Mois : avril 2020

Mesoscale coordination constructs

Nature Chemistry, Published online: 28 April 2020; doi:10.1038/s41557-020-0461-0A series of mesoscale supramolecular hexagonal grids have been constructed in solution through stepwise intra- then intermolecular coordination-driven self-assembly, and characterized with atomic resolution by scanning tunnelling microscopy and spectroscopy.Authors: Ruoning Lihttps://www.nature.com/articles/s41557-020-0461-0

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Ultrafast control of anisotropy

Nature Chemistry, Published online: 28 April 2020; doi:10.1038/s41557-020-0462-zSingle-molecule magnets are able to store information through their magnetic anisotropy, making them very promising systems for memory applications. Now, femtosecond-laser-initiated molecular dynamics that modulate magnetic anisotropy have been observed, paving the way for operation on ultrafast timescales.Authors: Eric Collethttps://www.nature.com/articles/s41557-020-0462-z

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Facile One-Pot Access to α-Diazo-β-ketosulfones from Sulfonyl Chlorides and α-Haloketones

http://dx.doi.org/10.1055/s-0040-1707525

Synthesis
DOI: 10.1055/s-0040-1707525

A convenient one-pot approach to the preparation of α-diazo-β-ketosulfones from sulfonyl chlorides is described. It involves the conversion of the sulfonyl chloride to sodium sulfinate, alkylation of the latter with α-haloketones followed by diazo transfer using the ‘sulfonyl-azide-free’ (‘SAFE’) protocol in aqueous medium. The simple and expedient method relies on readily available starting materials and provides facile access to a wide variety of valuable diazo reagents for organic synthesis.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Dar’in, Dmitry

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Transition-Metal-Free, Intermolecular Azidoheteroarylation of Alkenes: Efficient Access to β-Azidoalkylated Quinoxalinones and Preliminary Antifungal Evaluation Against Magnaporthe grisea

http://dx.doi.org/10.1055/s-0040-1707514

Synthesis
DOI: 10.1055/s-0040-1707514

An efficient, PhI(OAc)2-mediated, radical azidoheteroarylation of alkenes under transition-metal-free conditions is reported by employing TMSN3 and quinoxalin-2(1H)-ones as coupling partners. This domino reaction allows an efficient synthesis of valuable orangoazides containing quinoxalin-2(1H)-one derivatives and could be extended to phosphinyl-alkylated quinoxalin-2(1H)-one in a single step in moderate to excellent yields under mild conditions, as demonstrated by the preliminary antibacterial evaluation against Magnaporthe grisea for the first time. Mechanistic studies revealed that this transformation undergoes a cascade addition pathway controlled by a polar radical.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Du, Yiming

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A Straightforward Synthesis of N-Substituted Ureas from Primary Amides

http://dx.doi.org/10.1055/s-0040-1707103

Synthesis
DOI: 10.1055/s-0040-1707103

A direct and convenient method for the preparation of N-substituted ureas is achieved by treating primary amides with phenyliodine diacetate (PIDA) in the presence of an ammonia source (NH3 or ammonium carbamate) in MeOH. The use of 2,2,2-trifluoroethanol (TFE) as the solvent increases the electrophilicity of the hypervalent iodine species and allows the synthesis of electron-poor carboxamides. This transformation involves a nucleophilic addition of ammonia on the isocyanate intermediate generated in situ by a Hofmann rearrangement of the starting amide.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Saraiva Rosa, Nathalie

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Allyl 4-Chlorophenyl Sulfone as a Versatile 1,1-Synthon for Sequential α-Alkylation/Cobalt-Catalyzed Allylic Substitution

http://dx.doi.org/10.1055/s-0040-1707524

Synthesis
DOI: 10.1055/s-0040-1707524

Despite their unique potential as rare 1,1-dipole synthons, allyl sulfones are rarely used in target-oriented syntheses, likely due to the lack of a general catalytic method for their branch-selective allylic substitution. Herein, we identified allyl 4-chlorophenyl sulfone as a versatile linchpin for both base-mediated α-derivatization and subsequent cobalt-catalyzed allylic substitution. The sequential transformations allow for highly regioselective access to branched allylic substitution products with a variety of aliphatic side chains. The photoredox-enabled­ ­cobalt catalysis is indispensable for achieving high yields and regioselectivity­ for the desulfonylative substitution in contrast to traditional metal-catalyzed protocols, which lead to inferior outcomes in the corresponding transformations.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Sekino, Tomoyuki

