Reactions of hydroxybenzophenone with hydrazines

The reaction of 2,2′,4,4′-tetrahydroxybenzophenone with hydrazines under different conditions gave the corresponding indazol-1,3-benzenediol derivatives. It is an interesting and unique approach to the synthesis of indazoles. However, the reactions of 2-hydroxybenzophenone and 2,2′-dihydroxybenzophenone under the same conditions yielded only the hydrazones.