Catalysts

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12 pages, 1713 KiB

Open AccessArticle

Quaternary Ammonium Salts Interact with Enolates and Sulfonates via Formation of Multiple ⁺N-C-H Hydrogen Bonding Interactions

by Grazia Bencivenni, Nathalie Saraiva Rosa, Paolo Grieco, Malachi W. Gillick-Healy, Brian G. Kelly, Brendan Twamley and Mauro F. A. Adamo

Catalysts 2022, 12(7), 803; https://doi.org/10.3390/catal12070803 - 21 Jul 2022

Cited by 3 | Viewed by 3254

Abstract

We report herein sharp physical evidence, i.e., single-crystal X-ray diffraction and ¹H-NMR spectral data, confirming that quaternary ammonium species interact with anions via a set of directional ion–dipole cooperative ⁺N-C-H unusual H-bonding interactions and not via pure non-directional ionic electrostatic interactions. [...] Read more.

We report herein sharp physical evidence, i.e., single-crystal X-ray diffraction and ¹H-NMR spectral data, confirming that quaternary ammonium species interact with anions via a set of directional ion–dipole cooperative ⁺N-C-H unusual H-bonding interactions and not via pure non-directional ionic electrostatic interactions. This finding, which has been often invoked by calculations, is herein substantiated by the preparation of two model compounds and an analysis of their X-ray crystal structures in the solid state and ¹H-NMR spectra in solution. These observations are particularly pertinent for the rational design of novel catalyses and catalysts and providing guidance to an understanding of these species in solution and during asymmetric enantioselective catalysis. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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10 pages, 1843 KiB

Open AccessArticle

Efficient Synthesis of 3-Sulfonyl-2-sulfonylmethyl-2H-chromenes via Tandem Knoevenagel Condensation/Oxa-Michael Addition Protocol

by Lin Jiang, Peiying Peng, Min Li, Lu Li, Menglin Zhao, Minglong Yuan and Mingwei Yuan

Catalysts 2022, 12(5), 491; https://doi.org/10.3390/catal12050491 - 28 Apr 2022

Cited by 2 | Viewed by 2141

Abstract

An organocatalytic [4 + 2] cascade annulation of salicylaldehydes and 1,3-bisarylsulfonylpropenes has been developed. This protocol enables the efficient and straightforward synthesis of a new series of 3-sulfonyl-2-sulfonylmethyl-2H-chromenes that are useful for exploring pharmacologically valued compounds. Further reductive modifications result in [...] Read more.

An organocatalytic [4 + 2] cascade annulation of salicylaldehydes and 1,3-bisarylsulfonylpropenes has been developed. This protocol enables the efficient and straightforward synthesis of a new series of 3-sulfonyl-2-sulfonylmethyl-2H-chromenes that are useful for exploring pharmacologically valued compounds. Further reductive modifications result in 3-desulfonylated chromene or chromane derivatives. This protocol can be expanded to the synthesis of 3-sulfonyl-2-sulfonylmethyl 1,2-dihydroquinoline. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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9 pages, 2024 KiB

Open AccessArticle

Chiral Ionic Liquids Based on l-Cysteine Derivatives for Asymmetric Aldol Reaction

by Karolina Zalewska, Małgorzata E. Zakrzewska and Luis C. Branco

Catalysts 2022, 12(1), 47; https://doi.org/10.3390/catal12010047 - 1 Jan 2022

Cited by 3 | Viewed by 2502

Abstract

Structure, and consequently properties, of ionic liquids can be easily tailored by changing cation/anion combinations and/or attaching functional groups. By grafting enantiopure moieties to the framework of ionic liquid it is possible to prepare bioinspired chiral molecules that can serve as a reaction [...] Read more.

