NMR of enaminones. Part 8—1H, 13C and 17O NMR spectra of primary and secondary 1,2‐disubstituted enaminones: configuration, conformation and intramolecular hdydrogen bonding

Abstract

The 1H, 13C and 17O NMR spectra for four series of C-2-substituted enaminones are reported: MeCO(Me)C=CHNHR (1), EtCO(Me)=CHNHR (2), PhCO(Me)C=CHNHR (3) and MeCO(Me)C=CHNHR (4). The 1H, 13C and 17O NMR data for these enaminones show that 1 and 2 exist as mixtures of E- and Z-forms, 3 exists mainly in the E-form and 4 is in the Z-form. The E- and Z-forms exist in the E-s-E-s-E and Z-s-Z-s-E conformations, respectively. The 17O shift values of the carbonyl groups in the four series of enaminones show that the influence of N substituents is essentially identical and is additive. The shielding of the carbonyl O atom by intramolecular hydrogen bonding (ΔδHB), ca. -30 ppm, is dependent on the donor ability of the amino groups and the type of C-1 and C-2 substituents. Correlations of the 1H, 13C and 17O NMR data between the E- and Z-forms of enaminones are excellent. © 1998 John Wiley & Sons, Ltd.