Carbon Participation in the Solvolysis of 6-exo-substituted 2-exo- and 2-endo-Norbornylp-Toluenesulfonates. Norbornanes part 5
作者:Walter Fischer、Cyril A. Grob、Reinhard Hanreich、Georg von Sprecher、Adrian Waldner
DOI:10.1002/hlca.19810640735
日期:1981.11.4
2-exo-p-toluenesulfonates 1 to σ indicates an unusually strong inductive interaction between C(6) and the incipient cationic center at C(2). This interaction is ascribed to the participation of the pentacoordinate C(6)-atom, i. e. to 1,3-bridging, a consequence of steric hindrance of nucleophilic solvent participation in norbornanes. Donor substituents enhance 1,3-bridging, lead to faster reactions and to the formation
确定了6- exo-取代的2- exo - 1a - 1u和2-内-降冰片基对甲苯磺酸盐2a - 2u的溶剂分解速率和产物。通常,1和2的速率常数(log k)与C处取代基的感应常数σ(6)有很好的相关性。但是,在2- exo系列1中,它们对σ的敏感性要比2- endo系列2中对σ的敏感性大得多。极性效应的这种差异传递是减少2-的原因exo / 2-内含物比率从R = t -C 4 H 9的2388到R = Br的0.37,即随着取代基的电子吸引增加。2-异-对-甲苯磺酸盐1的速率常数对σ的高敏感性表明C(6)与C的初期阳离子中心之间异常强的感应相互作用。该相互作用归因于五配位的C(6)原子的参与,即1,3-桥联,这是降冰片烷中亲核溶剂参与的空间位阻的结果。供体替代品增强了1,3-桥连,导致更快的反应和2- exo的形成替代产品。相反,受体取代基减少了1,3-桥基,降低了速率并促进了2-内