Rearrangement of 1,4‐benzodiazepin‐2,4‐diones to 3,l‐benzoxazin‐4‐ones

Treatment of 7‐chloro‐3,4‐dihydro‐1 H ‐1,4‐benzodiazepin‐2,5‐dione (Ia) with refluxing acetic anhydride in the presence of pyridine afforded 6‐chloro‐2‐methyl‐4 H ‐3,1‐benzoxazin‐4‐one (IIa). A plausible reaction path for this novel rearrangement reaction is described: Ia → 4‐acetyl‐7‐chloro‐3,4‐dihydro‐l H ‐1,4‐benzodiazepin‐2,5‐dione → 7‐chloro‐1,4‐diacetyl‐3,4‐dihydro‐l H ‐1,4‐benzodiazepin‐2,4‐dione → IIa. When 7‐chloro‐3,4‐dihydro‐4‐methyl‐l H ‐1,4‐benzodiazepin‐2,5‐dione (Ib), 3,4‐dihydro‐4‐methyl‐1H‐1,4‐benzodiazepin‐2,5‐dione (Id) and 3,4‐dihydro‐1‐methyl‐1H‐1,4‐benzodiazepin‐2,5‐dione (Ie) were allowed to react with acetic anhydride under conditions similar to those used for the rearrangement reaction, only acetylation occurred.