Conformational Complexity in Seven-Membered Cyclic Triazepinone/Open Hydrazones. 1. 1D and 2D Variable Temperature NMR Study

Abstract

The stereochemistry and conformational behavior of a series of 22 2-methyl-2-alkyl(phenyl, aryl)-4-N-methyl-1,2,3,4-tetrahydro-5H-1,3,4-benzotriazepin-5-ones and their open-chain hydrazone tautomers in various solvents were studied by 1D and 2D NMR techniques in the temperature range from 193 K to 410 K. Molecular rearrangements involving interconversions of the ring and open-chain forms (the latter via amide bond and Z/E CN double bond isomerization), pseudorotation of the ring forms, and N-inversion processes with different rates on the NMR time scale took place, leading to the observation of average and deceptively simple 1H and 13C NMR spectra for most of them at room temperature.

N-(2-aminobenzoyl)-N-methylhydrazones of aldehydes and aldoses and their cyclization to benzo-1,3,4-triazepine derivatives

“…This conclusion follows from observation of the doublet for the NH protons at 5.70-5.90 ppm and signal with the corresponding multiplicity at 4.00-4.50 ppm for H-2. The signal for the sp 3 -hybridized carbon atom at 70-75 ppm for C(2) corresponds to triazepine form B in the 13 C NMR spectrum (Tables 2 and 3) [2,3].…”

“…The analogous signal for five-membered furanose form D would be found at 95-100 ppm. In case of seven-membered triazepine form B, the signal for atom C(1) should be found upfield at 70-75 ppm, which is characteristic for an sp 3 -hybridized carbon atom of a seven-membered ring attached to two nitrogen atoms [2,3,11]. A downfield 13 C NMR signal at 150 ppm related to the C=N bond should be diagnostic for aldosohydrazone form A.…”

“…The change in the 13 C NMR spectra of all these products indicates that they have the cyclic benzo-1,3,4-triazepine structure B in the crystalline state. The 13 C NMR signal for atom C(1) at 75-80 ppm characteristic for an sp 3 -hybridized carbon atom in a seven-membered ring attached to two nitrogen atoms [2,3,11] is diagnostic for benzo-1,3,4-triazepine form B. Signals corresponding to a second configurational isomer of the benzo-1,3,4-triazepine form B' are found in the 1 H and 13 C NMR spectra of compounds 4e-h in DMSO-d 6 .…”

N′‐(3‐Amino‐1H‐isoindol‐1‐ylidene)‐R‐carbohydrazides and Their Amide‐Type Isomerism

“…Moreover, (Z)/(E) isomerism could be observed in these molecules owing to the presence of an exocyclic C=N bond and the N-acyl hydrazone fragment may exhibit an amidetype isomerism. [12][13][14][15] For the first time we have examined the structures of the synthesized compounds in the solid state by X-ray diffraction. We demonstrated that in the solid state all of these compounds exist in one tautomeric form A with a (Z) orientation of the hydrazide residue at the exocyclic C=N bond and a (Z) orientation of the N-acyl hydrazone fragment irrespective of the substituent R (aliphatic, aromatic, or heteroaromatic, Figure 2).…”

“…1 H NMR (400 MHz, [D 6 ]DMSO): δ = 3.97 and 4.25 (2 s, 2 H, CH 2 ), 7.51 (t, J = 7.2 Hz, 1 H), 7.54 (t, J = 7.2 Hz, 1 H), 7.68 and 7.72 (2 d, J = 7.2 Hz, 1 H), 7.91 and 7.93 (2 d, J = 7.2 Hz, 1 H), 8.21 and 8.56 (2 br. s, 2 H, NH 2 ), 10.05 and 10.89 (2 s, 1 H, NH) ppm 13. C NMR: δ = 24.88 and 25.41 (CH 2 ), 116.74, 120.79, 121.40, 121.46, 122.49, 130.01, 131.44, 135.30, 138.31, 138.85, 155.71, 158.10, 159.10, 165.98, 168.17 and 168.35 (C=O) ppm.…”