作者:Johnathon E. Letourneau、Mark A. Wellman、D. Jean Burnell
DOI:10.1021/jo9707949
日期:1997.10.1
preference for syn addition with less encumbered dienophiles. This may indicate a conformational difference in its syn transition state relative to the transition states for addition syn to methyl, ethyl, or n-butyl substituents (dienes 1, 4, and 5). Dienophiles are more reluctant to add syn to the larger C-5 group with 1,2,3,4,5-pentamethyl-1,3-cyclopentadiene (2) and derivatives (3, and 7) and conformational
已经用多种亲二烯体评估了在C-5处被各种简单烷基取代的1,3-环戊二烯在狄尔斯-阿尔德反应中的表面选择性。结果与基于位阻的解释一致。在空间需求较少的亲二烯体中,更优选顺式添加。在C-5处被甲氧基甲基取代的二烯6,对顺式加成表现出显着的偏爱,其亲二亲物较少。这可能表明其顺式过渡态相对于向甲基,乙基或正丁基取代基(二烯1、4和5)加成顺式的过渡态的构象差异。亲双烯体更不愿意将1,2,3,4,5-五甲基-1,3-环戊二烯(2)和衍生物(3,