7-Chloro-3-hydroxy-5-(2'-fluorophenyl)-1,3-(dihydro-2H-1,4-benzodiazepin-2-one (I) is mixed with acrylonitrile (II), and after dropwise addition of triethylbenzylammonium chloride (A) and benzyl trimethylammonium hydroxide (B), stirring is continued for 8 hours. The crude material was recrystallized from acetonitrile.