Novel synthesis of 5,11‐dihydro‐6 H ‐pyrido[2,3‐ b ]‐[1,4]benzodiazepin‐6‐ones and related studies

5,11‐Dihydro‐6 H ‐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 the tetrahydro congener of 1 , i.e., compound 4 into 19 , which actually represents a tetrahedral intermediate in the transformation of 5 into 4 , is noticed. Further rearrangement of 19 into spiro compound 20 , and return of the latter into 5 is described.