The steric course of SE2 reactions of unstabilized α-aminoorganolithiums:: Distinguishing between SET and polar mechanisms
The steric course of SE2 reactions of unstabilized α-aminoorganolithiums:: Distinguishing between SET and polar mechanisms
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DOI：
10.1021/ja9923235
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发表时间：
2000-04-12
影响因子：
15
通讯作者：
Harris, R
中科院分区：
文献类型：
--
作者：
Gawley, RE;Low, E;Harris, R
比较了构型稳定和不稳定的α -氨基有机锂的亲电脂肪族取代反应（S(E)2）的空间过程的竞争机制。锂化吡咯烷和哌啶与亲电试剂反应的立体过程是可变的，例如在两个亲电试剂和一个有机锂之间进行比较，或在两个有机锂和一个亲电试剂之间进行比较。考虑的可能途径是单电子转移（SET）和竞争极性取代(S（E)2ret vs S(E)2inv）。亲电试剂对有机锂外消旋化的催化作用被排除为外消旋产物的可能来源。当产物完全外消旋时，我们的证据表明SET是最可能的机制；当极性途径起作用时，立体选择性从75%到100%不等，根据亲电试剂的不同，立体选择性在碳离子碳上可能是反转的或保留的。
The competing mechanisms that determine the steric course of electrophilic aliphalic substitution reactions (S(E)2) of configurationally stable, unstabilized alpha-aminoorganolithiums are compared. The steric course of the reaction of lithiated pyrrolidines and piperidines with electrophiles is variable, such as when comparisons are made between two electrophiles and a single organolithium, or between two organolithiums and a single electrophile. The possible pathways considered are single electron transfer (SET) and competing polar substitutions (S(E)2ret vs S(E)2inv). Catalysis of organolithium racemization by the electrophile was eliminated as a possible source of racemic products. When the products are completely racemic, our evidence suggests that SET is the most likely mechanism; when polar pathways are operative, stereoselectivities vary from 75 to 100%, and may be invertive or retentive at the carbanionic carbon, depending on the electrophile.