Effect of Double-Bond Substituents on the Rate of Cyclization of α-Carbomethoxyhex-5-enyl Radicals
作者:Arthur Han、Tudor Spataru、John Hartung、Gang Li、Jack R. Norton
DOI:10.1021/jo402499w
日期:2014.3.7
the corresponding acrylate esters 1 and the yields of cyclized products compared to the calculated rate constants. (The “cyclized products” include those from cyclohydrogenation, 4, and those from cycloisomerization, 9.) Two phenyl substituents on C6 (2i), or a phenyl and a methyl substituent (2g, 2h), increase the rate of cyclization, but a single phenyl substituent on C6 produces a greater increase
已经计算出速率常数,并将其与实验结果进行比较,以对在C6上具有各种取代基的1-甲氧基-1-甲基-5-己烯基自由基(2)进行环化。通过DFT在B3LYP / 6-311 ++ G **的理论水平上进行了计算。它们显示了C5和自由基中心之间的相当大的相互作用,即使在所有自由基2的基态下也是如此。在实验上,自由基是通过H •转移至相应的丙烯酸酯1生成的,并将环化产物的产率与计算出的速率常数进行比较。(“环化产物”包括来自环氢化的产物4和来自环异构化的产物9。)C6(2i)上的两个苯基取代基,或苯基和甲基取代基(2g,2h)提高环化率,但C6上的单个苯基取代基产生更大的环化。计算表明,两个苯基取代基在过渡态中被扭曲以进行环化,而单个苯基取代基在该过渡态中保持平坦。C6上的甲基取代基与单个苯基一起导致苯基在过渡态发生扭曲,并使环化的速率常数降低到H / Ph-取代的2e,2f之下。