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NUCLEOPHILIC SUBSTITUTION REACTION OF ARYL TRIFLATES VIA ARYL CATIONS

芳基三氟甲磺酸酯通过芳基阳离子的亲核取代反应

基本信息

批准号：
60550614
负责人：
SONODA Takaaki
金额：
$ 1.41万
依托单位：
Research Institute of Industrial Science, Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1986
项目状态：
已结题

项目摘要

The solvolytic generation of aryl cations from aryl triflates with trimethylsilyl group(s) and/or tert-butyl group(s) on the both ortho positions in the aromatic rings was demonstrated as a new type of nucleophilic aromatic substitution reactions.The trimethylsilyl groups on the both ortho positions of the aryl cations play important roles not only in stabilizing the cations, whose hyperconjugative stabilization energy was calculated to be more than 30 kcal <mol^(-1)> , but also in controlling sterically the attack of the nucleophilee on the cationic center.The selectivity values of the aryl cations toward several nucleophiles are obtained from the ration of the products from the reactions of the cations with the nucleophiles and the products from that with the solvent TFE in the solvolysis of the triflate in TFE in the presence of the nucleophiles; <k_(Nu)> / <k_(TFE)> = 7.7( <I^-> ), 6.5(PhCN), 5.8(MeCN), 4.3( <Br^-> ), 3.5 (EtSH), and 1.7(MeOH).The solvolysis of the triflate in HFIP, on the other hand, gave the products from the reactions with the external nucleophiles exclusively and no hexafluoroisopropyl ether from that with HFIP was formed due to the steric hindrance among the both trimethylsilyl groups of the distorted aryl cation and the bulky HFIP.A first example of the generation of the aryl cations was also shown in the photochemical solvolysis of the aryl triflates and halides, where the initially formed radical pairs by homolytic cleavage of the C-X bond undego subsequent electron transfer to afford an ion pair and cationic products. The carbene-cation character of the aryl cations was indicated in the formation of indane by the intramolecular C-H insertion reaction of 2-propylphenyl cation generated in the photolysis of 2-propylphenyl triflate.

芳香环邻位上带有三甲基硅和/或叔丁基的芳基三氟甲磺酸酯溶剂解生成芳香阳离子是一种新型的亲核芳香取代反应，芳香阳离子邻位上的三甲基硅不仅对阳离子起稳定作用，其超共轭稳定化能大于30 kcal <mol^（-1）>，还能在空间上控制亲核试剂对阳离子中心的进攻，由亲核试剂对阳离子中心的选择性计算得到芳基阳离子对几种亲核试剂的选择性。在三氟甲磺酸酯在TFE中在亲核试剂存在下的溶剂分解中，将来自阳离子与亲核试剂反应的产物和来自阳离子与溶剂TFE反应的产物进行定量;<k_（Nu）> / <k_（TFE）> = 7.7（I^-），6.5（PhCN），5.8（MeCN），4.3（<Br->）、3.5（EtSH）和1.7（MeOH）。另一方面，三氟甲磺酸酯在HFIP中的溶剂分解，仅从与外部亲核试剂的反应中得到产物，并且由于扭曲的芳基阳离子的三甲基甲硅烷基和大体积HFIP之间的空间位阻，没有从与HFIP的反应中形成六氟异丙基醚。芳基阳离子也在芳基三氟甲磺酸酯和卤化物的光化学溶剂分解中显示，其中通过C-X键的均裂最初形成的自由基对经历随后的电子转移以提供离子对和阳离子产物。芳基阳离子的卡宾阳离子的特征表明，在形成茚满的2-丙基苯基阳离子的分子内C-H插入反应中产生的2-丙基苯基三氟甲磺酸酯的光解。