Jonas Wuyts

Publication date: 30 January 2024

Source: Tetrahedron, Volume 151

Author(s): Christian Bruneau

O-Demethylation (ODM) is a strategic tool to unlock lignin applications for drop-in and new commodity, fine & specialty chemicals.

Abstract

Lignin represents the largest aromatic carbon resource in plants, holding significant promise as a renewable feedstock for bioaromatics and other cyclic hydrocarbons in the context of the circular bioeconomy. However, the methoxy groups of aryl methyl ethers, abundantly found in technical lignins and lignin-derived chemicals, limit their pertinent chemical reactivity and broader applicability. Unlocking the phenolic hydroxyl functionality through O-demethylation (ODM) has emerged as a valuable approach to mitigate this need and enables further applications. In this review, we provide a comprehensive summary of the progress in the valorization of technical lignin and lignin-derived chemicals via ODM, both catalytic and non-catalytic reactions. Furthermore, a detailed analysis of the properties and potential applications of the O-demethylated products is presented, accompanied by a systematic overview of available ODM reactions. This review primarily focuses on enhancing the phenolic hydroxyl content in lignin-derived species through ODM, showcasing its potential in the catalytic funneling of lignin and value-added applications. A comprehensive synopsis and future outlook are included in the concluding section of this review.

Synlett
DOI: 10.1055/s-0043-1763652

We report the synthesis of chiral N-heterocyclic carbene/guanidine bifunctional ligands from readily available amino alcohols. The resulting chiral bifunctional copper(I) complexes are active catalysts in an asymmetric hydrogenation of ketones. We show that the chiral linker unit can be employed for the transfer of stereoinformation.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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Using highly reactive gases is appealing for efficient organic synthesis but leads to inherent safety and processing limitations. Embracing continuous-flow technologies helps mitigating those while improving the performance of the systems. Tailored catalyst incorporation opens doors to novel reaction pathways and process intensification. Optimized mass transfer in multiphasic mixtures is key to its success, especially when solids are present.

Abstract

The use of reactive gaseous reagents for the production of active pharmaceutical ingredients (APIs) remains a scientific challenge due to safety and efficiency limitations. The implementation of continuous-flow reactors has resulted in rapid development of gas-handling technology because of several advantages such as increased interfacial area, improved mass- and heat transfer, and seamless scale-up. This technology enables shorter and more atom-economic synthesis routes for the production of pharmaceutical compounds. Herein, we provide an overview of literature from 2016 onwards in the development of gas-handling continuous-flow technology as well as the use of gases in functionalization of APIs.

A catalytic method to transfer formal equivalents of HF from fluoroalkanes to an alkyne is reported. The method leads to a simple approach generating geminal difluoroalkanes and it tolerates numerous sensitive functional groups including halogen, protected amine, ester and thiophene substituents. Poly(vinylidene difluoride) (PVDF) was shown to act as an HF donor in place of the fluoroalkane.

Abstract

In this paper, we report BF₃ ⋅ OEt₂ as a catalyst to shuttle equivalents of HF from a fluoroalkane to an alkyne. Reactions of terminal and internal aliphatic alkynes led to formation of difluoroalkane products, while diarylalkynes can be selectively converted into fluoroalkenes. The method tolerates numerous sensitive functional groups including halogen, protected amine, ester and thiophene substituents. Mechanistic studies (DFT, probe experiments) suggest the catalyst is involved in both the defluorination and fluorination steps, with BF₃ acting as a Lewis acid and OEt₂ a weak Lewis base that mediates proton transfer. In certain cases, the interconversion of fluoroalkene and difluoroalkane products was found to be reversible. The new catalytic system was applied to demonstrate proof-of-concept recycling of poly(vinylidene difluoride).

Abstract

Polybutylene succinate (PBS) is one of the most important biobased plastics, based on the amount produced. Owing to its high melting point and resemblance to petroleum-based plastics (i. e. PP), PBS becomes one of the emerging bioplastics with an array of applications. PBS is manufactured by polymerization of 1,4-butanediol and succinic acid. Thus, it is of great importance to ensure the use of renewable resources to produce the PBS precursors. As the second most abundant carbohydrate monomer on Earth, D-xylose will be a suitable candidate for this purpose. In this work, we combined protein engineering with chemical oxidation by gold catalyst to enable transformation of D-xylose to 1,4-butanediol and succinic acid simultaneously. In silico docking studies and semi rational design were employed to create variants of the key enzyme, branched chain α-keto acid decarboxylase (KdcA) with higher affinity for the intermediates in the production of 1,4-butanediol and succinic acid. Direct enzymatic biotransformation would result in a production of both monomers with 3:1 ratio, thus not readily suitable for a direct polymerization to PBS. By developing a one-pot multi-step chemo-enzymatic approach with a gold catalyst to perform the first oxidation step, we could achieve a final product ratio of 1:1. Application of an engineered KdcA variant allowed us to achieve >98% yield after four hours transformation. In contrast, after 24 h transformation, >10% intermediate was still observed when the original variant was used. We anticipate this new approach could serve as an alternative route for biotechnological productions of PBS and its precursors.

