LongLarf

Publication date: 6 August 2020

Source: Chem, Volume 6, Issue 8

Author(s): Jonas Börgel, Tobias Ritter

Getting greener with polymers: The production of new sustainable polymers is of high importance. As discussed in this Review, several methods and catalytic pathways are accessible to produce 2,5‐furandicarboxylic acid (FDCA) from furoic acid. However, this topic still lacks systematic studies. In this review various routes to FDCA by using noncatalytic and catalytic carboxylation processes are critically discussed.

Abstract

2,5‐furandicarboxylic acid (FDCA) is one of the most important bio‐sourced building blocks and several routes have been reported for its synthesis. FDCA is presumed to be an ideal green alternative to terephthalate, which is one of the predominant monomers in polymer industry. This Minireview concerns the synthesis of FDCA by using various carboxylation reactions and discusses the synthesis of FDCA starting from furoic acid and CO₂ and using different catalytic and stoichiometric processes. This process is of high interest, as it avoids the glucose isomerization step and selectivity issues observed during the 5‐hydroxymethylfurfural oxidation step of the current alternative route to FDCA. Discussion focuses on the main parameters that govern selectivity and activity in the carboxylation processes. Moreover, various previously described processes, such as the Henkel reaction and enzymatic, homogeneous catalytic, and photoelectrocatalytic processes, are also discussed.

What fluorine can do in CO₂ chemistry: Fluorinated materials in the form of homogeneous or heterogeneous states have demonstrated good performance in CO₂ chemistry in terms of capture and fixation. This Minireview focuses on the synthesis, characterization, performance, comparison, and interaction mechanism of the materials with CO₂ and other substrates, to shed light on the merits, outcomes, and potential progress in this field.

Abstract

CO₂ chemistry including capture and fixation has attracted great attention towards the aim of reducing the consumption of fossil fuels and CO₂ accumulation in the atmosphere. “CO₂‐philic” materials are required to achieve good performance owing to the intrinsic properties of the CO₂ molecule, that is, thermodynamic stability and kinetic inertness. In this respect, fluorinated materials have been deployed in CO₂ capture (physical and chemical pathway) or fixation (thermo‐ and electrocatalytic procedure) with good performances, including homogeneous (e. g., ionic liquids and small organic molecules) and heterogeneous counterparts (e. g., carbons, porous organic polymers, covalent triazine frameworks, metal–organic frameworks, and membranes). In this Minireview, these works are summarized and analyzed from the aspects of (1) the strategy used for fluorine introduction, (2) characterization of the targeted materials, (3) performance of the fluorinated systems in CO₂ chemistry, and comparison with the nonfluorinated counterparts, (4) the role of fluorinated functionalities in the working procedure, and (5) the relationship between performance and structural/electronic properties of the materials. The systematic summary in this Minireview will open new opportunities in guiding the design of “CO₂‐philic” materials and pave the way to stimulate further progress in this field.

Mobility of reactants and nearby solvent is more rapid than Brownian diffusion during several common chemical reactions when the energy release rate exceeds a threshold. Screening a family of 15 organic chemical reactions, we demonstrate the largest boost for catalyzed bimolecular reactions, click chemistry, ring-opening metathesis polymerization, and Sonogashira coupling. Boosted diffusion is also observed but to lesser extent for the uncatalyzed Diels-Alder reaction, but not for substitution reactions S_N1 and S_N2 within instrumental resolution. Diffusion coefficient increases as measured by pulsed-field gradient nuclear magnetic resonance, whereas in microfluidics experiments, molecules in reaction gradients migrate "uphill" in the direction of lesser diffusivity. This microscopic consumption of energy by chemical reactions transduced into mechanical motion presents a form of active matter.

Synlett
DOI: 10.1055/s-0040-1707214

A novel and efficient catalyst system was developed for homocoupling reactions of aryl halides. The catalyst system consists of Pd(OAc)2 and the peppery sensory component of tobacco leaves. This is the first time that a sensory component has been used in an organic reaction. Experiments using the catalyst system showed that the reactions proceeded smoothly under air in the absence of both an additional ligand and a reductant. Furthermore, the catalyst system can be applied to the coupling reactions of hetaryl iodides. Many functional groups (including a hydroxy group) are tolerated.
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© Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
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Nature Communications, Published online: 29 July 2020; doi:10.1038/s41467-020-17580-z

Synlett
DOI: 10.1055/s-0040-1707199

A new, direct, efficient, and transition-metal-free method is reported for the synthesis of β-bromostyrenes from styrenes by using N-bromosuccinimide as the brominating reagent and sodium persulfate (Na2S2O8) as the oxidant. This convenient and concise reaction is practical, operationally simple, and can be adapted for large-scale syntheses.
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© Georg Thieme Verlag Stuttgart · New York

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

The recent emergence of organic photoredox catalysts has been aided by the establishment of design strategies (e.g. structure–property/performance relationship, strongly twisted donor–acceptor scaffolds or computer‐guided approaches). In this minireview, we summarize organic photoredox catalysts that have been reported since 2016, with their design, properties, and applications in organic syntheses.

