末端アセチレンのロジウム触媒によるアンチ・マルコヴニコフ分子間ヒドロアルコキシル化
Masataka Kondo1, Takuya Kochi, Fumitoshi Kakiuchi
1Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan.
Journal of the American Chemical Society
|December 15, 2010
まとめ
この研究は,末端アルキンおよびアルコールからエノールエーテルを生成するための新しいロジウム触媒反応を導入しています. この無塩基法により,高収量とZ選択性が得られ,新しい合成経路が提供されます.
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
- 合成方法論 合成方法論
背景:
- アルキンのヒドロアルコキシル化は,有機合成における重要な変換である.
- 既存の方法は,しばしば厳しい条件や特定の指導グループを必要とします.
- 効率的で選択的な分子間ヒドロアルコキシル化の開発は依然として課題です.
研究 の 目的:
- ターミナルアルキネの新種のトランジション金属触媒型分子間ヒドロアルコキシル化を開発する.
- アルコールのアンチマルコヴニコフ的添加をアルキンC-C三重結合の横断で達成する.
- 未知の8-キノノリノラトロジウム複合体の触媒としての有用性を調査する.
主な方法:
- 8キノノリノラトロジウム複合体を触媒として利用する.
- 末端アルキン (アリル,アルケニル,アルキラセチレン) とアリファティックアルコールとの反応.
- 塩基のない条件下で反応を実行する.
主要な成果:
- 終末アルキンの最初の移行金属触媒抗マルコフニコフ分子間水酸化を成し遂げた.
- 生産されたエノールエーテルが,高収量で作られる.
- ほとんどの場合,高いZ選択性を示した.
- シンプルで,まだ十分に活用されていない,8-キノノリノラトロジウム触媒の有効性を示しました.
結論:
- 開発されたロジウム触媒反応は,エノールエーテルを合成するための効率的で選択的な方法を提供します.
- この塩基のないアプローチは,アルキンの機能化の範囲を拡大します.
- 8-キノノリノラトロジウム複合体は,複雑な有機変異のための有望な触媒である.
関連する概念動画
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.
01:25Radical 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.
01:17Radical Anti-Markovnikov Addition to Alkenes: Mechanism
The reaction of hydrogen bromide with alkenes in the presence of hydroperoxides or peroxides proceeds via anti-Markovnikov addition. The radical chain reaction comprises initiation, propagation, and termination steps.
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
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
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.
02:35Regioselectivity of Electrophilic Additions-Peroxide Effect
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.