サイクロプロパネスのイリジウム触媒によるC-Hボリル化
Carl W Liskey1, John F Hartwig
1Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States.
Journal of the American Chemical Society
|February 21, 2013
まとめ
この研究では,サイクロプロパンの新しいイリジウム触媒性ボリル化が報告され,メチレンC-H結合を選択的に機能化する. その結果生じるサイクロプロピルボロナートエステルは,様々なサイクロプロパン誘導体を合成するための多用途の中間物質です.
科学分野:
- 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
- オーガニック・シンセシス オーガニック・シンセシス
背景:
- サイクロプロパンは,独特の反応性を持つ3つ構成のリングを張っています.
- C-H結合の機能化は,効率的な合成経路を提供します.
- サイクロプロパン改変のための選択的触媒方法の開発は極めて重要です.
研究 の 目的:
- サイクロプロパネスの直接ボリル化のための新しい触媒システムを開発する.
- ボリレーション反応の選択性を調査する.
- ボリル化サイクロプロパン製品の合成的有用性を実証するために.
主な方法:
- イリジウム触媒,特に (η(6) -mes) IrBpin3 または [Ir(COD) OMe]2 を用いて,フェナントロリンリガンドと組み合わせる.
- ボリル化反応を最適化された条件下で実行する.
- ボリル化製品の特徴とその後の変換について.
主要な成果:
- サイクロプロパンにおけるメチレンC-H結合の選択的ボリル化が達成され,メチンとメチルC-H結合を上回った.
- 2,9-Me2phenanthrolineをリガンドとして使用する際に高いダイアステレオ選択性が観察されました.
- 生成されたサイクロプロピルボロナートエステルは,トリフローロボラート塩,ボロン酸,サイクロプロピラレン,サイクロプロピラミン,サイクロプロパノールを含む様々な有価な化合物に成功裏に変換されました.
結論:
- 開発されたイリジウム触媒型ボリレーションは,サイクロプロパネスを機能化するための効率的で選択的な方法を提供します.
- この方法論は,さまざまなサイクロプロパン誘導体にアクセスするための合成ツールボックスを拡張します.
- サイクロプロピルボロナートエステルの多用途性は,合成中間物質としての重要性を強調しています.
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.
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.
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.
02:46Halogenation 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.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
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.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.