbonyl carbon atoms and those of C-2/C-6 peaks are split. © 2007 Verlag der Zeitschrift für Naturforschung.