Arenediazonium Tetrafluoroborates Research Articles

Three-Component Syntheses of Functionalized Selenocyanates

AbstractA metal-free Meerwein-type arylation protocol of α,β-unsaturated compounds is reported. 4-Aryl-3-selenocyanatobutan-2-ones, methyl 3-aryl-2-selenocyanatopropanoates, 3-aryl-2-selenocyanatopropanenitriles, and 1-aryl-2-phenyl-2-selenocyanatoethanes were prepared by a selenocyanatoarylation reaction from easily available arenediazonium tetrafluoroborates, potassium selenocyanate, and methyl vinyl ketone, methyl acrylate, acrylonitrile, or styrene, respectively, in 39–84% yields. The reaction proceeds smoothly and quickly under mild reaction conditions. The reaction can be scaled to the gram scale. A mechanism for this reaction is proposed.

Synthesis of α-Bromo Arylethyl Sulfonyl Fluorides and β-Arylethenesulfonyl Fluorides via Copper-Catalyzed Meerwein Arylation.

A practical copper-catalyzed process for the synthesis of the β-arylethenesulfonyl fluorides is described. A series of α-bromo arylethyl sulfonyl fluorides was prepared via Meerwein reaction from arenediazonium tetrafluoroborates and ethenesulfonyl fluoride (ESF) under mild conditions. The following β-arylethenesulfonyl fluorides were further obtained through a β-elimination reaction. This protocol features excellent regio- and stereoselectivity and broad substrate scope.

Thermal analysis of arenediazonium tetrafluoroborate salts: Stability and hazardous evaluation

Arenediazonium salts represent an important class of aromatic organic compounds widely used as building blocks in academia and industry. Due to the high energy associated with the diazonium group, many of these salts are reported as thermally unstable and/or unsafe to work with. However, most of the tetrafluoroborate arenediazonium salts are fairly stable to handle at room temperature both in solution and when dry. Nevertheless, some of these salts, especially those containing heteroatoms in the aromatic moiety, are problematic for their synthesis, and some are indeed highly unstable. To bring some light on this controversial subject, the thermal stability and potential hazards of the 58 most common arenediazonium tetrafluoroborate salts used by us over the last two decades were evaluated under careful conditions. These results are expected to guide conscious decisions on the use and handling of arenediazonium tetrafluoroborates in organic synthesis.

Synthesis of 2H-1,2,3-triazole-4-carboxylic acids via Ru(II)-catalyzed rearrangement of 4-hydrazonoisoxazol-5-ones

An atom-economy, two-step synthesis of 2H-1,2,3-triazole-4-carboxylic acids from 3-arylisoxazol-5(4H)-ones and arenediazonium tetrafluoroborates is described. The formation of the 1,2,3-triazole ring is achieved by the [Ru(p-cymene)Cl2]2-catalyzed rearrangement of 4-hydrazonoisoxazol-5-ones which are resulted from the diazo coupling. The advantages of the method include the available starting compounds and the ability to purify target acids without the use of chromatography.

Palladium-Catalyzed Cyanation of Arenediazonium Tetrafluoroborate Derivatives with 2-(Piperidin-1-yl)acetonitrile as the Cyano Source

AbstractThe present study describes the one-pot palladium-catalyzed cyanation of commercially available aryldiazonium tetrafluoroborate derivatives with 2-(piperidin-1-yl)acetonitrile (an organic cyano reagent) under mild conditions. This process utilizes a Pd/(Me3Si)2 system and is applied to a wide scope of aromatic diazonium substrates to give the corresponding nitrile-containing products in moderate to high yields (59–92%). This methodology is employed for the preparation of etravirine, a drug used for the treatment of HIV, and for transformations of 1H-indole-2-carbonitrile into compounds that are used as a NMDA receptor antagonists and that have high potential against mutant HIV strains. The mechanism proposed for this Pd-catalyzed cyanation involves cyanide ions, as confirmed using indicator paper.

Metal-free synthesis of 5-trifluoromethyltetrazoles

An efficient transition-metal-free method for the synthesis of 5-trifluoromethyltetrazoles from arenediazonium tetrafluoroborates is reported, which relies on the use of trifluoroacetaldehyde N-tosylhydrazone as a convenient 2,2,2-trifluorodiazoethane source. The reaction proceeds in good to excellent yields and shows a high functional group tolerance.

