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首页> 外文期刊>Chemistry: A European journal >Intramolecular Carbolithiation Reactions of Chiral #alpha#-Amino-organolithium Species
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Intramolecular Carbolithiation Reactions of Chiral #alpha#-Amino-organolithium Species

机译：手性＃alpha＃-氨基有机锂物种的分子内碳锂化反应

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摘要

Enantiomerically enriched #alpha#-amino-organolithium species, in which the lithium atom is attached to a stereo-genic carbon center, have been found to be chemically stable at room temperature in a solvent of very low polarity and undergo intramolecular carbolithiation onto an unactivated alkene. The configurational stability of the chiral organolithium species, bearing a variety of N-alkenyl substituents, was probed by studying the enantiomeric purity of the cyclization products. With N-but-3-enyl-2-lithiopyrrolidine, cyclization to the five-membered ring is more rapid than racemization and a high yield of the pyrrolizidine alkaloid (+)-pseudoheliotridane was obtained with no loss of optical purity. In contrast, with N-pent-4-enyl-2-lithiopyrrolidine, cyclization to the six-membered ring was found to occur with signicant loss of optical purity. The cyclization to the six-membered ring was determined to occur wit a half-life, t_(1/2) approx 90 min at 23 deg C. The epimerization of this opganolithium species in hexane/Et_2O 4:1 was calculated to have a half-life, t_(1/2) approx 30 min at 23 deg C. Enhanced levels of enantioselectivity for the formation of the indolizidine ring system were obtained using an alkene bearing a terminal phenylthio substituent. With N-[(3-phenylthio)-prop-2-enyl]-2-lithiopyrrolidine, cyclization to the four-membered ring occurs with poor enantioselectivity at low temperature in THF but is highly enantio-selective at room temperature in a solvent of very low polarity.
机译：已发现对映体富集的＃alpha＃-氨基有机锂物质（其中锂原子连接到立体碳中心）在室温下在极性非常低的溶剂中化学稳定，并且会发生分子内碳环化反应，形成未活化的烯烃。通过研究环化产物的对映体纯度，探讨了带有多种N-烯基取代基的手性有机锂物种的构型稳定性。使用N-丁-3-烯基-2-硫代吡咯烷，到五元环的环化比消旋化更快，并且在不损失光学纯度的情况下获得了高产率的吡咯并立烷生物碱（+）-假三碘tri烷。相反，对于N-戊-4-基-2-基-2-硫代吡咯烷，发现到六元环的环化发生了显着的光学纯度损失。确定到六元环的环化反应在23℃下发生约90分钟的半衰期t_（1/2）。该opganolithium物种在己烷/ Et_2O 4：1中的差向异构体经计算具有半衰期，t_（1/2）在23℃时约30分钟。使用带有末端苯硫基取代基的烯烃，可获得增强的吲哚并咪唑环系统形成对映选择性。对于N-[（3-苯硫基）-丙-2-烯基] -2-硫代吡咯烷，在低温下在THF中对映体选择性差，对四元环的环化反应发生，但在室温下在溶剂中，对映体选择性高。极低的极性。

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