Gillesds

Asymmetric photocatalysis: This review provides a current overview of visible-light-induced asymmetric photocatalysis enabled by chiral organocatalysts. Innovative approaches including mono- and dual-catalysis are discussed. Chiral organocatalysis such as enamine catalysis, iminium-ion catalysis, Brønsted acid/base catalysis, and N-heterocyclic carbene catalysis have been exploited to induce chirality transfer of photocatalytic reactions. We hope that this review will spark new ideas for designing novel strategies in the field of asymmetric photocatalysis.

Abstract

Visible-light photocatalysis has advanced as a versatile tool in organic synthesis. However, attaining precise stereocontrol in photocatalytic reactions has been a longstanding challenge due to undesired photochemical background reactions and the involvement of highly reactive radicals or radical ion intermediates generated under photocatalytic conditions. To address this problem and expand the synthetic utility of photocatalytic reactions, a number of innovative strategies, including mono- and dual-catalytic approaches, have recently emerged. Of these, exploiting chiral organocatalysis, such as enamine catalysis, iminium-ion catalysis, Brønsted acid/base catalysis, and N-heterocyclic carbene catalysis, to induce chirality transfer of photocatalytic reactions has been widely explored. This Review aims to provide a current, comprehensive overview of asymmetric photocatalytic reactions enabled by chiral organocatalysts published through June 2021. The substrate scope, advantages, limitations, and proposed reaction mechanisms of each reaction are discussed. This review should serve as a reference for the development of visible-light-induced asymmetric photocatalysis and promote the improvement of the chemical reactivity and stereoselectivity of these reactions.

Nature Communications, Published online: 26 October 2021; doi:10.1038/s41467-021-26428-z

The facile synthesis of C-aryl nucleoside analogues from readily available furanose acetates and aryl iodides is disclosed. This nickel-catalyzed cross-electrophile coupling showed good functional-group compatibility and excellent β-selectivity. The high chemoselectivity with respect to aryl iodides enabled the efficient preparation of a variety of C-aryl halide furanosides suitable for various post-functionalization reactions.

Abstract

Canonical nucleosides are vulnerable to enzymatic and chemical degradation, yet their stable mimics—C-aryl nucleosides—have demonstrated potential utility in medicinal chemistry, chemical biology, and synthetic biology, although current synthetic methods remain limited in terms of scope and selectivity. Herein, we report a cross-electrophile coupling to prepare C-aryl nucleoside analogues from readily available furanosyl acetates and aryl iodides. This nickel-catalyzed modular approach is characterized by mild reaction conditions, broad substrate scope, excellent β-selectivity, and high functional-group compatibility. The exclusive chemoselectivity with respect to the aryl iodide enables efficient preparation of a variety of C-aryl halide furanosides suitable for various downstream transformations. The practicality of this transformation is demonstrated through the synthesis of a potent analogue of a naturally occurring NF-κB activator.

The Cu-catalyzed oxidative cross-coupling of phenols with methylboronic acid provides a synthetic route to aryl methyl ethers, expanding the scope of Chan-Evans-Lam alkylation. The reaction proceeds under “open flask” conditions with no additional oxidant. Electron-deficient phenol derivatives are methylated in high yields, and some N-heterocycles are tolerated.

Abstract

A Cu-catalyzed oxidative cross-coupling of phenols with methylboronic acid to form aryl methyl ethers has been developed, expanding the scope of Chan-Evans-Lam alkylation. Electron-deficient phenol derivatives with a broad array of functional groups are methylated in high yields. Increased reaction temperature and catalyst loading enables the methylation of substrates incorporating pyridine and dihydroquinolone motifs. Electron-rich phenol derivatives are poor substrates for the methylation; the characterization of C−H homodimerization products formed from these substrates illuminates a competing mechanistic pathway.

Reviewing glycerol: Steric hindrance and electronic configuration in Pt and Ir based nanostructured catalysts are critically important for tunable selectivity towards 1,3-propanediol during glycerol conversion. Sophisticated design of heterogeneous catalyst is highly desired for industrial technological development.

