Abstract 5, 11-Dihydro-6H-pyrido [2, 3-6][1, 4] benzodiazepin-6-one (1), a basic intermediate in the preparation of 11-α-aminoacetyl derivatives with important biological activities, has been obtained by a three-step synthesis starting from easily available isatoic anhydride and anhydro ornithine. Some model cyclisation reactions leading to 5-member ring derivatives 10 and 12 instead of 7-member ring analogues of 1, are reported. Easy transformations of ...