New synthetic strategy for chiral 2-oxazolidinones derivatives via rhodium-catalyzed asymmetric hydrogenation

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

Chiral phosphorus ligands play a crucial role in asymmetric catalysis for the efficient synthesis of useful optically active compounds. They are largely categorized into two classes: backbone chirality ligands and P-stereogenic phosphorus ligands. Most of the reported ligands belong to the former class. Privileged ones such as BINAP and DuPhos are frequently employed in a wide range of catalytic asymmetric transformations. In contrast, the latter class of P-stereogenic phosphorus ligands has remained a small family for many years mainly because of their synthetic difficulty. The late 1990s saw the emergence of novel P-stereogenic phosphorus ligands with their superior enantioinduction ability in Rh-catalyzed asymmetric hydrogenation reactions. Since then, numerous P-stereogenic phosphorus ligands have been synthesized and used in catalytic asymmetric reactions. This Review summarizes P-stereogenic phosphorus ligands reported thus far, including their stereochemical and electronic properties that afford high to excellent enantioselectivities. Examples of reactions that use this class of ligands are described together with their applications in the construction of key intermediates for the synthesis of optically active natural products and therapeutic agents. The literature covered dates back to 1968 up until December 2023, centering on studies published in the late 1990s and later years.

B(C6F5)3-catalyzed metal-free hydrogenation of 2-oxazolones

A metal-free hydrogenation of 2-oxazolones was successfully realized by using 10 mol% of B(C₆F₅)₃ as the catalyst, giving a variety of 2-oxazolidinones in 70-98% yields. An enamine to imine process was believed to be involved in this reaction.

Recent Advances in the Enantioselective Synthesis of Chiral Amines via Transition Metal-Catalyzed Asymmetric Hydrogenation

Chiral amines are key structural motifs present in a wide variety of natural products, drugs, and other biologically active compounds. During the past decade, significant advances have been made with respect to the enantioselective synthesis of chiral amines, many of them based on catalytic asymmetric hydrogenation (AH). The present review covers the use of AH in the synthesis of chiral amines bearing a stereogenic center either in the α, β, or γ position with respect to the nitrogen atom, reported from 2010 to 2020. Therefore, we provide an overview of the recent advances in the AH of imines, enamides, enamines, allyl amines, and N-heteroaromatic compounds.

Recent Advances in Asymmetric Hydrogenation Catalysis Utilizing Spiro and Other Rigid C-Stereogenic Phosphine Ligands

Transition-metal-catalyzed asymmetric reactions have been a powerful tool in organic synthesis for many years. The design of chiral ligands with the right configuration is fundamental to induce high regio- and stereoselectivity to catalytic reactions and to achieve high turnover numbers and high yields. A challenge is the control of prochiral centers with similar electronic properties in a similar steric environment within the same molecule. Over the last 10 years, a range of novel rigid C-stereogenic chiral phosphine ligands has been developed and successfully applied in various types of asymmetric transformations. Many of these ligands are of a di-, tri-, or multidentate nature. The purpose of this Perspective is to highlight recent synthetic achievements (since 2010) with spiro-phosphines and other rigid phosphines and discuss some mechanistic aspects of the catalytic reactions.

Design, Synthesis, and Biological Evaluation of a Series of Oxazolone Carboxamides as a Novel Class of Acid Ceramidase Inhibitors

Acid ceramidase (AC) is a cysteine hydrolase that plays a crucial role in the metabolism of lysosomal ceramides, important members of the sphingolipid family, a diversified class of bioactive molecules that mediate many biological processes ranging from cell structural integrity, signaling, and cell proliferation to cell death. In the effort to expand the structural diversity of the existing collection of AC inhibitors, a novel class of substituted oxazol-2-one-3-carboxamides were designed and synthesized. Herein, we present the chemical optimization of our initial hits, 2-oxo-4-phenyl-N-(4-phenylbutyl)oxazole-3-carboxamide 8a and 2-oxo-5-phenyl-N-(4-phenylbutyl)oxazole-3-carboxamide 12a, which resulted in the identification of 5-[4-fluoro-2-(1-methyl-4-piperidyl)phenyl]-2-oxo-N-pentyl-oxazole-3-carboxamide 32b as a potent AC inhibitor with optimal physicochemical and metabolic properties, showing target engagement in human neuroblastoma SH-SY5Y cells and a desirable pharmacokinetic profile in mice, following intravenous and oral administration. 32b enriches the arsenal of promising lead compounds that may therefore act as useful pharmacological tools for investigating the potential therapeutic effects of AC inhibition in relevant sphingolipid-mediated disorders.

