@article {Chatgilialoglu2002a,
	title = {{5- Endo-trig Radical Cyclizations: Disfavored or Favored Processes?}},
	journal = {J. Am. Chem. Soc.},
	volume = {124},
	number = {36},
	year = {2002},
	month = {sep},
	pages = {10765{\textendash}10772},
	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 {\texttimes} 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-exo mode 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 sp 2 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-trig cyclization were determined. In the absence of steric or conformational effects, the endo cyclization 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-exo path, 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.},
	issn = {0002-7863},
	doi = {10.1021/ja0261731},
	url = {http://pubs.acs.org/doi/abs/10.1021/ja0261731},
	author = {Chatgilialoglu, Chryssostomos and Ferreri, Carla and Guerra, Maurizio and Timokhin, Vitaliy and Froudakis, Georgios and Gimisis, Thanasis}
}
