Martinez E, Newcomb M
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, USA.
J Org Chem. 2006 Jan 20;71(2):557-61. doi: 10.1021/jo051953o.
[reaction: see text] N-Aryl-5,5-diphenyl-4-pentenamidyl radicals (3) were produced by 266 nm laser-flash photolysis of the corresponding N-(phenylthio) derivatives, and the rate constants for the cyclizations of these radicals were measured directly. The 5-exo cyclization reactions were fast (k(c) > 2 x 10(5) s(-1)), and radicals 3 generally behaved as electrophilic reactants with a Hammett correlation of rho = 1.9 for five of the six radicals studied. However, the p-methoxyphenyl-substituted radical 3f cyclized much faster than expected from the Hammett analysis. Variable temperature studies of parent radical 3a (aryl = phenyl) gave an Arrhenius function with log k = 9.2 - 4.4/2.3RT (kcal/mol). The rate constant for the reaction of p-ethylphenyl-substituted anilidyl radical 3b with Bu(3)SnH at 65 degrees C was k(T) = 4 x 10(5) M(-1) s(-1).
[反应：见正文] 通过对相应的N-（苯硫基）衍生物进行266nm激光闪光光解产生N-芳基-5,5-二苯基-4-戊烯酰胺基自由基（3），并直接测量这些自由基环化的速率常数。5-外向环化反应很快（k(c) > 2×10(5) s(-1)），对于所研究的六个自由基中的五个，自由基3通常表现为亲电反应物，哈米特相关系数ρ = 1.9。然而，对甲氧基苯基取代的自由基3f的环化速度比哈米特分析预期的要快得多。母体自由基3a（芳基 = 苯基）的变温研究得到一个阿仑尼乌斯函数，log k = 9.2 - 4.4/2.3RT（千卡/摩尔）。对乙基苯基取代的苯胺基自由基3b在65℃下与Bu(3)SnH反应的速率常数为k(T) = 4×10(5) M(-1) s(-1)。
