Asymmetric Synthesis of β-Hydroxy Amino Acids via Aldol Reactions Catalyzed by Chiral Ammonium Salts

Mettath, Sashikumar; Srikanth, G. S. C.; Dangerfield, Benjamin S.; Castle, Steven L.

doi:10.1021/jo049283u

Cited by 60 publications

(19 citation statements)

References 33 publications

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“…Since that time several new catalysts have been reported for this reaction, but the enantioselectivity of these processes remains low (Scheme 19). 264, 265 It is noteworthy that either diastereomer of adduct 214 can be favored (though in a modest excess) by choosing the appropriate catalyst.…”

Section: Non-enamine Organocatalysts For the Aldol Reactionmentioning

confidence: 99%

The direct catalytic asymmetric aldol reaction

2010

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Asymmetric aldol reactions are a powerful method for the construction of carbon-carbon bonds in an enantioselective fashion. Historically this reaction has been performed in a stoichiometric fashion to control the various aspects of chemo-, diastereo-, regio- and enantioselectivity, however, a more atom economical approach would unite high selectivity with the use of only a catalytic amount of a chiral promoter. This critical review documents the development of direct catalytic asymmetric aldol methodologies, including organocatalytic and metal-based strategies. New methods have improved the reactivity, selectivity and substrate scope of the direct aldol reaction and enabled the synthesis of complex molecular targets

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Section: Non-enamine Organocatalysts For the Aldol Reactionmentioning

confidence: 99%

The direct catalytic asymmetric aldol reaction

2010

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“…Thus, cinchonidium salt of type 392a (Figure 3.29) gave practically negligible enantioselectivity, while using catalyst 392b (17 mol%), in the presence of tert-butyliminotris(pyrrolidino)phosphorane (BEMP) as organic base (1.7 equiv), the expected products 391 were obtained in moderate results (34-78% 0-14% de, and 52-83% ee for syn-391) [447]. Owing to the instability of compounds 391, toward achieving chromatography isolation, they were transformed by hydrolysis of the imine and acylation to the more stable amide derivative.…”

Section: Phase-transfer Catalysismentioning

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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“…For example, cinchonidium salts 452 gave moderate results (34-78% yield, 0-14% de, 52-83% ee, Figure 19). 251 A significant improvement in quaternary ammonium salt-catalyzed aldol reactions was reported by Maruoka and coworkers. Highly enantioselective and anti-selective aldol reactions could be performed in the presence of 2 mol% of chiral C 2 -symmetric Figure 19 Types of cinchonidium salt catalysts.…”

Section: Aldol Reactions In Phase-transfer Catalysismentioning

confidence: 93%