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20 pages, 3429 KiB

Open AccessArticle

Design and Synthesis of Pyrrolidinyl Ferrocene-Containing Ligands and Their Application in Highly Enantioselective Rhodium-Catalyzed Olefin Hydrogenation

by Xin Li, Therese B. Brennan, Cian Kingston, Yannick Ortin and Patrick J. Guiry

Molecules 2022, 27(18), 6078; https://doi.org/10.3390/molecules27186078 - 17 Sep 2022

Cited by 2 | Viewed by 2435

Abstract

Herein, we report the design and synthesis of a series of chiral pyrrolidine-substituted ferrocene-derived ligands. The proficiency of this novel structural motif was demonstrated in the Rh-catalyzed asymmetric hydrogenation of dehydroamino acid esters and α-aryl enamides. The products were obtained with full conversions [...] Read more.

Herein, we report the design and synthesis of a series of chiral pyrrolidine-substituted ferrocene-derived ligands. The proficiency of this novel structural motif was demonstrated in the Rh-catalyzed asymmetric hydrogenation of dehydroamino acid esters and α-aryl enamides. The products were obtained with full conversions and excellent levels of enantioselectivities of up to >99.9% ee and 97.7% ee, respectively, using a BINOL-substituted phosphine-phosphoaramidite ligand which possesses planar, central, and axial chirality elements. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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15 pages, 2789 KiB

Open AccessArticle

A Plausible Mechanism for the Iridium-Catalyzed Hydrogenation of a Bulky N-Aryl Imine in the (S)-Metolachlor Process

by Amanda L. Kwan and Robert H. Morris

Molecules 2022, 27(16), 5106; https://doi.org/10.3390/molecules27165106 - 11 Aug 2022

Cited by 4 | Viewed by 2840

Abstract

The hydrogenation of N-(2-ethyl-6-methylphenyl)-1-methoxypropan-2-imine is the largest-scale asymmetric catalytic process for the industrial production of agrochemical (S)-metolachlor. The challenging hydrogenation across the sterically crowded carbon–nitrogen double bond was achieved using a mixture of [IrCl(COD)]₂, (R,S [...] Read more.

The hydrogenation of N-(2-ethyl-6-methylphenyl)-1-methoxypropan-2-imine is the largest-scale asymmetric catalytic process for the industrial production of agrochemical (S)-metolachlor. The challenging hydrogenation across the sterically crowded carbon–nitrogen double bond was achieved using a mixture of [IrCl(COD)]₂, (R,S_Fc)-Xyliphos, NBu₄I and acetic acid. Acetic acid was critical in achieving excellent productivity and activity. Despite its industrial significance, a mechanism that explains how the sterically hindered bond in the imine is reduced has yet to be proposed. We propose a plausible proton-first, outer-sphere mechanism based on density functional theory calculations that is consistent with the experimentally observed activity and the enantioselectivity of the industrial process. Key findings include transition states involving acetate-assisted dihydrogen splitting, and a hydride transfer from a five-coordinate iridium trihydride directed by a C-H∙∙∙Ir interaction. This article was submitted to a Special Issue in honor of Professor Henri Kagan. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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16 pages, 3733 KiB

Open AccessArticle

Post-Modification of Copolymers Obtained by ATRP for an Application in Heterogeneous Asymmetric Salen Catalysis

by Erigene Bakangura, Philippe Roger, Rafaela S. B. Soares, Mohamed Mellah, Nadine Barroca-Aubry, Anne-Chantal Gouget-Laemmel, François Ozanam, Ludovic Costa, Jean-Pierre Baltaze and Emmanuelle Schulz

Molecules 2022, 27(14), 4654; https://doi.org/10.3390/molecules27144654 - 21 Jul 2022

Cited by 2 | Viewed by 2128

Abstract

Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate [...] Read more.

Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate (MEMA), used as a spacer, for the ATRP synthesis of copolymers, and then post-functionalized with a propargyl chromium salen complex. The controlled homopolymerization of MEMA by ATRP was firstly described and proved to be more controlled in molar mass than that of AZMA for conversions up to 63%. The ATRP copolymerization of both monomers made it possible to control the molar masses and the composition, with nevertheless a slight increase in the dispersity (from 1.05 to 1.3) when the incorporation ratio of AZMA increased from 10 to 50 mol%. These copolymers were post-functionalized with chromium salen units by click chemistry and their activity was evaluated in the asymmetric ring opening of cyclohexene oxide with trimethylsilyl azide. At an equal catalytic ratio, a significant increase in enantioselectivity was obtained by using the copolymer containing the largest part of salen units, probably allowing, in this case, the more favorable bimetallic activation of both the engaged nucleophile and electrophile. Moreover, the catalytic polymer was recovered by simple filtration and re-engaged in subsequent catalytic runs, up to seven times, without loss of activity or selectivity. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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15 pages, 2943 KiB

Open AccessArticle

Enantioselective 1,3-Dipolar Cycloaddition Using (Z)-α-Amidonitroalkenes as a Key Step to the Access to Chiral cis-3,4-Diaminopyrrolidines

by Eduardo García-Mingüens, Marcos Ferrándiz-Saperas, M. de Gracia Retamosa, Carmen Nájera, Miguel Yus and José M. Sansano

Molecules 2022, 27(14), 4579; https://doi.org/10.3390/molecules27144579 - 18 Jul 2022

Cited by 6 | Viewed by 1772

Abstract

The enantioselective 1,3-dipolar cycloaddition between imino esters and (Z)-nitroalkenes bearing a masked amino group in the β-position was studied using several chiral ligands and silver salts. The optimized reaction conditions were directly applied to the study of the scope of the [...] Read more.