A lot of efforts have been made for the development of novel organic photoredox catalysts (PCs) due to their gratifying replacement for conventional transition metal‐based PCs in photoredox catalysis. In this minireview, we summarized and classified the recently reported organic PCs into several categories based on functional groups (e.g. cyanoarene, phenazine, xanthene, and others) with their applications to various organic transformations including polymerization reactions. The strategies used to design organic PCs then also introduced. The emerging trends for the discovery of organic PCs are systematic approaches which include computer‐aided and mechanism‐based design. We anticipate that this minireview will provide not only the characteristics of the recently reported organic PCs, but also an insight into the design and discovery of organic PCs for desired applications.

The nemesis of organo‐alkali‐metal reagents, that is, ambient moisture, can remarkably accelerate the alkali‐metal amide induced hydroamination of styrenes. A practically simple aerobic procedure for these hydroaminations under air and in renewable 2‐methyltetrahydrofuran is revealed.

Abstract

A straightforward alkali‐metal‐mediated hydroamination of styrenes using biorenewable 2‐methyltetrahydrofuran as a solvent is reported. Refuting the conventional wisdom of the incompatibility of organolithium reagents with air and moisture, shown here is that the presence of moisture is key in favoring formation of the target phenethylamines over competing olefin polymerization products. The method is also compatible with sodium amides, with the latter showing excellent promise as highly efficient catalysts under inert atmosphere conditions.

Nature Communications, Published online: 20 May 2020; doi:10.1038/s41467-020-16369-4

Photoredox and NHC catalysis in concert: A novel strategy for the preparation of β‐trifluoromethylketones via radical alkene acyltrifluoromethylation has been developed. The three‐component cascades proceed under mild conditions with readily available aroyl fluorides, styrenes and the Langlois reagent as the reaction partners.

Abstract

Despite the great potential of radical chemistry in organic synthesis, N‐heterocyclic carbene (NHC)‐catalyzed reactions involving radical intermediates are not well explored. This communication reports the three‐component coupling of aroyl fluorides, styrenes and the Langlois reagent (CF₃SO₂Na) to give various β‐trifluoromethylated alkyl aryl ketones with good functional group tolerance in moderate to high yields by cooperative photoredox/NHC catalysis. The alkene acyltrifluoromethylation proceeds via radical/radical cross coupling of ketyl radicals with benzylic C‐radicals. The ketyl radicals are generated via SET reduction of in situ formed acylazolium ions whereas the benzylic radicals derive from trifluoromethyl radical addition onto styrenes.

Nature Reviews Chemistry, Published online: 21 July 2020; doi:10.1038/s41570-020-0205-0

Carbohydrate based ionic liquids are naturally derived materials containing chiral information with the prospect of acting as future‐oriented substitutes for established ionic liquids. This minireview gives an extensive overview of this subclass of chiral ionic liquids, including their synthesis, properties and applications in asymmetric chemistry.

Carbohydrate based ionic liquids (CHILs) are a sub‐class of ionic liquids which first emerged in 2007 and has since then attracted a steadily growing community of organic chemists. Since carbohydrates are naturally occurring materials with a broad spectrum of diastereomers, they are fitting materials for ionic liquids bearing stereochemical information. This review gives an up‐to‐date overview of all CHILs and their applications in asymmetric chemistry.

CO₂ reduction: Well‐defined Mn(I)‐PNP pincer‐type complexes catalyze the selective reduction of CO₂ to boryl‐protected MeOH, using HBpin and 9‐BBN in the presence of Lewis acids such as borates under mild reaction conditions (1 bar CO₂, 60 °C).

Abstract

Well‐defined Mn(I)‐PNP pincer‐type complexes were tested as non‐precious transition metal catalysts for the selective reduction of CO₂ to boryl‐protected MeOH in the presence of hydroboranes (HBpin, 9‐BBN) and borates as Lewis acids (LA) additives. The best performance was obtained under mild reaction conditions (1 bar CO₂, 60 °C) in the presence of the hydridocarbonyl complex [MnH(PNP^NH–iPr)(CO)₂] and B(OPh)₃ as co‐catalyst. Preliminary mechanistic studies suggest that the initial activation step may occur by cationization of the metal center by the strong LA, and that both metal‐catalyzed and metal‐free steps are present in the overall catalytic system.

Picture perfect: A photocatalytic approach for the Corey–Seebach reaction is presented. This base‐ and metal‐free reaction exploits the combination of photo‐ and HAT‐catalysis furnishing the desired product under mild conditions with a high functional group tolerance. The reactive intermediate is generated by hydrogen atom abstraction followed by radical reduction rendering a carbanion nucleophile capable of adding to aldehydes and ketones.

Abstract

A metal‐free generation of carbanion nucleophiles is of prime importance in organic synthesis. Herein we report a photocatalytic approach to the Corey–Seebach reaction. The presented method operates under mild redox‐neutral and base‐free conditions giving the desired product with high functional group tolerance. The reaction is enabled by the combination of photo‐ and hydrogen atom transfer (HAT) catalysis. This catalytic merger allows a C−H to carbanion activation by the abstraction of a hydrogen atom followed by radical reduction. The generated nucleophilic intermediate is then capable of adding to carbonyl electrophiles. The obtained dithiane can be easily converted to the valuable α‐hydroxy carbonyl in a subsequent step. The proposed reaction mechanism is supported by emission quenching, radical–radical homocoupling and deuterium labeling studies as well as by calculated redox‐potentials and bond strengths.