Tomas Horsten

Multiple 2D H-bonded macrocycles are threaded onto a box-like cationic cyclophane, which further assembles into higher order dimeric shish-kebab-like structures. Such ring-in-ring(s) superstructures maximize their stability through the conformational adaptivity of both host and guest.

Abstract

Use of abiotic chemical systems for understanding higher order superstructures is challenging. Here we report a ring-in-ring(s) system comprising a hydrogen-bonded macrocycle and cyclobis(paraquat-o-phenylene) tetracation ( o -Box) or cyclobis(paraquat-p-phenylene) tetracation (CBPQT ⁴⁺, p -Box) that assembles to construct discrete higher order structures with adaptive conformation. As indicated by mass spectrometry, computational modeling, NMR spectroscopy, and single-crystal X-ray diffraction analysis, this ring-in-ring(s) system features the box-directed aggregation of multiple macrocycles, leading to generation of several stable species such as H4G (1 a/ o -Box) and H5G (1 a/ o -Box). Remarkably, a dimeric shish-kebab-like ring-in-rings superstructure H7G2 (1 a/ o -Box) or H8G2 (1 a/ p -Box) is formed from the coaxial stacking of two ring-in-rings units. The formation of such unique dimeric superstructures is attributed to the large π-surface of this 2D planar macrocycle and the conformational variation of both host and guest.

Synthesis
DOI: 10.1055/a-2019-1532

Under mild irradiation conditions using violet light-emitting diodes, a catalytic amount of a thiolate of N-(4-mercaptophenyl)pivalamide promotes monoselective defluoroalkylation of trifluoroacetates with a variety of aliphatic alkenes in the presence of a formate salt. The reactions allow facile and low-cost synthesis of valuable α,α-difluoro substituted aliphatic carboxylate esters under mild conditions, and demonstrate the dual-functional role of arenethiolates in photocatalysis as both a strong photoreductant in a redox cycle and a hydrogen-atom-transfer catalyst.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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The oxidative conversion of technical Kraft lignin into vanillin is reported in high yields. Through the ex-cell electrolysis of aqueous carbonate, peroxodicarbonate is produced and serves as a “green” oxidizer for the degradation of lignin.

Abstract

Lignin, the world's largest resource of renewable aromatics, with annually roughly 50 million tons of accruing technical lignin, mainly Kraft lignin, is highly underdeveloped regarding the production of monoaromatics. We demonstrate the oxidative depolymerization of Kraft lignin at 180 °C to produce vanillin 1 in yields up to 6.2 wt % and 92 % referred to the maximum yield gained from the quantification reaction utilizing nitrobenzene. Using peroxodicarbonate (C₂O₆ ²⁻) as “green” oxidizer for the degradation, toxic and/or harmful reagents are prevented. Also, the formed waste can serve as makeup chemical in the pulping process. Na₂C₂O₆ is synthesized in an ex-cell electrolysis of aqueous Na₂CO₃ at BDD anodes, achieving a yield of Na₂C₂O₆ with 41 %. At least, the oxidation and degradation of Kraft lignin is analysis via UV/Vis and NMR spectroscopy.

Electrochemically initiated [3 2] cycloaddition reactions of readily available and less toxic starting materials enable a facile synthesis of pyrazolines and pyrazoles. Application of a biphasic system and sodium iodide in a dual role as mediator and electrolyte allows for selective reactions with outstanding robustness towards scalability.

Abstract

Pyrazolines and pyrazoles are common and important motifs of pharmaceutical agents and agrochemicals. Herein, the first electrochemical approach for their direct synthesis from easily accessible hydrazones and dipolarophiles up to decagram scale is presented. The application of a biphasic system (aqueous/organic) even allows for the conversion of highly sensitive alkenes, wherein inexpensive sodium iodide is employed in a dual role as supporting electrolyte and mediator. In addition, mechanistic insight into the reaction is given by the isolation of key step intermediates. The relevance of the presented reaction is underlined by the synthesis of commercial herbicide safener mefenpyr-diethyl in good yields.

Synlett
DOI: 10.1055/a-1890-9162

Electrosynthesis is undergoing a renaissance, but it is still far from being considered a standard method within the chemists’ synthetic toolbox. In this article, we will demystify organic electrochemistry by reviewing some practical methodologies developed in our laboratory to prepare highly reactive synthetic intermediates.1 Introduction2 Acyloxy Radicals3 Orthoesters4 Isocyanates5 Isocyanides6 Diazo Compounds7 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Nature Chemistry, Published online: 25 July 2022; doi:10.1038/s41557-022-00997-y

Perfluoroalkylated (hetero)arenes are commonly utilized in many areas such as medicinal chemistry, agrochemistry and material sciences. This review article discusses methods for the direct perfluoroalkylation of C(sp²)-H bonds in (hetero)arenes, one of the most attractive and straightforward entry to perfluoroalkylated (hetero)arenes, with a special focus on the reagents utilized, reaction mechanisms and their regioselectivity.

Double trouble: Dual Ni/photoredox catalysis is a prominent approach to forge valuable C−C and C−heteroatom bonds of synthetic relevance. This Review summarizes the most relevant examples within this field, highlighting the great evolution of the different photocatalytic systems synergistically employed together with the Ni catalyst. These span from metal-based complexes to organic dyes, along with heterogeneous semiconductors.

Abstract

Recently, the field of dual photocatalysis has grown rapidly, to become one of the most powerful tools for the functionalization of organic molecules under mild conditions. In particular, the merging of Earth-abundant nickel-based catalytic systems with visible-light-activated photoredox catalysts has allowed the development of a number of unique green synthetic approaches. This goes in the direction of ensuring an effective and sustainable chemical production, while safeguarding human health and environment. Importantly, this relatively new branch of catalysis has inspired an interdisciplinary stream of research that spans from inorganic and organic chemistry to materials science, thus establishing itself as one dominant trend in modern organic synthesis. This Review aims at illustrating the milestones on the timeline evolution of the photocatalytic systems used, with a critical analysis toward novel applications based on the use of photoactive two-dimensional carbon-based nanostructures. Lastly, forward-looking opportunities within this intriguing research field are discussed.

A para-selective C−H trifluoromethylation of benzamide derivatives was developed that makes use of iminium intermediates. The iminium species, formed in situ from Tf₂O, pyridine and amides, feature greatly enhanced reactivity at the para-position towards radical-type nucleophilic C−H trifluoromethylation.

Abstract

The direct C−H trifluoromethylation of arenes via a radical pathway has attracted considerable attention recently. However, a major challenge of C−H trifluoromethylation is the lack of site-selectivity on the phenyl ring especially para-selectivity. Herein we show a new strategy for para-selective C−H trifluoromethylation of benzamide derivatives using iminium activation. The reaction undergoes a radical-type nucleophilic substitution instead of a radical-type electrophilic substitution owing to iminium activation as a result of lowering the LUMO (lowest unoccupied molecular orbital). A wide range of substrates are compatible with this method giving almost exclusive para-trifluoromethylated products.

The Front Cover demonstrates that electrochemistry in continuous flow is so convenient and reliable that even kids could do it. Electrochemical hydroxylation of sensitive electron-rich arenes was achieved by the implementation of a flow setup. Our goal is to motivate organic chemists, who tend to be quite conservative, to apply the modern techniques in their everyday research and explore new reaction pathways. Cover artwork by Alina Andreyenka. More information can be found in the Research Article by M. Ošeka et al.

Publication date: July 2022

Source: Trends in Chemistry, Volume 4, Issue 7

Author(s): Thomas Scattolin, Andreas Simoens, Christian V. Stevens, Steven P. Nolan