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

The stereochemistry and conformational behavior of a series of 22 2-methyl-2-alkyl(phenyl, aryl)-4- N -methyl-1,2,3,4-tetrahydro-5 H -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 1 H and 13 C NMR spectra for most of them at room temperature.