Characterization of cation radical reactions. Aminium salt-catalysed Diels–Alder reactions
- 1 January 1996
- journal article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 8,p. 1761-1766
- https://doi.org/10.1039/p29960001761
Abstract
Kinetic studies of the Diels–Alder cycloadditions of a series of trans-stilbenes (2) to 2,3-dimethylbuta-1,3-diene (3), catalysed by tris(4-bromophenyl)aminium hexachloroantimonate (1˙+), reveal a curved Hammett–Brown plot, consistent with a mechanistic transition from reversible to rate determining ionization of 2 to 2˙+ as the substituents become progressively more electron donating. Further, substituent effects in mono- and di-substituted stilbenes are essentially multiplicative, describing a distribution of positive charge which is symmetrical with respect to both aryl rings. The symmetry of the charge development is inconsistent with an electrophilic addition to the substrates, proceeding via a carbocation. The combination of the magnitude and symmetry of the positive charge distribution provides strong evidence for a cation radical mechanism.Keywords
This publication has 14 references indexed in Scilit:
- Electron Transfer Reactions in Organic Chemistry. XXI. New Catalysts for the Diels--Alder Dimerization of 1,3-Cyclohexadiene: Brönsted, Lewis and Redox Catalysts.Acta Chemica Scandinavica, 1992
- Photochemical generation, isomerization, and oxygenation of stilbene cation radicalsJournal of the American Chemical Society, 1990
- Thermodynamic significance of .rho.+ and .rho.- from substituent effects on the redox potentials of arylmethyl radicalsJournal of the American Chemical Society, 1990
- Cation radical cycloadditions and related sigmatropic reactionsTetrahedron, 1989
- Mechanistic diagnosis of aminium salt initiated Diels-Alder cycloadditions in the diene/diene formatJournal of the American Chemical Society, 1987
- Distinction between aminium cation radical and protic acid catalyzed Diels-Alder reactionsJournal of the American Chemical Society, 1984
- Acid-catalyzed intramolecular "Diels-Alder" reactions. The cycloaddition of allyl cations to 1,3-dienesJournal of the American Chemical Society, 1984
- Mutual correlation between nonaqueous oxidation-reduction potentials and electronic spectra, and its extension to describe the substituent effect on electronic spectra by means of substituent constants.CHEMICAL & PHARMACEUTICAL BULLETIN, 1983
- Cation-radical catalyzed Diels-Alder reactionJournal of the American Chemical Society, 1981
- Triarylaminium Salt Free Radicals1Journal of the American Chemical Society, 1955