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Catalyst- and Solvent-Free Hydrophosphorylation of Ketones with Secondary Phosphine Oxides: Green Synthesis of Tertiary α-Hydroxyphosphine Oxides

http://dx.doi.org/10.1055/s-0040-1707945

Synthesis
DOI: 10.1055/s-0040-1707945

Tertiary α-hydroxyphosphine oxides have been synthesized via the catalyst- and solvent-free reaction between available secondary phosphine oxides and aliphatic, aromatic and heteroaromatic ketones at 20–62 °C in near to 96–98% yield. The developed method meets the requirements of green chemistry and the PASE (pot, atom, step economy) paradigm. According to quantum-chemical calculations at the B3LYP/6-311++G(d,p) level, the synthesized hydroxyphosphine oxides feature a weak (≈3 kcal·mol–1) O−H···O=P intramolecular hydrogen bond.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Gusarova, Nina K.

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BF3·OEt2-Catalyzed Aldol Condensation of Steroid Sapogenins and 2-Oxoacids: A Single Step Conversion of Steroid Spiroketals into Branched α,β-Unsaturated Spirolactones

http://dx.doi.org/10.1055/s-0040-1708018

Synthesis
DOI: 10.1055/s-0040-1708018

BF3·OEt2-catalyzed aldol reaction of steroid sapogenins with glyoxylic acid or pyruvic acid led to compounds in which the novel spirocyclic side chain bears an α,β-unsaturated lactone. The structures of the new spirolactones were established with the aid of combined 1D and 2D NMR techniques. A plausible mechanism is described.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Hernández-Martínez, Juan E.

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Enhanced reactivity of twisted amides inside a molecular cage

Nature Chemistry, Published online: 20 April 2020; doi:10.1038/s41557-020-0455-yThe distortion of an amide group away from a planar conformation typically enhances its reactivity and such activation is usually achieved through the chemical synthesis of twisted amides. Now, it has been shown that a non-covalent activation strategy leading to accelerated hydrolysis can be achieved by binding a reactive twisted amide conformer inside a molecular cage.Authors: Hiroki Takezawahttps://www.nature.com/articles/s41557-020-0455-y

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Enantioselective photoinduced cyclodimerization of a prochiral anthracene derivative adsorbed on helical metal nanostructures

Nature Chemistry, Published online: 20 April 2020; doi:10.1038/s41557-020-0453-0The photoinduced dimerization of a prochiral anthracenecarboxylic acid occurs in an enantioselective fashion when the molecules are adsorbed on helical metal nanostructures. This enantiopreference arises mostly from the helicity of the silver and copper substrates—prepared using shear forces during the deposition process—and may also be influenced by chiroplasmonic effects.Authors: Xueqin Weihttps://www.nature.com/articles/s41557-020-0453-0

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A silicon–carbonyl complex stable at room temperature

Nature Chemistry, Published online: 20 April 2020; doi:10.1038/s41557-020-0456-xCompounds of main-group elements rarely undergo direct carbonylation reactions. Now, an electron-rich silylene intermediate has been shown to readily react with CO to form a silylene carbonyl complex that is stable at room temperature. This complex engages in CO substitution as well as oxidative addition reactions.Authors: Chelladurai Ganesamoorthyhttps://www.nature.com/articles/s41557-020-0456-x

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Reductive Amination of Aryl Boronic Acids: Parallelism of the Catalytic Reactivity of Transition Metals and Main Group Elements in the C(sp2)–N Bond-Forming Reactions

http://dx.doi.org/10.1055/s-0039-1690893

Synthesis
DOI: 10.1055/s-0039-1690893

The results of the DFT studies on the mechanism of the PIII/PV=O catalyzed reductive amination of nitrosoarenes using ArB(OH)2 yielding diaryl amines are reported. This allowed a comparison of the reaction paths and key intermediates of the Cu(I)- and P(III)-mediated reductive aminations of aryl boronic acids using alkylnitrites, nitroso- or nitroarenes, and revealed important similarities in the catalytic reactivity of transition-metal and main-group elements in C(sp2)–N bond-forming reactions. It is shown that both transformations occur via ambiphilic nitrenoid-type key intermediates, the reactivity of which towards the aryl boronic acid is attributed to the presence of both a Lewis acid center (Cu or P) and a Lewis base center (the N or O atoms of the ‘N=O’ component).
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Levitskiy, Oleg A.

