Organocatalytic SuFEx click reactions of SO2F2

An organocatalytic method for the SuFEx click reaction of gaseous SO2F2 is described. Different organic bases such as DBU, TBD, triethylamine and Hünig's base can efficiently catalyze the SuFEx of SO2F2 with various phenols to produce aryl fluorosulfates in 61-97% yields. Under the same conditions, pyridone, pyrazolone and amines can also react with SO2F2 to afford the corresponding heteroaryl fluorosulfates or sulfamoyl fluorides in good yields. In this process, molecular sieves absorb the acidic HF efficiently, avoiding the use of stoichiometric amounts of organosilicon reagents and excess bases.

Streamlining Thionyl Tetrafluoride (SOF4) and Pentafluoro-Oxosulfate [OSF5]- Anions Syntheses

A one pot room temperature synthesis of thionyl tetrafluoride (SOF4) from elemental fluorine (F2) and thionyl fluoride (SOF2) is reported. The selective decagram scale process (100 mmol) allows a quantitative preparation of SOF4 with high purity. The solid-state structure has also been elucidated and compared with the reported gas phase one. The use of this reagent for the formation of the emerging pentafluorooxosulfate [cat][OSF5] anions led to the preparation of multiple ion-pairs (cat=Ag, NEt3Me, PPN, PPh4) in different organic solvents. The SuFEx reservoir ability of this anion was studied and by tuning the solvent system, the reactivity of pure thionyl tetrafluoride was observed using Ag[OSF5] in THF and acetone.

Isolation and Reactivity of Arylnickel(II) Complexes in Nickel-Catalyzed Borylation of Aryl Fluorosulfates

Aryl fluorosulfates have emerged as versatile SuFExable substrates, harnessing the reactivity of the S-F bond. In this study, we unveil their alternative synthetic utility in nickel-catalyzed borylation via C-O bond activation. This method highlights mild reaction conditions, a broad substrate scope, and moderate functional group tolerance, rendering it a practical and appealing approach for synthesizing a diverse array of aryl boronate esters. Furthermore, computational analysis sheds light on the reaction pathways, uncovering the participation of LNi(0) and LNi(II)ArX species. This insight is supported by the 31P NMR reaction monitoring along with isolation and single-crystal X-ray structural elucidation of well-defined arylnickel(II) intermediates obtained from the oxidative addition of aryl fluorosulfates. A comprehensive investigation, merging experimental and computational approaches, deepens our understanding of the alternative reactivity of SuFExable substrates.

Arylazo sulfones: multifaceted photochemical reagents and beyond

The photochemical action of arylazo sulfones under visible light irradiation has recently gained considerable attention for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. The inherent dyedauxiliary group (-N2SO2R) embedded in the reagent is responsible for the absorption of visible light even in the absence of a photocatalyst, additive or oxidant, leading to the generation of three different radicals, viz. aryl (carbon-centred), sulfonyl (sulphur-centred) and diazenyl (nitrogen-centred) radicals, under different reaction conditions. Encountering a reagent with such a versatile behaviour is quite rare, which makes arylazo sulfones a highly interesting class of compounds. The mild reaction conditions under which these reagents can operate are an added advantage. Recently, they are also being used as non-ionic photoacid generators (PAGs), electron acceptors, and hydrogen atom transfer (HAT) and imination reagents in a number of synthetic transformations. They have displayed substantial damaging effect on the structure of DNA in the presence of light which can lead to their use as phototoxic pharmaceuticals for cancer treatment. Moreover, their photochemistry is also being exploited in polymerization reactions (as photoinitiators) and in materials chemistry (surface modification).

AITF (4-acetamidophenyl triflimide) mediated synthesis of amides, peptides and esters

A simple, broadly applicable protocol for amidation and esterification reactions is described. Thereby, 4-acetamidophenyl triflimide (AITF), a crystalline stable reagent, is employed for the activation of carboxylic acids. The use of AITF as a coupling agent is demonstrated in the synthesis of peptides, amides and esters under mild conditions in good to excellent yields. Notably, peptide segment condensations were also accomplished. A diverse array of synthetic protocols showcasing a broad substrate scope and good functional group compatibility were accomplished. Herein, we systematically summarized the use of AITF in peptide synthesis strategies.