Structure, and consequently properties, of ionic liquids can be easily tailored by changing cation/anion combinations and/or attaching functional groups. By grafting enantiopure moieties to the framework of ionic liquid it is possible to prepare bioinspired chiral molecules that can serve as a reaction medium, additive or even asymmetric catalyst. In this context, new chiral ionic liquids (CILs), based on biomolecules, such as aminoacids (l-Cysteine derivatives), have been synthesised and tested in asymmetric aldol condensation of aldehydes and ketones. The best results were obtained for CILs composed of S-methyl-l-cysteine cation and bis(trifluoromethane)sulfonimide anion, in the reaction of 2- or 4-nitrobenzaldehyde with acetone or cyclohexanone, giving the aldol product in moderate yields 70–76% and high ee values (up to 96%). Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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19 pages, 4880 KiB

Open AccessFeature PaperArticle

Flow-Through Macroporous Polymer Monoliths Containing Artificial Catalytic Centers Mimicking Chymotrypsin Active Site

by Mariia Stepanova, Olga Solomakha, Daria Ten, Tatiana Tennikova and Evgenia Korzhikova-Vlakh

Catalysts 2020, 10(12), 1395; https://doi.org/10.3390/catal10121395 - 30 Nov 2020

Cited by 7 | Viewed by 2686

Abstract

Synthetic catalysts that could compete with enzymes in term of the catalytic efficiency but surpass them in stability have a great potential for the practical application. In this work, we have developed a novel kind of organic catalysts based on flow-through macroporous polymer [...] Read more.

Synthetic catalysts that could compete with enzymes in term of the catalytic efficiency but surpass them in stability have a great potential for the practical application. In this work, we have developed a novel kind of organic catalysts based on flow-through macroporous polymer monoliths containing catalytic centers that mimic the catalytic site of natural enzyme chymotrypsin. It is known that chymotrypsin catalytic center consists of L-serine, L-histidine, and L-aspartic acid and has specificity to C-terminal residues of hydrophobic amino acids (L-phenylalanine, L-tyrosine, and L-tryptophan). In this paper, we have prepared the macroporous polymer monoliths bearing grafted polymer layer on their surface. The last one was synthesized via copolymerization of N-methacryloyl-L-serine, N-methacryloyl-L-histidine, and N-methacryloyl-L-aspartic acid. The spatial orientation of amino acids in the polymer layer, generated on the surface of monolithic framework, was achieved by coordinating amino acid-polymerizable derivatives with cobalt (II) ions without substrate-mimicking template and with its use. The conditions for the preparation of mimic materials were optimized to achieve a mechanically stable system. Catalytic properties of the developed systems were evaluated towards the hydrolysis of ester bond in a low molecular substrate and compared to the results of using chymotrypsin immobilized on the surface of a similar monolithic framework. The effect of flow rate increase and temperature elevation on the hydrolysis efficiency were evaluated for both mimic monolith and column with immobilized enzyme. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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7 pages, 5153 KiB

Open AccessFeature PaperCommunication

Organocatalyzed Michael Addition to Nitroalkenes via Masked Acetaldehyde

by Giuliana Giorgianni, Valeria Nori, Andrea Baschieri, Laura Palombi and Armando Carlone

Catalysts 2020, 10(11), 1296; https://doi.org/10.3390/catal10111296 - 9 Nov 2020

Cited by 8 | Viewed by 3897

Abstract

A novel and safe reaction protocol for the enantioselective enamine-catalysed addition of acetaldehyde to nitroalkenes is presented; this protocol makes use of a safe acetaldehyde precursor to access important intermediates to Active Pharmaceutical Ingredients (APIs), and allows the use of fewer equivalents of [...] Read more.

A novel and safe reaction protocol for the enantioselective enamine-catalysed addition of acetaldehyde to nitroalkenes is presented; this protocol makes use of a safe acetaldehyde precursor to access important intermediates to Active Pharmaceutical Ingredients (APIs), and allows the use of fewer equivalents of acetaldehyde and lower catalyst loadings. The reaction developed proved to be suitable to be performed on gram-scale and to produce key intermediates for the synthesis of pharmacologically active compounds such as pregabalin. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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13 pages, 4503 KiB

