Khrapunovich Marina, Zelenova Ekaterina, Seu Lillian, Sabo Alexis N, Flaherty Aidan, Merrer Dina C
Department of Chemistry, Barnard College, 3009 Broadway, New York, New York 10027, USA.
J Org Chem. 2007 Sep 28;72(20):7574-80. doi: 10.1021/jo071203+. Epub 2007 Sep 7.
Dihalocarbenes add regioselectively to aryl-substituted benzocyclopropenes to produce dihalobenzocyclobutenes. The regioselectivity of addition is not due to steric effects but depends on the electronic donor or acceptor ability of the substituent. B3LYP/6-31G* calculations show preferential :CCl2 addition to substituted benzocyclopropene through electrophilic attack on the benzocyclopropene pi-system (Ea = 1.1-2.4 kcal/mol) rather than C-C sigma-bond insertion into the cyclopropenyl moiety (Ea = 5-24 kcal/mol). pi-Addition proceeds regioselectively through a single transition state to xylylene intermediates or directly to benzocyclobutene products.
二卤卡宾区域选择性地加成到芳基取代的苯并环丙烯上，生成二卤苯并环丁烯。加成的区域选择性并非源于空间效应，而是取决于取代基的给电子或吸电子能力。B3LYP/6 - 31G*计算表明，二氯卡宾优先通过对苯并环丙烯π体系的亲电进攻（活化能Ea = 1.1 - 2.4千卡/摩尔）加成到取代的苯并环丙烯上，而不是通过碳 - 碳σ键插入环丙烯基部分（活化能Ea = 5 - 24千卡/摩尔）。π - 加成通过单一过渡态区域选择性地生成亚二甲苯基中间体或直接生成苯并环丁烯产物。
