Abstract: This disclosure describes a process for the preparation of 1,5-benzothiazepinone derivatives. The process involves the use of sulfonic acids as catalysts to effect ring closure to form the 1,5-benzothiazepinone ring. The resulting compounds have well known pharmaceutical properties.

Abstract: There is disclosed a process for preparing 1,5-benzothiazepine derivatives represented by the formula: ##STR1## wherein one of R.sup.1 and R.sup.2 is a lower alkyl group or halogen atom, and the other is hydrogen atom, R.sup.3 is a lower alkyl group or a lower alkoxy group, which comprises subjecting a propionic acid compound represented by the formula (II): ##STR2## wherein R.sup.1, R.sup.2 and R.sup.3 have the same meanings as defined above, and R.sup.4 represents hydrogen atom or an ester residue, to intramolecular ring closing reaction in the presence of a sulfonic acid compound represented by the formula (III):R.sup.5 SO.sub.3 H (III)wherein R.sup.5 represents a lower alkyl group or a substituted or unsubstituted phenyl group.