イリジウム触媒によるバイシクロアルケネスの分子間非対称性ヒドロテロアリレーション
Christo S Sevov1, John F Hartwig
1Division of Chemical Sciences, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Journal of the American Chemical Society
|January 26, 2013
まとめ
この研究は,非対称な水素アリレーションのための新しい触媒的方法を導入し,インドールやチオフェンなどのヘテロアレンを高収量とエナチオセレクティブ性で直接アルキル化することを可能にします. 反応は中性条件下で進行し,従来の酸触媒方法の補完的なアプローチを提供します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- カタリシス カタリシス カタリシス
- アシンメトリック・シンセシス
背景:
- 触媒性水酸化は,軽度な条件下でC-H結合の機能化のための経路を提供します.
- 既存の方法は,しばしば地域選択性が欠けているか,または厳しい酸性条件を必要とする.
- 直接的,選択的なヘテロアレンアルキル化のための触媒システムを開発することは非常に望ましい.
研究 の 目的:
- ヘテロアレンC-H結合の分子間非対称な添加をバイシクロアルケーンに開発する.
- ヘテロアレンアルキル化で高収量とエナティオメール過剰を達成するために.
- 酸触媒反応の補完的な地域選択性を探求する.
主な方法:
- C-H結合の活性化のために中性イリジウム (((I)) 触媒を使用した.
- 電気愛好性パートナーとしてバイサイクロアルケンを使用した.
- インドル,チオフェン,ピロール,フランを含む様々なヘテロアレンとの反応を調査した.
主要な成果:
- 高収量と,分子間添加における高エナティオメア過剰を達成した.
- 保護されていないインドルでさえも,ヘテロ原子への地域選択性アルキル化オルトーが実証されています.
- オレフィンの横のC-H結合の結合添加が観察されました.
結論:
- ヘテロアレンの非対称な水素アリレーションのための新しい触媒システムを開発した.
- この方法は,独特の選択性を持つ酸触媒反応に補完的な戦略を提供します.
- 機械学的研究は,C-H酸化添加が触媒サイクルの最初のステップであることを示しています.
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.
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
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.
02:34Regioselectivity 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.
01:25Radical Anti-Markovnikov Addition to Alkenes: Overview
The addition of hydrogen bromide to alkenes in the presence of hydroperoxides or peroxides proceeds via an anti-Markovnikov pathway and yields alkyl bromides.