NMR of Enaminones Part 7 1 1H-, 13C-, and 17O-NMR and X-Ray Structure Determinations of 1,2-Disubstituted Conjugated 3-[(tert-Butyl)amino]enones

Article abstract of DOI:10.1002/hlca.19970800713

¹H-, ¹³C-, and ¹⁷O-NMR spectra for the 2-substituted enaminones MeC(O)C(Me)=CHNH(t-Bu) (1), EtC(O)C(Me)=CHNH(t-Bu) (2), PhC(O)C(Me)=CHNH(t-Bu) (3), and MeC(O)C(Me)=CHNH(t-Bu) (4) are reported. These data show that 3 exists mainly in the (E)-form, 4 in (Z)-form, and 1 and 2 as mixtures of both forms. Polar solvents favour the (E)-form. The (Z)- and (E)-forms exist in the 1,2-syn,3,N-anti and 1,2-anti,3,N-anti conformations A and B, respectively. The structures of the (E)- and (Z)-form are confirmed by X-ray crystal-structure determinations of 3 and 4. The shielding of the carbonyl O-atom in the ¹⁷O-NMR spectrum by intramolecular H-bonding (Δδ_HB), ranging from -28 to -41 ppm, depends on the substituents at C(1) and C(2). Crystals of 3 at 90 K are monoclinic, with a = 9.618(2) A, b = 15.792(3) A, c = 16.705(3) A. and β = 94.44(3)°, and the space group is P2₁/c with Z = 8 (refinement to R = 0.0701 on 3387 independent reflections). Crystals of 4 at 101 K are monoclinic, with a = 16.625(8) A, b = 8.637(6) A, c = 11.024(7) A, and β = 101.60(5)°, and the space group is Cc with Z = 4 (refinement to R = 0.0595 on 2106 independent reflections).