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首页> 外文期刊>Chemistry: A European journal >Planar-Chirla (2E,7Z)-and (2Z,7E)-Cyclonona-2,7-dien-1-yl Carbamates by Asymmetric, Bis-Allylic #alpha#,#alpha#'-Cycloalkylation-Studies on Their Conformational Stability
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Planar-Chirla (2E,7Z)-and (2Z,7E)-Cyclonona-2,7-dien-1-yl Carbamates by Asymmetric, Bis-Allylic #alpha#,#alpha#'-Cycloalkylation-Studies on Their Conformational Stability

机译：平面Chirla（2E，7Z）和（2Z，7E）-Cyclonona-2,7-dien-1-yl氨基甲酸酯的不对称，双烯丙基#alpha＃，＃alpha＃'-环烷基化-构象稳定性研究

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摘要

Enantiomerically enriched (>80% ee) (M,1R,2Z,7E)-and (M,1R,2E,7Z)-cyclonona-2,7-dienyl carboamates have been synthesized by an intramolecular cycloalkylation of the corresponding 1-lithio-9-chloronona-2,7-dienyl carboamates. The enantioenriched precursors were generated by asymmetric deprotonation of the dienylcarbamates by means of n-BuLi/(-)-sparteine. The primarily obtained cyclononadienes, each bearing one element of planar and centre chirality, were formed by an #alpha#,#alpha#' coupling of both allylic moieties. These are the thermodynamically less favoured epimers, which arise from those allyllithiums bearing the carbomamoyloxy residue in a 1-endo position. Both (M,R)-cyclononadienes epimerize slowly (t_(1/2)-209 min and 328 min at 308 K) with inversion of the planar chirality to the corresponding, more stable (P)-epimers(ratios 3:97)and 30:70). The kinetics were measured by ~1H NMR spectroscopy, the activation energies E_A were found to be 26.4 and 27.5 kcal mol~(-1). From quantum-chemical calculations with the B3LYP density functional, the epimerization process was shown to consist of two coupled major conformational changes with high energy barriers. The calculated values matech well with the observed ones.
机译：对映体富集（> 80％ee）（M，1R，2Z，7E）-和（M，1R，2E，7Z）-cyclonona-2,7-二烯基氨基甲酸酯已通过相应的1-lithio的分子内环烷基化反应合成-9-chloronona-2,7-二烯基氨基甲酸酯。通过n-BuLi /（-）-天冬氨酸通过二烯基氨基甲酸酯的不对称去质子化而产生了对映体富集的前体。最初获得的环壬二烯，每个都带有一个平面和中心手性的元素，是通过两个烯丙基部分的#alpha＃，＃alpha＃'偶联形成的。这些是在热力学上较不受欢迎的差向异构体，其由在1-内位上带有氨基甲酰氧基残基的那些烯丙基锂产生。两种（M，R）-环壬二烯均缓慢发生差向异构（t_（1/2）-209 min和308 K在328 min处），平面手性反转为相应的更稳定的（P）-顶基（比例3:97）和30:70）。通过〜1H NMR光谱测定动力学，发现活化能E_A为26.4和27.5kcal mol〜（-1）。从具有B3LYP密度泛函的量子化学计算中，差向异构化过程显示为由两个具有高能垒的耦合主要构象变化组成。计算值与观察值比较吻合。

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