Recent Developments in Transition-Metal-Catalyzed Asymmetric Hydrogenation of Enamides

The catalytic asymmetric hydrogenation of prochiral olefins is one of the most widely studied and utilized transformations in asymmetric synthesis. This straightforward, atom economical, inherently direct and sustainable strategy induces chirality in a broad range of substrates and is widely relevant for both industrial applications and academic research. In addition, the asymmetric hydrogenation of enamides has been widely used for the synthesis of chiral amines and their derivatives. In this review, we summarize the recent work in this field, focusing on the development of new catalytic systems and on the extension of these asymmetric reductions to new classes of enamides.

1 Introduction

2 Asymmetric Hydrogenation of Trisubstituted Enamides

2.1 Ruthenium Catalysts

2.2 Rhodium Catalysts

2.3 Iridium Catalysts

2.4 Nickel Catalysts

2.5 Cobalt Catalysts

3 Asymmetric Hydrogenation of Tetrasubstituted Enamides

3.1 Ruthenium Catalysts

3.2 Rhodium Catalysts

3.3 Nickel Catalysts

4 Asymmetric Hydrogenation of Terminal Enamides

4.1 Rhodium Catalysts

4.2 Cobalt Catalysts

5 Rhodium-Catalyzed Asymmetric Hydrogenation of Miscellaneous Enamides

6 Conclusions

Spiro[indene-1,4'-oxa-zolidinones] Synthesis via Rh(III)-Catalyzed Coupling of 4-Phenyl-1,3-oxazol-2(3H)-ones with Alkynes: A Redox-Neutral Approach

Transition-metal-catalyzed C-H activation synthesis of heterocyclic spiro[4,4]nonanes has persistently witnessed the use of additional stoichiometric transition-metal oxidant when employing C═C bond as the spiro ring closure site. Herein, we have addressed the issue by reporting a redox-neutral strategy for spiro[indene-1,4'-oxa-zolidinones] synthesis via Rh(III)-catalyzed coupling of 4-phenyl-1,3-oxazol-2(3H)-ones with alkynes. The synthesis features a broad substrate scope and high regiospecificity.

Enantioselective synthesis of 2-oxazolidinones by ruthenium(ii)-NHC-catalysed asymmetric hydrogenation of 2-oxazolones

A highly enantioselective synthesis of optically active 4-substituted 2-oxazolidinones was described via ruthenium(ii)–NHC-catalysed asymmetric hydrogenation of 2-oxazolones.

An efficient synthesis of optically active 4-substituted 2-oxazolidinones by the ruthenium(ii)–NHC-catalysed asymmetric hydrogenation of 2-oxazolones was developed. Excellent enantioselectivities (up to 96% ee) and yields (up to 99%) were obtained for a variety of substrates, bearing a range of functional groups and useful motifs. The hydrogenation reaction was successfully scaled up to gram scale using low catalyst loading. Moreover, the utility of this methodology was demonstrated by the transformation of the enantioenriched product into the corresponding chiral β-amino alcohol, a bisoxazoline ligand, and the formal synthesis of (–)-aurantioclavine.

Synthesis of oxazolidinones: rhodium-catalyzed C-H amination of N-mesyloxycarbamates

N-Mesyloxycarbamates undergo intramolecular C-H amination reactions to afford oxazolidinones in good to excellent yields in the presence of rhodium(ii) carboxylate catalysts. The reaction is performed under green conditions and potassium carbonate is used, forming biodegradable potassium mesylate as a reaction by-product. This method enables the production of electron-rich, electron-deficient, aromatic and heteroaromatic oxazolidinones in good to excellent yields. Conformationally restricted cyclic secondary N-mesyloxycarbamates furnish cis-oxazolidinones in high yields and selectivity; DFT calculations are provided to account for the observed selectivity. trans-Oxazolidinones were prepared from acyclic secondary N-mesyloxycarbamates using Rh₂(oct)₄. The selectivity was reverted with a cytoxazone N-mesyloxycarbamate precursor using large chiral rhodium(ii) carboxylate complexes, affording the corresponding cis-oxazolidinone. This orthogonal selectivity was used to achieve the formal synthesis of (-)-cytoxazone.

Asymmetric hydrogenation of α-hydroxy ketones with an iridium/f-amphox catalyst: efficient access to chiral 1,2-diols

We successfully applied f-amphox ligands to the Ir-catalyzed asymmetric hydrogenation of α-hydroxy ketones to afford chiral 1,2-diols with excellent results.