The Solvent Effects on the Photochemical Isomerization of 5-Cyano-5<i>H</i>-benzocycloheptene
作者:Hisako Kobayashi、Keizo Takatoku、Masahiko Kato、Toshio Miwa
DOI:10.1246/bcsj.56.3449
日期:1983.11
The photochemical reaction of 5-cyano-5H-benzocycloheptene (1b) has been studied kinetically in various solvents. The main reactions were (1) a 1,7-hydrogen shift, with simultaneous cyclization, to give 7b-cyanola,7b-dihydro-1H-cyclopropa[a]naphthalene and (2) a 4π-electrocyclic ring closure to give cyclobutenes. The former reaction was found to show rather complicated solvent effects, but the latter was accelerated in less polar solvents. The conformational equilibrium between exo- and endo-forms was also observed in the NMR spectra of 1b under various conditions. From a consideration of the solvent effects on the product distribution, the ground-state conformations of 1b could be reflected in the ratio of the exo and endo forms of the cyclization products.
对 5-氰基-5H-苯并环庚烯(1b)在各种溶剂中的光化学反应进行了动力学研究。主要反应有:(1)1,7-氢转移,同时发生环化,生成 7b-氰基-7b-二氢-1H-环丙[a]萘;(2)4π-电环闭环,生成环丁烯。发现前一种反应显示出相当复杂的溶剂效应,但后一种反应在极性较低的溶剂中会加速。在不同条件下,1b 的核磁共振光谱中也观察到了外型和内型之间的构象平衡。考虑到溶剂对产物分布的影响,1b 的基态构象可以通过环化产物中外型和内型的比例反映出来。