機能化された1,1-非置換オレフィンのRh触媒による非対称な水酸化
Xiao Wang1, Stephen L Buchwald
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Journal of the American Chemical Society
|November 1, 2011
まとめ
研究者らは,1,1-非置換オレフィンに対して,ロジウム触媒による新型水酸化法を開発した. この技術は,特定のフォスフィンリガンドを使用して,ベータキラリティを持つ線形アルデヒドを効率的に生成します.
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:
- ハイドロフォームミレーションはアルデヒドを合成するための重要な工業プロセスです.
- 1,1-非置換オレフィンの水酸化で高いエナンチオセレクティビティを達成することは,依然として重要な課題です.
- 非対称合成のための効率的な触媒システムの開発は,キラル分子の生産に不可欠です.
研究 の 目的:
- 1,1-非置換オレフィンのロジウム触媒化水酸化のための最初の高度なエナンチオセレクティブ法を確立する.
- 水酸化過程中のステレオ化学を制御するP-キロゲンリンヒリンリガンドの有用性を調査する.
主な方法:
- 水酸化反応のためにロジウム触媒を用いた.
- P-キロゲン性フォスフィンリガンド,特にBenzP*とQuinoxP*を用い,エナチオ選択性を誘導する.
- 化学的および地域選択性を最適化するために反応条件を調査した.
主要な成果:
- 1,1-非置換オレフィンの高度なエナチオセレクティブ性ロジウム触媒化水酸化のための方法を成功裏に開発しました.
- ベータ・キラリティを持つ線形アルデヒドの形成において高いエナチオセレクティビティを達成した.
- 触媒過程で良好な化学的および地域選択性を示した.
結論:
- 開発された方法は,非対称的水酸化成形における重要な進歩を表しています.
- BenzP* と QuinoxP* のようなP-キロゲンリンリンガンドは,この変換のエナチオ選択性を制御するのに有効です.
- この研究は,キラル線形アルデヒドの合成のための貴重な経路を提供します.
さらに関連する動画
関連する概念動画
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...
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.
02:35Electrophilic 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.
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.