Cyclization of 2-methoxy-6-(substituted benzyloxy)acetophenone hydrazones in the presence of polyphosphoric acid(PPA)

Cyclization of 2-methoxy-6-benzyloxy acetophenone hydrazone gave 3-methyl-4-meth-oxy indazole and 3-methyl-4-methoxy-7-benzyl indazole in the presence of polyphosphoric acid(PPA).The hydrazone was probably converted to 2-hydroxy-6-methoxy acetophenone hydra-zone and 2-hydroxy-3-benzyl-6-methoxy acetophenone hydrazone followed by cyclization to thecorresponding indazoles in acidic conditions.Cyelization of 2-methoxy-6-(halo or alkyl or arylbenzyloxy)acetophenone hydrazones gave similar products.Cyclization of 2-methoxy-6-(p-nitrobenzyloxy)acetophenone hydrazone gave 2-(p-nitrophenyl)-3-methyl-4-methoxy benzo-furan and 3-methyl-4-methoxy indazole while 2-methoxy-6-(m-nitrobenzyloxy)acetophenonehydrazone gave 3-methyl-4-methoxy indazole,3-methyl-4-methoxy-7-(m-nitrophenyl)indazole and3-methyl-4-(m-nitrobenzyloxy)indazole.

Cyclization of 2-methoxy-6-( substituted benzyloxy) acetophenone hydrazones in the presence of polyphosphoric acid (PPA)

Cyclization of 2-methoxy-6-benzyloxy acetophenone hydrazone gave 3-methyl-4-methoxy indazole and 3-methyl-4-methoxy-7-benzyl indazole in the presence of polyphosphoric acid (PPA). The hydrazone was probably converted to 2-hydroxy-6-methoxy acetophenone hydrazone and 2-hydroxy-3-benzyl-6-methoxy acetophenone hydrazone followed by cyclization to the corresponding indazoles in acidic conditions. Cyclization of 2-methoxy-6-(halo or alky] or aryl benzyloxy) acetophenone hydrazones gave similar products. Cyclization of 2-methoxy-6-(p-nitrobenzyloxy) acetophenone hydrazone gave 2-(p-nitrophenyl)-3-methyl-4-methoxy benzofuran and 3-methy]-4-methoxy indazole while 2-methoxy-6-(m-nitrobenzyloxy) acetophenone hydrazone gave 3-methyl-4-methoxy indazole, 3-methyl-4-methoxy-7-(m-nitrophenyl) indazole and 3-methyl-4-(m-nitrobenzyloxy) indazole.