Comparison of hydrogen abstraction and homolytic substitution in pentacyclo[4.n.0.02,5.03,8.04,7]alkanesElectronic supplementary information (ESI) available: experimental details (GC-MS) for photobrominations of basketane and homocubane. See http://www.rsc.org/suppdata/p2/b2/b200699e/
作者:Phillip Lightfoot、Patrizia Pareschi、John C. Walton
DOI:10.1039/b200699e
日期:2002.4.29
The rate of hydrogen atom abstraction from basketane (pentacyclo[4.4.0.02,5.03,8.04,7]decane) by tert-butoxyl radicals to produce 9-basketyl radicals was shown by EPR spectroscopy to be ca. 50 mol−1 dm3 s−1 at 165 K. A similar study with homocubane (pentacyclo[4.3.0.02,5.03,8.04,7]nonane) showed that the rate constant was even smaller (<4 mol−1 dm3 s−1 at 165 K). Photobromination of basketane gave a mixture of 9-bromobasketane, bromochlorotricyclodecenes, dibromotricyclodecenes and tetrabromotricyclodecanes. These products were accounted for by a mechanism involving competition between the initial bromine atom abstracting a methylene hydrogen, or homolytically substituting at one or other of the three different cube bridgehead C-atoms. Photobromination of homocubane was also studied but gave only dihalotricycloalkenes
and tetrabromotricycloalkanes from homolytic substitution. The two pentacycloalkanes furnish two more examples of the rare homolytic cleavage of carbon–carbon bonds shared by two cyclobutane rings.
EPR光谱显示,在165 K时,叔丁氧基自由基从篮烷(五环[4.4.0.02,5.03,8.04,7]癸烷)中提取氢原子生成9-癸基自由基的速率约为50 mol·1 dm3·s-1。对同立方烷(五环[4.3.0.02,5.03,8.04,7]壬烷)进行的类似研究显示,速率常数甚至更小(在165 K时小于4 mol·1 dm3·s-1)。篮烷的光溴化反应生成9-溴篮烷、溴氯三环癸烯、二溴三环癸烯和四溴三环癸烷的混合物。这些产物可通过一种机制来解释,即初始溴原子与亚甲基氢发生竞争,或者同素异构地取代三个不同立方桥头C原子中的一个或另一个。研究人员还研究了同立方烷的光溴化反应,但仅通过同素异构取代反应生成二卤代三环烷炔和四溴三环烷。这两种五环烷提供了两个罕见的同素异构碳-碳键断裂的例子,这种断裂存在于两个环丁烷环之间