((II) 催化选择性的分子内 [2 + 2 + 2] 基环氧三聚化
Yoshihiko Yamamoto1, Takayasu Arakawa, Ryuji Ogawa
1Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan. yamamoto@apchem.nagoya-u.ac.jp
Journal of the American Chemical Society
|October 2, 2003
概括
催化使1,6-二烯与单二烯的化学选择性反应能够形成双循环衍生物. 这种方法为不对称的diynes提供了出色的区域选择性,也可以实现分子内循环三聚化.
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:
- 复合物是有机合成中的多功能催化剂.
- 循环添加反应是构建循环有机分子的基础.
- 替代衍生物的高效合成仍然是一个关键的挑战.
研究的目的:
- 开发一种新催化方法,用于合成双环衍生物.
- 研究涉及不对称的1,6-diynes和monoalkynes的循环添加反应的区域选择性.
- 探索这种催化系统在分子内基因循环三聚化中的应用.
主要方法:
- 用Cp*RuCl(cod) 的方法,对1,6-二因与单基因进行催化反应.
- 通过X射线分析合成和结构性表征一个ruthenabicycle复合体.
- 密度函数理论 (DFT) 研究以阐明反应机制.
主要成果:
- 在良好的产量中,从1,6-diynes和monoalkynes中产生双循环衍生物的化学选择性形成.
- 观察到高区域选择性不对称的diynes的循环添加,产生元替代产品.
- 成功地进行了triynes的分子内循环三元化,形成三环芳香化合物.
- 一个关键的ruthenacycle中间体的隔离和表征.
结论:
- Cp*RuCl ((cod) 是二烯-基因循环添加和三烯循环分离的有效催化剂.
- 开发的协议容纳了广泛的功能组.
- 反应机制涉及氧化循环转化为鲁特纳环中间体,然后再插入基.
相关概念视频
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
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.
01:17Thermal 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.
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
![[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2Ffiles%2Fmedia%2Fscience-education%2Fscience-education-thumbs%2F12417.jpg&w=3840&q=75)
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.
01:12Cycloaddition 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.