Preparation of Sulfonyl Chlorides by Oxidative Chlorination of Thiols and Disulfides using HNO3/HCl/O2 in a Flow Reactor

A continuous flow metal-free protocol for the synthesis of sulfonyl chlorides from thiols and disulfides in the presence of nitric acid, hydrochloric acid and oxygen was developed. The influence of the reaction parameters was investigated under batch and flow conditions. Online 19F NMR was successfully implemented to investigate different reaction conditions within a single experiment. The sulfonyl chlorides were isolated (mostly in 70-81 % yield) after performing a simple aqueous washing procedure. In particular, the protocol was successfully operated for >6 hours to convert diphenyl disulfide to its corresponding sulfonyl chloride, achieving a throughput of 3.7 g h-1. The environmental impact of the protocol was assessed and compared to an existing continuous flow protocol using 1,3-dichloro-5,5-dimethylhydantoin (DCH) as reagent. The process mass intensity (PMI) for the newly-developed flow protocol (15) compared favorably to the DCH flow process (20).

Photoredox-Catalyzed Preparation of Sulfones Using Bis-Piperidine Sulfur Dioxide - An Underutilized Reagent for SO2 Transfer

Sulfonyl groups are widely observed in biologically relevant molecules and consequently, SO2 capture is an increasingly attractive method to prepare these sulfonyl-containing compounds given the range of SO2 -surrogates now available as alternatives to using the neat gas. This, along with the advent of photoredox catalysis, has enabled mild radical capture of SO2 to emerge as an effective route to sulfonyl compounds. Here we report a photoredox-catalyzed cross-electrophile sulfonylation of aryl and alkyl bromides making use of a previously under-used amine-SO2 surrogate; bis(piperidine) sulfur dioxide (PIPSO). A broad selection of alkyl and aryl bromides were photocatalytically converted to their corresponding sulfinates and then trapped with various electrophiles in a one-pot multistep procedure to prepare sulfones and sulfonamides.

An Automated Continuous Synthesis and Isolation for the Scalable Production of Aryl Sulfonyl Chlorides

In this work, a continuous system to produce multi-hundred-gram quantities of aryl sulfonyl chlorides is described. The scheme employs multiple continuous stirred-tank reactors (CSTRs) and a continuous filtration system and incorporates an automated process control scheme. The experimental process outlined is intended to safely produce the desired sulfonyl chloride at laboratory scale. Suitable reaction conditions were first determined using a batch-chemistry design of experiments (DOE) and several isolation methods. The hazards and incompatibilities of the heated chlorosulfonic acid reaction mixture were addressed by careful equipment selection, process monitoring, and automation. The approximations of the CSTR fill levels and pumping performance were measured by real-time data from gravimetric balances, ultimately leading to the incorporation of feedback controllers. The introduction of process automation demonstrated in this work resulted in significant improvements in process setpoint consistency, reliability, and spacetime yield, as demonstrated in medium- and large-scale continuous manufacturing runs.

Radiosynthesis of 18F-Labeled Arenesulfonyl Fluorides through Two-Bond Construction with [18F]Fluoride

A novel ¹⁸F labeling strategy was developed to directly construct aryl-SO₂-¹⁸F from arenediazonium tosylates with a SO₂ source and [¹⁸F]fluoride. This approach is compatible with a wide range of substrates and enabled the production of ¹⁸F-labeled drug-like derivatives through late-stage ¹⁸F fluorination, representing a significant advance in the radiosynthesis of ¹⁸F-labeled arenesulfonyl fluorides. A reactive ¹⁸F labeling synthon, bearing a maleimide-based prosthetic group, allowed for the generation of ¹⁸F-labeled temperature-sensitive biomolecules containing cysteine residues via maleimide-cysteine chemistry.

Scalable, Chemoselective Nickel Electrocatalytic Sulfinylation of Aryl Halides with SO2

Simple access to aryl sulfinates from aryl iodides and bromides is reported using an inexpensive Ni-electrocatalytic protocol. The reaction exhibits a broad scope, uses stock solution of simple SO2 as sulfur source, and can be scaled up in batch and recycle flow settings. The limitations of this reaction are clearly shown and put into context by benchmarking with state-of-the-art Pd-based methods.

