Abstract
In addition to variable-temperature experiments and the analysis of vicinal coupling constants, a quantitative treatment of T1 values and nuclear Overhauser effect (NOE) factors was applied to the conformation analysis of novel heterocycles, substituted 4, 1-benzothiazepine (1) and 5, 1-benzothiazocine (2). The most probable conformations of the seven-and eight-membered rings of 1 and 2, respectively, could be distinguished by comparing the observed T1 values and NOE factors with those calculated for several possible conformers.
By the quantitative analysis of T1 values at-90.2 °C and at room temperature (24.5°C), 1 was found to be in an equilibrium state of rapid ring inversion between two chair forms in the ratio of 0.7 : 0.3 (at 24.5 °C), and the major conformer was the chair form with 5-methyl group equatorial.
The X-ray analysis of 2 showed that the eight-membered ring adopted a boat-boat like conformation in the crystal. Although this conformation seemed to be consistent with most of the observed relaxation data obtained in solution, the significant shielding effect expected on H4a was not observed. By a systematic search of the conformers, a boat-chair like conformer was found to satisfy all the observed relaxation and shielding data.
