易于通过稳定的碳类物种激活的B-H键
Hadrien Heuclin1, Samuel Y-F Ho, Xavier F Le Goff
1Laboratoire Hétéroéléments et Coordination, Ecole Polytechnique, CNRS, Route de Saclay, 91120 Palaiseau, France.
Journal of the American Chemical Society
|June 8, 2013
概括
高电友性碳化物化合物现在可以插入-键,这种反应性以前无法通过核友性碳或金属碎片来实现. 这一突破为合成化学开辟了新的途径.
科学领域:
- 有机金属化学 有机金属化学
- 主群 化学 化学
- 催化剂是一种催化剂.
背景情况:
- 稳定的核性碳基在E-H键激活中模仿金属反应性 (E = H,SiR3,NH2,PR2).
- 之前没有报道过单个碳原子或金属碎片将 (BH3) 插入到 (BH3) 的BH键中.
- 的强烈的易斯酸性对直接的B-H键功能化提出了挑战.
研究的目的:
- 为了研究设计的,高度电友的碳化物碎片的潜力,以实现B-H键插入.
- 探索单个碳原子的受控反应性,以挑战键激活.
- 通过计算验证实验结果,并将反应性与核性碳化合物进行比较.
主要方法:
- 新型,稳定,电友性碳化物化合物的合成 (4和6).
- 实验调查碳酸和 (BH3) 之间的反应.
- 密度函数理论 (DFT) 计算以阐明反应机制和能量学.
主要成果:
- 在化合物4和6中设计的电友性碳化物碎片成功地实现了对BH3.3的B-H键的受控插入.
- 这是第一次将单个碳原子插入到BH3B-H键中.
- DFT的计算证实了实验观察结果,并强调了核碳酸在这种转化过程中缺乏反应性.
结论:
- 稳定,高度电友的碳化物化合物可以调解具有挑战性的插入到BH3B-H键中.
- 这种反应性与核性碳化合物和以前研究的金属碎片的惰性形成鲜明对比.
- 这些发现扩大了碳化合物化学的范围,并为功能化提供了新的策略.
相关概念视频
03:08Hydroboration-Oxidation of Alkenes
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.
02:36Regioselectivity and Stereochemistry of Hydroboration
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 stereochemistry.
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 stereochemistry.
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.
01:17Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene
The electrophilic addition of hydrogen halides such as HBr to alkenes and nonconjugated dienes gives a single product as per Markovnikov’s rule.
02:15Preparation of Alcohols via Addition Reactions
Overview
The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
01:14Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.