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Zeolites Catalyze the Nazarov Reaction and the tert-Butylation of Alcohols by Stabilization of Carboxonium Intermediates

http://dx.doi.org/10.1055/s-0039-1690896

Synthesis
DOI: 10.1055/s-0039-1690896

Zeolites are the most used catalysts worldwide in petrochemistry processes, with particular ability to stabilize carbocations. However, the use of zeolites in organic synthesis is still scarce. We show here that representative carboxonium-mediated organic reactions, such as the Nazarov cyclization and the tert-butylation of alcohols with tert-butyl acetate, typically performed with very strong acid catalysts in solution such as triflic acid, can be catalyzed by simple zeolites with high yield and selectivity. The aluminosilicate framework stabilizes the intermediate carboxonium species and overrides the need for superacid protons in solution.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Tejeda-Serrano, María

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Further Development of the Tin-Catalyzed Transcarbamoylation Reaction

http://dx.doi.org/10.1055/s-0040-1708020

Synthesis
DOI: 10.1055/s-0040-1708020

Studies carried out to further develop tin-catalyzed trans­carbamoylation reactions demonstrated that transcarbamoylation of cinnamyl alcohol in the context of allyl cyanate-to-isocyanate rearrangement can be efficiently carried out on a ten-gram scale and that tin-­catalyzed transcarbamoylation is a valuable alternative to the method using trichloroacetyl isocyanate. In addition, methyl carbamate was found to be an economical carabamoyl donor in tin-catalyzed transcarbamoylation, which showed broad functional group tolerance and allowed a streamlined workup procedure. Finally, a unique synthetic method was developed for the preparation of carbamate-tethered terpene glycoconjugates.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Ichikawa, Yoshiyasu

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An Unusual Triazole Synthesis from Aurones

http://dx.doi.org/10.1055/s-0040-1708019

Synthesis
DOI: 10.1055/s-0040-1708019

Attempts to prepare azido-substituted aurones via a copper-catalyzed azidation failed to afford the desired product, but instead resulted in an unusual triazole formation reaction. Further efforts noted that copper was not required for this reaction, but simply thermal treatment with sodium azide in a polar aprotic solvent. A wide range of substitution patterns were tolerated in this reaction to afford the interesting salicyl-substituted triazoles in modest to excellent yield. While the mechanism is not yet clear, a simple elimination/cyclization pathway seems unlikely given the failure of the reaction on the corresponding thioaurones, which feature an even better thiol leaving group. Regardless, the potential utility of these easily accessible, multifunctional compounds should engender further interest and applications.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Kafle, Arjun

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Manifestation of the β-Silicon Effect in the Reactions of Unsaturated Systems Involving a 1,2-Silyl Shift

http://dx.doi.org/10.1055/s-0039-1690898

Synthesis
DOI: 10.1055/s-0039-1690898

Many chemical transformations of organosilicon compounds proceed due to the capability of silyl substituents to stabilize a positive charge in its β-position. This short review provides an overview of the present understanding of the β-silicon effect and focusses on the synthetic applications of 1,2-silyl shifts resulting from non-vertical stabilization of alkylcarbenium ions and vinyl cations. The reactions of silicon containing unsaturated starting materials, alkenes, allenes, and alkynes, involving β-silyl group stabilized cationic intermediates, transition metal carbenes, or vinylidene complexes will be discussed.1 Introduction2 Origins of the β-Silicon Effect3 Reactions of Allenylsilanes4 Reactions of Alkynes4.1 Propargylsilanes4.2 Alkynylsilanes5 Reactions of Alkenes5.1 Allylsilanes5.2 Vinylsilanes6 Conclusions
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Beļaunieks, Rūdolfs

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Direct Synthesis of 5-Acyl-3-oxy-4-pyrones Based On Acid-­Catalyzed Acylation of Enaminodiones with Acylbenzotriazoles via Soft Enolization

http://dx.doi.org/10.1055/s-0040-1707471

Synthesis
DOI: 10.1055/s-0040-1707471

A novel convenient acid-catalyzed acylation of enaminodiones with acylbenzotriazoles via soft enolization has been developed for the direct synthesis of hard-to-reach 5-acyl-3-oxy-4-pyrones. The important advantages of the reaction include broad substrate scope, mild conditions, scalability, and readily isolation of products by crystallization without the use of chromatography. Further modification of the pyrone ring and synthesis of various azaheterocycles via ring-opening transformation have been demonstrated for the preparation of potential scaffolds for inhibition of metalloenzymes.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Obydennov, Dmitrii L.