Open AccessArticle

Baeyer-Villiger-Including Domino Two-Step Oxidations of β-O-Substituted Primary Alcohols: Reflection of the Migratory Aptitudes of O-Substituted Alkyl Group in the Outcome of the Reaction

by Tom Targel and Moshe Portnoy

Catalysts 2020, 10(11), 1275; https://doi.org/10.3390/catal10111275 - 3 Nov 2020

Cited by 1 | Viewed by 2860

Abstract

Following the recent development of the one-pot two-step oxidation protocol for primary β-alkoxy alcohols, additional primary β-oxy alcohols were examined under similar conditions. The outcome of these reactions closely follows the migratory aptitudes of the related α-oxy-alkyls in Baeyer-Villiger oxidation vs. that of [...] Read more.

Following the recent development of the one-pot two-step oxidation protocol for primary β-alkoxy alcohols, additional primary β-oxy alcohols were examined under similar conditions. The outcome of these reactions closely follows the migratory aptitudes of the related α-oxy-alkyls in Baeyer-Villiger oxidation vs. that of hydrogen. Thus, these experiments helped to establish the correct order of these aptitudes for α-oxy-alkyls. Furthermore, in the case of primary β,β-dialkoxyalcohols, the formation of dialkoxymethyl formates by the domino oxidation reaction was followed by secondary reactions, forming a number of interesting products. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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13 pages, 4200 KiB

Open AccessArticle

Double Spirocyclization of Arylidene-Δ²-Pyrrolin-4-Ones with 3-Isothiocyanato Oxindoles

by Sebastijan Ričko, Žan Testen, Luka Ciber, Franc Požgan, Bogdan Štefane, Helena Brodnik, Jurij Svete and Uroš Grošelj

Catalysts 2020, 10(10), 1211; https://doi.org/10.3390/catal10101211 - 19 Oct 2020

Cited by 7 | Viewed by 2973

Abstract

Arylidene-Δ²-pyrrolin-4-ones undergo organocatalyzed double spirocyclization with 3-isothiocianato oxindoles in a domino 1,4/1,2-addition sequence. The products contain three contiguous stereocenters (ee up to 98%, dr up to 99:1, 12 examples). The absolute configuration of the major diastereomer was determined by single [...] Read more.

Arylidene-Δ²-pyrrolin-4-ones undergo organocatalyzed double spirocyclization with 3-isothiocianato oxindoles in a domino 1,4/1,2-addition sequence. The products contain three contiguous stereocenters (ee up to 98%, dr up to 99:1, 12 examples). The absolute configuration of the major diastereomer was determined by single crystal X-ray analysis. Along with heterocyclic Michael acceptors based on oxazolone, isoxazolone, thiazolidinone, pyrazolone, and pyrimidinedione, the reported results display the applicability of unsaturated Δ²-pyrrolin-4-ones (pyrrolones) for the organocatalyzed construction of 3D-rich pyrrolone-containing heterocycles. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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8 pages, 1503 KiB

Open AccessArticle

Stereoselective ROP of rac- and meso-Lactides Using Achiral TBD as Catalyst

by Sébastien Moins, Sébastien Hoyas, Vincent Lemaur, Beste Orhan, Kayla Delle Chiaie, Roberto Lazzaroni, Daniel Taton, Andrew P. Dove and Olivier Coulembier

Catalysts 2020, 10(6), 620; https://doi.org/10.3390/catal10060620 - 3 Jun 2020

Cited by 17 | Viewed by 4300

Abstract

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) polymerizes rac-lactide (rac-LA) to form highly isotactic polylactide (PLA) with a P_m = 0.88, while meso-LA yields heterotactic PLA (P_m ~ 0.8) at −75 °C. The stereocontrol of the cryogenic-based ring-opening polymerization comes from [...] Read more.

