催化不对称化N-Boc-imidazoles和oxazoles的催化方式
Ryoichi Kuwano1, Nao Kameyama, Ryuhei Ikeda
1Department of Chemistry, Graduate School of Sciences, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581, Japan. rkuwano@chem.kyushu-univ.jp
Journal of the American Chemical Society
|April 29, 2011
概括
研究人员使用一种新型的催化剂,实现了被替代的伊米达和奥克萨在性伊米达和奥克萨中高度酶选择性化. 这一突破使得五个成员的异环芳香环的催化不对称的减少成为可能.
科学领域:
- 有机化学 有机化学
- 不对称的催化剂.
- 异环化学 异环化学
背景情况:
- 状异环化合物是制药和材料科学中至关重要的组成部分.
- 有效的催化方法可以合成纯净的imidazolines和oxazolines,这是非常受欢迎的.
- 以前用于减少五个组成的芳香 heterocycles 的方法往往缺乏立体选择性或需要苛刻的条件.
研究的目的:
- 开发一种新型的催化系统,以不对称地化替代的伊米达和氧.
- 为了在减少含有和氧异原子的五个成员芳香环中实现高的选择性.
- 建立一种新方法来合成合性伊米达佐林和奥克萨佐林.
主要方法:
- 使用性催化剂化替代的伊米达和氧.
- 催化剂在现场由Ru (η) (3) -methallyl () () () 和一个转化性性双氨酸连接体PhTRAP生成.
- 使用奇拉色谱 (chiral chromatography) 分析等离子体过量 (ee).
主要成果:
- 成功化伊米达和奥克萨到它们相应的性伊米达和奥克萨.
- 在产品中达到高达99%的反体过剩 (ee).
- 证明了第一个成功的催化不对称的减少5个成员的芳香环与多个异原子.
结论:
- 开发的-PhTRAP催化系统为不对称化提供了一个高度有效的途径.
- 这种方法在合成富含酵素的性伊米达佐林和佐林方面取得了显著的进步.
- 代表了具有挑战性的异环芳香基质的催化不对称降解的突破.
相关概念视频
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
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02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
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