LongLarf

S_NAc with organolithiums under air: Aliphatic and (hetero)aromatic ketones are quickly (20 s reaction time) obtained in up to 93 % yield in a straightforward and chemoselective manner and with a broad substrate scope by reacting organolithium reagents with a variety of amides at ambient temperature under air in the environmentally friendly cyclopentyl methyl ether (CPME). Gram‐scale preparations and recyclability of the reagents are also successfully demonstrated.

Abstract

We report that the nucleophilic acyl substitution reaction of aliphatic and (hetero)aromatic amides by organolithium reagents proceeds quickly (20 s reaction time), efficiently, and chemoselectively with a broad substrate scope in the environmentally responsible cyclopentyl methyl ether, at ambient temperature and under air, to provide ketones in up to 93 % yield with an effective suppression of the notorious over‐addition reaction. Detailed DFT calculations and NMR investigations support the experimental results. The described methodology was proven to be amenable to scale‐up and recyclability protocols. Contrasting classical procedures carried out under inert atmospheres, this work lays the foundation for a profound paradigm shift of the reactivity of carboxylic acid amides with organolithiums, with ketones being straightforwardly obtained by simply combining the reagents under aerobic conditions and with no need of using previously modified or pre‐activated amides, as recommended.

The conversion of unactivated carbon-hydrogen (C–H) bonds to carbon–nitrogen (C–N) bonds is a highly valued transformation. Existing strategies typically accomplish such reactions at only a single C–H site because the first derivatization diminishes the reactivity of surrounding C–H bonds. Here, we show that alkylated arenes can undergo vicinal C–H diamination reactions to form 1,2-diamine derivatives through an electrophotocatalytic strategy, using acetonitrile as both solvent and nitrogen source. The reaction is catalyzed by a trisaminocyclopropenium (TAC) ion, which undergoes anodic oxidation to furnish a stable radical dication while the cathodic reaction reduces protons to molecular hydrogen. Irradiation of the TAC radical dication (wavelength of maximum absorption of 450 to 550 nanometers) with a white-light compact fluorescent light generates a strongly oxidizing photoexcited intermediate. Depending on the electrolyte used, either 3,4-dihydroimidazole or aziridine products are obtained.

(1S,2R)‐2‐Amino‐1‐indanol was identified as a chiral nitrogen source in an oxidative rearrangement of prochiral cyclobutanones. Building on strain release as the driving force, this downstream stereoinduction enables a variety of γ‐lactams to be synthesized including those bearing quaternary stereocenters. In addition, drug molecules pregabalin, baclofen, and brivaracetam are accessible, which underlines the broad applicability of this method.

Abstract

Asymmetric access to γ‐lactams is achieved via a cyclobutanone ring expansion using widely available (1S,2R)‐1‐amino‐2‐indanol for chiral induction. Mechanistic analysis of the key N,O‐ketal rearrangement reveals a Curtin–Hammett scenario, which enables a downstream stereoinduction (up to 88:12 dr) and is corroborated by spectroscopic, crystallographic, and computational studies. In combination with an easy deprotection protocol, this operationally simple sequence allows the synthesis of a range of optically pure γ‐lactams, including those bearing all‐carbon quaternary stereocenters. In addition, the formal synthesis of drug molecules baclofen, brivaracetam, and pregabalin further demonstrates the synthetic utility and highlights the general applicability of the presented method.

The direct CO₂ capture and reduction with tetraalkylammonium borohydride is reported. A phase transition from solid to liquid occurs during the absorption, making the product ready to use for HCOOH synthesis or N‐formylation reactions.

Abstract

We demonstrate the ability of tetraalkylammonium borohydrides to capture large amounts of CO₂, even at low CO₂ concentrations, and reduce it to formate under ambient conditions. These materials show CO₂ absorption capacities up to 30 mmol  g⁻¹ at room temperature and 1 bar CO₂. Every BH₄ ⁻ anion can react with three CO₂ molecules to form triformatoborohydride ([HB(OCHO)₃]⁻). The thermodynamics and kinetics of the reaction were monitored by a magnetic suspension balance (MSB). Direct CO₂ capture and reduction from air was achieved with tetraethyl, ‐propyl, and ‐butylammonium borohydride. The alkyl chain length played an important role in the kinetics and thermodynamics of the reaction, especially in CO₂ diffusivity (crystallinity and free‐volume), activation energy (charge‐transfer dependent on the alkyl chain), and hydrophobicity. Adding HCl gave formic acid and the corresponding chloride ammonium salt, which can be recycled. In addition, transfer of formate was achieved for the N‐formylation of an amine.

The Cover Feature shows the excited cuckoo dashing out of his (radical) clock, because the mechanism of the cerium‐catalyzed radical coupling reaction of β‐oxoesters, enol acetates, and dioxygen was finally elucidated by the introduction of cyclopropyl substituents as radical clocks. Furthermore, the introduction of stereocenters in the starting materials causes a stir, since the 1,2‐alkyl shift within the endoperoxidic oxycarbenium intermediate was proved to proceed with retention of configuration. More information can be found in the Full Paper by J. Christoffers et al.

