Coupling between ethylamine derivative (I) and acid chloride (II) by means of DMAP in pyridine affords benzamide (III), which is then subjected to reaction with chlorosulfonic acid followed by treatment with aqueous ammonia to provide benzenesulfonamide (IV). Finally, the desired product is obtained by condensation of (IV) with methyl isothiocyanate in DMF by means of K2CO3.