催化 [4 + 2] 循环添加与基因的阴离子
Ichiro Koyama1, Takuya Kurahashi, Seijiro Matsubara
1Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
Journal of the American Chemical Society
|January 29, 2009
概括
一种新的催化反应使得从和中合成多替代的. 该机制涉及介导的氧化循环和插入,形成一个关键的氧-循环中间体.
科学领域:
- 有机金属化学 有机金属化学
- 有机合成 有机合成
- 催化剂是一种催化剂.
背景情况:
- 皮兰是重要的异环化合物,存在于许多天然产品和药品中.
- 在有机化学中,高效的合成方法用于构建多替代型皮兰是非常受欢迎的.
- 催化为开发新型碳-碳和碳-异原子键形成反应提供了一个多功能平台.
研究的目的:
- 开发一种新的催化 [4 + 2] 循环添加反应.
- 通过使用易于获得的和基因原料合成多替代.
- 阐明拟议的催化循环的机械路径.
主要方法:
- 采用催化剂,用于和之间的 [4 + 2] 循环添加反应.
- 使用标准光谱技术 (NMR,质谱) 进行反应产品的表征.
- 计算研究和中间陷实验,以支持机械的建议.
主要成果:
- 在和之间成功开发了催化 [4 + 2] 循环添加反应.
- 获得了各种多重置换型皮兰的高产量.
- 提出了一种可能的反应机制,涉及氧化循环,基内插入和还原性消除,其中包括一个氧-环中间体.
结论:
- 开发的催化反应提供了一条有效的途径,以多替代的pyrans.
- 机理学研究为介导的循环添加过程提供了宝贵的见解.
- 这种方法扩大了合成有价值的异环化合物的工具包.
相关概念视频
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.
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
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.
01:26Synthesis of α-Substituted Carbonyl Compounds: The Stork Enamine Reaction
α-Substituted ketones or aldehydes can be synthesized from enamines by the Stork enamine reaction, named after its pioneer Gilbert Stork. Enamines are useful synthetic intermediates where the lone pair on nitrogen is in conjugation with the C=C bond. They resemble enolate ions, as the resonance forms of both species have a nucleophilic α carbon.
02:27Preparation of Alkynes: Alkylation Reaction
Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
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.