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Three-Component Reaction of Homophthalic Anhydride with Carbonyl Compounds and Ammonium Acetate: New Developments

http://dx.doi.org/10.1055/s-0040-1708017

Synthesis
DOI: 10.1055/s-0040-1708017

The earlier described reaction of homophthalic anhydrides with aromatic ketones and ammonium acetate was tested for cyclic ketones (yielding spirocyclic motifs) and aliphatic aldehydes. In contrast to previous findings, the reaction was found to require no catalyst at all and to be applicable, in the non-catalyzed format, to these new carbonyl substrates as well as aromatic ketones. The reaction typically proceeds with high diastereoselectivity; if not, the initial diastereomeric mixture can be quantitatively equilibrated into a single, trans-diastereomer on treatment with aqueous base.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Safrygin, Alexander

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Theoretical realities

Nature Reviews Chemistry, Published online: 15 April 2020; doi:10.1038/s41570-020-0182-3An autobiography by Martin Karplus, from his childhood and continuing right through to a journey to Stockholm to receive the 2013 Nobel prize.Authors: Alfred C. Chinhttp://feeds.nature.com/~r/natrevchem/rss/current/~3/yDrEY78c4Tw/s41570-020-0182-3

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Running rings around chloride

Nature Reviews Chemistry, Published online: 15 April 2020; doi:10.1038/s41570-020-0185-0Anions can act as efficient templates for the formation of macrocyclic peptides.Authors: Stephen G. Daveyhttp://feeds.nature.com/~r/natrevchem/rss/current/~3/fpbqLDUFAk4/s41570-020-0185-0

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Synthesis of a Novel 1,4-Dicarbonyl Scaffold – Ethyl 3-Formyl-4,5-dihydrofuran-2-carboxylate – and Its Application to the Synthesis of Pyridazines

http://dx.doi.org/10.1055/s-0039-1690886

Synthesis
DOI: 10.1055/s-0039-1690886

The 1,4-dicarbonyl scaffold ethyl 3-formyl-4,5-dihydrofuran-2-carboxylate was obtained through the rearrangement of the parent ethyl 2-(4,5-dihydrofuran-3-yl)-2-oxoacetate and applied to the synthesis of a series of 7-alkoxy-2,3-dihydrofuro[2,3-d]pyridazines. Twelve pyridazines­ were obtained in yields of up to 70%.
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Marangoni, Mário A.

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Asymmetric Synthesis of Ethers by Catalytic Alkene Hydro­alkoxy­lation

http://dx.doi.org/10.1055/s-0039-1690874

Synthesis
DOI: 10.1055/s-0039-1690874

Many chiral ethers have important physiological activities. Although many asymmetric hydroalkoxylations of olefins with alcohols or phenols have been developed to make chiral ethers, challenges still remain in achieving high reactivity and selectivity over an ever-increasing diversity of alkenes and alcohols. In this review, recent developments on catalytic asymmetric alkene hydroalkoxylations are summarized based on the substitution patterns of alkenes.1 Introduction2 Asymmetric Hydroalkoxylation of Non-Activated Alkenes2.1 Intramolecular Additions2.2 Intermolecular Additions3 Asymmetric Hydroalkoxylation of Enol Ethers3.1 Intramolecular Additions3.2 Intermolecular Additions4 Asymmetric Hydroalkoxylation of α,β-Unsaturated Carbonyl Compounds4.1 α,β-Unsaturated Ketones and Aldehydes as Substrates4.2 α,β-Unsaturated Esters, Amides and Carboxylic Acids as Substrates5 Asymmetric Hydroalkoxylation of Allenes5.1 Intramolecular Additions5.2 Intermolecular Additions6 Conclusion
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Xie, Wen-Bin

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5-Iodo-1H-1,2,3-triazoles as Versatile Building Blocks

http://dx.doi.org/10.1055/s-0039-1690858

Synthesis
DOI: 10.1055/s-0039-1690858

Copper-catalyzed azide–alkyne cycloaddition is a useful tool for the synthesis of both 1,2,3-triazoles and 5-iodo-1H-1,2,3-triazoles starting from either terminal alkynes or iodoalkynes. 5-Iodotriazoles have been recognized as very useful building blocks for the synthesis of diverse 1,4,5-trisubstituted 1,2,3-triazoles. Synthetic application of 5-iodo-1,2,3-triazoles through the creation of a new C–C, C–heteroatom, or C–D(T) bond along with the application areas of both iodotriazoles and products of their modification including radiolabeled compounds are discussed.1 Introduction2 Synthetic Approaches to 5-Iodo-1H-1,2,3-triazoles3 5-Iodotriazoles in C–C Bond Formation3.1 Intermolecular C–C Cross-Coupling3.2 Intramolecular Cross-Coupling: Direct Arylation and C–I/C–I Homocoupling­3.3 Other Transformations4 5-Iodotriazoles in Radiolabeling, Halogen Exchange, and Heterocoupling Reactions5 Summary
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© Georg Thieme Verlag Stuttgart · New York

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Authors: Danilkina, Natalia A.

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