ELECTROPHILIC IPSO-SUBSTITUTIONS. PART 1. REACTION OF 3-SUBSTITUTED INDOLES WITH NITRONIUM AND NITROSONIUM IONS

3-Substituted indoles react with nitronium and nitrosonium ions to yield 3-nitroindole. In both cases the reaction was interpreted as an electrophilic ipso-substitution. The reaction mechanism is interpreted by hypothesizing the formation of a σ-complex-like intermediate, which is some cases is preceded by an electron-transfer process. An order for the leaving abilities of the different electrofugal groups is discussed.