Abstract

Catalytic conversion of glycerol to 1,3-propanediol represents a most promising synthetic route for various specialty products in plastics, pharmaceuticals and textile industries. How to enhance chemoselectivity of 1,3-propanediol over other co-products still remains a grand challenge in this area in the past two decades. While particle size, metal-support and surface acidity have been extensively investigated for catalyst development in literature, fundamental studies on spatial and electronic configuration of “metal-solid acid” interfacial catalysts for tunable activity and selectivity are yet to be established in this field. In this context, interfacial steric hindrance and electronic transfer effect is critical for tunable activity and selectivity for metal catalysts. Therefore, in this review article, we have conducted a comprehensive and critical discussion on how steric hindrance and electronic coupling at metal-acid interfaces affect catalytic activation of internal −OH group in glycerol molecule. Selected highlights on the mechanistic investigation for ex-situ and in-situ formed Brønsted acidity over Pt-WO_x and Ir−ReO_x catalysts, have been discussed with experimental and computational details. The outcome of this review will provide important insights on controllable manipulation of spatial and electronic structures for selective hydrogenation reactions with broader industrial applications.

Nature Communications, Published online: 12 October 2021; doi:10.1038/s41467-021-26170-6

Secondary PNP-pincer complexes are found to outperform tertiary analogue in various reactions as the former one exhibits metal-ligand cooperativity (MLC). But in a recent experiment of CO₂ reduction reaction in alkaline medium, the tertiary complex has shown a much higher turnover number than the secondary complex and the underline reason is assumed to deteriorate effects of MLC on the secondary complex. So, here detailed density functional theory based kinetic calculations have been carried out explaining the actual reason for this anomaly.

Abstract

Pincer ligated coordination complexes of base metals have shown remarkable catalytic activity for hydrogenation/dehydrogenation of CO₂. The recently reported MeN[CH₂CH₂(ⁱPr₂)]₂Co(I)PNP-pincer complex was shown to exhibit substantially higher catalytic activity in comparison to the corresponding catalyst, HN[CH₂CH₂(ⁱPr₂)]₂Co(I)PNP, bearing a secondary nitrogen center on the pincer ligand. Here, we computationally investigate the mechanisms for hydrogenation of CO₂ to formate catalyzed by these two Co-PNP complexes to explain how such a small structural difference could have a sizable impact on their catalytic activity. Plausible hydrogenation routes were examined in details and our findings provide solid support for the experimental observations. Our results reveal that such trends in catalytic activity could be explained from the lower activation barrier for the hydride transfer step upon changing the pincer nitrogen center from secondary to tertiary.

Water is the green solvent of choice for many reactions, but it can be challenging to extract polar compounds from aqueous solution. This problem can often be addressed with n-butanol, which can be produced sustainably from biomass. The wet n-butanol phase is a nanomaterial where polar compounds can be accommodated in inverse micelles of water. Ways to determine a priori whether n-butanol is a suitable extractant are also discussed.

Abstract

Water is the solvent of choice in terms of greenness and sustainability. However, it can be difficult to isolate very polar products from water. Here, we discuss the use of n-butanol as a solvent to extract polar compounds from aqueous solution. n-Butanol produces high yields and can also be sourced sustainably from biomass, which makes it attractive from a climate perspective. The reason for its high efficiency is that the wet n-butanol phase is a nanomaterial that incorporates little pockets of water that can stabilize the polar solute. Thus, the environment remains very water-like, and the presence of hydrophobic groups can tip the equilibrium towards the n-butanol phase. We also discuss a simple estimate whether n-butanol will be an efficient extraction solvent for the compound of interest based on common public databases. This should help to guide practicing organic chemists during the solvent selection process.

Abstract

The use of transition-metal complexes as photocatalysts have allowed the performance of diverse organic transformations in an outstanding manner, characterized not only by high yields, TOF, and selectivity values, but also by modulating and providing access to novel molecular structures that, without them, would be difficult if not impossible. However, one of the biggest concerns regarding the use of these photocatalysts relies on the difficulties associated with their isolation from reaction media and reutilization once the chemical process ends. The above, besides contaminating reaction products and requiring out tedious purification processes, prompts the inevitable loss of the catalyst, directly affecting its recyclability. In addition, this situation results in negative outcomes from an economic and environmental perspective, since transition-metal complexes are usually expensive materials, and their unsuccessful recovery could result in leakage into the environment. These drawbacks served as inspiration for the elaboration of the present review focused on the development of novel strategies developed during the last decade for the successful recovery of these species. The strategies summarized herein, whether for homogeneous or heterogeneous systems, are based on the use of thermotropic solvents, changes in the hydrophilic balance of the catalyst, the employment of polymers, copolymers, porous macromolecular structures, and inorganic nanostructures as support of these entities. Moreover, the use of organized and confining media, such as micelles and gels in this context, is also discussed. We hope that this review will motivate the search for new strategies to develop novel catalytic systems, understanding that high performance is based not only on yields but also on recyclability, sustainability, and responsibility to the environment.