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) polymerizes rac-lactide (rac-LA) to form highly isotactic polylactide (PLA) with a P_m = 0.88, while meso-LA yields heterotactic PLA (P_m ~ 0.8) at −75 °C. The stereocontrol of the cryogenic-based ring-opening polymerization comes from a perfect imbrication of both chiral LA and the propagating chiral end-group interacting with the achiral TBD catalyst. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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11 pages, 1113 KiB

Open AccessArticle

ADMET Polymerization of Dimeric Cinchona Squaramides for the Preparation of a Highly Enantioselective Polymeric Organocatalyst

by Mohammad Shahid Ullah, Sadia Afrin Chhanda and Shinichi Itsuno

Catalysts 2020, 10(5), 591; https://doi.org/10.3390/catal10050591 - 25 May 2020

Cited by 2 | Viewed by 3095

Abstract

Under the acyclic diene metathesis (ADMET) reaction condition, the C3-vinyl groups of cinchona alkaloids readily react with each other to form a C-C bond. A novel type of cinchona alkaloid polymers was synthesized from dimeric cinchona squaramides using the Hoveyda-Grubbs’ second-generation catalysts ( [...] Read more.

Under the acyclic diene metathesis (ADMET) reaction condition, the C3-vinyl groups of cinchona alkaloids readily react with each other to form a C-C bond. A novel type of cinchona alkaloid polymers was synthesized from dimeric cinchona squaramides using the Hoveyda-Grubbs’ second-generation catalysts (HG₂) by means of ADMET reaction. The chiral polymers, containing cinchona squaramide moieties in their main chains, were subsequently employed as catalysts for the enantioselective Michael reaction to give the corresponding chiral adducts in high yields with excellent enantioselectivity and diastereoselectivity. Both enantiomers from the asymmetric Michael reaction were distinctively prepared while using the polymeric catalysts, possessing pseudoenantiomeric structures. The catalysts were readily recovered from the reaction mixture and recycled several times due to the insolubility of the cinchona-based squaramide polymers. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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Review

Jump to: Research, Other

20 pages, 7158 KiB

Open AccessReview

Catalytic Foldamers: When the Structure Guides the Function

by Baptiste Legrand, Julie Aguesseau-Kondrotas, Matthieu Simon and Ludovic Maillard

Catalysts 2020, 10(6), 700; https://doi.org/10.3390/catal10060700 - 22 Jun 2020

Cited by 27 | Viewed by 5434

Abstract

Enzymes are predominantly proteins able to effectively and selectively catalyze highly complex biochemical reactions in mild reaction conditions. Nevertheless, they are limited to the arsenal of reactions that have emerged during natural evolution in compliance with their intrinsic nature, three-dimensional structures and dynamics. [...] Read more.

Enzymes are predominantly proteins able to effectively and selectively catalyze highly complex biochemical reactions in mild reaction conditions. Nevertheless, they are limited to the arsenal of reactions that have emerged during natural evolution in compliance with their intrinsic nature, three-dimensional structures and dynamics. They optimally work in physiological conditions for a limited range of reactions, and thus exhibit a low tolerance for solvent and temperature conditions. The de novo design of synthetic highly stable enzymes able to catalyze a broad range of chemical reactions in variable conditions is a great challenge, which requires the development of programmable and finely tunable artificial tools. Interestingly, over the last two decades, chemists developed protein secondary structure mimics to achieve some desirable features of proteins, which are able to interfere with the biological processes. Such non-natural oligomers, so called foldamers, can adopt highly stable and predictable architectures and have extensively demonstrated their attractiveness for widespread applications in fields from biomedical to material science. Foldamer science was more recently considered to provide original solutions to the de novo design of artificial enzymes. This review covers recent developments related to peptidomimetic foldamers with catalytic properties and the principles that have guided their design. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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36 pages, 10549 KiB

Open AccessFeature PaperEditor’s ChoiceReview

New Trends in Enantioselective Cross-Dehydrogenative Coupling

by Ana Maria Faisca Phillips, Maria de Fátima C. Guedes da Silva and Armando J. L. Pombeiro

Catalysts 2020, 10(5), 529; https://doi.org/10.3390/catal10050529 - 11 May 2020

Cited by 31 | Viewed by 5560

Abstract

The development of cross-dehydrogenative coupling in recent years has simplified the synthesis of many materials, as a result of facile C–H activation, which, together with its greater atom economy and environmental friendliness, has made an impact on modern organic chemistry. Indeed, many C–C [...] Read more.

