Thermal Rearrangements of Di- and Triphenyl-Substituted Benzocyclobutenes and Correspondingo-Quinodimethanes
作者:Thomas Paul、Roland Boese、Ingo Steller、Heinz Bandmann、Georg Gescheidt、Hans-Gert Korth、Reiner Sustmann
DOI:10.1002/(sici)1099-0690(199903)1999:3<551::aid-ejoc551>3.0.co;2-2
日期:1999.3
rearrangements following initial electrocyclic ring-opening to the corresponding 7,8-diphenyl- (2c,d) and 7,8,8-triphenyl-o-quinodimethanes (2e–h). meso-1c was found to undergo a facile meso/rac isomerization at room temperature, indicating that other processes such as a symmetry-forbidden disrotatory ring-opening or a stepwise reaction compete with the symmetry-allowed conrotatory process. An estimate of the energy
7,8-二甲氧基-7,8-二苯基-(1c), 7,8-二甲基-7,8-二苯基-(1d), 7-甲氧基-7,8,8-三苯基-(1e), 7-甲基-7,8,8-三苯基-(1f)、7-异氰基-7,8,8-三苯基-(1g) 和 7,7,8-三苯基苯并环丁烯 (1h) 可进行以下各种热重排初始电环开环至相应的 7,8-二苯基-(2c,d) 和 7,8,8-三苯基-o-醌二甲烷 (2e-h)。发现 meso-1c 在室温下容易发生内消旋/外消旋异构化,这表明其他过程,例如禁止对称的反旋开环或逐步反应,与允许对称的旋转过程竞争。通过动力学模拟结合中间体邻醌二甲烷 (2c) 的氧捕获和半经验 PM3 计算,对 1c/2c 反应系统的能量分布进行了估计,并揭示对称禁止途径的障碍仅比对称允许途径的障碍高约 4 kJ·mol–1。o-Quinodimethanes 2c、2g、2e 和 2h 在 20 到 80