The condensation of 3,11-dichloro-6,11-dihydro-6-methyldibenzo[c,f][1,2]thiazepine S,S-dioxide (I) with ethyl 7-aminoheptanoate (II) in nitromethane gives ethyl 7-[(3-chloro-6,11-dihydro-6-methyldibenzo[c,f][1,2]thiazepin-11-yl)amino]heptanoate S,S-dioxide (III), which is then hydrolyzed with NaOH in refluxing ethanol.