Selectivity in the reactions of less stable carbocations with magnesium halides in aprotic solvents. A theoretical approach to the constant selectivity principle
作者:A.García Martínez、R.Martínez Alvarez、E. Teso Vilar、A. García Fraile、J. Osío Barcina、L.R. Subramanían
DOI:10.1016/0040-4020(95)00388-o
日期:1995.6
and 4-camphenyl triflate (4a) in carbon disulfide or diethyl ether with added MgI2 and MgBr2 yields a mixture of the corresponding halides 5b-e, 6b-c, 7b-c and 8b-c. The ionization of the triflate group is favoured by coordination with the magnesium halides. The reaction with MgI2 was found to be second-order and is about 50 times more reactive than MgBr2. The selectivities of the intermediate cations
7,7-双(三氟甲基磺酰氧基)-2-降冰片烯(1a),1-三氟甲基磺酰氧基-1-苯基乙烯(2a),2-甲基-1-环己烯-1-基三氟甲磺酸酯(3a)和4-camphenyl triflate的溶剂分解(4a)在添加了MgI 2和MgBr 2的二硫化碳或乙醚中,产生相应的卤化物5b-e,6b-c,7b-c和8b-c的混合物。与卤化镁的配位有利于三氟甲磺酸酯基团的电离。已发现与MgI 2的反应是二级反应,反应活性是MgBr 2的约50倍。中间阳离子5-8的选择性尽管溶剂分解速率相差十次以上的三次幂,但是朝向亲核试剂的MgI 2和MgBr 2几乎是恒定的。给出了恒定选择性原理的理论解释。