The acylation of 2,3,4,5-tetrahydrobenzo-1,5 thiazepine (I) with 3-bromopropionyl bromide (II) by means of pyridine in toluene gives 5-(3-bromo-propionyl)-2,3,4,5 tetrahydrobenzo-1,5-thiazepine (III), which is then condensed with 2-(3,4-dimethoxyphenyl)ethylamine (IV) in refluxing dichloromethane, and treated with fumaric acid.