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

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