高度二选择性化导致以氧保护形式的β-氧三角乳. 一个对delta-lactone形状的修改图
Svante Brandänge1, Magnus Färnbäck, Hans Leijonmarck
1Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden. svante@organ.su.se
Journal of the American Chemical Society
|September 25, 2003
概括
在化催化剂上化不和的三角乳,产生具有高分选择性的和乳. 形态分析揭示了超出先前公认的模型的多样化环结构.
科学领域:
- 有机化学 有机化学
- 立体化学是一种立体化学.
- 计算化学的计算化学
背景情况:
- 催化化是有机合成中的一个关键反应.
- 了解化的立体化学结果对于控制分子架构至关重要.
- 德尔塔乳是天然产品和药品中重要的结构动图.
研究的目的:
- 为了研究替代的α,β不和三角乳的化过程中的立体化学控制.
- 开发一种立体化学概括,用于化转-5,6-非替代的1-oxa-3-环-2-ones.
- 用实验和计算方法探索和三角洲乳酸盐的构造景观.
主要方法:
- 使用碳上帕拉 (Pd/C) 化乙醇MEM和乙醇乙酸.
- 对67种和的三角乳化合物的X射线晶体学数据的分析.
- 开始计算 (HF/6-31G) 来确定形态能量和过渡状态.
主要成果:
- 乙醇MEM和乙醇酸的化以非常高的二选择性 (>99%) 向和的三角乳酸进行.
- 形成了一个立体化学规则:从侧面的trans到C(6) - 替代物的转-5,6-非替代的1-oxa-3-cyclohexen-2-ones化物.
- 形状分析显示,和的三角乳酸盐具有显著的多样性,在狭窄的能量范围内具有多个可访问的符合性 (半椅子,船,椅子,信封,斜) .
结论:
- 催化化提供了优秀的立体化学控制,用于合成和的三角乳.
- 和型三角乳酸盐的形状行为比以前认为的要复杂得多,涉及到更广泛的可访问形状.
- 这些发现提供了对立体选择性的机制性理解,并扩展了三角乳酸盐的构成范式.
相关概念视频
02:06Newman Projections
Different notations are used to represent the three-dimensional structure of molecules on two-dimensional surfaces. One of the most commonly used representations is the dash-wedge formula. The dashed wedges, solid wedges, and the plane lines indicate the groups situated behind the plane, coming out of the plane, and in the plane, respectively.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers.
02:04Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
01:57Preparation of Diols and Pinacol Rearrangement
Compounds bearing two hydroxyl groups are known as diols. When the hydroxyl groups are located on adjacent carbon atoms, the diols are called vicinal diols or glycols. Under acidic conditions, vicinal diols undergo a specific reaction called pinacol rearrangement.
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
01:28Structures of Carboxylic Acid Derivatives
Structure of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
01:18β-Dicarbonyl Compounds via Crossed Claisen Condensations
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction involving esters, with both containing α hydrogen, results in a mixture of four different products that are difficult to isolate. This reduces the synthetic utility of the reaction.
01:28Stability of Conjugated Dienes
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.