银催化 [2 + 2] 循环添加的西洛基基因
Randy F Sweis1, Michael P Schramm, Sergey A Kozmin
1University of Chicago, Department of Chemistry, 5735 South Ellis Ave, Chicago, Illinois 60637, USA.
Journal of the American Chemical Society
|June 17, 2004
概括
这项研究引入了第一个使用西洛基和不和碳烯化合物的催化 [2+2] 循环添加. 银三甲硫胺有效地促进这些反应,具有高选择性和广泛的基质范围.
科学领域:
- 有机化学 有机化学
- 催化剂是一种催化剂.
- 循环添加反应的反应
背景情况:
- 循环添加反应是有机合成的基础.
- 基基是多功能构建块.
- 开发用于循环添加的新型催化系统仍然是一个活跃的研究领域.
研究的目的:
- 描述第一个催化 [2+2] 循环添加的基基与不和碳烯化合物.
- 研究银在这种转化中的机制和催化作用.
- 确定发生反应的范围和选择性.
主要方法:
- 采用微量含量的银三甲硫胺作为催化剂.
- 通过与各种不和碳烯化合物反应各种氧基因.
- 使用光谱技术对反应产品进行表征.
- 机械学研究,包括动力学分析和中间捕获.
主要成果:
- 首次成功实现了与不和碳烯化合物氧基因的 [2+2] 循环添加.
- 在循环添加产品中表现出高的区域和 diastereoselectivity.
- 建立了反应的广泛基质范围.
- 毫不含糊地阐明了一步骤反应机制,涉及基于银的氧基激活.
结论:
- 开发的白银催化 [2+2] 循环添加提供了一条新且高效的途径,以获得有价值的有机化合物.
- 银在通过复杂化激活基基中起着至关重要的作用,促进了1,4-添加.
- 反应的高选择性和广泛范围使其成为合成化学家的强大工具.
相关概念视频
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.
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.
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.
01:16Cycloaddition Reactions: Overview
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
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01:16[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
01:16Cycloaddition Reactions: MO Requirements for Thermal Activation
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.