Stereochemistry of 1,5-Benzo­thiazepin-4-one <i>S</i>‑Oxide: Insight into the Stereogenic Elements at the Sulfur Atom and Axis

Oxidation of 1,5-benzo­thiazepin-4-one (<b>5</b>-<b>A</b>) stereoselectively afforded the <i>S</i>-oxide <b>8I</b>-<b>A</b> (a<i>S</i>,1<i>S</i>) in preference to the diastereomer <b>8II</b>-<b>A</b> (a<i>S</i>,1<i>R</i>) affected by the remote stereogenic axis. All the enantiomers (<b>8I</b>-<b>A</b>/<b>8I</b>-<b>B</b> and <b>8II</b>-<b>A</b>/<b>8II</b>-<b>B</b>) were separated and isolated, and the interconversion between <b>8I</b> and <b>8II</b> (equilibrium ratio ≈5:1) was unequivocally verified to be caused by the rotation around the axis.