Comparative study on the preparation of <i>C</i>(3)‐hydroxy‐1,3‐dihydro‐2<i>H</i>‐1,4‐benzodiazepin‐2‐ones

Abstract

Abstract C (3)‐Hydroxy‐1,4‐benzodiazepin‐2‐ones 1–3 have been prepared in high yields using a new, two step approach. In the first step, the 3‐deoxy‐precursors 4–6 were acetylated at C (3) using the redox‐system lead tetraacetate and iodine, or potassium iodide, in acetic acid. The intermediary acetates 9–11 were quantitatively hydrolyzed into 1–3 in non‐aqueous conditions, i.e. in a methanol‐methylene chloride solvent mixture in the presence of sodium methoxide. Another route to the title compounds has been improved as follows. The yields of C (3)‐bromination of compounds 4–6 has been significantly augmented in relation to the known methods using the strong trifluoroacetic acid in very dilute carbon tetrachloride solutions as a catalyst for NBS mediated bromination. The intermediary C (3)‐bromo derivatives have been acetoxylated in situ , and compounds 9–11 have been isolated in over 80% yield. These compounds were solvolyzed into 1–3 as described above. The third part of this paper describes the search for feasible reaction conditions in the synthesis of 3 according to a known method (Scheme 1.); optimization of the yields in all steps was performed.