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Factors controlling the Selectivity of ipso-Attack in Homolytic Aromatic Substitutions. Reactions of Alkyl Radicals with Nitrothiophen Derivatives

DOI: 10.1039/P29800001331

Source and publish data:

Journal of the Chemical Society. Perkin transactions II p. 1331 - 1335 (1980)

Update date:2022-08-05

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Authors:

Cogolli, PietroCogolli, Pietro

Maiolo, FilippoMaiolo, Filippo

Testaferri, LorenzoTestaferri, Lorenzo

Tiecco, MarcelloTiecco, Marcello

Tingoli, MarcoTingoli, Marco

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Article abstract of DOI:10.1039/P29800001331

The reactions of the nearly electroneutral methyl and of the nucleophilic 1-adamantyl radical with some selected nitrothiophen derivatives have been investigated in order to elucidate the factors which control the positional selectivity of radical addition to an aromatic substrate.With 5-nitro-2-X-thiophens (II), (V), and (VI) and 3,5-dinitro-2-methoxycarbonylthiophen (III) the adamantyl radical gave exclusively the products of ipso-attack, whereas the methyl radical selectively added at the unsubstituted 4-position.On the other hand, with 4-nitro-2-methoxycarbonylthiophen (I) both radicals added at the 5-position and with 4,5-dinitro-2-methoxycarbonylthiophen (IV) both radicals gave the products of ipso-substitution by displacing the nitro-group from the 5-position.These changes in positional selectivity are explained by assuming that the nature of the transition state of the addition step changes as a function of the polar character of the radical and of the electron deficiency of the aromatic substrates.

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