Enolizable ketones react with m-nitroaniline in the presence of strong base such as t-BuOK to give 4- and 6-substituted nitroindoles. The reaction proceeds via oxidative nucleophilic substitution of hydrogen in m-nitroaniline with enolate anions in positions ortho to the amino group giving anionic σH adducts that are additionally stabilized by intramolecular interaction between the amino and the carbonyl
[3,3]-Sigmatropic rearrangement of N-triflluoroacetyl enehydrazines provides a novel method for the construction of indoles. N-Trifluoroacetyl enehydrazine having a cyclopentene ring smoothly underwent [3,3]-sign-tatropic rearrangement followed by cyclization to give indolines in excellent yield. On the other hand, both cyclohexenyl N-trifluoroacetyl enchydrazine and acyclic N-trifluoroacetyl enehydrazine gave indoles in good yield. Additionally, the substituent effect on the benzene ring was also studied. The rearrangement of N-trifluoroacetyl enchydrazines proceeded smoothly even Linder either aqueous or solvent-free conditions. (c) 2006 Elsevier Ltd. All rights reserved.
Plant, Journal of the Chemical Society, 1929, p. 2497