Palladium-Catalysed Intermolecular Direct C–H Bond Arylation of Heteroarenes with Reagents Alternative to Aryl Halides: Current State of the Art

Abstract:

Abstract: This unprecedented review with 322 references provides a critical up-to-date picture of the Pd-catalysed intermolecular direct C–H bond arylation of heteroarenes with arylating reagents alternative to aryl halides that include aryl sulfonates (aryl triflates, tosylates, mesylates, and imidazole-1-sulfonates), diaryliodonium salts, [(diacetoxy)iodo]arenes, arenediazonium salts, 1-aryltriazenes, arylhydrazines and N’-arylhydrazides, arenesulfonyl chlorides, sodium arenesulfinates, arenesulfinic acids, and arenesulfonohydrazides. Particular attention has been paid to summarise the preparation of the various arylating reagents and to highlight the practicality, versatility, and limitations of the various developed arylation protocols, also comparing their results with those achieved in analogous Pd-catalysed arylation reactions involving the use of aryl halides as electrophiles. Mechanistic proposals have also been briefly summarised and discussed. However, data concerning Pd-catalysed direct C–H bond arylations involving the C–H bonds of aryl substituents of the examined heteroarene derivatives have not been taken into account.

Sulfonyl fluorides as targets and substrates in the development of new synthetic methods

The advent of sulfur(VI)-fluoride exchange (SuFEx) processes as transformations with click-like reactivity has invigorated research into electrophilic species featuring a sulfur-fluorine bond. Among these, sulfonyl fluorides have emerged as the workhorse functional group, with diverse applications being reported. Sulfonyl fluorides are used as electrophilic warheads by both medicinal chemists and chemical biologists. The balance of reactivity and stability that is so attractive for these applications, particularly the resistance of sulfonyl fluorides to hydrolysis under physiological conditions, has provided opportunities for synthetic chemists. New synthetic approaches that start with sulfur-containing substrates include the activation of sulfonamides using pyrilium salts, the deoxygenation of sulfonic acids, and the electrochemical oxidation of thiols. Employing non-sulfur-containing substrates has led to the development of transition-metal-catalysed processes based on palladium, copper and nickel, as well as the use of SO₂F₂ gas as an electrophilic hub. Selectively manipulating molecules that already contain a sulfonyl fluoride group has also proved to be a popular tactic, with metal-catalysed processes again at the fore. Finally, coaxing sulfonyl fluorides to engage with nucleophiles, when required, and under suitable reaction conditions, has led to new activation methods. This Review provides an overview of the challenges in the efficient synthesis and manipulation of these intriguing functional groups.

Revisiting aromatic diazotization and aryl diazonium salts in continuous flow: highlighted research during 2001–2021

Aryl diazonium salts play an important role in chemical transformations; however their explosive nature limits their applications in batch.

A continuous flow investigation of sulfonyl chloride synthesis using N-chloroamides: optimization, kinetics and mechanism

We develop a continuous flow protocol for the synthesis of sulfonyl chlorides from disulfides and thiols, using 1,3-dichloro-5,5-dimethylhydantoin (DCH) as a dual-function reagent for oxidative chlorination.

The Same Oxidation-State Introduction of Hypervalent Sulfur via Transition-Metal Catalysis

Sulfonyl compounds have attracted considerable interest due to their extensive applications in drug discovery, agricultural, and material science. The access to the assembly of SO₂ -containing compounds via the same oxidative-state introduction of hypervalent sulfur has come to the fore in the recent years. Especially, the transition-metal-involved synthesis of hypervalent sulfur compounds is the most effective strategy since SO₂ is easy to insert into the metal-carbon bonds. This review discusses the application of the same oxidation-state introduction of hypervalent sulfur strategy under the transition-metal-catalyzed conditions, and presents according to different metal catalysts and the synthesized diversity hypervalent sulfur-containing compounds skeletons, including sulfonamides, sulfones, sulfinamides, sulfonyl acids and sulfonyl fluorides.

