The reaction of dibenzo[b,f][1,4]thiazepin-11(10H)-one (I) with refluxing POCl3 and dimethylaniline gives 11-chlorodibenzo[b,f][1,4]thiazepine (II), which is then condensed with 4-[2-(2-hydroxyethoxy)ethyl]piperazine (III) by means of NaOH in refluxing xylene to afford the free base of the title product (IV). Finally, this compound is treated with fumaric acid in ethanol.