Mathias

A new family of metal nanoparticles loaded COFs catalysts have been prepared via one-pot construction strategy without lab-cost procedures, demonstrating excellent hydrogenation performance under mild conditions. The new strategy can be further evolved as into a versatile platform to create new COFs materials and explore the resultant applications.

Abstract

The catalysis performance of metal nanoparticles (NPs) will be significantly deteriorated because of their spontaneous agglomeration during practical applications. Covalent-organic frameworks (COFs) materials with functional groups and well-defined channels benefit for the dispersion and anchor of metal ions and the confined growth of metal NPs, working as an ideal platform to compose catalytic systems. In this article, we report a one-pot strategy for the preparation of metal NPs loaded COFs without the need of post-modification. During the polymerization process, the pre-added metal ions were stabilized by the rapidly formed COF oligomers and hardly disturb the construction of COFs. After reduction, metal NPs are uniformly anchored on the COF matrix. Eventually, a wide spectrum of metal NPs, including Au, Pd, Pt, AuPd, CuPd, CuPt and CuPdPt, loaded COFs are successfully prepared. The versatility and metal ions anchoring mechanism are verified with four different COF matrixes. Taking AuPd NPs as example, the resultant AuPd NPs loaded COF materials can selectively decompose ammonium formate and produce hydrogen in-situ, exhibiting over 99 % conversion of hydrodechlorination for chlorobenzenes and nitro-reduction reaction for nitroaromatic compounds under ambient temperature in aqueous solution.

A highly efficient synthesis of triazoles from lignin major linkages through one-pot cascade reactions was reported in yields up to 97 %. The reaction pathway includes selective cleavage of double C−O bonds, cycloaddition, and dehydrogenation. This route provides a promising alternative for pharmaceutically triazoles beyond classic “click reaction”, which paves the way for widening applications of lignin functionalize end products of lignin to meet future biorefinery demands.

Abstract

An efficiently catalyzed synthesis of pharmaceutically relevant 1,2,3-trazoles from renewable resources is highly desirable. However, due to incompatible catalysis conditions, this endeavor remained challenging so far. Herein, a practical access protocol to 1,2,3-triazoles, starting from lignin phenolic β-O-4 with γ-OH group utilizing a vanadium-based catalyst is presented. A broad substrate scope reaching up to 97 % yield of 1,2,3-triazoles are obtained. The reaction pathway includes selective cleavage of double C−O bonds, cycloaddition, and dehydrogenation. Mechanistic studies and density-functional theory (DFT) calculations suggest that the V-based complex acts as a bifunctional catalyst for both selective C−O bonds cleavage and dehydrogenation. This synthetic pathway has been applied for the synthesis of pharmacological and biological active carbohydrate derivatives starting from biomass components as feedstock, enabling a potential sustainable route to triazolyl carbohydrate derivatives, which paves the way for lignin-based heterocyclic aromatics in the pharmaceutical applications.

Electrochemical oxidation of lignin-derived guaiacols & syringols leads to cyclohexadienone intermediates in moderate to good yields. These react with ethyl glycinate hydrochloride under mild conditions to afford lignin-based anilines. This methodology can be incorporated to reductive catalytic fractionation processes towards selective obtention of 4-propanol-2-methoxyaniline (1Gb) and 4-propyl-2-methoxyaniline (2Gb) in up to 4.6 wt% yield.

Abstract

The development of environmentally friendly methods for the valorization of important phenolic platform chemicals originating directly from lignin-first depolymerization into value-added N-chemicals, such as aniline derivatives, is of high industrial interest. In this work, we tackle this challenging transformation by the judicious combination of electrochemical conversion and chemical functionalization steps. In the first step, lignin-derived para-substituted guaiacols and syringols undergo an atom-efficient, room-temperature anodic oxidation using methanol both as solvent and reagent towards the formation of the corresponding cyclohexadienone derivatives, which are subsequently converted to synthetically challenging ortho-methoxy substituted anilines by reaction with ethyl glycinate hydrochloride under mild conditions. The developed method was applied to crude lignin depolymerization bio-oils, derived from reductive catalytic fractionation (RCF) mediated either by copper-doped porous metal oxide (Cu₂₀PMO) or Ru/C, allowing the selective production of 4-propanol-2-methoxyaniline (1Gb) and 4-propyl-2-methoxyaniline (2Gb), respectively, from pine lignocellulose. Finally, the application of 2Gb was further studied in the synthesis of carbazole 2Gc, a lignin-derived analogue of biologically active alkaloid murrayafoline A.

