鉄触媒による1,3-ダイエンの1,4-ヒドロボレーション
Jessica Y Wu1, Benoît Moreau, Tobias Ritter
1Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.
Journal of the American Chemical Society
|August 26, 2009
まとめ
新しい鉄触媒反応により,ダイエンの選択的1,4-ヒドロボレーションが可能になり,高価なガンマ異置換アルリルボランを生成します. この方法では,2-置換されたダイエンから (E) -三置換された二重結合のみが得られます.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 有機金属化学 有機金属化学
- カタリシス カタリシス カタリシス
背景:
- アリルボランは,汎用性の高い合成中間物質です.
- 水酸化反応はC-B結合形成に不可欠である.
- 複雑な分子合成のための選択的触媒方法の開発は,依然として課題です.
研究 の 目的:
- ダイエンの新種の鉄触媒型1,4-ヒドロボレーションを開発する.
- ガンマ変位アリルボランの化学,地域,およびステレオ選択的合成を達成するために.
- 置換ダイエンの水酸化によるステレオ化学的結果を調査する.
主な方法:
- 鉄触媒反応 鉄触媒反応 鉄触媒反応 鉄触媒反応
- 様々なダイエンの1,4-ヒドロボレーション.
- 特定のボロン反応剤の使用.
- NMRスペクトロスコピーやその他の分析技術を用いた製品構造の分析.
主要な成果:
- 化学,地域,およびステレオセレクティブの鉄触媒による1,4-水酸化の成功開発.
- ガンマ変位アルリルボランの合成.
- アリルボラン製品における (E) - 三置換の二重結合の形成は,2置換のダイエネからスタートするときにのみ行われる.
結論:
- 開発された鉄触媒メソッドは,価値あるガンマ非置換アリルボランに効率的なアクセスを提供します.
- この反応は,合成的に有用な,独占的な (E) -ステレオ化学を含む,高い選択性を提供します.
- この方法論は,特定のアルケンの幾何学を含む複雑な有機分子を構築するためのツールキットを拡張します.
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.
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.
02:47Alkynes 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.
01:14Electrophilic 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.
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.
02:34Regioselectivity 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.