Metal- and Reagent-Free Electrochemical Synthesis of Alkyl Arylsulfonates in a Multi-Component Reaction

This work presents the first electrochemical preparation of alkyl arylsulfonates by direct anodic oxidation of electron-rich arenes. The reaction mechanism features a multi-component reaction consisting of electron-rich arenes, an alcohol of choice and excess SO2 in an acetonitrile-HFIP reaction mixture. In-situ formed monoalkyl sulfites are considered as key intermediates with bifunctional purpose. Firstly, this species functions as nucleophile and secondly, excellent conductivity is provided. Several primary and secondary alcohols and electron-rich arenes are implemented in this reaction to form the alkyl arylsulfonates in yields up to 73 % with exquisite selectivity. Boron-doped diamond electrodes (BDD) are employed in divided cells, separated by a simple commercially available glass frit.

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.

One Amine-3 Tasks: Reductive Coupling of Imines with Olefins in Batch and Flow

Owing to their wide range of biological properties, γ-aminobutyric acid derivatives (GABA) have been extensively studied and found noteworthy industrial applications. However, atom-economical and efficient processes for their production are scarce and would greatly benefit from further investigations. Herein, we demonstrate that an iridium-based photocatalyst promotes the direct reductive cross-coupling of imines with olefins upon irradiation with visible light to give GABA derivatives in good yields and selectivities. We also stress the enabling triple role of tributylamine additive in this process, discuss the advantages of strategies based on proton-coupled electron transfer (PCET) and demonstrate the scale-up of this reaction in continuous flow.

Formation of an unexpected 3,3-diphenyl-3H-indazole through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate

The one-pot reaction of 2,6-bis(diphenylmethyl)-4-methoxyaniline with tert-butylnitrite, BTEAC and DABSO in the presence of CuCl2 provided an unexpected 3H-indazole product 8. The structure of the compound was determined by HRMS, IR, NMR and further confirmed by single crystal X-ray crystallography. The compound crystallises in the triclinic P-1 space group, with unit cell parameters a = 9.2107 (4), b = 10.0413 (5), c = 14.4363 (6) Å, α = 78.183 (2), β = 87.625 (2), γ = 71.975 (2)°. The formation of 8 proceeded through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate 9. The molecules of 8 are organised by edge-face Ar-H···π, face-face π···π, and bifurcated OCH2-H···N interactions. In addition to these, there are Ar-H···H-Ar close contacts, (edge-edge and surrounding inversion centres) arranged as infinite tapes along the a direction.

Visible-light mediated sulfonylation of thiols via insertion of sulfur dioxide

Photocatalytically generated sulfenyl radicals were coupled with arylsulfonyl radicals at room temperature for accessing unsymmetrical organic thiosulfonates.

One-pot fluorosulfurylation of Grignard reagents using sulfuryl fluoride

Herein, we report a new method for the one-pot syntheses of sulfonyl fluorides.

Insertion of sulfur dioxide via a radical process: an efficient route to sulfonyl compounds

This review is focused on the recent advances in the chemistry of sulfur dioxide fixation through a radical process. Diverse sulfonyl compounds can be obtained efficiently under mild conditions.

Benzylic C(sp3)–H bond sulfonylation of 4-methylphenols with the insertion of sulfur dioxide under photocatalysis

Sulfonylation of the benzylic C–H bond is developed through a three-component reaction of aryldiazonium tetrafluoroborates, 4-methylphenols and sodium metabisulfite (Na₂S₂O₅). The inorganic sulfite of sodium metabisulfite is used as the SO₂ surrogate.

Aromatic Chlorosulfonylation by Photoredox Catalysis

Visible-light photoredox catalysis enables the efficient synthesis of arenesulfonyl chlorides from anilines. The new protocol involves the convenient in situ preparation of arenediazonium salts (from anilines) and the reactive gases SO₂ and HCl (from aqueous SOCl₂ ). The photocatalytic chlorosulfonylation operates at mild conditions (room temperature, acetonitrile/water) with low catalyst loading. Various functional groups are tolerated (e.g., halides, azides, nitro groups, CF₃ , SF₅ , esters, heteroarenes). Theoretical and experimental studies support a photoredox-catalysis mechanism.

Transition-metal-free oxidative reaction of hydrazines and potassium metabisulfite for preparation of sulfonohydrazides

A coupling reaction for the synthesis of sulfonohydrazides from two types of hydrazines and K₂S₂O₅ under air was developed.