The development of cross-dehydrogenative coupling in recent years has simplified the synthesis of many materials, as a result of facile C–H activation, which, together with its greater atom economy and environmental friendliness, has made an impact on modern organic chemistry. Indeed, many C–C and C–X (X = N, O, P, S, B, or Si) coupling reactions can now be performed directly between two C–H bonds or a C–H and an X–H bond, simply by adding catalytic amounts of a metal salt to a mixture of the two and an oxidant to accept the two hydrogen atoms released. Chiral organocatalysts or chiral ligands have been joined to promote enantioselective processes, resulting in the development of efficient reaction cascades that provide products in high yields and high levels of asymmetric induction through cooperative catalysis. In recent years, photochemical oxidation and electrochemistry have widened even more the scope of cross-dehydrogenative coupling (CDC). In this review, we summarized the recent literature in this subject, hoping that it will inspire many new synthetic strategies. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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Other

Jump to: Research, Review

11 pages, 3430 KiB

Open AccessPerspective

Asymmetric Organocatalysis—A Powerful Technology Platform for Academia and Industry: Pregabalin as a Case Study

by Giuliana Giorgianni, Luca Bernardi, Francesco Fini, Fabio Pesciaioli, Francesco Secci and Armando Carlone

Catalysts 2022, 12(8), 912; https://doi.org/10.3390/catal12080912 - 18 Aug 2022

Cited by 2 | Viewed by 4152

Abstract

Enantioselective organocatalysis has quickly established itself as the third pillar of asymmetric catalysis. It is a powerful technology platform, and it has a tremendous impact in both academic and industrial settings. By focusing on pregabalin, as a case study, this Perspective aims to [...] Read more.

Enantioselective organocatalysis has quickly established itself as the third pillar of asymmetric catalysis. It is a powerful technology platform, and it has a tremendous impact in both academic and industrial settings. By focusing on pregabalin, as a case study, this Perspective aims to show how a process amenable to industry of a simple chiral molecule can be tackled in several different ways using organocatalysis. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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13 pages, 3878 KiB

Open AccessPerspective

Horizons in Asymmetric Organocatalysis: En Route to the Sustainability and New Applications

by Sandra Ardevines, Eugenia Marqués-López and Raquel P. Herrera

Catalysts 2022, 12(1), 101; https://doi.org/10.3390/catal12010101 - 16 Jan 2022

Cited by 14 | Viewed by 4628

Abstract

Nowadays, the development of new enantioselective processes is highly relevant in chemistry due to the relevance of chiral compounds in biomedicine (mainly drugs) and in other fields, such as agrochemistry, animal feed, and flavorings. Among them, organocatalytic methods have become an efficient and [...] Read more.

Nowadays, the development of new enantioselective processes is highly relevant in chemistry due to the relevance of chiral compounds in biomedicine (mainly drugs) and in other fields, such as agrochemistry, animal feed, and flavorings. Among them, organocatalytic methods have become an efficient and sustainable alternative since List and MacMillan pioneering contributions were published in 2000. These works established the term asymmetric organocatalysis to label this area of research, which has grown exponentially over the last two decades. Since then, the scientific community has attended to the discovery of a plethora of organic reactions and transformations carried out with excellent results in terms of both reactivity and enantioselectivity. Looking back to earlier times, we can find in the literature a few examples where small organic molecules and some natural products could act as effective catalysts. However, with the birth of this type of catalysis, new chemical architectures based on amines, thioureas, squaramides, cinchona alkaloids, quaternary ammonium salts, carbenes, guanidines and phosphoric acids, among many others, have been developed. These organocatalysts have provided a broad range of activation modes that allow privileged interactions between catalysts and substrates for the preparation of compounds with high added value in an enantioselective way. Here, we briefly cover the history of this chemistry, from our point of view, including our beginnings, how the field has evolved during these years of research, and the road ahead. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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