The enantioselective 1,3-dipolar cycloaddition between imino esters and (Z)-nitroalkenes bearing a masked amino group in the β-position was studied using several chiral ligands and silver salts. The optimized reaction conditions were directly applied to the study of the scope of the reaction. The determination of the absolute configuration was evaluated using NMR experiments and electronic circular dichroism (ECD). The reduction and hydrolysis of both groups was performed to generate in an excellent enantiomeric ratio the corresponding cis-2,3-diaminoprolinate. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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9 pages, 2933 KiB

Open AccessArticle

Observation of Hyperpositive Non-Linear Effect in Asymmetric Organozinc Alkylation in Presence of N-Pyrrolidinyl Norephedrine

by Thibault Thierry, Yannick Geiger and Stéphane Bellemin-Laponnaz

Molecules 2022, 27(12), 3780; https://doi.org/10.3390/molecules27123780 - 11 Jun 2022

Cited by 4 | Viewed by 2341 | Correction

Abstract

Phenomena related to asymmetric amplification are considered to be key to understanding the emergence of homochirality in life. In asymmetric catalysis, theoretical and experimental models have been studied to understand such chiral amplification, in particular based on non-linear effects. Three decades after the [...] Read more.

Phenomena related to asymmetric amplification are considered to be key to understanding the emergence of homochirality in life. In asymmetric catalysis, theoretical and experimental models have been studied to understand such chiral amplification, in particular based on non-linear effects. Three decades after the theoretical demonstration that a chiral catalyst, when not enantiopure, could be more enantioselective than its enantiopure counterpart, we show here a new experimental example of nonlinear hyperpositive effect. We report here our investigations in the enantioselective zinc-catalyzed alkylation of benzaldehyde with N-pyrrolidinyl norephedrine as partially resolved chiral ligand, which shows a significant hyperpositive non-linear effect. A study of the underlying mechanism was conducted, which allows us to confirm a mechanism that implies a monomeric and a dimeric complex both catalyzing the reaction at a steady state and giving different enantioselectivities. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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36 pages, 13000 KiB

Open AccessArticle

Synthesis of Polysubstituted Ferrocenesulfoxides

by Min Wen, William Erb, Florence Mongin, Yury S. Halauko, Oleg A. Ivashkevich, Vadim E. Matulis and Thierry Roisnel

Molecules 2022, 27(6), 1798; https://doi.org/10.3390/molecules27061798 - 9 Mar 2022

Cited by 6 | Viewed by 2498

Abstract

The purpose of the study is to design synthetic methodologies, especially directed deprotometalation using polar organometallic reagents, to access polysubstituted ferrocenesulfoxides. From enantiopure 2-substituted (SiMe₃, PPh₂) S-tert-butylferrocenesulfoxides, a third substituent was first introduced at the 5 [...] Read more.

The purpose of the study is to design synthetic methodologies, especially directed deprotometalation using polar organometallic reagents, to access polysubstituted ferrocenesulfoxides. From enantiopure 2-substituted (SiMe₃, PPh₂) S-tert-butylferrocenesulfoxides, a third substituent was first introduced at the 5 position (SiMe₃, I, D, C(OH)Ph₂, Me, PPh₂, CH₂NMe₂, F) and removal of the trimethylsilyl group then afforded 2-substituted ferrocenesulfoxides unreachable otherwise. Attempts to apply the “halogen dance” reaction to the ferrocenesulfoxide series led to unexpected results although rationalized in light of calculated pK_a values. Further functionalizations were also possible. Thus, new enantiopure, planar chiral di- and trisubstituted ferrocenes have been obtained, in addition to several original 2-substituted, 2,3- and 2,5-disubstituted, 2,3,5-trisubstituted and even 2,3,4,5-tetrasubstituted ferrocenesulfoxides, also enantiopure. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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15 pages, 2811 KiB

Open AccessEditor’s ChoiceArticle

Straightforward Access to Enantioenriched cis-3-Fluoro-dihydroquinolin-4-ols Derivatives via Ru(II)-Catalyzed-Asymmetric Transfer Hydrogenation/Dynamic Kinetic Resolution

by Ricardo Molina Betancourt, Phannarath Phansavath and Virginie Ratovelomanana-Vidal

Molecules 2022, 27(3), 995; https://doi.org/10.3390/molecules27030995 - 1 Feb 2022

Cited by 7 | Viewed by 2270

Abstract

Herein we report a practical method for the asymmetric transfer hydrogenation/dynamic kinetic resolution of N-Boc 3-fluoro-dihydrotetrahydroquinolin-4-ones into the corresponding cis-fluoro alcohols in 70–96% yields, up to 99:1 diastereomeric ratio (dr) and up to >99% ee (enantiomeric excess) by using the ruthenium [...] Read more.

