一个关于2-pyrones和alkynylboranes的易斯基导向循环添加的机制研究
Damien F P Crépin1, Joseph P A Harrity, Julong Jiang
1Department of Chemistry, University of Sheffield , Sheffield S3 7HF, U.K.
Journal of the American Chemical Society
|May 24, 2014
概括
这项研究表明,基基化酸盐和BF3·OEt2显著加快迪尔斯-阿尔德反应,产生具有高区域控制的功能化芳香物. 该机制涉及易斯酸协调和产品平衡.
科学领域:
- 有机化学 有机化学
- 催化剂是一种催化剂.
- 反应机制 反应机制
背景情况:
- 迪尔斯-阿尔德反应是有机合成中的一个基本的循环添加反应.
- 功能化芳香化合物在制药和材料科学中至关重要.
- 控制循环添加的区域选择性仍然是一个关键的挑战.
研究的目的:
- 为了研究基和2-皮龙的迪尔斯-阿尔德反应中的速度增强.
- 探索使用基酸酸盐和易斯酸来提高反应效率.
- 阐明观察到的速度加速和区域控制背后的机制.
主要方法:
- 使用基化三酸和三化乙酸 (BF3·OEt2) 作为一种催化系统.
- 使用密度函数理论 (DFT) 计算来研究反应途径.
- 分析机械见解和替代的易斯酸促进剂的实验证据.
主要成果:
- 在测试条件下,在Diels-Alder反应中观察到显著的速度增强.
- 反应成功地产生了功能化芳香化合物,具有完全的区域控制.
- DFT研究表明了一种机制,涉及基质协调到基中间体和易斯酸介导平衡.
- 发现了替代的易斯酸可以进一步促进循环添加.
结论:
- 基酸和BF3·OEt2的组合提供了一种高效的方法来合成功能化的芳香化合物.
- 涉及易斯酸协调和产品平衡的拟议机制解释了观察到的速率提升.
- 这种方法为有机化学中的区域选择性合成提供了有价值的工具.
相关概念视频
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
19.7K
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.
19.7K
03:08Hydroboration-Oxidation of Alkenes
10.0K
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
10.0K
01:16Cycloaddition Reactions: Overview
2.4K
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.
2.4K
01:16Cycloaddition Reactions: MO Requirements for Thermal Activation
29.7K
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
29.7K
02:36Regioselectivity and Stereochemistry of Hydroboration
7.8K
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
7.8K
02:38Electrophilic Addition to Alkynes: Halogenation
7.3K
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.
7.3K