在CpRu(CH(3) CN)(3) PF(6) 中的机械二分法催化了其他循环异构化
1Department of Chemistry, Stanford University, Stanford, California, 94305,USA.
Journal of the American Chemical Society
|May 2, 2002
概括
埃尼因的鲁催化循环异构化有效地形成了五个和六个成员的环. 在动物中引入四元中心会通过不同的机制形成七个环.
科学领域:
- 有机化学 有机化学
- 有机金属化学 有机金属化学
- 催化剂是一种催化剂.
背景情况:
- enynes是有机合成中的多功能构建块.
- 催化剂对于介导的循环反应是有效的.
- 在循环异构反应中控制环形大小是一个关键的合成挑战.
研究的目的:
- 为了研究1,6-和1,7-enynes的催化循环异构化.
- 探索结构修改,特别是四元中心对反应结果和机制的影响.
- 阐明这些循环异构反应中涉及的机械路径.
主要方法:
- 在中性条件下使用催化剂的循环异构化反应.
- 采用各种替代的1,6和1,7和酸.
- 机械学研究,包括对进行标记,以探测反应中间体.
主要成果:
- 1,6-和1,7-enynes的催化循环异构化有效地产生了五和六个成员的环.
- 在基和基部分上具有多种替代物的enynes是兼容的.
- 在一个1,6-enynoate的propargylic位置引入一个四元中心的结果形成一个七个成员的环在高产量.
- 机械学研究揭示了不同的途径:简单的恩因和C-H插入的ruthenacyclopentene介质,形成一个pi-allylruthenium介质的enynoates.
结论:
- 催化提供了一种温和而高效的方法,用于从中合成各种循环结构.
- 与基邻的四元中心的存在显著改变了反应机制和产品选择性.
- 了解该机制的结构依赖性,可以针对不同的环形大小进行有针对性的合成.
相关概念视频
02:05Prochirality
The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:17Electrophilic Aromatic Substitution: Friedel–Crafts Alkylation of Benzene
Friedel–Crafts reactions were developed in 1877 by the French chemist Charles Friedel and the American chemist James Crafts. Friedel–Crafts alkylation refers to the replacement of an aromatic proton with an alkyl group via electrophilic aromatic substitution. A Lewis acid catalyst such as aluminum chloride reacts with an alkyl halide to form a carbocation. The resulting carbocation then reacts with the aromatic ring and undergoes a series of electron rearrangements before giving the final...
01:13Olefin Metathesis Polymerization: Overview
Recently, the development of olefin metathesis polymerization advanced the field of polymer synthesis. Simply put, the reorganization of substituents on their double bonds between two olefins in the presence of a catalyst is known as the olefin metathesis reaction. The use of metathesis reaction for polymer synthesis is called olefin metathesis polymerization.
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a...
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a...
01:16Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)
Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...