Publication date: 14 December 2023

Source: Chem, Volume 9, Issue 12

Author(s): Raquel Sánchez-Bento, Baptiste Roure, Josep Llaveria, Alessandro Ruffoni, Daniele Leonori

Publication date: 14 December 2023

Source: Chem, Volume 9, Issue 12

Author(s): Petros L. Gkizis, Ierasia Triandafillidi, Christoforos G. Kokotos

Synthesis
DOI: 10.1055/s-0042-1751503

Direct reductive coupling of nitro compounds with C-coupling partners is an atom- and step-economical strategy to access polyfunctional advanced amines. Due to the extremely complex process involved in the reduction of nitro compounds and the high reactivity of N,O-intermediates, few reliable methodologies have been reported for the reductive coupling of nitro compounds since the initial studies. To address this significant challenge, numerous endeavors have been devoted to this important area over the past hundred years. In this short review, we summarize recent advances in this domain and discuss the mechanisms of these appealing reductive coupling transformations.1 Introduction2 Reductive Coupling of Nitro Compounds with Organometallic Reagents3 Reductive Coupling of Nitro Compounds with Arylboronic Acids4 Reductive Coupling of Nitro Compounds with Alkenes5 Reductive Coupling of Nitro Compounds with Alkyl/Aryl Halides6 Reductive Coupling of Nitro Compounds with Alcohols and Their Derivatives7 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Described herein is the synthesis of sulfonyl-protected azoxy compounds from nitroso arenes and iminoiodinanes by using visible light irradiation. The bench-stable sulfonyl azoxy compounds can be used in azoxy group transfer reactions for C(sp3)−H functionalization of ether molecules and 1,2-difunctionalization of vinyl ethers.

Abstract

The azoxy functional group is an important structural motif and represents the formally oxidized counterpart of the azo group. Azoxy compounds find numerous applications ranging from pharmaceuticals to functional materials, yet their synthesis remains underdeveloped with a main focus on the formation symmetric azoxy compounds. To overcome challenges in the synthesis of such unsymmetric azoxy compounds, we designed a process employing readily accessible nitroso compounds and iminoiodinanes. This method builds on the use of visible light irradiation to generate a triplet nitrene from iminoiodinanes, which is trapped by nitroso arenes to give access to sulfonyl-protected azoxy compounds with a good substrate scope and functional group tolerance. We further describe two applications of these sulfonyl-protected azoxy compounds as radical precursors in synthesis, where the whole azoxy group can be transferred and employed in C(sp³)−H functionalization of ethers or 1,2-difunctionalization of vinyl ethers. All of the reactions occurred at room temperature under visible light irradiation without the addition of any photoredox catalysts and additives. Control experiments, mechanism investigations, and DFT studies well explained the observed reactivity.

Synlett
DOI: 10.1055/a-2153-6687

We report the first visible-light-promoted synthesis of vinyloxaziridines from simple conjugated nitrones. We have found that vinyl nitrones formed by the condensation reaction between conjugated carbonyls and hydroxylamines undergo visible-light-promoted energy-transfer isomerization to the respective vinyloxaziridines in very high yields and selectivities. The reaction scope expands to a large array of substitution patterns, and evidence indicates that the proposed energy-transfer pathway is the predominant mechanism for this transformation.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Photoredox catalysis: This perspective highlights the challenges faced by the pharmaceutical industry in transferring a successful photoredox process to scale for API development and manufacture. Examples of successful use in API development and the difficulties that were overcome are presented and demonstrate the advantages this technology can bring to the industry.

Abstract

Photoredox catalysis has advanced significantly over the last fifteen years, with improvements in technology facilitating implementation in both academic and industrial settings. Despite these advances, the uptake of photoredox catalysis in pharmaceutical development and manufacture has been slow, in part due to the challenge of developing a robust, transferable process. This perspective provides insight on the successes and difficulties encountered when applying photoredox catalysis to pharmaceutical development. It is hoped greater understanding of the challenges faced by the pharmaceutical industry will inform future research and encourage collaboration.

Metal-catalyzed C−H functionalization of aldehydes and ketones has recently significantly grown thanks to a concept of transient directing group. In this strategy, the directing group is generated in situ which limits the functional group manipulation as well as allows new reactivities. This review presents the latest research works carried out in this area over the period 2020–2023.

