Highly Enantioselective Organocatalyzed Construction of Quaternary Carbon Centers <i>via</i> Cross‐Aldol Reaction of Ketones in Water

Zheng, Changwu; Wu, Yuanzhao; Wang, Qianqian; Zhao, Gang

doi:10.1002/adsc.200800248

Cited by 74 publications

(48 citation statements)

References 94 publications

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“…Catalyst with longer or shorter alkyl chains gave lower results pointing out the importance of the alkyl chain length to generate the emulsion need for the reaction to proceeded [283].…”

Section: Aldehydes As Source Of Nucleophilementioning

confidence: 99%

Organocatalyzed Aldol Reactions

Guillena¹

2013

Modern Methods in Stereoselective Aldol Reactions

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The use of catalytic enantioselective methods to perform an aldol reaction provides a direct entry for the synthesis of chiral compounds and is probably the most attractive way to achieve this goal with high control of the chemo-, regio-, diastereo-, and enantioselectivity. The application of biochemical methods based on enzyme aldolases or antibodies, which are discussed in other chapters, avoid the use of preformed enolates or their equivalents for enhancing the global atom efficiency of the process [1] for which the narrow substrate scope is a major drawback. The discovery of methodologies to carry out the enantioselective direct aldol reaction [2] has eluded the production of stoichiometric by-products increasing the substrate scope. This task could be accomplished by using small molecules as catalysts, such as metal complexes (which are covered along this book) and organic molecules, also known as organocatalysts [3]. The growth of this last research area and the direct aldol reaction are closely linked [4], with the report on the use of (S)-proline as catalyst for the intermolecular aldol [5] definitely being the push for the development of the organocatalytic methods as a competitive methodology for the synthesis of chiral compounds.In a strict sense, an organocatalyzed reaction is a process in which all the involved reagents and catalysis are purely organic compounds of low-molecular weight, excluding boron-and silicon-containing derivatives. However, in some cases, the presence of a silyl group only plays a steric role and therefore can also be considered as an organocatalyzed process. Also, if the organocatalyst involved in a reaction is immobilized in a polymer, a dendrimer, or even an inorganic material that serves only as a support to facilitate its recovery [6], it could still be considered as an organocatalyst, although those types of derivatives have been scarcely used in the natural product synthesis and therefore will be excluded from this chapter. Therefore, a comprehensive overview of the direct aldol reaction [7], emphasizing the reactivity, scope, selectivity, and limitations of the methodology and giving several examples of their application to the synthesis of biologically active compounds, is discussed in this chapter.

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“…Catalyst with longer or shorter alkyl chains gave lower results pointing out the importance of the alkyl chain length to generate the emulsion need for the reaction to proceeded [283].…”

Section: Aldehydes As Source Of Nucleophilementioning

confidence: 99%

Organocatalyzed Aldol Reactions

Guillena¹

2013

Modern Methods in Stereoselective Aldol Reactions

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“…[39] They investigated several catalysts in the aldol reaction in the presence of water showing that the most effective were proline derivatives with a hydrophobic moiety such as trans-siloxy-l-proline or cis-siloxy-dproline. [40] Hayashi also reported the use of 4-substituted acyl-A C H T U N G T R E N N U N G oxyproline derivatives, such as compound 6, for the enantioselective aldehyde cross-aldol reaction with excellent results without the need of additional co-solvent or additives (Scheme 10). Indeed, poor results were obtained when neat reaction conditions or dry organic solvents were employed.…”

Section: Prolines Substituted In the 4-positionmentioning

confidence: 99%

Water in Stereoselective Organocatalytic Reactions

2009

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In this review, recent advances in asymmetric organocatalytic reactions carried out with variable amounts of water, from substoichiometric to a large excess (reaction medium), are discussed. We also summarize several proposed mechanisms for the different possibilities of the action of water both in the increased activity of the catalyst and in the asymmetric induction. Finally, the application of this catalytic methodology to the enantioselective synthesis of valuable compounds through enamine or iminium catalysis is presented.

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“…Addition of water to the brine raised reaction rate considerably, but it had a negative effect both on yield as well as enantioselectivity [11]. Zhao found that Hayashi's catalyst C5 is effective also for cross aldol reaction of ketones with , -unsaturated keto esters (Scheme 3) [12].…”

Section: Aldol Reactions In Watermentioning

confidence: 98%

Organocatalytic Reactions Under Unusual Conditions

Tomá¹,

Šebesta²,

Mečiarová

2011

COC

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Organocatalyzed reactions can often be advantageously performed in non-traditional reaction media. Use of ionic liquids, water or brine often leads to improved yields and selectivities of organocatalytic transformations. In terms of energy source, organocatalyzed reactions can be significantly accelerated by microwave irradiation, ultrasound or high pressure. Reactions without solvent and performed in ball mills are also reviewed.

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Highly Enantioselective Organocatalyzed Construction of Quaternary Carbon Centers via Cross‐Aldol Reaction of Ketones in Water

Cited by 74 publications

References 94 publications

Organocatalyzed Aldol Reactions

Organocatalyzed Aldol Reactions

Water in Stereoselective Organocatalytic Reactions

Organocatalytic Reactions Under Unusual Conditions

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