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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.

芳基三氟酸酯与芳环上两个邻位上的三甲基硅基(S)和/或叔丁基(S)反应生成的芳基阳离子是一种新型的亲核芳香取代反应。芳基阳离子的两个邻位上的三甲基硅基不仅对阳离子的稳定起着重要的作用，其超共轭稳定能大于30kcal；芳基阳离子对几种亲核试剂的选择性是由阳离子与亲核剂反应的产物与TFE在亲核剂存在下与TFE在TFE中的溶解反应产物的比例得到的；&lt；k_(Nu)&gt；/&lt；k_(TFE)&gt；=7.7(&lt；i^-&gt；)、6.5(PHCN)、5.8(MeCN)、4.3(&lt；BR^-&gt；)，3.5(EtSH)和1.7(MeOH)。另一方面，三氟酸盐在HFIP中的溶解只得到与外部亲核试剂反应的产物，由于扭曲的芳基阳离子的三甲基硅基和大体积HFIP之间的空间位阻，与HFIP反应没有生成六氟异丙基醚。第一个例子也显示在芳基三氟酸盐和卤化物的光化学分解中，最初通过C-X键的均质裂解形成的自由基对随后进行电子转移得到离子对和阳离子产物。3-丙基苯基三氟酸异丙酯光解生成的2-丙基苯基阳离子在分子内的C-H插入反应生成了吲哚，说明了芳基阳离子的卡宾阳离子性质。