Additive‐Free Visible‐Light‐Mediated Hydro‐/Deuterodediazoniation of Arenediazonium Tetrafluoroborates in THF/THF‐d8

AbstractA visible‐light‐irradiated reductive hydrodediazoniation of arenediazonium tetrafluoroborates in THF is described. The reaction proceeded at ambient temperature under catalyst‐ and additive‐free conditions to afford hydrodediazoniated products in good yields. This protocol was also suitable for deuterodediazoniation of arenediazonium tetrafluoroborates in THF‐d8, supplying the corresponding deuterated arenes in excellent yields. Advantages of this dediazoniation strategy include mildness, simplicity, visible‐light irradiation, a wide range of substrates, good functional group tolerance, with no use of catalysts and additives, and feasibility of a one‐pot diazotization/hydrodediazoniation process, which allows for a safe and convenient way to (deuterated)arenes from anilines.

How do arenediazonium salts behave in deep eutectic solvents? A combined experimental and computational approach

Despite the growing use of Deep Eutectic Solvents (DESs) as green reaction media in a number of organic syntheses, no significant reactions of diazonium salts in these solvents are known in the literature. In this paper, we present the behavior of arenediazonium tetrafluoroborates in new halide salts/polyol-based DESs, the nature of which is investigated by means of a combined computational and experimental approach. A relatively fast (strictly depending on the electronic effects of the substituents bound to the aromatic ring) reduction reaction occurs initiated by the formation of a glycerolate-like species as proved by a thorough computational study aiming at elucidating the involved mechanism.

Copper catalysed Gomberg-Bachmann-Hey reactions of arenediazonium tetrafluoroborates and heteroarenediazonium o-benzenedisulfonimides. Synthetic and mechanistic aspects

Gomberg-Bachmann-Hey reactions were carried out in the presence of copper as a catalyst and gave rise to biaryls or heterobiaryls in good yields and in mild reaction conditions. A computational study of some key points of the reaction was performed. The results are coherent with the experimental data and confirm some aspects of the mechanism. The reaction free energies for the reduction in benzene by CuI of a set of 40 (hetero)arenediazonium tetrafluoroborates were calculated. Both the experiments and the calculations showed that in the coupling with substituted solvents (toluene, bromobenzene, nitrobenzene and anisole) the binding to the ortho position was always favoured. • Gomberg-Bachmann-Hey reactions were carried out in the presence of copper as a catalyst. • Good yields of biaryls or heterobiaryls in mild reaction conditions. • Computational study of some key points of the reaction. • Aryl radicals are key intermediates to generate the target products.

Fluorosulfonylation of arenediazonium tetrafluoroborates with Na2S2O5 and N-fluorobenzenesulfonimide

A transition-metal-free Sandmeyer-type fluorosulfonylation reaction has been achieved by the three-component reaction of arenediazonium tetrafluoroborates, Na2S2O5, and N-fluorobenzenesulfonimide (NFSI). The reaction proceeds through a radical tandem process, affording various arenesulfonyl fluorides in moderate to high yields. This protocol not only provides a complement to the previous fluorosulfonylation reactions, but also extends the applications of Sandmeyer reaction.

Gold-catalyzed reaction of alkynes with diazonium salts under photoirradiation revisited: New alkoxyarylation variant leading to enol ethers

Since earlier work on the use of arenediazonium tetrafluoroborates under gold-photoredox co-catalyzed activation of alkynes has been developed using Ar3PAuCl salts, we focused on modifying the gold precatalyst. The use of the gold complex [Ph3PAuNTf2] allowed for a direct alkoxyarylation of alkynes to form enol ethers in a stereoselective manner, instead of the previously obtained ketones. The synthetic utility of these enol ethers was demonstrated with the controlled preparation of deuterated ketones and fluorinated ketals. Additionally, the mechanism of this alkoxyarylation variant has been explored with density functional theory (DFT) calculations.

Photocatalytic Synthesis of Stilbenes via Cross‐Coupling of Alkenyl Boronic Acids and Arenediazonium Tetrafluoroborate Salts

AbstractIn this article, we describe the development of a new method for the photocatalytic synthesis of (E)‐stilbenes by the coupling of alkenyl boronic acids and aryldiazonium salts. In our operatively simple and metal‐free system, visible light is used as an energy source and a “green” mixture of water and ethanol is used as solvent. A mechanistic explanation is presented which is supported by several control experiments. The reaction proceeds via a radical pathway, from both the diazonium salt and boronic acid in the presence of visible light.

Base-free Pd-MOF catalyzed the Suzuki-Miyaura cross-coupling reaction of arenediazonium tetrafluoroborate salts with arylboronic acids

A convenient and environmental benign synthesis of biaryls has been demonstrated by a straightforward reaction catalyzed by the palladium-containing metal-organic framework (Pd-MOF) [Pd (2-pymo)2]n (2-pymo = 2-pyrimidinolate). A series of functionalized biaryl derivatives have been synthesized in good to excellent yields by the Suzuki-miyaura cross-couplings of sustainable arenediazonium salts with a variety of arylboronic acids and the reactions were catalyzed by the Pd-MOF using methanol as a benign solvent. Those base- and additive-free catalytic reactions proceeded smoothly under non-anhydrous and non-degassed condition. Such transformation avoided high reaction temperature, tolerated many functional groups and presented a wide substrate scope. The catalyst could be recovered by filtration and reused for four successive cycles before collapse of the MOF structure.

