Thermal Stereomutations and Stereochemically Elucidated [1,3]-Carbon Sigmatropic Shifts of 1-(<i>E</i>)-Propenyl-2-methylcyclobutanes Giving 3,4-Dimethylcyclohexenes
作者:John E. Baldwin、Richard C. Burrell
DOI:10.1021/ja030516t
日期:2003.12.1
thermal stereomutations and [1,3] carbon sigmatropic shifts shown by (+)-(1S,2S)-trans-1-(E)-propenyl-2-methylcyclobutane and by (-)-(1S,2R)-cis-1-(E)-propenyl-2-methylcyclobutane in the gas phase at 275 degrees C leading to 3,4-dimethylcyclohexenes have been followed. The reaction-time-dependent data for concentrations and enantiomeric excess values for substrates and [1,3] shift products have been deconvoluted
(+)-(1S,2S)-trans-1-(E)-propenyl-2-methylcyclobutane 和 (-)-(1S,2R)-cis 显示的热立体突变和 [1,3] 碳 σ σ 位移-1-(E)-丙烯基-2-甲基环丁烷在 275 摄氏度的气相中产生 3,4-二甲基环己烯。底物和 [1,3] 变换产物的浓度和对映体过量值的反应时间相关数据已被解卷积以提供离散异构化过程的速率常数。反式和顺式底物都通过四个立体化学不同的 [1,3] 碳位移路径发生反应。对于反式反应物的一种对映异构体,相对速率常数为 k(si) = 58%、k(ar) = 5%、k(sr) = 33% 和 k(ai) = 4%。对于顺式反应物的单个对映异构体,k'(si) = 18%、k'(ar) = 11%、k'(sr) = 51% 和 k'(ai) = 20%。反式起始材料通过轨道对称性进行反应,允许 63% 的时间产生反式-3