Synthesis of Chiral Organocatalysts derived from Aziridines: Application in Asymmetric Aldol Reaction

Gandhi, Shikha; Singh, Vinod K.

doi:10.1021/jo8019863

Cited by 94 publications

(28 citation statements)

References 58 publications

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“…Initially, various solvents were screened with 3a at room temperature. It was found that brine [43][44][45][46] was the more suitable reaction medium (entry 6). Higher stereoselectivity and diastereoselectivity were obtained in brine compared to organic solvent (entry 1-5).…”

Section: Resultsmentioning

confidence: 99%

l-Valine Dipeptide Organocatalysts with Two Amide Units for the Direct Asymmetric Aldol Reaction in Brine

Huang

Tian

et al. 2011

Catal Lett

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A series of valine dipeptide organocatalysts containing a primary amine group and two amide units have been developed and evaluated in the direct asymmetric intermolecular aldol reaction of 4-nitrobenzaldehyde and cyclohexanone. When 2,4-dinitrophenol (DNP) was used as an acidic additive, the catalyzed reactions of various aldehydes and ketones gave the corresponding aldol products with moderate to high enantioselectivities (up to 95%) and diastereoselectivities (up to [99/1, anti/ syn) in the presence of 3c in brine.

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Section: Resultsmentioning

confidence: 99%

l-Valine Dipeptide Organocatalysts with Two Amide Units for the Direct Asymmetric Aldol Reaction in Brine

Huang

Tian

et al. 2011

Catal Lett

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“…Also using brine as the reaction media, prolinamide 158a (Figure 3.6, 2 or 5 mol%) was able to promote the reaction between several ketones (4 equiv), such as acetone (52a), cyclohexanone (52c), and tetrahydrothiopyran-4-one (61), with aromatic aldehydes providing the corresponding aldol products with good results (60-99% yield, 80-96% de, and 67-99% ee) at −5 • C. Remarkably, very high diastereo-and enantioselectivity (96% de, 93% ee) for the anti-isomer was encountered in the reaction between cyclopentanone and p-nitrobenzaldehyde. The chiral aldol products achieved were further converted to chiral azetidine rings [218]. Compound 158b (10 mol%) bearing an aryl thiourea group was tested in the aldol reaction in toluene at −20 • C in the presence of 4-nitrobenzoic acid as cocatalysts providing aldols (54) in good results (64-100%, 40-96% de, and 88-99% ee) [219].…”

Section: Proline Derivatives As Organocatalysts 189mentioning

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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“…Compound 21 has been applied to an aldol reaction of ketones with 1,2-diketones, [31] whilst very similar compounds (SO2Ph in place of Ts) have been prepared via ring opening of a sulfonated aziridine ring and applied to the organocatalysis of aldol reactions. [32] Several derivatives of C2-symmetric DPEN and of trans 1,2-diaminocyclohexane, bearing the combination of prolinamide and carbamate/thiocarbamate, [33][34][35][36][37] or dialkyl substituents, [38] have been reported in organocatalytic asymmetric transformations. We first attempted acetophenone reduction using 20 and 21 with a 5:2 mixture of FA/TEA as the solvent and hydrogen donor (Table 1).…”

Section: Resultsmentioning

confidence: 99%

Application of Proline‐Functionalised 1,2‐Diphenylethane‐1,2‐diamine (DPEN) in Asymmetric Transfer Hydrogenation of Ketones

Manville

Docherty²,

Padda³

et al. 2011

Eur J Org Chem

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Synthesis of Chiral Organocatalysts derived from Aziridines: Application in Asymmetric Aldol Reaction

Cited by 94 publications

References 58 publications

l-Valine Dipeptide Organocatalysts with Two Amide Units for the Direct Asymmetric Aldol Reaction in Brine

l-Valine Dipeptide Organocatalysts with Two Amide Units for the Direct Asymmetric Aldol Reaction in Brine

Organocatalyzed Aldol Reactions

Application of Proline‐Functionalised 1,2‐Diphenylethane‐1,2‐diamine (DPEN) in Asymmetric Transfer Hydrogenation of Ketones

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