Aryldiazonium Tetrafluoroborates Research Articles

Rhodium(III)-Catalyzed B(4)-Azo Coupling of o-Carboranes with Aryl Diazonium Tetrafluoroborates.

Rh(III)-catalyzed B(4)-azo coupling reactions of o-carborane acids with aryl diazonium tetrafluoroborates have been developed, leading to the regioselective formation of B(4)-azo-coupled o-carboranes. Moreover, B(4)-azo-coupled o-carboranes can be further functionalized by introducing a second azo group, producing B(4)-C(1)-di(arylazo) o-carborane. The B(4)-azo group as an efficient directing group enables catalytic C-H amidation reactions, providing a new synthetic route for complex o-carborane derivatives.

Catalyst-Free Radical Carbosulfonylation of Enamides with Indoles, Aryldiazonium Tetrafluoroborates, and DABCO·(SO2)2.

Herein, we have developed a catalyst-free four-component carbosulfonylation of enamides involving indoles, DABCO·(SO2)2, and aryldiazonium tetrafluoroborates for the preparation of various β-amidosulfone products in moderate to excellent yields. This approach features mild reaction conditions, high step-efficiency, and broad substrate scope, which provides a green and efficient strategy for carbosulfonyl difunctionalization of enamides. Based on the results of mechanism studies, a radical tandem reaction process is proposed for the transformation.

Four-Component Radical 1,2-Selenosulfonylation of Allenes.

Selenosulfones, as pivotal pharmaceutical molecule frameworks, have become a research hotspot in modern organic synthesis due to their vital need for efficient preparation. Herein, we have developed an iron-catalyzed four-component controllable radical tandem reaction of allenes involving cycloketone oxime esters, 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO), and diphenyl diselenides for the synthesis of complex selenosulfones. This is the first case of achieving the 1,2-selenosulfonylation of allenes via a radical process, wherein precise control of radical rates and polarity matching enhance high regioselective conversion. The reaction conditions are ecofriendly and mild with step-efficiency by forming two new C-S bonds and one C-Se bond in one pot. Moreover, the 1,2-selenosulfonylation of allenes can be achieved by replacing cycloketone oxime esters with aryldiazonium tetrafluoroborates in this system.

Synthesis of Sulfonyl‐Containing spiro[5,5]trienones from Sodium Metabisulfite

AbstractAn efficient three‐component reaction of biaryl ynones, sodium metabisulfite and aryldiazonium tetrafluoroborates is developed. The reaction occurs at room temperature without any additives, thus offering a sustainable approach to access sulfonyl‐containing spiro[5,5]trienones. This protocol features mild conditions, broad substrate scope and high functional group compatibility, furnishing the target products in moderate to good yields. Mechanistic studies indicate that the reaction undergoes a 6‐exo‐trig dearomative spirocyclization process which is initated by an aryl radical with the insertion of sulfur dioxide.

Synthesis of Unsymmetrical Diaryl Tellurides Under Mechanical Ball Milling in Room Temperature

Abstract: An efficient transition metal catalyst-free protocol for the synthesis of unsymmetrical diaryl tellurides has been developed by the reaction of diaryl tellurides and aryl diazonium tetrafluoroborates under mechanical ball milling in the absence of any solvent and base under room temperature. InBr (Indium Bromide) plays an important role in generating the organotelluride nucleophile via the Te-Te bond cleavage of ditelluride. A library of diaryl tellurides bearing both electron-donating and withdrawing groups in the aromatic ring has been synthesized in good to excellent yields by this protocol. Despite very high synthetic importance of diaryl tellurides in the field of organic synthesis, very few protocols have been reported to date for their synthesis. The reactions were also performed on a gram scale without any considerable change in the yields, which surely broadened the applicability of this methodology in the industrial field.

Deconstructive diversification of cyclic 1,3-diketones for accessing hydrazonylated 1,n-ketoesters

A mild base-promoted three-component deconstructive functionalization reaction of cyclic 1,3-diketones with aryl diazonium tetrafluoroborates in the presence of alcohols is reported, enabling direct ring-opening of unstrained cyclic ring systems to produce three types of skeletally diverse 1,n-ketoesters, namely, linear 1,5- and 1,4-ketoesters and ortho-ketobenzoates, with moderate to good yields. The methodology has the potential to be widely used throughout organic synthesis due to the use of easily accessible substrates, such as cyclic 1,3-diketones and aryl diazonium tetrafluoroborates, with different substitution patterns and mild reaction conditions.

