Are n-BuLi/TMEDA-mediated arene ortholithiations directed?: Substituent-dependent rates, substituent-independent mechanisms
Are n-BuLi/TMEDA-mediated arene ortholithiations directed?: Substituent-dependent rates, substituent-independent mechanisms
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DOI：
10.1021/ja001471o
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发表时间：
2000-09-13
影响因子：
15
通讯作者：
Collum, DB
中科院分区：
文献类型：
--
作者：
Chadwick, ST;Rennels, RA;Collum, DB
对n-BuLi/TMEDA混合物对苯和相关烷氧基取代芳烃锂化反应的速率研究表明，质子转移具有类似的机制，其中质子转移速率受到化学计量[（n-BuLi）（2）（TMEDA）（2）（Ar-H）]双匕首过渡结构的限制（Ar-H =苯，C6 H5 OCH 3，m-C6 H4（OCH 3）（2），C6 H5 OCH 2 OCH 3和C6 H5 OCH 2CH 2N（CH 3）（2））。合作取代基效应和诱导效应的明显重要性表明，烷氧基-锂相互作用在限速过渡结构中是次要的或不存在的机制。在从头计算的支持下，讨论了三重离子[（n-Bu）（2）Li]（-）//Li+（TMEDA）（2）的跃迁结构.
Rate studies of the lithiation of benzene and related alkoxy-substituted aromatics by n-BuLi/TMEDA mixtures implicate similar mechanisms in which the proton transfers are rate limiting with transition structures of stoichiometry [(n-BuLi)(2)(TMEDA)(2)(Ar-H)]double dagger (Ar-H = benzene, C6H5OCH3, m-C6H4(OCH3)(2), C6H5OCH2OCH3, and C6H5OCH2CH2N(CH3)(2)). Cooperative substituent effects and an apparent importance of inductive effects suggest a mechanism in which alkoxy-lithium interactions are minor or nonexistent in the rate-limiting transition structures. Supported by ab initio calculations, transition structures based upon triple ions of general structure [(n-Bu)(2)Li](-)//Li+(TMEDA)(2) are discussed.