Role of Conformation and Electronic Structure in the Chemistry of Ground and Excited State <i>o-</i>Pyrazolylphenylnitrenes
作者:Claudio Carra、Thomas Bally、Angelo Albini
DOI:10.1021/ja043988w
日期:2005.4.1
dehydroazepines (via benzoazirines) is calculated to be competitive in both nitrenes, but in the dimethyl derivative, 2b, attack onto the N lone pair (which is made more nucleophilic by the methyl groups) is favored. The higher barriers (by 4-8 kcal/mol) in singlet 2a cause 60-70% of this nitrene to decay by intersystem crossing to the triplet. Thus, the seemingly straightforward formation of benzo-fused
单线态 2a 中较高的势垒(4-8 kcal/mol)导致 60-70% 的氮烯通过系统间穿过三线态而衰变。因此,通过单线态苯基硝烯对吡唑啉 N 孤对的分子内攻击看似直接形成苯并稠合杂环只能在有利的情况下克服扩环和分子间反应。相对持久的三线态氮烯以基质为特征,光环化产物的产率(主要是 2a 的吡唑并[1,5-a]苯并咪唑 (7) 和 5,6-二氢吡唑并[1,5-a] 喹喔啉 (8) 2b) 显示取决于起始叠氮化物和氮烯的优选构象。通过单线态苯基硝基对吡唑啉N孤对的分子内攻击,看似直接形成苯并稠合杂环只能在有利条件下克服扩环和分子间反应。相对持久的三线态氮烯以基质为特征,光环化产物的产率(主要是来自 2a 的吡唑并[1,5-a]苯并咪唑 (7) 和来自 5,6-二氢吡唑并[1,5-a] 喹喔啉 (8) 2b) 显示取决于起始叠氮化物和氮烯的优选构象。通过单线态苯基硝基对吡唑啉N孤对的分子内攻