Fischer Indolization and Its Related Compounds. V. Indolization of Ethyl Pyruvate 2-Methoxyphenylhydrazone and Its N-Methyl Derivative with Protic Acids. Unpredictable Products and the Mechanism

Fischer indolization of ethyl pyruvate 2-methoxyphenylhydrazine (1) and its N-methyl derivative with protic acids give a variety of unpresumable indole products. Main products have been found to be 6-substituted indole derivatives formed by substitution of the methoxy group of the starting phenylhydrazone (1) with nucleophiles in the reaction medium. The tentative mechanism including an important key intermediate cation (15) is presented for the formation of the unexpected indole products.