Substituent Effects in the Fischer Indolization of (2-Sulfonyloxyphenyl)-hydrazones (Fischer Indolization and Related Compounds . XXX)

The effects of a variety of additional substituents of ethyl pyruvate 2-(2-methanesulfonyloxy)phenylhydrazone (7) in Fischer indolization were examined, When the substituent was a methyl group at the 3-, 4-, or 5-position, the yields of normal 7-methanesulfonyloxyindoles depended upon the position. The hydrazones having a methyl group at the position nearer to the methanesulfonyloxy group tended to give normal 7-methanesulfonyloxyindole in a higher percentage to total indolic products. In a series of 4-substituted phenylthydrazones (7d, e, f), more electron-withdrawing substituents tended to give normal 7-methanesulfonyloxyindole in a higher percentage to total indolic products than electron-donating ones. A hydrazone with a strong electron-withdrawing subsitiuent at the 4-position (7f) underwent intramolecular aromatic nucleophilic substitution by the enehydrazine moiety to give the cinnoline derivative.