Visible-Light Photoredox-Catalyzed and Copper-Promoted Trifluoromethoxylation of Arenediazonium Tetrafluoroborates.

We report the development of photoredox-catalyzed and copper-promoted trifluoromethoxylation of arenediazonium tetrafluoroborates, with trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent. This new method takes advantage of visible-light photoredox catalysis to generate the aryl radical under mild conditions, combined with copper-promoted selective trifluoromethoxylation. The reaction is scalable, tolerates a wide range of functional groups, and proceeds regioselectively under mild reaction conditions. Furthermore, mechanistic studies suggested that a Cs[Cu(OCF3 )2 ] intermediate might be generated during the reaction.

Visible‐Light Photoredox‐Catalyzed and Copper‐Promoted Trifluoromethoxylation of Arenediazonium Tetrafluoroborates

AbstractWe report the development of photoredox‐catalyzed and copper‐promoted trifluoromethoxylation of arenediazonium tetrafluoroborates, with trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent. This new method takes advantage of visible‐light photoredox catalysis to generate the aryl radical under mild conditions, combined with copper‐promoted selective trifluoromethoxylation. The reaction is scalable, tolerates a wide range of functional groups, and proceeds regioselectively under mild reaction conditions. Furthermore, mechanistic studies suggested that a Cs[Cu(OCF3)2] intermediate might be generated during the reaction.

Organic photoredox catalysis enabled cross-coupling of arenediazonium and sulfinate salts: synthesis of (un)symmetrical diaryl/alkyl aryl sulfones.

We disclose herein the first transition-metal- and external oxidant/reductant-free visible-light-mediated synthesis of (un)symmetrical diaryl/alkyl aryl sulfones from arenediazonium tetrafluoroborates and sodium sulfinates using eosin Y as an organic photoredox catalyst. The utilization of visible light as an inexpensive and ecosustainable energy source, operational simplicity, ambient temperature and clean reaction in aqueous acetonitrile are the salient features of the developed protocol. The desired sulfones were also synthesized via a one-pot, two-step process directly from anilines and sulfinate salts in good to excellent yields.

Copper‐Mediated Di‐ and Monofluoromethanesulfonylation of Arenediazonium Tetrafluoroborates: Probing the Fluorine Effect

A copper‐mediated di‐ and monofluoromethanesulfonylation of arenediazonium tetrafluoroborates using di‐ and monofluoromethanesulfinate reagents provides aryl difluoromethyl (or monofluoromethyl) sulfones in good yields. It was found that the relative reactivity of these sodium fluoroalkanesulfinates in the present reactions decreases in the following order: CH2FSO2Na > CF2HSO2Na > CF3SO2Na.

Synthesis of Sulfonated Benzo[d][1,3]oxazines by Merging Photoredox Catalysis and Insertion of Sulfur Dioxide

AbstractA photocatalytic reaction of N‐(2‐vinylphenyl)amides, DABCO⋅(SO2)2 and arenediazonium tetrafluoroborates for the synthesis of 4‐((arylsulfonyl)methyl)‐4H‐benzo[d][1,3]oxazines under mild conditions is reported. This synthetic approach is enabled by merging photoredox catalysis and insertion of sulfur dioxide via a radical process. The specific role of photoredox catalysis in this transformation is supported by mechanistic investigations and theoretical calculations.magnified image

Chemoselective synthesis of diaryl disulfides via a visible light-mediated coupling of arenediazonium tetrafluoroborates and CS2.

A highly efficient and chemoselective method for the synthesis of diaryl disulfides is developed via a visible light-promoted coupling of readily accessible arenediazonium tetrafluoroborates and CS2. This practical and convenient protocol provides a direct pathway for the assembly of a series of disulfides in an environmentally friendly manner with good to excellent yields.

Efficient copper-catalyzed N-arylation of NH-containing heterocycles and sulfonamides with arenediazonium tetrafluoroborates

ABSTRACTA practical copper-catalyzed N-arylation of NH-containing heterocycles with arenediazonium tetrafluoroborates has been developed using CuCl as catalyst and K2CO3 as additive under ligand-free conditions. This reaction system has wide substrate scope including imides, 1H-pyrazole, 1H-tetrazoles, 1,2-benzisothiazol-3(2H)-one, and related sulfonamides and gives moderate to excellent yields (up to 95%) of the desired products. This strategy is very general, simple, environmentally friendly, and tolerant of oxygen.