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Relevant academic research and scientific papers

A chemo-enzymatic oxidation/aldol sequential process directly converts arylbenzyl alcohols and cyclohexanol into chiral β-hydroxy carbonyls

The development of a combination enzyme and organocatalyst for aqueous sequential organic transformation has great significance, in that it is not only environmentally friendly but also overcomes only a single methodological drawback, either in the chemical or biological process. Herein, through the utilization of the bulky steric hindrance of chiral proline derivatives, an integrated laccase and proline as a chemo-enzymatic co-catalyst system is developed. It enables an efficient oxidation/aldol enantioselective sequential reaction to be accomplished, overcoming the mutual deactivation issue. As we present in this study, this one-pot organic transformation, an initial laccase-mediated oxidation of arylbenzyl alcohols and cyclohexanol to form aldehydes and cyclohexanone, followed by a subsequent proline derivative-catalyzed aldol condensation of the in situ generated intermediates, provides various 1,2-diastereoisomeric chiral β-hydroxy ketones with acceptable yields and high enantio-/diastereoselectivities.

3,3′-Bithiophene-Based Chiral Bisphosphine Oxides as Organocatalysts in Silicon-Derived Lewis Acid Mediated Reactions

This account summarizes the development of new biheteroaromatic chiral bisphosphine oxides. 3,3′-Bithiophene-based phosphine oxides (BITIOPOs) have been successfully used as organocatalysts to promote Lewis base catalyzed, Lewis acid mediated stereoselective transformations. These highly electron-rich compounds, in combination with trichorosilyl derivatives (allyltrichlorosilane and silicon tetrachloride), generate hypervalent silicon species that act as chiral Lewis acids in highly diastereo- and enantioselective organic reactions. Several relevant examples related to these applications are discussed in detail. 1 Introduction 2 The BITIOPO Family 3 Enantioselective Opening of Epoxides 4 Enantioselective Allylation of Aldehydes 5 Stereoselective Direct (Double) Aldol-Type Reaction with Ketones 6 Stereoselective Direct Aldol-Type Reaction with Ester Derivatives 7 Conclusions.

Design and preparation of a novel prolinamide-based organocatalyst for the solvent-free asymmetric aldol reaction

The preparation of four novel organocatalysts as highly diastereo and enantioselective catalysts for the solvent-free asymmetric aldol reaction was described. These organocatalysts were synthesized in eight steps applying simple and commercially available starting materials. The best results were obtained for the proline-derived catalyst, providing access to the desired adducts in up to 95% yield, 1:19 syn/anti and 98% e.e. Moreover, even sterically bulky aldehydes and substituted cyclohexanones were well tolerated. DFT calculations and control experiments indicated that several hydrogen bonding interactions between the aldehyde and the enamine intermediate are responsible for the stereoselective chiral induction process and that the trifluoroacetate counter-anion is crucial for the attainment of higher stereoselectivities.

Prolinamides of Aminouracils, Organocatalyst Modifiable by Complementary Modules

We report the synthesis and evaluation of prolinamide organocatalysts that incorporate aminouracils. The features of these catalysts are enhanced NH acidity of the amide because of the electron-withdrawing nature of the heterocycle, an additional hydrogen-bond donor at the α or β positions of this functional group (using 6-aminouracil or 5,6-diaminouracil respectively), and it can be recovered due to its low solubility and used again without decreasing the enantioselectivity. A unique feature of these systems is the self-assembly capability with complementary modules by Watson–Crick interactions. These supramolecular adducts behave differently from the catalyst alone, some of them have lower performance but others improve the selectivity of the product. Therefore, this approach avoids the synthesis of many catalysts.

Different bio/Lewis acid-catalyzed stereoselective aldol reactions in various mediums

In this work eight different crude biocatalysts together with six Lewis and three Br?nsted acids were used for asymmetric aldol reactions of aromatic, heteroaromatic, cyclic, and acyclic six ketones and eleven aldehydes. Optimum reaction conditions were d

(2S,4R)-Hyp-(S)-Phe-OMe dipeptide supported on imidazolium tagged molecules as recoverable organocatalysts for asymmetric aldol reactions using water as reaction medium

Four novel chiral imidazolium tagged molecules derived from dipeptide (2S,4R)-Hyp-(S)-Phe-OMe were prepared and evaluated as organocatalysts in the asymmetric aldol reaction using water as solvent. It was found that catalysts incorporating the hexanoyl linker are active down to 5 mol% and afford aldol products with up to 94% yield, up to 98:2 dr and up to 97:3 er. This chiral imidazolium catalyst was reused up to 6 times without any loss in the stereoselectivity of asymmetric aldol reactions. By contrast, organocatalysts containing an acetyl linker proved to be highly unstable in protic solvents, and for that reason they could not be recovered and reused.

A phosphotungstic acid-supported multifunctional organocatalyst containing 9-amino(9-deoxy): Epi -cinchonidine and Br?nsted acid and its application in asymmetric aldol reaction

A novel type of supported multifunctional organocatalyst CDNH2(n)-HPW combined 9-amino(9-deoxy)epi-cinchonidine (CDNH2) with Br?nsted acid in the backbone of phosphotungstic acid was developed via facile precipitation of sodium tungs

The 4,5-methano-l-proline as a chiral organocatalysts in direct asymmetric aldol reactions

The 4,5-methano-l-proline was studied for the direct asymmetric aldol reaction of acetone or cyclohexanone with various aromatic and aliphaticaldehydes at -20 °C or 0 °C. A loading of only 5mol % of derivative 1a was employed in this catalytic system, and excellent enantioselectivities (up to 99% ee) and yields (up to 98% yield) could be achieved.

The high catalytic activity and reusability of the proline functionalized cage-like mesoporous material SBA-16 for the asymmetric aldol reaction proceeding in methanol-water mixed solvent

The cage-like mesoporous material SBA-16 has been successfully functionalized with l-4-hydroxyproline and characterized by Fourier transform infrared (FT-IR) spectroscopy, Small-angle X-ray powder diffraction (XRD), N2 sorption detection, trans

AZT-prolinamide: The nucleoside derived pyrrolidine catalysts for asymmetric aldol reactions using water as solvent

New pyrrolidine catalysts based on a nucleoside and proline, AZT-prolinamides, were synthesized and successfully employed for the enantioselective direct aldol reaction of aldehydes with ketones. These catalysts proved to be effective in promoting the rea