Clarification of the Stereochemical Course of Nucleophilic Substitution of Arylsulfonate-Based Nucleophile Assisting Leaving Groups
Clarification of the Stereochemical Course of Nucleophilic Substitution of Arylsulfonate-Based Nucleophile Assisting Leaving Groups
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DOI：
10.1021/jo900991z
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发表时间：
2009-08-21
影响因子：
3.6
通讯作者：
Broadwith, Phillip
中科院分区：
文献类型：
--
作者：
Braddock, D. Christopher;Pouwer, Rebecca H.;Broadwith, Phillip
当在丙酮中用卤化锂回流处理时，被修饰为对甲苯磺酸盐、聚乙二醇磺酸盐或二异氰酸酯的仲醇经历构型脂肪的反转反应中心，其中聚乙二醇磺酸盐和二异氰酸酯的活性大得多。在受到严重阻碍的情况下，淘汰是一个相互竞争的过程。相反，当用TiCl4处理时，简单的仲磺酸盐得到的氯产物的构型部分颠倒。在这些条件下，在给定的烷基磺酸盐底物中观察到的任何构型的保留都可能是邻近基团参与或对碳正离子(或离子对)的非对映选择性攻击的线索，而不是S(N)I机制。
Secondary alcohols modified as tosylates, PEG-sulfonates, or quisylates undergo inversion of configuration fat the reacting center when treated with lithium halide in acetone at reflux, where the PEG-sulfonates and quisylates are substantially more reactive. In sterically hindered cases, elimination is a competing process. In contrast, when treated with TiCl4, simple secondary sulfonates give chloride products with partial inversion of configuration. Any observed retention of configuration in a given alkyl sulfonate substrate under these conditions is likely clue to neighboring group participation or diastereoselective attack on a carbocation (or ion pair) rather than an S(N)i mechanism.