Herein we report a practical method for the asymmetric transfer hydrogenation/dynamic kinetic resolution of N-Boc 3-fluoro-dihydrotetrahydroquinolin-4-ones into the corresponding cis-fluoro alcohols in 70–96% yields, up to 99:1 diastereomeric ratio (dr) and up to >99% ee (enantiomeric excess) by using the ruthenium complex Ts-DENEB and a formic acid/triethylamine (1:1) mixture as the hydrogen donor under mild conditions. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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19 pages, 3376 KiB

Open AccessArticle

Rational Design of Simple Organocatalysts for the HSiCl₃ Enantioselective Reduction of (E)-N-(1-Phenylethylidene)aniline

by María Maciá, Raúl Porcar, Vicente Martí-Centelles, Eduardo García-Verdugo, Maria Isabel Burguete and Santiago V. Luis

Molecules 2021, 26(22), 6963; https://doi.org/10.3390/molecules26226963 - 18 Nov 2021

Cited by 2 | Viewed by 2775

Abstract

Prolinamides are well-known organocatalysts for the HSiCl₃ reduction of imines; however, custom design of catalysts is based on trial-and-error experiments. In this work, we have used a combination of computational calculations and experimental work, including kinetic analyses, to properly understand this process [...] Read more.

Prolinamides are well-known organocatalysts for the HSiCl₃ reduction of imines; however, custom design of catalysts is based on trial-and-error experiments. In this work, we have used a combination of computational calculations and experimental work, including kinetic analyses, to properly understand this process and to design optimized catalysts for the benchmark (E)-N-(1-phenylethylidene)aniline. The best results have been obtained with the amide derived from 4-methoxyaniline and the N-pivaloyl protected proline, for which the catalyzed process is almost 600 times faster than the uncatalyzed one. Mechanistic studies reveal that the formation of the component supramolecular complex catalyst-HSiCl₃-substrate, involving hydrogen bonding breaking and costly conformational changes in the prolinamide, is an important step in the overall process. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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Review

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15 pages, 7197 KiB

Open AccessReview

Coinage Metal-Catalyzed Asymmetric Reactions of ortho-Alkynylaryl and Heteroaryl Aldehydes and Ketones

by Romain Melot and Véronique Michelet

Molecules 2022, 27(20), 6970; https://doi.org/10.3390/molecules27206970 - 17 Oct 2022

Cited by 5 | Viewed by 1664

Abstract

Coinage metals have become the metal of choice due to their excellent catalytic activity in organic transformation processes. Combining various chiral ligands and coinage metals became a productive area of research and access to heterocyclic derivatives according to an efficient and sustainable manner. [...] Read more.

Coinage metals have become the metal of choice due to their excellent catalytic activity in organic transformation processes. Combining various chiral ligands and coinage metals became a productive area of research and access to heterocyclic derivatives according to an efficient and sustainable manner. This review was devoted to the various recently developed coinage metal-catalyzed domino processes of ortho-alkynylaryl and heteroaryl aldehydes and ketones leading to functionalized heterocycles. Various gold chiral complexes were presented, and methods of preparations of chromenes along with indoles were covered. Ag-chiral complexes are also prone to interesting activities such as cyclization followed by reduction and functionalization with enolizable ketones or (diazomethyl)phosphonate. Asymmetric Cu-catalyzed domino cyclization and asymmetric transfer hydrogenation reactions efficiently led to functionalized chromenes. Some remarkable examples involving copper associated with ruthenium in the context of a cyclization and asymmetric hydrogenation process were also presented. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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23 pages, 6636 KiB

Open AccessReview

Stereoselective Processes Based on σ-Hole Interactions

by Paola Peluso and Victor Mamane

Molecules 2022, 27(14), 4625; https://doi.org/10.3390/molecules27144625 - 20 Jul 2022

Cited by 11 | Viewed by 2914

Abstract

The σ-hole interaction represents a noncovalent interaction between atoms with σ-hole(s) on their surface (such as halogens and chalcogens) and negative sites. Over the last decade, significant developments have emerged in applications where the σ-hole interaction was demonstrated to play a key role [...] Read more.

The σ-hole interaction represents a noncovalent interaction between atoms with σ-hole(s) on their surface (such as halogens and chalcogens) and negative sites. Over the last decade, significant developments have emerged in applications where the σ-hole interaction was demonstrated to play a key role in the control over chirality. The aim of this review is to give a comprehensive overview of the current advancements in the use of σ-hole interactions in stereoselective processes, such as formation of chiral supramolecular assemblies, separation of enantiomers, enantioselective complexation and asymmetric catalysis. Full article

(This article belongs to the Special Issue A Wonderful Journey in the Asymmetric Catalysis World: A Themed Issue in Honor of Prof. Henri B. Kagan)

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