Direct C−H Sulfonylation of Hydrazones Involving the Insertion of SO2

A three-component reaction of aldehyde-derived hydrazones with DABSO and aryldiazonium tetrafluoroborates is described. By using organic DABSO as the source of SO2, this straightforward sulfonylation tactic provides an elegant access...

Electro-oxidative coupling of Bunte salts with aryldiazonium tetrafluoroborates: a benign access to unsymmetrical sulfoxides.

An electrochemical strategy for the synthesis of unsymmetrical sulfoxides has been explored using Bunte salts and aryldiazonium tetrafluoroborates under constant current electrolysis at room temperature. In addition to being eco-safe and using mild conditions, the present protocol is free from the use of metal/oxidant, and is endowed with a broad substrate scope and good functional group tolerance.

Synthesis of trifluoromethyl formazans by reaction of trifluoromethyl N-acylhydrazones/N-Aryl hydrazones and aryldiazonium tetrafluoroborates

An efficient direct azo-coupling reaction of trifluoromethyl N-acylhydrazones/N-aryl hydrazones with aryldiazonium tetrafluoroborates was developed for the synthesis of various trifluoromethyl formazans. This protocol has the advantages of mild reaction condition, broad substrate scope and easy operation, which extends the application of trifluoromethyl N-acylhydrazones/N-aryl hydrazones as versatile trifluoromethyl building blocks in organic synthesis.

Mechanochemical Synthesis of Aryl Fluorides by Using Ball Milling and a Piezoelectric Material as the Redox Catalyst

AbstractAryl fluorides are important structural motifs in many pharmaceuticals. Although the Balz–Schiemann reaction provides an entry to aryl fluorides from aryldiazonium tetrafluoroborates, it suffers from drawbacks such as long reaction time, high temperature, toxic solvent, toxic gas release, and low functional group tolerance. Here, we describe a general method for the synthesis of aryl fluorides from aryldiazonium tetrafluoroborates using a piezoelectric material as redox catalyst under ball milling conditions in the presence of Selectfluor. This approach effectively addresses the aforementioned limitations. Furthermore, the piezoelectric material can be recycled multiple times. Mechanistic investigations indicate that this fluorination reaction may proceed via a radical pathway, and Selectfluor plays a dual role as both a source of fluorine and a terminal reductant.

Mechanochemical Synthesis of Aryl Fluorides by Using Ball Milling and a Piezoelectric Material as the Redox Catalyst.

Aryl fluorides are important structural motifs in many pharmaceuticals. Although the Balz-Schiemann reaction provides an entry to aryl fluorides from aryldiazonium tetrafluoroborates, it suffers from drawbacks such as long reaction time, high temperature, toxic solvent, toxic gas release, and low functional group tolerance. Here, we describe a general method for the synthesis of aryl fluorides from aryldiazonium tetrafluoroborates using a piezoelectric material as redox catalyst under ball milling conditions in the presence of Selectfluor. This approach effectively addresses the aforementioned limitations. Furthermore, the piezoelectric material can be recycled multiple times. Mechanistic investigations indicate that this fluorination reaction may proceed via a radical pathway, and Selectfluor plays a dual role as both a source of fluorine and a terminal reductant.

Annulative Aminosulfonylation of Unactivated Alkenes for Accessing Pyrazolines via Multicomponent SO2 Insertion.

A direct arylsulfonylation of β,γ-unsaturated hydrazones method, in which sulfonated pyrazolines are accessed by a three-component reaction of β,γ-unsaturated hydrazones, DABSO, and aryldiazonium tetrafluoroborates, has been developed without external oxidants or catalysts. This transformation is triggered by the formation of arylsulfonyl radicals in situ from the reaction of aryldiazonium tetrafluoroborates and DABSO, and is enabled by controllable generation of C center radical, in which DABSO was utilized as the sulfone source and an oxidant in this radical-mediated cascaded reaction. A wide range of substrates can be applied in this process to afford pyrazolines in good yield, and it is amenable for gram-scale synthesis.

Copper-Catalyzed 1,4-Trifluoromethylthio-Arylsulfonylation of 1,3-Enynes via the Insertion of Sulfur Dioxide.

A copper-catalyzed trifluoromethylthio-arylsulfonylation between 1,3-enynes, AgSCF3, aryldiazonium tetrafluoroborates, and SO2 (from SOgen) is presented, which could introduce sulfone, SCF3, and allene moieties into one molecule simultaneously. This strategy features mild reaction conditions, good substrate compatibility, and excellent regioselectivity. The products obtained have the potential for further conversion into other valuable compounds. Initial investigations into the reaction mechanism suggest that it may proceed via a radical pathway. Notably, SOgen was proven as a uniquely effective SO2 surrogate in this transformation.

