亜鉛化ヒドラゾーン,アルケニルボロナート,および電極性の連続結合により,複数の連続したステレオゲンなセンターが形成されます
Masaharu Nakamura1, Takuji Hatakeyama, Kenji Hara
1Department of Chemistry, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. masaharu@chem.s.u-tokyo.ac.jp
Journal of the American Chemical Society
|November 4, 2004
まとめ
新しいワンポット反応は,アルケニルボロナートにステレオ特異的に亜鉛化ヒドラゾンを加えることで複雑な分子を作り出します. この方法は,高ダイアステレオ選択性を持つ有価なガンマボリルヒドラゾンを効率的に生成し,複数のステレオセンターを形成します.
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
- ステレオセレクティブ合成
背景:
- ヒドラゾンは,多用途の合成中間物質です.
- オーガノボロン化合物は,有機合成において極めて重要です.
- ステレオセレクティブ合成は,複雑な分子構造の鍵です.
研究 の 目的:
- ガンマ-ボリルヒドラゾンを合成するための新しいワンポット・メソッドの開発.
- 複数のステレオセンターの形成において,高いステレオ選択性とダイアステレオ選択性を達成する.
- 亜鉛化されたN,N-ジメチルヒドラゾンとアルケニルボロナートをステレオ特異的な合成添加物として利用する.
主な方法:
- E-またはZ-アルケニルボロナートに亜鉛化N,N-ジメチルヒドラゾンのステレオ特異的合成添加.
- ガンマ-Zn/B二金属中間物質の形成.
- 中間物質が炭酸エレクトロフィールと反応する.
主要な成果:
- ガンマ-ボリルヒドラゾンの合成が成功し,生産性が良好でした.
- 優れたダイアステレオ選択性が達成されました.
- ワンポット反応は,2〜4つの連続したステレオジェニックセンターを効率的に生み出します.
結論:
- 開発された方法は,複雑なキラル分子への効率的な経路を提供します.
- このアプローチは,立体選択合成のための強力なツールを提供します.
- この反応は,タンデム反応における亜鉛化ヒドラゾンとオルガノボロナートの有用性を強調しています.
さらに関連する動画
関連する概念動画
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.
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
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.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
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.