Nature, Published online: 01 December 2023; doi:10.1038/d41586-023-03393-9

Synlett
DOI: 10.1055/a-2184-5115

Oxocarbenium cations are key intermediates for the stereocontrolled construction of carbon–carbon bonds. In particular, we have developed a wide range of stereoselective aldol-like processes that take advantage of the high reactivity of the oxocarbenium species arising from acetals, glycals, and orthoesters with metal enolates. This Account describes the development and optimization of such processes, together with other significant contributions, with a particular emphasis on their application to the synthesis of natural products.1 Introduction2 Substrate-Controlled Processes2.1 Additions to Acyclic Acetals2.2 Additions to Cyclic Acetals3 Chiral-Auxiliary-Based Processes3.1 Additions to Acyclic Acetals3.2 Additions to Cyclic Acetals and Glycals4 Chiral-Catalysis-Based Processes4.1 Organocatalysis4.2 Metal Catalysis5 Conclusions
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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Synlett
DOI: 10.1055/a-2170-2976

Highly volatile organic compounds (VOCs) with boiling points (bp) around or below room temperature are generally difficult to manipulate precisely in liquid-phase organic reactions although they offer significant atom-economic advantages. We have developed a novel approach using a jacketed syringe pump to enable the formylation of organolithium species in a continuous-flow system under ambient pressure. Methyl formate (bp 32 °C) worked as a formylating agent and was successfully delivered to the continuous operation for over 30 minutes in our microflow system. This methodology was successfully expanded to the application of acetaldehyde (bp 21 °C) and heptafluoropropyl bromide (bp 12 °C).
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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A Fe-catalyzed N -formylation protocol for amines by using bio-derived glycolic acid as a C1 building block is presented. This protocol exemplifies a modified heterogeneous Fenton system being repurposed for the synthesis of fine chemicals from bio-feedstocks, offering highly competitive product yields.

Abstract

Due to current global issues involving climate change and energy crises, it requires several complete overhauls in process developments sectors of energy and chemical manufacturing industries towards more sustainable and readily applicable protocols. As a contribution to this goal with an example of iron-based catalysis, this work presents a synthetic protocol for synthesis of N-formamides with glycolic acid as a C1 bio-building block, which is catalyzed through earth abundant and magnetically active Fe powder as catalyst. The protocol was applied to a wide variety of substrates affording yields in the range of 68–94 % and also performed well at 1 gram and 5 gram scale with yields of up to 86 % and 83 %, respectively. The catalyst was shown to be reusable up to 4 runs and the spent catalyst has been studied using PXRD and XPS analyses to determine catalyst deactivation and its remediation. Plausible reaction pathway has been suggested based on control experiments and GC-MS results for the process.

Recent advances in the application of molybdenum carbide-based catalysts for catalytic reactions in the field of hydrogenation and dehydrogenation are reviewed. Molybdenum carbide is a transition metal carbide-based catalyst that can effectively replace noble metal catalysts and can be modified for de-/hydrogenation by doping, morphology control, supporting and encapsulation. An outlook for future work is summarized.

Abstract

The catalytic de/hydrogenation process is important in the fields of petrochemical refining, fuel synthesis, drug synthesis, CO₂ conversion, and hydrogen synthesis, where the construction of low-cost and high-efficiency de/hydrogenation catalysts attracting significant attentions. Molybdenum carbide (Mo_xC), as a non-noble transition metal carbide catalyst, has been widely investigated for hydrogen activation. Herein, research progress and achievements of molybdenum carbide for catalytic de/hydrogenation are reviewed. Additional attention is paid to the structure and crystal phase of molybdenum carbide, and various modification strategies related to the catalytic activity regulation are summarized. Finally, the application prospect of molybdenum carbide catalysts is also discussed. This review provides a framework reference for further understanding the design and utilization of molybdenum carbide catalysts for catalytic de/hydrogenation and the key research problems to be addressed.

Nitrogen, oxygen codoped onion-like carbon exhibits relatively high dimethoxymethane (DMM) selectivity from methanol at low reaction temperature (150 °C). The present research does not only demonstrate that nanocarbon is a promising catalyst for one-step synthesis of DMM but also highlights the key to increase the selectivity of DMM is to balance the redox and acidity of carbon catalysts.

