5-endo-trig radical cyclization:disfavored or favored processes? (Articolo in rivista)

Type
Label
  • 5-endo-trig radical cyclization:disfavored or favored processes? (Articolo in rivista) (literal)
Anno
  • 2002-01-01T00:00:00+01:00 (literal)
Alternative label
  • Chatgilialoglu C., Ferreri C., Guerra M., Timokhin V., Froudakis G., Gimisis T. (2002)
    5-endo-trig radical cyclization:disfavored or favored processes?
    in Journal of the American Chemical Society (Print)
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • Chatgilialoglu C., Ferreri C., Guerra M., Timokhin V., Froudakis G., Gimisis T. (literal)
Pagina inizio
  • 10765 (literal)
Pagina fine
  • 10772 (literal)
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  • Impact factor della rivista 6.516 (literal)
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  • 124 (literal)
Rivista
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  • Lo studio della ciclizzazione mediante meccanismo radicalico è molto importante per le strategie sintetiche di molecole di interesse biologico e farmacologico. Inoltre, la combinazione di studi chimici della ciclizzazione con l'isolamento dei prodotti, e studi teorici con la proposizione di un meccanismo di reazione rappresenta un approccio interdisciplinare molto efficiente per raggiungere acquisizioni importanti in chimica organica. Infatti, le osservazioni contenute nel lavoro hanno un'importante ricaduta sulle regole che danno per sfavorito il processo di ciclizzazione radicalica 5-endo-trig (Baldwin-Beckwith rules). (literal)
Note
  • ISI Web of Science (WOS) (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • ISOF, Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy Department of Chemistry, UniVersity of Crete, 71409 Heraklion, Greece, Department of Chemistry, UniVersity of Athens, 15771 Athens, Greece (literal)
Titolo
  • 5-endo-trig radical cyclization:disfavored or favored processes? (literal)
Abstract
  • Relative kinetic data were determined for the 5- endo- trig cyclization of radical 12 compared to hydrogen abstraction from (TMS)3SiH in the temperature range of 344-430 K, which allows for the estimation of a rate constant of 2 x 10(4) s-1 at 298 K with an activation energy of ca. 9 kcal/mol for the cyclization process. The 5- endo- trig cyclization of a variety of radicals that afford five-membered nitrogen-containing heterocycles was addressed computationally at the UB3LYP/6-31G* level. The 5- endo vs 4- exomode of cyclication and the effect of delocalization of the unpaired electron in the transition state were investigated. Because the ring formed during cyclization contains five sp2 centers, electrocyclization via a pentadienyl like resonance form was also considered. For comparison, similar calculations were performed for 4-penten-1-yl and related radicals. The factors that affect the activation energies of homolytic 5- endo- trigcyclization were determined. In the absence of steric or conformational effects, the endocyclization to form the five membered ring was strongly favored over exo cyclization to form the four-membered ring not only on thermodynamic grounds but also kinetically. When a substituent on the double bond was able to delocalize the unpaired electron in the transition state of the 4- exopath, the two modes of cyclization became kinetically comparable. These results have an important bearing on the generalization of the Baldwin-Beckwith rules, which classified the 5- endo- trig radical cyclization as a “disfavored” process. (literal)
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