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产生和捕获环乙烯金物种:四种通往多环化合物的途径
Gilles Lemière1, Vincent Gandon, Kevin Cariou
1UPMC Paris 06, Laboratoire de Chimie Organique (UMR CNRS 7611), Institut de Chimie Moléculaire (FR 2769), case 229, 4 place Jussieu, F-75252 Paris cedex 05, France.
Journal of the American Chemical Society
|February 13, 2009
概括
从乙烯烯中获得的黄金碳经历了多种变化. 这项研究探讨了它们的反应选择性,使得复杂分子的合成成为可能,包括天然产品Delta-capnellene.
科学领域:
- 有机金属化学 有机金属化学
- 有机合成 有机合成
- 计算化学计算化学
背景情况:
- 乙烯可以通过类似纳扎罗夫的机制形成环乙烯金复合体.
- 这些黄金碳是多功能中间体,能够经历多个反应路径.
研究的目的:
- 为了研究黄金碳化合物的不同转变的选择性.
- 利用这些发现来有效合成复杂的分子架构.
- 将开发的方法应用于德尔塔912)) - 烯的总合成.
主要方法:
- 纳扎罗夫式循环化乙烯来形成黄金碳.
- 探索四种不同的反应途径:电友性循环化,C-H插入,C-C迁移和质子转移.
- 密度函数理论 (DFT) 计算以阐明反应机制.
主要成果:
- 这项研究系统地分析了四个碳化合物转化途径的选择性.
- 获得了有关这些反应结果的关键因素的关键见解.
- 该方法被成功地应用到达达尔塔912)) -capnellene的总合成.
结论:
- 了解碳反应性,可以对多环框架进行受控的合成.
- 黄金催化反应为复杂的自然产品提供了一条有效的途径.
- DFT计算为合成规划提供了有价值的机制理解.
相关概念视频
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.
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
01:18Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...
01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.