Synthesis of 11-amino-3-chloro-6,11-dihydro-5,5-dioxo-6-methyl dibenzo(c,f)(1,2)thiazepine (I) and its salts, from 3-chloro-6,11-dihydro-6-methyl-5,5,11-trioxo dibenzo(c,f)(1,2)thiazepine (III). Synthesis of 11-amino-3-chloro-6,11-dihydro-5,5-dioxo-6-methyl dibenzo(c,f)(1,2)thiazepine of formula (I) and its salts, from 3-chloro-6,11-dihydro-6-methyl-5,5,11-trioxo dibenzo(c,f)(1,2)thiazepine of formula (III): Independent claims are also included for the use of (I) to prepare tianeptine (II) and its salts.