Asymmetrische Organokatalyse

Dalko, Peter I.; Moisan, Lionel

doi:10.1002/1521-3757(20011015)113:20<3840::aid-ange3840>3.0.co;2-m

Cited by 321 publications

(22 citation statements)

References 301 publications

(115 reference statements)

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“…[11] For example, the most commonly used organocatalyst, secondary amines, are usually used in combination with a certain acid cocatalyst. [12] Furthermore, many organocatalysts can promote several types of reactions through different activation models.…”

Section: By Multiple Organocatalystsmentioning

confidence: 99%

Recent Advances in Multicatalyst Promoted Asymmetric Tandem Reactions

Zhou

2010

Chemistry An Asian Journal

443

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Dedicated to the 150th anniversary of Japan-UK diplomatic relations FOCUS REVIEWSAbstract: Multicatalyst promoted asymmetric tandem reactions have emerged as a powerful strategy to improve the synthetic efficiency. It enables the synthesis of complex molecules with high selectivity from simple starting materials in an almost biomimetic-like way. The use of multiple catalyst systems can enlarge the substrate and reaction scope for the reaction design, improve the reactivity, and benefit the control of selectivity. In this FocusReview, the current achievement of this promising field is discussed, including the advantages and difficulties of this research, and the strategies applied to address these problems.

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Section: By Multiple Organocatalystsmentioning

confidence: 99%

Recent Advances in Multicatalyst Promoted Asymmetric Tandem Reactions

Zhou

2010

Chemistry An Asian Journal

443

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“…[1] The aromatic substitution reaction (S N Ar) is a fundamental reaction in organic chemistry which normally requires aromatic compounds that have electronwithdrawing substituents to activate the aromatic moiety for nucleophilic attack.…”

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confidence: 99%

Organocatalytic Highly Enantioselective α‐Arylation of β‐Ketoesters

Alemán¹,

Richter²,

Jørgensen³

2007

Angew Chem Int Ed

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Dedicated to Prof. Roald Hoffmann on the occasion of his 70th birthdayDuring the last years, the field of organocatalysis has received much attention and become a powerful tool in the field of organic chemistry.[1] The aromatic substitution reaction (S N Ar) is a fundamental reaction in organic chemistry which normally requires aromatic compounds that have electronwithdrawing substituents to activate the aromatic moiety for nucleophilic attack.[2] A number of nucleophiles can be used, such as carbon-, oxygen-, and amine-type nucleophiles, with aromatic compounds that have electron-withdrawing substituents.[3] Recently, the first asymmetric nucleophilic aromatic substitution was presented, allowing the synthesis of optically active a-aryl-b-ketoesters (Scheme 1, left), [4] by addition of activated b-ketoesters to activated aryl compounds and applying organocatalysis. However, this reaction allows the synthesis of optically active electron-poor aromatic systems only; therefore it is desirable to have a complementary procedure for obtaining a-aryl-b-ketoesters that contain electron-rich aromatic rings (Scheme 1, right). Herein, we present the first organocatalytic enantioselective addition of b-ketoesters to quinones leading to optically active hydroquinones or quinones, depending on the reaction conditions (Scheme 2). Furthermore, we show that this is an easy procedure for the synthesis of optically active a-aryl-bketoesters, in which various transformations of the electron-rich aromatic ring have been performed.Quinones are important compounds which are widely distributed in nature and undergo a number of biochemical transformations. From a biological point of view quinones are significant in many compounds, [5] and furthermore they are also used in industry on the ton scale as dye reagents. As a result of their importance, a large number of reactions have been performed with quinones. One class of reagents which have been widely used for the functionalization of quinones are nucleophiles such as thiols and nitrogen-, oxygen-, halogen-, phosphorus-, and activated methylene-based nucleophiles.[6] In all these cases, the addition has been applied in a racemic version, most likely as a result of the incompatibility of the different asymmetric catalytic metal systems with the redox quinine-hydroquinone system. [7] Thus, we decided to perform the addition of substituted bketoesters to 1,4-naphthoquinone under organocatalysis. We started out by studying the reaction under phase-transfer conditions using cinchona alkaloids. Unfortunately, the reaction failed under these conditions, probably owing to the instability of the quinone-hydroquinone system under the basic aqueous conditions. Therefore, we attempted the reaction of b-ketoester 1 a with 1,4-naphthoquinone (2 a) in the presence of cinchona alkaloids as chiral base catalysts [Eq. (1)].[8] Scheme 1. Synthetic approaches of electron-poor a-aryl b-ketoesters and the complementary electron-rich a-arylation. EWG: electron-withdrawing group; EDG: electrondonating group...

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“…In recent years, organocatalysis has become a powerful tool in the field of organic chemistry. [1] Organocatalysts that possess both an acidic and a basic/nucleophilic structural moiety constitute an increasingly powerful platform for the development of asymmetric catalysis. [2] Among them, the catalytic enantioselective conjugate addition of compounds using organocatalysts with a prochiral nucleophilic carbon atom to a,bsubstituted Michael acceptors provides one of the most versatile and attractive approaches for the generation of optically active compounds.…”

mentioning

confidence: 99%