不安定なボロン酸に対する一般的な解決策は,空気に安定したMIDAボロナートからゆっくりと放出するクロスカップリングです
David M Knapp1, Eric P Gillis, Martin D Burke
1Roger Adams Lab, Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Journal of the American Chemical Society
|May 2, 2009
まとめ
不安定なボロン酸は,現在,貯蔵され,効果的に使用することができます. 新しい方法により,安定したMIDAボロナートからゆっくりと放出され,様々な化学合成のための効率的なクロスカップリング反応が可能です.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 合成化学 合成化学とは
- 薬用化学 薬用化学について
背景:
- 2-ヘテロサイクリック,ビニル,サイクロプロピルなどの多くの価値あるボロン酸派生物は,固有の不安定性を表しています.
- この不安定性は,実験室での実用的な有用性を制限し,ベンチトップの貯蔵を制限し,クロスカップリング反応の効率的な参加を妨げます.
研究 の 目的:
- 様々なボロン酸誘導体の不安定性を克服するための一般的で堅固な方法を開発する.
- 不安定なボロン酸を,有機合成のための耐久性があり容易に使用可能な構成要素に変換する.
主な方法:
- この研究は,不安定なボロン酸の局所緩やかな放出を含む新しいアプローチを導入しています.
- この放出は,その対応するN-メチリミノアセティック酸 (MIDA) ボロナート前駆体から達成され,それらは空気に安定しています.
主要な成果:
- 開発された方法は,以前に不安定なボロン酸の3つのクラス: 2-ヘテロサイクリック,ビニル,およびサイクロプロピル誘導体を安定させることに成功しました.
- これらの安定したボロン酸は,MIDAボロナートから in situ で生成され,非常に効果的な構成要素として機能します.
- 彼らは,多様なアリル塩化物とヘテロアリル塩化物との効率的なクロスカップリング能力を実証しています.
結論:
- MIDAボロナートからのin situ緩解戦略は,不安定なボロン酸を扱うための一般的な解決策を提供します.
- このアプローチにより,これらの重要な合成中間物質のアクセシビリティと有用性が著しく向上します.
- この方法は,挑戦的なボロン酸基板を含むクロスカップリング反応の範囲を拡大します.
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.
01:14Crossed Aldol Reaction Using Weak Bases
This lesson deals with the crossed aldol reaction using weak bases. The self-condensation of an aldehyde having α hydrogen is prevented by adding it slowly to a mixture of formaldehyde and weak bases like hydroxide and alkoxide. Upon slow addition of the aldehyde, the base deprotonates the α carbon of the aldehyde to form the corresponding enolate. The enolate subsequently attacks the formaldehyde to form a single crossed product. Figure 1 depicts the aforementioned reaction.
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...
01:14Alkylation of β-Diester Enolates: Malonic Ester Synthesis
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.