Aryl sulfonyl fluoride synthesis via organophotocatalytic fluorosulfonylation of diaryliodonium salts

A mild and efficient synthesis of various aryl sulfonyl fluorides from diaryliodonium salts under organophotocatalysis via a radical sulfur dioxide insertion and fluorination strategy is presented. Diaryliodonium salts are used as aryl radical precursors, the 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO) as a sulfonyl source and cheap KHF2 as a desirable fluorine source, respectively. Notably, the electronic properties of substituents on the aromatic rings in diaryliodonium salts have a significant influence on the reaction yields.

Aliphatic Sulfonyl Fluoride Synthesis via Decarboxylative Fluorosulfonylation of Hypervalent Iodine(III) Carboxylates

We disclose herein a photocatalytic decarboxylative fluorosulfonylation reaction of various hypervalent iodine(III) carboxylates in combination with 1,4-diazabicyclo[2.2.2]octane-bis(sulfur dioxide) adduct as a sulfonyl source and KHF2 as a desirable fluorine source via a radical sulfur dioxide insertion and fluorination strategy. A one-pot photocatalytic decarboxylative fluorosulfonylation reaction of various carboxylic acids mediated by PhI(OAc)2 was realized, as well. Notably, this transformation can be performed under heating conditions without the need for catalysts.

New Chemical Transformations Involving SO2 F2 -Mediated Alcohol Activation

Sulfuryl fluoride is a gas produced on a multi-ton scale for its use as a fumigant. In the last decades, it has gained interest in organic synthesis as a reagent with unique properties in terms of stability and reactivity when compared to other sulfur-based reagents. Sulfuryl fluoride has not only been used for sulfur-fluoride exchange (SuFEx) chemistry but also encountered applications in classic organic synthesis as an efficient activator of both alcohols and phenols, forming a triflate surrogate, namely a fluorosulfonate. A long-standing industrial collaboration in our research group drove our work on the sulfuryl fluoride-mediated transformations that will be highlighted below. We will first describe recent works on metal-catalyzed transformations from aryl fluorosulfonates while emphasizing the one-pot processes from phenol derivatives. In a second section, nucleophilic substitution reactions on polyfluoroalkyl alcohols will be discussed and the value of polyfluoroalkyl fluorosulfonates in comparison to alternative triflate and halide reagents will be brought to light.

FSO2N3-Enabled Synthesis of Tetrazoles from Amidines and Guanidines

Herein we report the facile syntheses of tetrazoles enabled by FSO2N3 under mild conditions. FSO2N3 has been shown as the most powerful diazotizing reagent, which converts thousands of primary amines to azides fast and orthogonally. As the follow-up studies of the diazo transfer reaction using FSO2N3, we discover that amidines and guanidines are rapidly transformed into tetrazole derivatives when reacting with FSO2N3 under an aqueous environment, which is unprecedented for tetrazole synthesis.

Synthesis of aliphatic nitriles from cyclobutanone oxime mediated by sulfuryl fluoride (SO2F2)

A SO₂F₂-mediated ring-opening cross-coupling of cyclobutanone oxime derivatives with alkenes was developed for the construction of a range of δ-olefin-containing aliphatic nitriles with (E)-configuration selectivity. This new method features wide substrate scope, mild conditions, and direct N-O activation.

Advances in the construction of diverse SuFEx linkers

Sulfur fluoride exchange (SuFEx), a new generation of click chemistry, was first presented by Sharpless, Dong and co-workers in 2014. Owing to the high stability and yet efficient reactivity of the S^VI-F bond, SuFEx has found widespread applications in organic synthesis, materials science, chemical biology and drug discovery. A diverse collection of SuFEx linkers has emerged, involving gaseous SO₂F₂ and SOF₄ hubs; SOF₄-derived iminosulfur oxydifluorides; O-, N- and C-attached sulfonyl fluorides and sulfonimidoyl fluorides; and novel sulfondiimidoyl fluorides. This review summarizes the progress of these SuFEx connectors, with an emphasis on analysing the advantages and disadvantages of synthetic strategies of these connectors based on the SuFEx concept, and it is expected to be beneficial to researchers to rapidly and correctly understand this field, thus inspiring further development in SuFEx chemistry.

