Fischer Indolization and Its Related Compounds. XXIV. Fischer Indolization of Ethyl Pyruvate 2-(2-Methoxyphenyl)phenylhydrazone

• Published in: Chem. Pharm. Bull Vol. 39; no. 3; pp. 572 - 578
• Main Authors: WATANABE, Toshiko, KOGUSURI, Kimiko, ISHI, Hisashi, SUGIURA, Takao, MURAKAMI, Yasuoki
• Format: Journal Article
• Language: English
• Published: Tokyo The Pharmaceutical Society of Japan 1991; 公益社団法人日本薬学会; Japan Science and Technology Agency
• Subjects: chlorinated diphenylamine; Fischer indolization; N-arylphenylhydrazone; o-quinone imine; Ulmann-Goldberg reaction
• ISSN: 0009-2363; 1347-5223
• DOI: 10.1248/cpb.39.572

In order to clarify the mechanism of Fischer indolization of 2-methoxyphenylhydrazones, Fischer indolization of ethyl pyruvate 2-(2-methoxyphenyl)phenylhydrazone (2) was carried out with hydrochloric acid in ethanol and zinc chloride in acetic acid. The reactions proceeded smoothly to give N-arylindoles (11-14) and some chlorinated diphenylamine derivatives (8-10) as by-products. Consideration of the indole products revealed that the Fischer indolization proceeded mainly at the unsubstitued phenyl nucleus rather than at the 2-methoxyphenyl nucleus. This result is inconsistent with the previous result that Fischer indolization of diarylhydrazones proceeded at the electron-richer nucleus. The structures of the diphenylamines were determined by chemical means and the mechanism of their formation is discussed.