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相关概念视频

Base-Catalyzed Ring-Opening of Epoxides02:26

Base-Catalyzed Ring-Opening of Epoxides

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Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
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[3,3] Sigmatropic Rearrangement of Allyl Vinyl Ethers: Claisen Rearrangement01:24

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The Claisen rearrangement is a [3,3] sigmatropic rearrangement of allyl vinyl ethers to unsaturated carbonyl compounds. The rearrangement is a concerted pericyclic reaction proceeding via a chair-like transition state.
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Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)01:16

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

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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...
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Acid-Catalyzed Ring-Opening of Epoxides02:24

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Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
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ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

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All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
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Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry01:29

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Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
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通过vinyl carbocation中间体访问中等尺寸的环.

Zhenqi Zhao1, Stasik Popov2, Woojin Lee2

  • 1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.

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概括

合成中型环 (8-11个成员) 是很困难的. 本研究介绍了一种利用乙烯基碳酸中间体的催化方法,通过弗里德尔-克拉夫茨反应有效形成8和9个成员的环.

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科学领域:

  • 有机化学 有机化学
  • 合成化学 合成化学

背景情况:

  • 与较小的环 (5-7个成员) 相比,中型环 (8-11个成员) 由于环应变而存在合成挑战.
  • 中型碳循环的高效构造仍然是有机合成的一个关键目标.

研究的目的:

  • 开发一种新的催化方法,用于合成8和9个环的环.
  • 为了克服与中型环形形成相关的合成困难.

主要方法:

  • 使用分子内弗里德尔 - 克拉夫特反应.
  • 用催化方式产生乙烯基碳化介质.
  • 使用易斯酸性离子-弱协调性离子盐来电离乙烯二硫酸盐.

主要成果:

  • 成功的催化形成了8和9个成员的环.
  • 展示了一条通往中型碳轮车的新途径.
  • 该方法通过乙烯基碳化介质进行.

结论:

  • 一种新的催化方法可以有效地合成中型环.
  • 开发的方法克服了中型环形建筑中常见的挑战.
  • 这项工作为访问8个和9个成员的碳轮车提供了一个有价值的工具.