Abstract

One-step synthesis of dimethoxymethane (DMM) via methanol oxidation under the catalysis of nanocarbon is a green and sustainable chemical industrial process. In this work, nitrogen, oxygen codoped onion-like carbon (NOLC) were prepared via a simple thermal treatment method, which was applied to one-step synthesis of DMM. The physicochemical characterization results revealed that nitrogen and oxygen elements were successfully introduced into the onion-like carbon (OLC) catalyst. The proposed NOLC catalysts exhibited DMM selectivity of 75 % at relatively low reaction temperature (150 °C) and long stability over 10 h. In-situ titration experiments revealed that the carboxylic acid groups on NOLC surface were the main acidic active sites. The Clemmensen reduction control experiment revealed that the carbonyl groups were the active sites for the formation of formaldehyde. The basic reaction kinetics and mechanism such as reaction orders, apparent activation energy and rate determining step etc. for one-step synthesis of DMM via methanol were studied systematically. The present work shows an important structure-function relation for designing highly efficient nanocarbon catalyzed methanol conversion reaction system that the appropriate redox/acid intensity on catalyst surface through the modulation of N and O elements would effectively improve the selectivity of DMM.

Publication date: 16 November 2023

Source: Tetrahedron, Volume 148

Author(s): Zilin Fang, Kaishuo Zhao, Xixuan Zhao, Shuai Peng, Yongguo Liu, Baoguo Sun, Hongyu Tian, Sen Liang

The concept of support engineering using phosphorus-modified silica is used to modulate catalyst-support interactions and to stabilize catalytically active species on the support. Following this approach, an enhanced catalytic performance and catalyst stability as well as a reduction of metal leaching can be achieved for Pd₃P.

Abstract

Herein we report the use of a supported Pd₃P catalyst for Heck coupling reactions. For the stabilisation of Pd₃P and Pd, as reference system, the silica support material was modified via phosphorus doping (0.5 and 1 wt % P). Through this so-called support engineering approach, the catalytic activity of Pd₃P was clearly enhanced. Whereas an iodobenzene conversion of 79 % was witnessed for Pd₃P@SiO₂ in the coupling of styrene and iodobenzene in 1 h, 90 % conversion could be achieved using Pd₃P@1P-SiO₂. This improved catalytic activity probably stems from an electronic modulation of the support surface via the introduction of phosphorus. Simultaneously, the recyclability was boosted and the Pd₃P@1P-SiO₂ catalyst has shown to maintain its catalytic activity over several recovery tests. Hereby, metal leaching could almost be suppressed completely to 3 % by the use of a P-modified silica support.

The Cover Feature shows a lab journal in a library with, on the left-hand page, examples from the literature, and on the right-hand page, the catalytic reaction that is envisioned. In their Research Article, E. Nicolas, T. Cantat and co-workers describe a new cobalt-based catalytic system that enables the carbonylation of acrylic acid into succinic anhydride. Optimisation of the various parameters, such as metal, ligand, temperature, pressure, and gas composition, enables to perform this reaction in high yield and selectivity, using mild conditions. More information can be found in the Research Article by E. Nicolas, T. Cantat and co-workers.

Nature Communications, Published online: 17 August 2023; doi:10.1038/s41467-023-40640-z

Publication date: September 2023

Source: Chemical Engineering Research and Design, Volume 197

Author(s): Gianfranco Giorgianni, Siglinda Perathoner, Gabriele Centi, Siu-Ha Soo-Tang, Ed de Jong, Jan C. van der Waal, Salvatore Abate

Catalytic carbonylation with CO₂ : The latest updates on C1-carbonylative homologation of carbon scaffolds by means of metal catalyzed fixation of CO₂ are collected in the present Review article. Innovative catalytic systems, enabling technologies and mechanistic investigations are contributing to the current developments of this fascinating research field.

Abstract

The utilization of CO₂ as an efficient and environmentally friendly chemical analogue of CO is becoming a solid reality in the chemical scenario. CO₂-based carbonylations have started paralleling the more consolidated carboxylation procedures, opening new horizons and perspectives in the utilization of carbon dioxide as an organic C1-containing building block. The advent of efficient and site-selective metal-catalyzed protocols for the fixation of CO₂ into organic scaffolds, under controlled reductive conditions, contributed substantially to the development of robust, efficient, and convenient protocols. In the present Review article, a collection of the most recent examples of metal-catalyzed CO₂-based carbonylations is documented with a particular emphasis on mechanistic aspects.

Here we report that two very important catalytic transformations i. e., N-alkylation of amines with alcohols and β-alkylation of secondary alcohols with primary alcohols that is generally carried out with transition metal-based catalysts can be performed with a catalytic amount of base under air in a closed vessel without using transition metals or any other additives generating only water as byproduct.

Abstract

Borrowing hydrogen (BH) reactions are very useful for the sustainable synthesis of C−C and C−N bonds. They generally operate with transition metal-based catalysts along with stoichiometric/catalytic amounts of added base. Here we report that two catalytic transformations, generally carried out with the BH methodology, i. e. N-alkylation of amines with alcohols and β-alkylation of secondary alcohols with primary alcohols, can be performed very effectively with just catalytic amounts of base under air without using any transition metal-based catalyst. The mechanism is proposed to be based on air oxidation of the alcohol to aldehyde followed by condensation to an unsaturated intermediate which undergoes transfer hydrogenation with alcohol to the product.