Kinetics of the [2+ + 4]-Cycloaddition Reactions of 1,3-Dithian-2-ylium Ions with 1,3-Dienes
作者:Herbert Mayr、Joachim Henninger
DOI:10.1002/(sici)1099-0690(199809)1998:9<1919::aid-ejoc1919>3.0.co;2-e
日期:1998.9
The kinetics of the [2+ + 4] cycloadditions of 1,3-dithian-2-ylium ions (1) with 1,3-dienes was investigated photometrically in dichloromethane. The second-order rate constants determined for the reactions of 1 with 2,3-dimethyl-1,3-butadiene (2a) and isoprene (2b) were identical to those calculated for the first step of a stepwise cycloaddition pathway by the correlation lg k = s (E + N). Though a
在二氯甲烷中以光度计研究了 1,3-dithian-2-ylium 离子 (1) 与 1,3-二烯的 [2+ + 4] 环加成动力学。为 1 与 2,3-二甲基-1,3-丁二烯 (2a) 和异戊二烯 (2b) 的反应确定的二级速率常数与通过相关性 lg 为逐步环加成途径的第一步计算的那些相同k = s (E + N)。尽管这一发现并未排除协同环加成途径,但很明显,这些反应的过渡态并没有因同时形成两个新的 σ 键而显着稳定。