The Synthesis of Fluorinated Carbohydrates Using Sulfuryl Fluoride as the Deoxyfluorination Reagent

Fluorination of carbohydrates has been one of the strategies to increase their enzymatic and chemical stabilities and reduce their hydrophilicities, making this modification attractive for drug discovery purposes. The synthesis of monofluorinated carbohydrates was achieved under mild conditions by using SO₂F₂ as the deoxyfluorination reagent in the presence of a base without extra fluoride additives. This method features low toxicity, easy availability, low cost, and high efficiency and can be subjected to diverse sugar units.

Selective Fluorosulfonylation of Thianthrenium Salts Enabled by Electrochemistry

A practical electrochemically driven method for fluorosulfonylation of both aryl and alkyl thianthrenium salts has been disclosed. The strategy does not need external redox reagents or metal catalysts. In combination with C-H thianthrenation of aromatics, this method provides a new tool for the site-selective fluorosulfonylation of drugs.

Facile synthesis of sulfonyl fluorides from sulfonic acids

Herein, we demonstrate two complementary strategies for the syntheses of sulfonyl fluorides using sulfonic acids and their salts. One strategy involves the conversion of sulfonic acid sodium salts to sulfonyl fluorides using thionyl fluoride in 90-99% yields in one hour. Lessons learned from the mechanism of this reaction also have enabled a complementary deoxyfluorination of sulfonic acids using Xtalfluor-E® - a bench stable solid - allowing for the conversion of both aryl and alkyl sulfonic acids and salts to sulfonyl fluorides in 41-94% yields. Notably, using Xtalfluor-E® enabled milder conditions and the use of both sulfonic acids and their sodium salts.

A late-stage functionalization tool: sulfonyl fluoride mediated deoxymethylation of phenols

The late-stage functionalization of drugs and natural products has been identified as a promising approach to accelerate the discovery of new bioactive compounds. Due to the presence of the "Magic Methyl Effect", the direct deoxymethylation of phenolic hydroxyl groups, which are widespread in natural molecules, is a challenging task. A mild and rapid strategy for direct phenol deoxymethylation under metal catalysis using SO₂F₂ is described in this paper, while good functional group tolerance and high chemoselectivity allow this strategy to be one of the powerful tools for LSF. The power of this new platform is showcased through gram-scale and orthogonal experiments.

Introducing SuFNucs: Sulfamoyl-Fluoride-Functionalized Nucleosides That Undergo Sulfur Fluoride Exchange Reaction

The reaction between ribonucleosides and ex situ generated sulfonyl fluoride has been developed. The reaction takes place at the −NH₂ groups of nucleobases, and the resulting nucleosides are equipped with a sulfamoyl fluoride moiety, dubbed SuFNucs. These species undergo a selective sulfur fluoride exchange (SuFEx) reaction with various amines, leading to sulfamide-functionalized derivatives of adenosine, guanosine, and cytidine (SulfamNucs). The scope and examples of further SuFNucs fuctionalization leading to nucleotides, oligonucleotides, and peptide–nucleoside conjugates are presented.

Thionyl Fluoride-Mediated One-Pot Substitutions and Reductions of Carboxylic Acids

Thionyl fluoride (SOF₂) is an underutilized reagent that is yet to be extensively studied for its synthetic applications. We previously reported that it is a powerful reagent for both the rapid syntheses of acyl fluorides and for one-pot peptide couplings, but the full scope of these nucleophilic acyl substitutions had not been explored. Herein, we report one-pot thionyl fluoride-mediated syntheses of peptides and amides (35 examples, 45-99% yields) that were not explored in our previous study. The scope of thionyl fluoride-mediated nucleophilic acyl substitutions was also expanded to encompass esters (24 examples, 64-99% yields) and thioesters (11 examples, 24-96% yields). In addition, we demonstrate that the scope of thionyl fluoride-mediated one-pot reactions can be extended beyond nucleophilic acyl substitutions to mild reductions of carboxylic acids using NaBH₄ (13 examples, 33-80% yields).

