カーベン安定化ボラボリエンの生成とそのC-H結合への挿入
Philipp Bissinger1, Holger Braunschweig, Alexander Damme
1Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
Journal of the American Chemical Society
|October 29, 2011
まとめ
研究者らは,新しい5基のボラサイクルを合成し,新しいNHCアダクトのdihalodiborane ((4)) とKC ((8) の還元を用いた. これは,NHCで安定したボラボリレン中間体によるC-H挿入を伴う可能性が高い.
科学分野:
- オルガノボロン化学 オルガノボロン化学
- メイングループ 化学
- カルベンの化学反応
背景:
- N-ヘテロサイクリックカルベン (NHCs) は,主要グループ化学における多用途リガンドである.
- ディボラン (((4) 化合物は,ユニークな反応経路を提供しています.
- 低値ボロン種の安定化は,活発な研究分野である.
研究 の 目的:
- 新しい5つ組のボラサイクルを合成し,特徴づけること.
- ディハロディボランのNHC添加物の反応性を調査する.
- ボラサイクルの形成のメカニズムを解明する.
主な方法:
- ディハロディボランの新しいNHCアダクトの反応 ((4)) とKC ((8)).
- 結果として得られるボラサイクルの製品の特徴.
- 反応経路を提案するメカニズム研究.
主要な成果:
- 新しい5基のボラサイクル (化合物2) の合成が成功しました.
- この反応は,KCによってダイハロディボランアダクト (化合物1) の還元によって進行する (8).
- 証拠は,NHCで安定した自由ボラ-ボリレン中間物質が関与していることを示唆しています.
結論:
- 5つ構成のボラサイクルのための新しい合成経路が確立されました.
- この研究は,反応性ボロン種を安定させるためのNHCリガンドの有用性を強調しています.
- C-H挿入を含む提案されたメカニズムは,ボロン-カルベン相互作用の洞察を提供します.
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
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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.
02:46Halogenation of Alkenes
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
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02:10Carbocations
Carbocations are one of the reaction intermediates formed during several nucleophilic substitutions or elimination reactions. A carbocation is an electron-deficient species with the central carbon atom having six electrons and three bonded atoms. The central carbon in a carbocation is sp2 hybridized with trigonal planar geometry. It has an empty p orbital perpendicular to the plane of the structure that can accept electrons. Thus, carbocations act as strong electrophiles and may react with any...
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...
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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.
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