Radical Cascade Cyclization of Unactivated Alkene-Tethered Indoles with Aryldiazonium Salt and Sodium Metabisulfite to Access Azo- and Sulfonylated-2,3-Dihyro-1H-pyrrolo[1,2-a]indoles.

A method for the construction of heterocyclic scaffold 2,3-dihyro-1H-pyrrolo[1,2-a]indoles via arylsulfonyl radical-triggered cascade cyclization of unactivated alkene-tethered indoles in the absence of any external photocatalyst has been developed. This protocol features easily accessible starting materials such as sodium metabisulfite and aryldiazonium tetrafluoroborates at room temperature and offers good functional group compatibility, enabling the introduction of various functionalized sulfonyl and azo groups into pyrrolo[1,2-a]indoles.

Multicomponent Annulative SO2 Insertion of Heteroatom‐Linked 1,7‐Diynes for Accessing Tricyclic Sulfones

AbstractA metal‐free radical multicomponent bicyclization of heteroatom‐linked 1,7‐diynes with aryl diazonium tetrafluoroborates and DABCO‐bis(sulfurdioxide) (DABSO) is reported, enabling annulative SO2 insertion access to produce two types of skeletally diverse tricyclic sulfones, namely, thieno[3,4‐c]quinoline 2,2‐dioxides and thieno[3,4‐c]chromene 2,2‐dioxides, with moderate to good yields by simply tuning the linkers of the 1,7‐diynes. This protocol demonstrates remarkable compatibility regarding N‐ and O‐linked 1,7‐diynes with different substitution patterns and aryl diazonium tetrafluoroborates.magnified image

Organophotoredox-mediated Formal [3+2]-Cycloaddition of 2H-Azirines with Aryldiazonium Salts: Direct Access to Trisubstituted 1,2,4-Triazoles.

The present work documents an organophotoredox-mediated formal [3+2]-cycloaddition of 2H-azirines with aryl diazonium tetrafluoroborate salts to furnish 1,3,5-trisubstituted 1,2,4-triazoles. The reaction furnishes a regioisomeric mixture of 1,2,4-triazoles in case of unsymmetrically substituted azirines. It is noteworthy that aryl radical generation from diazonium salt under visible light photoredox conditions could be successfully avoided by carefully selecting the reaction conditions.

Copper-Catalyzed Sulfonylation Reaction of NH-Sulfoximines with Aryldiazonium Tetrafluoroborates and Sulfur Dioxide: Formation of N-Sulfonyl Sulfoximines.

An efficient and practical SO2 insertion protocol of NH-sulfoximines with aryldiazonium tetrafluoroborates and DABSO toward N-sulfonyl sulfoximines has been developed under mildly basic conditions. This transformation features easy operation, readily available substrates, and mild conditions. A tentative mechanism is proposed, which indicates that the aryldiazonium tetrafluoroborates would be radical donors under standard reaction conditions. The aryl radical produced in situ from diazonium salts would be trapped by SO2 to generate an arylsulfonyl radical and then undergo further transformation to generate the final N-sulfonyl sulfoximines.

Visible light mediated organocatalytic dehydrogenative aza-coupling of 1,3-diones using aryldiazonium salts.

An efficient protocol for diazenylation of 1,3-diones under photoredox conditions is presented herein. C-N bond forming Csp3 -H functionalization of cyclic and alkyl diones by unstable aryl diazenyl radicals is achieved through reaction with aryldiazonium tetrafluoroborates by organocatalysts under visible light irradiation. The reaction has wide substrate scope, gives excellent yields, and is also efficient in water as a green solvent. This method provides an easy access to aryldiazenyl derivatives that are useful key starting materials for the synthesis of aza heterocycles as well as potential pharmacophores.

Photosensitizer-free, visible light-mediated recyclable gold-catalyzed cross-coupling of aryldiazonium salts and alkynyltrimethylsilanes

Photosensitizer-free visible light-mediated cross-coupling of aryldiazonium tetrafluoroborates and alkynyltrimethylsilanes has been achieved using a recyclable SBA-15-anchored triphenylphosphine–gold(i) complex as a catalyst.

Construction of β-Amino Sulfones from Sodium Metabisulfite via a Radical 1,4-Amino Migration.

A three-component reaction of alkenyl-tethered oxime ethers, sodium metabisulfite, and aryldiazonium tetrafluoroborates under mild conditions is developed. This reaction proceeds at room temperature without any oxidants or additives, affording β-amino sulfones with good functional group tolerance through aminosulfonylation of unactivated alkene. Mechanistic studies show that this transformation undergoes a radical process, including radical trapping with sulfur dioxide and radical 1,4-amino migration.