Quantitative and convenient real-time reaction monitoring using stopped-flow benchtop NMR

We present a stopped-flow benchtop NMR system (composed of commercially available hardware components) that allows for quantitative reaction monitoring to be completed with relative ease, even with experimentally complex reaction systems.

Photocatalytic fluorosulfonylation of aliphatic carboxylic acid NHPI esters

SO2 radical insertion/fluorination via a photocatalytic redox strategy is developed, providing an efficient and reliable approach for the synthesis of alkylsulfonyl fluorides.

Aliphatic sulfonyl fluoride synthesis via reductive decarboxylative fluorosulfonylation of aliphatic carboxylic acid NHPI esters

A general and efficient approach to various aliphatic sulfonyl fluorides by the reductive decarboxylative fluorosulfonylation of aliphatic carboxylic acids via a radical sulfur dioxide insertion and fluorination strategy was developed.

Rapid and column-free syntheses of acyl fluorides and peptides using ex situ generated thionyl fluoride

Thionyl fluoride (SOF₂) was first isolated in 1896, but there have been less than 10 subsequent reports of its use as a reagent for organic synthesis. This is partly due to a lack of facile, lab-scale methods for its generation. Herein we report a novel protocol for the ex situ generation of SOF₂ and subsequent demonstration of its ability to access both aliphatic and aromatic acyl fluorides in 55-98% isolated yields under mild conditions and short reaction times. We further demonstrate its aptitude in amino acid couplings, with a one-pot, column-free strategy that affords the corresponding dipeptides in 65-97% isolated yields with minimal to no epimerization. The broad scope allows for a wide range of protecting groups and both natural and unnatural amino acids. Finally, we demonstrated that this new method can be used in sequential liquid phase peptide synthesis (LPPS) to afford tri-, tetra-, penta-, and decapeptides in 14-88% yields without the need for column chromatography. We also demonstrated that this new method is amenable to solid phase peptide synthesis (SPPS), affording di- and pentapeptides in 80-98% yields.

SO2F2-Mediated N-Alkylation of Imino-Thiazolidinones

The N-alkylation of ambident and weakly nucleophilic imino-thiazolidinones has been developed via substitution with alkyl fluorosulfonates. These reactive electrophiles are obtained through the transformation of nontoxic, economic, and commercially available alcohol derivatives on exposure to SO₂F₂ gas. The use of electron-withdrawing groups and DMAc as solvent affords a (Z)- and N-endocyclic selectivity for the easy introduction of a variety of alkyl and polyfluoroalkyl chains.

A Compendium of the Most Promising Synthesized Organic Compounds against Several Fusarium oxysporum Species: Synthesis, Antifungal Activity, and Perspectives

Vascular wilt caused by F. oxysporum (FOX) is one of the main limitations of producing several agricultural products worldwide, causing economic losses between 40% and 100%. Various methods have been developed to control this phytopathogen, such as the cultural, biological, and chemical controls, the latter being the most widely used in the agricultural sector. The treatment of this fungus through systemic fungicides, although practical, brings problems because the agrochemical agents used have shown mutagenic effects on the fungus, increasing the pathogen's resistance. The design and the synthesis of novel synthetic antifungal agents used against FOX have been broadly studied in recent years. This review article presents a compendium of the synthetic methodologies during the last ten years as promissory, which can be used to afford novel and potential agrochemical agents. The revision is addressed from the structural core of the most active synthetic compounds against FOX. The synthetic methodologies implemented strategies based on cyclo condensation reactions, radical cyclization, electrocyclic closures, and carbon-carbon couplings by metal-organic catalysis. This revision contributes significantly to the organic chemistry, supplying novel alternatives for the use of more effective agrochemical agents against F. oxysporum.

A Broad-Spectrum Catalytic Amidation of Sulfonyl Fluorides and Fluorosulfates*

A broad-spectrum, catalytic method has been developed for the synthesis of sulfonamides and sulfamates. With the activation by the combination of a catalytic amount of 1-hydroxybenzotriazole (HOBt) and silicon additives, amidations of sulfonyl fluorides and fluorosulfates proceeded smoothly and excellent yields were generally obtained (87-99 %). Noticeably, this protocol is particularly efficient for sterically hindered substrates. Catalyst loading is generally low and only 0.02 mol % of catalyst is required for the multidecagram-scale synthesis of an amantadine derivative. In addition, the potential of this method in medicinal chemistry has been demonstrated by the synthesis of the marketed drug Fedratinib via a key intermediate sulfonyl fluoride 13. Since a large number of amines are commercially available, this route provides a facile entry to access Fedratinib analogues for biological screening.

