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Homolytic aromatic substitution of heterocyclic compounds. Part XIII. Arylation and heteroarylation of coumarin and benzo[ b ]furan using triazenes as the source of radicals. An experimental and theoretical study
Author(s) -
Vernin Gaston,
Coen Serge,
Metzger Jacques,
Párkányi Cyril
Publication year - 1979
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570160120
Subject(s) - homolysis , chemistry , furan , radical , reactivity (psychology) , coumarin , medicinal chemistry , stereochemistry , organic chemistry , medicine , alternative medicine , pathology
The homolytic arylation (substituents in the phenyl radical: none, p‐methyl, p‐fluoro, p‐chloro, p‐bromo, o‐chloro, 2,4‐dichloro, 3,5‐dichloro, 2,3,4‐trichloro, 2,3,5‐trichloro, o‐carbomethoxy, p‐carboethoxy, and o‐phenyl) and heteroarylation (2‐thiazolyl, 2‐benzothiazolyl, 3‐pyridyl) of coumarin and benzo[ b ] furan has been studied. The radicals were generated by thermal decomposition of the corresponding 1,3‐diaryltriazenes in the presence of isoamyl nitrite. Homolytic substitution of coumarin takes place exclusively in the position 3 , in agreement with the prediction based on SCF‐MO free valences. In the case of benzo[ b ]furan, all the reactivity indices (F, S r , and A r ) predict the position 2 to be most reactive, in agreement with the experimental results. Comparison of the mass spectra of the products indicates similarities between the spectra of arylcoumarins and arylbenzo[ b ]furans and the existence of a common intermediate in their fragmentation pattern, viz ., the benzo[ b ]furan cation radical. One of the authors (G.V.) wishes to thank Prof. A. Maquestiau (Mons, Belgium) for useful suggestions concerning mass spectrometry. One of the authors (CP.) should like to thank the Ministere de l'Education Nationale, le Secretariat d Etat aux Universités, Paris, for a visiting professorship, and the National Science Foundation, Washington, D. C. for a travel grant. Also, the authors wish to express thanks to Mrs. G. Vernin for her careful technical assistance.