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π面ジアステレオ選択性発現機構に関する研究

π面非对映选择性表达机制研究

基本信息

批准号：
07454161
负责人：
TOMODA Shuji
金额：
$ 4.99万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

The theoretical model for pi-facial stereoselectivity of hydride redution of cyclic ketones, which was proposed last fiscal year, has been completed and the results were submitted as a letter and a full paper. This model named as Exterior Frontier Orbital Extension Model (EFOE Model) is based on the simple assumption that orbital extension with respect to both side of the pi-plane should be the origin of pi-facial stereoselectivity of carbonyl reduction. The EFOE densities, defined as an electron density of LUMO in the exterior area of a ketone, were nicely correlated with experimentally-determined activation enthalpies for alkyl-substituted cyclohexanones.These results clearly suggested that major conventional theoretical models (Cieplak Model and Felkin-Anh Model), whith simply focus on the transition tate (TS), completly neglect another, but the most important origin of pi-facial stereoselectivity-the effect of substrate LUMO.In fact, quantitative evaluation of anti-periplanar effects and torsional strain for the TS of cyclohexanone (B3LYP/6-31G**) indicated that these are only marginal with the Cieplak hyperconjugation effect greater than the Felkin-Anh effect.Importance of frontier orbital effects was found also in typical electrophilic addition to C=C bond -hydroboration of olefins. 2,3-R,R-7-methylene-bicyclo[2.2.1]heptanes(R=Me, Et, CH_2OMe, -CH_2OCH_2-, CO_2Me) were synthesized and stereoselectivity for hydroboration was determined. Surprisingly, reversed stereoselectivity was found for R=CH_2OMe and -CH_2OCH_2-, Which are electronically similar. The conventional models apparently fail to explain these puzzling results, but the initial complex and TS calculations (HF/6-31G** and NBO) indicated the interaction between HOMO of olefin and LUMO of BH_3 should dictate pi-facial stereoselectivity of hydroboration.

上个财政年度提出的氢化物还原环状酮的π-面立体选择性的理论模型已经完成，结果以信函和全文形式提交。该模型被称为外前线轨道扩展模型（Exterior Frontier Orbital Extension Model，EFOE模型），它基于一个简单的假设，即相对于π平面两侧的轨道扩展是羰基还原π-面立体选择性的起源。定义为酮外部区域LUMO电子密度的EFOE密度与实验测定的烷基取代环己酮的活化能很好地相关。（Cieplak模型和Felkin-Anh模型），只关注过渡状态（TS），完全忽略了另一个，而是π-面立体选择性的最重要来源-底物LUMO的影响。事实上，环己酮TS的反平面效应和扭转应变的定量评价（B3 LYP/6- 31 G **）的计算结果表明，Cieplak超共轭效应大于Felkin-Anh效应，前线轨道效应对C=C键的亲电加成反应也很重要。烯烃的硼氢化。合成了2，3-R，R-7-亚甲基双环[2.2.1]庚烷（R=Me，Et，CH_2OMe，-CH_2OCH_2-，CO_2Me），并测定了其硼氢化反应的立体选择性。令人惊讶的是，发现了相反的立体选择性R=CH_2OMe和-CH_2OCH_2-，这是电子相似的。传统的模型显然不能解释这些令人困惑的结果，但初始络合物和TS计算（HF/6- 31 G ** 和NBO）表明，烯烃的HOMO和BH_3的LUMO之间的相互作用决定了硼氢化反应的π面立体选择性。