Current applications of organocatalysts in asymmetric aldol reactions: An update

Heravi, Majid M.; Zadsirjan, Vahideh; Dehghani, Mahzad; Hosseintash, Nastaran

doi:10.1016/j.tetasy.2017.04.006

Cited by 63 publications

(24 citation statements)

References 409 publications

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“…To improve enantioselectivity, we optimized the reaction conditions for a 3g-catalyzed reaction between 1a and 2 ( Table 1, entries [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. This reaction was carried out in various solvents ( Table 1, entries [8][9][10][11][12][13].…”

Section: Resultsmentioning

confidence: 99%

“…Following the introduction of a proline-catalyzed asymmetric aldol reaction of aldehydes reported by List et al [19], prolinamide catalysts for this reaction have been actively developed [20,21]. Synthetic peptides in prolinamide catalysts, are recognized as effective catalysts for the direct asymmetric aldol reaction using aldehydes as electrophiles [22][23][24][25][26][27][28][29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

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Tripeptide-Catalyzed Asymmetric Aldol Reaction Between α-ketoesters and Acetone Under Acidic Cocatalyst-Free Conditions

et al. 2019

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Here, we report the tripeptide-catalyzed asymmetric aldol reaction between α-ketoesters and acetone under acidic cocatalysts-free conditions. H-Pro-Tle-Gly-OH 3g-catalyzed reactions between α-ketoesters and acetone resulted in up to 95% yield and 88% ee. Analysis of the transition state using density functional theory (DFT) calculations revealed that the tert-butyl group in 3g played an important role in enantioselectivity.Catalysts 2019, 9, 514 2 of 8 trifluoromethyl ketones with acetone ( Figure 1a) [37,38]. These catalysts, under acidic cocatalyst-free conditions, displayed good enantioselectivity and kinetics in these reactions. Herein, we will report the direct asymmetric aldol reaction between α-ketoesters and acetone catalyzed by tripeptide under acidic cocatalyst-free conditions (Figure 1b).

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tripeptide-Catalyzed Asymmetric Aldol Reaction Between α-ketoesters and Acetone Under Acidic Cocatalyst-Free Conditions

et al. 2019

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“…This concertedness is not surprising a priori and should be the lowest energy pathway. The well-known catalytic versions, such as those involving proline or prolinamide catalysts among others, with a booming research activity for more than 2 decades, 59 may also proceed via nonstepwise mechanisms. However, the catalyst often forms H-bonds with the aldehyde that stabilizes the transition structure and reduces the activation barrier.…”

Section: Resultsmentioning

confidence: 99%

On the asymmetric autocatalysis of aldol reactions: The case of 4‐nitrobenzaldehyde and acetone. A critical appraisal with a focus on theory

2018

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Under neutral conditions, spontaneous mirror symmetry breaking has been occasionally reported for aldol reactions starting from achiral reagents and conditions. Chiral induction might be interpreted in terms of autocatalysis exerted by chiral mono-aldol or bis-aldol products as source of initial enantiomeric excesses, which may account for such experimental observations. We describe here a thorough Density Functional Theory (DFT) study on this complex and otherwise difficult problem, which provides some insights into this phenomenon. The picture adds further rationale to an in-depth analysis by Moyano et al, who showed the isolation and characterization of bis-aldol adducts and their participation in a complex network of reversible steps. However, the lack of enantiodiscrimination (ees vanish rapidly in solution) suggests, according to the present results, a weak association in complexes formed by the catalysts and substrates. The latter would also be consistent with almost flat transition states having similar heights for competitive catalyst-bound transition structures (actually, we were unable to locate them at the level explored). Overall, neither autocatalysis as once conjectured nor mutual inhibition of enantiomers appears to be operating mechanisms. Asymmetric amplification in early stages harnessing unavoidable enantiomeric imbalances in reaction mixtures of chiral products represents a plausible interpretation.

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“…Taking into account these considerations, we have developed, for the synthesis of AN analogues, innovative catalytic routes based on organocatalysis and biocatalysis . In particular, organocatalysis has emerged as a promising area for the sustainable, efficient and selective carbon–carbon bond formation using small organic molecules as catalysts . In contrast to biocatalysts, that are highly substrate specific, organocatalysts catalyse reactions with a wide range of substrates .…”

Section: Introductionmentioning

confidence: 99%

“…[8] In particular, organocatalysis has emerged as a promising area for the sustainable, efficient and selective carbon-carbon bond formation using small organic molecules as catalysts. [9][10][11] In contrast to biocatalysts, that are highly substrate specific, organocatalysts catalyse reactions with a wide range of substrates. [12] Additionally, these strategies allowed the successful achievement of a large number of asymmetric transformations.…”

Section: Introductionmentioning

confidence: 99%

Keto‐Enol Tautomerism in Nucleobase‐Substituted Aldols

et al. 2018

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Acyclic nucleosides, which exhibit significant antiviral activity, are usually synthesised using traditional chemical strategies. However, the efficient and selective formation of carbon‐carbon bonds using small organic molecules as catalysts provides a promising alternative route for the sustainable synthesis of this family of compounds. Following this organocatalytic strategy, 5‐(adenyl, thyminyl and cytosyl)‐4‐hydroxy‐2‐pentanones were prepared by the pyrrolidine catalysed reaction between the 2‐oxoethyl derivative of the corresponding nucleobases and acetone. In order to investigate the keto‐enol equilibrium of these compounds in basic media, H‐D exchange studies were carried out by 1H and 13C NMR spectroscopy. The obtained results suggest that the mechanism by which this exchange occurs is of first order with respect to all the substrates, but of second order with regard to pyrrolidine in the case of the cytosine and adenine derivatives and of first order for the thymine analogue. Theoretical calculations of the structures involved in this equilibrium also suggest that the stability of the different ionic intermediates depends on the pKa of the corresponding nucleobases.

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Current applications of organocatalysts in asymmetric aldol reactions: An update

Cited by 63 publications

References 409 publications

Tripeptide-Catalyzed Asymmetric Aldol Reaction Between α-ketoesters and Acetone Under Acidic Cocatalyst-Free Conditions

Tripeptide-Catalyzed Asymmetric Aldol Reaction Between α-ketoesters and Acetone Under Acidic Cocatalyst-Free Conditions

On the asymmetric autocatalysis of aldol reactions: The case of 4‐nitrobenzaldehyde and acetone. A critical appraisal with a focus on theory

Keto‐Enol Tautomerism in Nucleobase‐Substituted Aldols

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