Palladium-Catalyzed Cross-Couplings by C-O Bond Activation

Although palladium-catalyzed cross-coupling of aryl halides and reactive pseudohalides has revolutionized the way organic molecules are constructed today across various fields of chemistry, comparatively less progress has been made in the palladium-catalyzed cross-coupling of less reactive C-O electrophiles. This is despite the fact that the use of phenols and phenol derivatives as bench-stable cross-coupling partners has been well-recognized to bring about major advantages over aryl halides, such as (1) natural abundance of phenols, (2) avoidance of toxic halides, (3) orthogonal cross-coupling conditions, (4) prefunctionalization of phenolic substrates by electrophilic substitution or C-H functionalization, (5) ready availability of phenols from a different pool of precursors than aryl halides. In this review, we present an overview of recent advances made in the field of palladium-catalyzed cross-coupling of C-O electrophiles with a focus on (1) catalytic systems, (2) reaction type, and (3) class of C-O coupling partners. Although the field has been historically dominated by nickel catalysis, it is now evident that the use of more versatile, more functional group tolerant and highly active palladium catalysts supported by appropriately designed ancillary ligands enables the cross-coupling with improved substrate scope and generality, and likely represents a practical solution to the broadly applicable cross-coupling of various C-O bonds across diverse chemical disciplines. The review covers the period through June 2020.

Sulfuryl Fluoride Mediated Synthesis of Amides and Amidines from Ketoximes via Beckmann Rearrangement

A metal-free and redox-neutral method for Beckmann rearrangement employing inexpensive and readily available SO₂ F₂ gas is described. The reported transformation proceeds at ambient temperature and is compatible with a wide range of sterically and electronically diverse aromatic, heteroaromatic, aliphatic and lignin-like oximes providing amides in good to excellent yields. The reaction proceeds through the formation of an imidoyl fluoride intermediate that can also be used for the synthesis of amidines.

Halide-Accelerated Acyl Fluoride Formation Using Sulfuryl Fluoride

Herein, we report a new one-pot sequential method for SO₂F₂-mediated nucleophilic acyl substitution reactions starting from carboxylic acids. A mechanistic study revealed that SO₂F₂-mediated acid activation proceeds via the anhydride, which is then converted to the corresponding acyl fluoride. Tetrabutylammonium chloride or bromide accelerate the formation of acyl fluoride. Optimized halide-accelerated conditions were used to synthesize acyl fluorides in 30-80% yields, and esters, amides, and thioesters in 72-96% yields without reoptimization for each nucleophile.

SO2F2-Mediated one-pot cascade process for transformation of aldehydes (RCHO) to cyanamides (RNHCN)

A simple, mild and practical cascade process for the direct conversion of aldehydes to cyanamides was developed featuring a wide substrate scope and great functional group tolerability. This method allows for transformations of readily available, inexpensive, and abundant aldehydes to highly valuable cyanamides in a pot, atom, and step-economical manner with a green nitrogen source. This protocol will serve as a robust tool for the installation of the cyanamide moiety in various complicated molecules.

Arenesulfonyl Fluoride Synthesis via Copper-Catalyzed Fluorosulfonylation of Arenediazonium Salts

We report herein a general and practical copper-catalyzed fluorosulfonylation reaction of a wide range of abundant arenediazonium salts to smoothly prepare various arenesulfonyl fluorides using the 1,4-diazabicyclo[2.2.2]octane-bis(sulfur dioxide) adduct as a convenient sulfonyl source in combination with KHF₂ as an ideal fluorine source and without the need for additional oxidants. Interestingly, the electronic character of the arene ring in the starting arenediazonium salts has a significant impact on the reaction mechanistic pathway.

Ex situ gas generation for lab scale organic synthesis

This review discusses recent examples of ex situ generated gaseous reagents, and their use in organic synthesis.