地域選択的にトリシル化されたヘクソピラノシドは,同質的に触媒化されたシランアルコヒロシスを介して発生する
Mee-Kyung Chung1, Marcel Schlaf
1The Guelph-Waterloo Centre for Graduate Work in Chemistry (GWC), Department of Chemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Journal of the American Chemical Society
|December 22, 2005
まとめ
イリジウム触媒は,炭水化物の地域選択的シリレーションを可能にし,貴重なグリコシド誘導体を生成します. この方法では,二酸化炭素と三酸化炭素化合物が効率的に生成され,炭水化物の改変のための新しい経路を提供します.
科学分野:
- 有機金属化学 有機金属化学
- 炭水化物化学 炭水化物の化学
- カタリシス カタリシス カタリシス
背景:
- シリレーションは,炭水化物の改変における重要なステップです.
- 炭水化物の合成には,効率的で地域選択的なシリレーション方法の開発が不可欠である.
研究 の 目的:
- 炭水化物の地域選択的二・三化のためのイリジウム複合体の触媒的活性を調べる.
- 様々な炭水化物誘導体に対するこの触媒システムの範囲と効率を調査する.
主な方法:
- イリジウム複合体の反応とDMA中のテルトブチルジメチルシラン.
- メチルヘクソピラノシド,ベータ-1,6-アンヒドロヘクソピラノシド,および1,3,5-O-メチリデネイノシトールのカタリティック・レジオセレクティブ・ディ・およびトリシル化.
- クロマトグラフィックおよびスペクトロスコピーによる反応製品の分析.
主要な成果:
- イリジウム触媒は,様々な炭水化物の地域選択的二酸化と三酸化を効果的に促進する.
- 2,3,6-シリル化イソマーの出力は,単一ポット反応では,47~89%,2,4,6-イソマーの出力は9~25%であった.
- マノサン,ギャラクトサン,1,3,5-O-メチリデネ・イノシトール,およびパシリライテッド・レボグルコサンの2,4-デシリライテッド誘導体では,高収量 (>85%) が達成されました.
- 均質な触媒は,ナノ粒子触媒とは異なり,高収量には極めて重要です.
結論:
- 開発されたイリジウム触媒方式は,炭水化物の地域選択性シリレーションのための効率的な経路を提供します.
- このアプローチは,複雑なシライ化炭水化物誘導体を合成するための貴重なツールを提供します.
- この研究は,この変換のための高効率を達成するために,均質な触媒の重要性を強調しています.
関連する概念動画
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.
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.
02:26Preparation and Reactions of Sulfides
Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
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.