The Steric Course of S<sub>E</sub>2 Reactions of Unstabilized α-Aminoorganolithiums: Distinguishing between SET and Polar Mechanisms
作者:Robert E. Gawley、Eddy Low、Qianhui Zhang、Roy Harris
DOI:10.1021/ja9923235
日期:2000.4.1
possible pathways considered are singleelectrontransfer (SET) and competing polar substitutions (SE2ret vs SE2inv). 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
比较了确定构型稳定、不稳定的 α-氨基有机锂的亲电脂肪族取代反应 (SE2) 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空间过程是可变的,例如在两种亲电试剂和单一有机锂之间进行比较时,或在两种有机锂和单一亲电试剂之间进行比较时。考虑的可能途径是单电子转移(SET)和竞争性极性取代(SE2ret vs SE2inv)。亲电子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。当产品完全外消旋时,我们的证据表明 SET 是最可能的机制;当极地路径有效时,
Alkylation of 2-lithio-N-methylpiperidines and -pyrrolidines: scope, limitations, and stereochemistry
作者:Robert E. Gawley、Qianhui Zhang
DOI:10.1021/jo00123a008
日期:1995.9
The scope and limitations of the alkylation of racemic and nonracemic 2-lithiopiperidines and -pyrrolidines, obtained by transmetalation of the corresponding stannanes, is reported. These organolithiums react with a variety of electrophiles to afford 2-substituted pyrrolidines and piperidines in excellent yield. With primary alkyl halides the reaction proceeds with net inversion of configuration at the metal-bearing carbon in the piperidines; in the pyrrolidines there is a mixture of inversion and retention, with the former predominating. With most carbonyl electrophiles (carbon dioxide, dimethyl carbonate, methyl chloroformate, pivaloyl chloride, benzaldehyde, and dialkyl ketones), retention is observed in both cases. Electrophiles such as benzophenone, benzyl bromide, and tert-butyl bromoacetate afford racemic coupling products. A mechanistic interpretation is presented.
Central Stimulants. α,α-Disubstituted 2-Piperidinemethanols and 1,1-Disubstituted Heptahydroöxazolo [3,4-a]pyridines
作者:Frederick J. McCarty、Charles H. Tilford、M. G. Van Campen