安定したカルベノイド種によってボランのB-H結合が容易に活性化される
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
まとめ
高度に電性カルベノイド化合物は,今,ボロン-水素結合に挿入することができ,以前は核性カルベンや金属断片によって達成できなかった反応性があります. この画期的な発見は,合成化学の新たな道を開く.
科学分野:
- 有機金属化学 有機金属化学
- メイングループ 化学
- カタリシス カタリシス カタリシス
背景:
- 安定した核性カルベンは,E=H,SiR3,NH2,PR2のE-H結合活性化において金属の反応性を模倣する.
- ボラン (BH3) のB-H結合に単一の炭素原子または金属断片による挿入は,以前報告されていませんでした.
- ボランの強いルイス酸性は,直接のB-H結合機能化に課題をもたらす.
研究 の 目的:
- 設計された,高度に電性カルベノイドの断片がB-H結合挿入を達成する可能性を調査する.
- 結合活性化に挑戦するために単一の炭素原子で制御された反応性を探求する.
- 実験結果を計算的に検証し,核愛カルベンとの反応性を比較する.
主な方法:
- 新しい,安定した,電性カルベノイド化合物の合成 (4および6).
- カルベノイドとボラン (BH3) の間の反応の実験的調査.
- 密度関数理論 (DFT) の計算により,反応機構とエネルギー学が解明される.
主要な成果:
- 化合物4と6の設計された電性カルベノイド断片は,BH3.3のB-H結合に制御された挿入を成功裏に達成しました.
- これは,BH3 B-H結合に単一の炭素原子が挿入された最初の例を表しています.
- DFTの計算により,実験上の観測が確認され,この変換における核性カルベンの反応性の欠如が強調された.
結論:
- 安定した,高度に電離性のカルベノイド化合物は,BH3 B-H結合への挑戦的な挿入を媒介することができます.
- この反応性は,核性カルベンの惰性と,以前に研究された金属断片と対照的です.
- この発見は,カルベノイド化学の範囲を拡大し,ボロン機能化のための新しい戦略を提供します.
関連する概念動画
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.