Ewoud

Synlett
DOI: 10.1055/a-1951-2950

A visible-light-induced O–H insertion reaction of diazo compounds is reported. This synthetic method, unlike conventional pathways, does not rely on transition metals, Lewis acids, or Brønsted acids; does not use any catalyst; and produces valuable α-hydroxy and α-alkoxy esters in good yields of up to 98%. The protocol exhibits a broad substrate scope and good functional-group tolerance. Notably, a gram-scale synthesis has been performed in a photochemical continuous-flow mode.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

We demonstrate a cobalt-catalyzed aminocarbonylation of aniline-derived trialkylammonium salts promoted by visible light via a challenging C(sp²)−N cleavage. The reaction is suitable for late-stage functionalization and is amenable to telescoped carbonylations directly from anilines. Mechanistic studies and DFT calculations support a novel mechanism involving a key visible light-induced carbonyl photodissociation and S_NAr-type oxidative addition.

Abstract

Catalytic carbonylations of aryl electrophiles via C(sp²)−N cleavage remains a significant challenge. Herein, we demonstrate an aminocarbonylation of aniline-derived trialkylammonium salts promoted by visible light with a simple cobalt catalyst. The reaction proceeds under mild conditions suitable for late-stage functionalization and is amenable to telescoped carbonylations directly from anilines. A range of alkylamines are successful partners, and alkoxycarbonylation is also demonstrated. Mechanistic studies and DFT calculations support a novel mechanism for catalytic carbonylations of aryl electrophiles involving a key visible light-induced carbonyl photodissociation.

Predicting organic transformations is one of the most critical challenges in molecular syntheses. The synergy between machine learning and chemical knowledge provides a distinctive and powerful strategy for syntheses predictions. This Minireview summarizes the state-of-the-art embedding approaches and model designs for developing synthesis-sensitive machine learning models to allow for robust yield and selectivity predictions in molecular syntheses.

Abstract

Recent years have witnessed a boom of machine learning (ML) applications in chemistry, which reveals the potential of data-driven prediction of synthesis performance. Digitalization and ML modelling are the key strategies to fully exploit the unique potential within the synergistic interplay between experimental data and the robust prediction of performance and selectivity. A series of exciting studies have demonstrated the importance of chemical knowledge implementation in ML, which improves the model's capability for making predictions that are challenging and often go beyond the abilities of human beings. This Minireview summarizes the cutting-edge embedding techniques and model designs in synthetic performance prediction, elaborating how chemical knowledge can be incorporated into machine learning until June 2022. By merging organic synthesis tactics and chemical informatics, we hope this Review can provide a guide map and intrigue chemists to revisit the digitalization and computerization of organic chemistry principles.

Structural and functional polymers provide functions, sustainability benefits, and CO₂ savings during their use phase, but present challenges at end of life. Polymer science and adjacent disciplines can enable a circular economy of polymers via biodegradation or recycling through the application of strategies for molecular and system design that leverage the latest advances in the field.

Abstract

To achieve a sustainable circular economy, polymer production must start transitioning to recycled and biobased feedstock and accomplish CO₂ emission neutrality. This is not only true for structural polymers, such as in packaging or engineering applications, but also for functional polymers in liquid formulations, such as adhesives, lubricants, thickeners or dispersants. At their end of life, polymers must be either collected and recycled via a technical pathway, or be biodegradable if they are not collectable. Advances in polymer chemistry and applications, aided by computational material science, open the way to addressing these issues comprehensively by designing for recyclability and biodegradability. This Review explores how scientific progress, together with emerging regulatory frameworks, societal expectations and economic boundary conditions, paint pathways for the transformation towards a circular economy of polymers.

Nature, Published online: 15 September 2022; doi:10.1038/s41586-022-05290-z

Nature Catalysis, Published online: 15 September 2022; doi:10.1038/s41929-022-00841-z

Lignin valorization: Technical lignin is a large-volume and low-cost industrial resource for making renewable aromatic chemicals. Oxidative depolymerization with heterogeneous catalysts allows viable upgrading to value-added aromatic monomers and more sustainable biorefineries. This Review summarizes and discusses performance–reactivity patterns and product analytics and recovery for the efficient oxidative valorization of technical lignin.

Abstract

The efficient valorization of lignin is crucial if we are to replace current petroleum-based feedstock and establish more sustainable and competitive lignocellulosic biorefineries. Pulp and paper mills and second-generation biorefineries produce large quantities of low-value technical lignin as a by-product, which is often combusted on-site for energy recovery. This Review focuses on the conversion of technical lignins by oxidative depolymerization employing heterogeneous catalysts. It scrutinizes the current literature describing the use of various heterogeneous catalysts in the oxidative depolymerization of lignin and includes a comparison of the methods, catalyst loadings, reaction media, and types of catalyst applied, as well as the reaction products and yields. Furthermore, current techniques for the determination of product yields and product recovery are discussed. Finally, challenges and suggestions for future approaches are outlined.

One-pot synthesis: A sustainable and efficient protocol for the transition-metal-free one-pot synthesis of quinoxaline derivatives from lignin β-O-4 models and polymer in the presence of organic N-sources and KOH is presented. With this protocol, a wide range of functionalized quinoxalines are synthesized from lignin β-O-4 model compounds and β-O-4 polymer.

Abstract

The construction of N-heterocyclic compounds from lignin remains a great challenge due to the complex lignin structure and the involvement of multiple steps, including the cleavage of lignin C−O linkages and the formation of heterocyclic aromatic rings. Herein, the first example of KOH mediated sustainable synthesis of quinoxaline derivatives from lignin β-O-4 model compounds in a one-pot fashion under transition-metal-free conditions has been achieved. Mechanistic studies suggested that this transformation includes highly coupled cascade steps of cleavage of C−O bonds, dehydrative condensation, sp³ C−H bond oxidative activation, and intramolecular dehydrative coupling reaction. With this protocol, a wide range of functionalized quinoxalines, including an important drug compound AG1295, were synthesized from lignin β-O-4 model compounds and β-O-4 polymer, showcasing the application potential of lignin in pharmaceutical synthesis.

A dearomative trifluoromethylative aminocarbonylation of arenes via bifunctional coordination to chromium has been firstly developed for amide construction, which expands the boundary of aminocarbonylations from conventional C=C bond substrates to arenes. Furthermore, a switchable 1,2-difunctionalization of arene C−H bonds and concise synthesis of amide-type drug analogs were successfully achieved.

Abstract

Amides are ubiquitous in physical and life sciences. Given the significant abundance of arenes, dearomative aminocarbonylation of arenes would lead to a large and underexplored chemical space for amide discovery. However, such reactions are challenging due to the high degree of resonance stabilization and selectivity issues. Herein, we disclose an unprecedented dearomative trifluoromethylative aminocarbonylation of arenes via bifunctional coordination to chromium, providing a modular platform for the construction of amides possessing trifluoromethyl (CF₃) groups and three-dimensional rings. Its versatility further enabled a switchable difluoromethylation or trifluoromethylation aminocarbonylation of arene C−H bonds. A possible mechanism was proposed based on control experiments. Finally, the synthetic utility was well demonstrated by diverse applications in the total synthesis of CF₃-functionalized amide-type drugs, including praziquantel, nateglinide, maraviroc and alloyohimbane.