Synthesis of 2-nitroindoles via the Sundberg indole synthesis

Synthesis of aromatic heterocycles

“…95 The Sundberg indole synthesis has been used to provide the first preparation of 2-nitroindole: 2-azido-β-nitrostyrene was heated in xylene to give the indole in 54% yield. 96 The cyclisation of 2-alkynylaniline derivatives provides a versatile synthesis of indoles and several new variants of the reaction have been reported. 3-Arylindoles are obtained by the palladium catalysed endo cyclisation of 2-ethynyltrifluoroacetanilide and trapping of the intermediate palladium species with aryl iodides (Scheme 32).…”

The nitration of some 4,6-dimethoxyindoles

“…The reactions of indoles with nitrous acid and other nitrosating agents have been well studied. 1,22,23 Preferred attack is at C3 and the 3-nitroso-indole is usually isolated as its tautomeric isomer, the 3-oximino-3H-indole, which can be oxidized to the related 3-nitro-indole. The nitrosation of 3-aryl-4,6-dimethoxyindoles was examined under both acidic (sodium nitrite in acetic acid) and basic (iso-pentyl nitrate and potassium carbonate in dimethylformamide) conditions.…”

Novel chemistry of indole in the synthesis of heterocycles

“…Our initial work in this area involved 1,2-bis(phenylsulfonyl)indole (25), and we found that this compound undergoes smooth addition of lithium dialkylcuprates to yield the corresponding 3-alkyl-2-(phenylsulfonyl)indoles devoid of the N-phenylsulfonyl group (Scheme 10) [15,20,21]. Furthermore, we were able to intercept the presumed intermediate C-2 anion with methyl iodide to give 2,3-dimethyl-1-(phenylsulfonyl)indole (26) in 70 % yield.…”

“…Our initial synthesis of 24 utilized the reliable Sundberg indole synthesis starting from 2-nitrobenzaldehyde (Scheme 8) [15].…”