Abstract

In order to directly functionalize C−H bonds of complex molecules and, in particular, to control the regioselectivity of the reaction, a wide range of directing groups has been used. However, these directing groups need to be installed and removed for further applications, which may limit the use of C−H activation in synthesis. Concerning aldehydes and ketones, a transient directing group strategy has recently emerged to overcome this drawback. The addition of an additive, in general an amine, allowed the in situ formation of the real directing group to achieve C−H activation. This review presents the latest developments in the field over the period 2020–2023.

This work demonstrates a hydrogen-transfer reductive catalytic fractionation of lignocellulose. By incorporating a hydrogen bond acceptor of choline chloride, high yields of aromatic monomers with switchable selectivity are achieved. Choline chloride greatly improves lignin dissolution and tailors the hydrogenolysis of lignin. The proposed strategy promotes the development of targeted lignin valorization and lignin-first biorefinery.

Abstract

Lignin solubilization and in situ hydrogenolysis are crucial for reductive catalytic fractionation (RCF) of lignocellulose to aromatic monomers. In this study, we reported a typical hydrogen bond acceptor of choline chloride (ChCl) to tailor the hydrogen-donating environment of the Ru/C-catalyzed hydrogen-transfer RCF of lignocellulose. The ChCl-tailored hydrogen-transfer RCF of lignocellulose was conducted under mild temperature and low-pressure (<1 bar) conditions, which was applicable to other lignocellulosic biomass sources. We obtained an approximate theoretical yield of propylphenol monomer of 59.2 wt % and selectivity of 97.3 % using an optimal content of ChCl (10 wt %) in ethylene glycol at 190 °C for 8 h. When the content of ChCl in ethylene glycol was increased to 110 wt %, the selectivity of propylphenol switched toward propylenephenol (yield of 36.2 wt % and selectivity of 87.6 %). The findings in this work provide valuable information for transforming lignin from lignocellulose into value-added products.

Cleave the bond: For the first time, efficient aerobic oxidative conversion of secondary aromatic alcohols into aromatic aldehydes is achieved, using non-noble metal catalysts and environmentally benign O₂ without any additional base.

Abstract

Effective cleavage and functionalization of C(OH)−C bonds is of great importance for the production of value-added chemicals from renewable biomass resources such as carbohydrates, lignin and their derivatives. The efficiency and selectivity of oxidative cleavage of C(OH)−C bonds are hindered by their inert nature and various side reactions associated with the hydroxyl group. The oxidative conversion of secondary alcohols to produce aldehydes is particularly challenging because the generated aldehydes tend to be over-oxidized to acids or the other side products. Noble-metal based catalysts are necessary to get satisfactory aldehyde yields. Herein, for the first time, the efficient aerobic oxidative conversion of secondary aromatic alcohols into aromatic aldehydes is reported using non-noble metal catalysts and environmentally benign oxygen, without any additional base. It was found that Cu^I−1,10-phenanthroline (Cu−phen) complex showed outstanding performance for the reactions. The C(OH)−C bonds of a diverse array of aromatic secondary alcohols were effectively cleaved and functionalized, selectively affording aldehydes with excellent yields. Detailed mechanism study revealed a radical mediated pathway for the oxidative reaction. We believe that the findings in this work will lead to many explorations in non-noble metal catalyzed oxidative reactions.

Synthesis
DOI: 10.1055/a-2081-1830

The ubiquity of carboxylic acids as naturally derived or man-made chemical feedstocks has spurred the development of powerful, decarboxylative C–C bond-forming transformations for organic synthesis. Carboxylic acids benefit not only from extensive commercial availability, but are stable surrogates for organohalides or organometallic reagents in transition-metal-catalysed cross-coupling. Open shell reactivity of carboxylic acids (or derivatives thereof) to furnish carbon-centred radicals is proving transformative for synthetic chemistry, enabling novel and strategy-level C(sp3)–C bond disconnections with exquisite chemoselectivity. This short review will summarise several of the latest advances in this ever-expanding area.1 Introduction2 Improved Decarboxylative Arylations3 sp3–sp3 Cross-Coupling of Carboxylic Acids with Aliphatic Bromides4 sp3–sp3 Cross-Coupling of Carboxylic Acids with Aliphatic Alcohols and Amines5 Doubly Decarboxylative sp3–sp3 Cross-Coupling of Carboxylic Acids6 Decarboxylative C–C Bond Formation from (Hetero)aryl Carboxylic Acids7 Conclusions
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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