Nature Chemistry, Published online: 01 February 2021; doi:10.1038/s41557-020-00628-4

Plant potential: Demand for cannabidiol (CBD) has increased drastically in the recent years, so highly pure cannabinoids and its intermediates are an emerging market for use as an antiepileptic product. Despite numerous studies describing the isolation and purification of CBD from plant material, its production is still limited. A detailed analysis of the history behind cannabinoid compounds and their optimization is provided.

Abstract

The current state of evidence and recommendations for cannabidiol (CBD) and its health effects change the legal landscape and aim to destigmatize its phytotherapeutic research. Recently, some countries have included CBD as an antiepileptic product for compassionate use in children with refractory epilepsy. The growing demand for CBD has led to the need for high‐purity cannabinoids on the emerging market. The discovery and development of approaches toward CBD synthesis have arisen from the successful extraction of Cannabis plants for cannabinoid fermentation in brewer's yeast. To understand different contributions to the design and enhancement of the synthesis of CBD and its key intermediates, a detailed analysis of the history behind cannabinoid compounds and their optimization is provided herein.

A sustainable COOL technique: The fixation of ubiquitous and naturally abundant carbon dioxide as a C₁‐feedstock onto organic staples delivering commodity chemicals and consumer products has an impactful influence on sustainable chemistry. This Minireview mainly highlights the emerging reports on CO₂ incorporation reactions using light‐harvesting photoredox catalysis for C−C and C−X bond‐forming reactions for the synthesis of carboxylic acid derivatives and heterocyclic compounds.

Abstract

CO₂ is a highly abundant, green, and sustainable carbon feedstock. Despite its kinetic inertness and thermodynamic stability, the development of various catalytic techniques has enabled the conversion of CO₂ to value‐added products such as carboxylic acids, amino acids, and heterocyclic compounds, where visible‐light photocatalysis has emerged to be an efficient promoter of these processes. This Minireview covers the progress in the areas of CO₂ incorporation onto organic matters based on the combined venture of renewable resources of CO₂ and light energy with significant emphasis on the last three years’ developments.

Synlett
DOI: 10.1055/a-1349-3543

Nickel-catalyzed carbon–oxygen bond activation is one of the most powerful strategies for the direct construction of various biaryl compounds. Under nickel catalysis, efficiently produced and naturally abundant arenol-based electrophiles can be activated and coupled with different aryl nucleophiles, including nucleophiles containing magnesium, zinc, boron, etc., to produce biaryl structural units. This Account summarizes recent progress on biaryl synthesis via nickel-catalyzed C–O bond activation.1 Introduction2 Coupling of Arenols and Arenol Derivatives with Aryl Magnesium Reagents3 Coupling of Arenols and Arenol Derivatives with Aryl Zinc Reagents4 Coupling of Arenols and Arenol Derivatives with Aryl Boron Reagents5 Others6 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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Abstract

The photochemistry of organophosphorus compounds and their reactions with carbon‐centred radicals was studied from the 1950s to the 70s, but has not been well exploited in synthetic chemistry until very recently. This review discusses the various modes of reactivity that phosphorus compounds display in radical C−C bond forming reactions, including the role of phosphonium salts as radical precursors, phosphines and phosphites as deoxygenating agents from oxygen‐centred radicals and phosphines in electron‐ and charge‐transfer chemistry. We also highlight the potential that these processes have in the future development of new reactions and cascade processes.

Vicinal dibromides and dichlorides are important commodity chemicals and indispensable synthetic intermediates in modern chemistry that are traditionally synthesized using hazardous elemental chlorine and bromine. Meanwhile, the environmental persistence of halogenated pollutants necessitates improved approaches to accelerate their remediation. Here, we introduce an electrochemically assisted shuttle (e-shuttle) paradigm for the facile and scalable interconversion of alkenes and vicinal dihalides, a class of reactions that can be used both to synthesize useful dihalogenated molecules from simple alkenes and to recycle waste material through retro-dihalogenation. The reaction is demonstrated using 1,2-dibromoethane, as well as 1,1,1,2-tetrachloroethane or 1,2-dichloroethane, to dibrominate or dichlorinate, respectively, a wide range of alkenes in a simple setup with inexpensive graphite electrodes. Conversely, the hexachlorinated persistent pollutant lindane could be fully dechlorinated to benzene in soil samples using simple alkene acceptors.

Revised pK _a scale, containing 231 acids and spanning almost 30 orders of magnitude of acidities in acetonitrile, one of the most useful solvents for non‐aqueous acid‐base chemistry, is presented.

Abstract

The equilibrium acidity scale (pK _a scale) in acetonitrile has been supplemented by numerous new compounds and new ΔpK _a measurements. It now contains altogether 231 acids – over twice more than published previously – linked by 569 ΔpK _a measurements and spans between the pK _a values of hydrogen iodide (2.8) and indole (32.57), covering close to 30 orders of magnitude. Measurement results acquired over the last 15 years were added to the scale and new least‐squares treatment was carried out. The treatment yielded revised pK _a values for the compounds published previously, with the root mean square difference between revised and previous values 0.04, demonstrating very good stability of the scale. Correlation equations were developed for estimating pK _a values for the studied types of compounds in water, DMSO, DMF, and 1,2‐dichloroethane on the basis of pK _a values in acetonitrile. These equations enable predicting pK _a values with an average error around or less than 1 pK _a unit, which is a sufficient accuracy for many applications. The scale is expected to be a useful tool for the widest possible research areas in organic chemistry, electrochemical power sources, catalysis, etc.