Synthesis of Chiral Tritylpyrrolidine Derivatives and Their Application to Asymmetric Benzoyloxylation

α-Acyloxylation of Ketones/Cyclic Ethers Mediated by Hypervalent Iodine(III) Reagents as Oxidants and Nucleophilic Sources

This study describes a catalyst-free α-acyloxylation of ketones and a KBr-mediated α-acyloxylation of cyclic ethers. These conversions are effectively mediated by hypervalent iodine(III) reagents serving dual roles as the oxidant and nucleophilic source. Consequently, esters are produced directly in moderate to excellent yields. The proposed method features good functional group compatibility, a broad substrate scope, and high synthetic efficiency and is remarkably environmentally friendly.

Ginger blotches on Agaricus bisporus due to monoacetylphloroglucinol production by the pathogen Pseudomonas 'gingeri'

BACKGROUND

Agaricus bisporus is the most widely cultivated and consumed mushroom worldwide. Pseudomonas 'gingeri' is the only pathogenic causative agent of ginger blotch in A. bisporus. Current research on mushroom pathogenic biotoxins is limited to P. tolaasii, which causes brown blotch, while understanding of P. 'gingeri' is lacking, therefore identifying the toxins produced by P. 'gingeri' and evaluating their toxicity on A. bisporus is essential for understanding its pathogenic mechanisms.

RESULTS

A pathogenic bacterium isolated from fruiting bodies of A. bisporus with ginger blotch was identified as P. 'gingeri', and its main toxin identified as 2', 4', 6'-trihydroxyacetophenone monohydrate, also known as monoacetylphloroglucinol (MAPG). Its first known extraction from a mushroom pathogen is reported here. MAPG at 250 μg/mL significantly inhibited the host's mycelial growth, increased branching, caused the structure to become dense and resulted in folds appearing on the surface. An MAPG concentration of 750 μg/mL MAPG led to mycelial death. P. 'gingeri' had high MAPG production in medium containing 0.1 mol/L of either glucose or mannitol (4.30 and 1.85 μg/mL, respectively), and mycelia were inhibited by 69.6% and 41.1%, respectively. The MAPG content was significantly lower in other carbon source media.

CONCLUSION

This work provides a detailed description of the structure and virulence of the P. 'gingeri' biotoxin, which has implications for understanding its pathogenic mechanism and for exploring precise control strategies for A. bisporus ginger blotch disease, such as the development of MAPG inhibitory factors. © 2023 Society of Chemical Industry.

Construction of three contiguous stereocenters through amine-catalyzed asymmetric aldol reactions

Three contiguous stereocenters were constructed by an amino acid-catalyzed asymmetric aldol reaction of α-siloxyketones with racemizable α-haloaldehydes via dynamic kinetic resolution. One-pot catalytic asymmetric synthesis of the highly functionalized products could also be accomplished by the α-bromination of simple aldehydes and the subsequent asymmetric aldol reaction.

Recent Advances in Asymmetric Synthesis of Pyrrolidine-Based Organocatalysts and Their Application: A 15-Year Update

In 1971, chemists from Hoffmann-La Roche and Schering AG independently discovered a new asymmetric intramolecular aldol reaction catalyzed by the natural amino acid proline, a transformation now known as the Hajos-Parrish-Eder-Sauer-Wiechert reaction. These remarkable results remained forgotten until List and Barbas reported in 2000 that L-proline was also able to catalyze intermolecular aldol reactions with non-negligible enantioselectivities. In the same year, MacMillan reported on asymmetric Diels-Alder cycloadditions which were efficiently catalyzed by imidazolidinones deriving from natural amino acids. These two seminal reports marked the birth of modern asymmetric organocatalysis. A further important breakthrough in this field happened in 2005, when Jørgensen and Hayashi independently proposed the use of diarylprolinol silyl ethers for the asymmetric functionalization of aldehydes. During the last 20 years, asymmetric organocatalysis has emerged as a very powerful tool for the facile construction of complex molecular architectures. Along the way, a deeper knowledge of organocatalytic reaction mechanisms has been acquired, allowing for the fine-tuning of the structures of privileged catalysts or proposing completely new molecular entities that are able to efficiently catalyze these transformations. This review highlights the most recent advances in the asymmetric synthesis of organocatalysts deriving from or related to proline, starting from 2008.

Visible light-assisted organocatalytic α-acyloxylation of ketones using carboxylic acids and N-halosuccinimides

The α-acyloxylcarbonyl motif can be found in many important pharmaceuticals and biologically active natural products and their derivatives. In this manuscript, the direct synthesis of α-acyloxylketones from ketones and readily available carboxylic acids was realized using a photo-assisted halogen bond-mediated organocatalytic α-acyloxylation reaction. The desired α-acyloxylation products were obtained in good to high yields.

Regioselective benzoyloxylative dearomatization of naphthols by benzoyl peroxide under catalyst-free conditions

A direct regioselective benzoyloxylative dearomatization of both α- and β-naphthols by benzoyl peroxide under an air atmosphere, and radical inhibitor- and catalyst-free conditions at room temperature is described. The methodology provides a new efficient strategy for the construction of α-ketol derivatives bearing an oxo-quaternary carbon center from naphthols with good to excellent yields.

Green Chemistry Meets Asymmetric Organocatalysis: A Critical Overview on Catalysts Synthesis

Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (EG factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process.

Synthesis of enantioenriched α-heteroatom functionalised aldehydes by chiral organocatalysis and their synthetic applications

Asymmetric organocatalysis is a versatile method for the enantioselective α-functionalisation of aldehydes. The synthetic scope for chiral α-heteroatom substituted aldehydes is examined including their applications in synthesis.

A supramolecular bifunctional iridium photoaminocatalyst for the enantioselective alkylation of aldehydes

The construction of a hybrid metal-organo-photoredox catalyst based on the conjugation of an imidazolidinone organocatalyst and Ir(ppy)2(bipy) (ppy = 2-phenylpyridine, bipy = bipyridine) is described. The introduction of the desired organocatalyst into the bipyridine moiety is quite modular, allowing the preparation of different hybrid photocatalysts, and is realized though a simple click reaction. The hybrid photocatalysts obtained were employed in the benchmark photoredox alkylation of aldehydes. Remarkably, the conjugation of a first-generation MacMillan catalyst produces an active and stereoselective hybrid photoredox catalyst.

Recent developments in stereoselective organocatalytic oxyfunctionalizations

In this chapter, asymmetric at carbon oxidations using organocatalytic systems reported from 2012 up to 2018 have been illustrated. Asymmetric epoxidations and oxidation of heteroatom-containing molecules were not included. The processes selected encopass alpha-hydroxylation of carbonyl compounds, dihydroxylation and dioxygenation of alkenes, Baeyer-Villiger and oxidative desymmetrization reactions.

Chiral amine-catalyzed asymmetric conjugate addition of aldehydes to α-phenylselenoenones as formal Z-allylating agents

α-Selenoenones could be employed as Z-allyl precursors in the chiral amine-catalyzed asymmetric conjugate addition of aldehydes.

Construction of half-sandwich multinuclear complexes including tunnel architectures via C–H-activation-directed assembly

Half-sandwich bi-, tetra-, hexa- and octanuclear complexes were prepared via C–H-activation-directed assembly based on three aromatic ligands. A series of tunnel architectures were observed in the complexes, with guest molecules in certain parts.