Sulfonyl hydrazides as sulfonyl sources in organic synthesis

Synthesis of meta-Sulfonylpyridines via Copper(II)-Catalyzed Cascade Sulfonylation/Cyclization/Aromatization of Tertiary Enamides with Sulfonylhydrazides

A copper(II)-catalyzed radical cascade reaction of N-propargyl enamides with sulfonyl hydrazides was developed, which provided an unprecedented method for the direct synthesis of meta-sulfonylpyridines in high efficiency with good functional group compatibility and simple operation. Mechanistic studies indicated that this tandem process might be composed of the radical addition, intramolecular cyclization and oxidative aromatization.

Synthesis of 2-Sulfonyl Carbazoles via Oxidative C-H Functionalization of Tetrahydrocarbazoles with Sulfonyl Hydrazides

Herein, we report an approach for the synthesis of 2-sulfonyl carbazoles from the oxidative C-H sulfonylation of tetrahydrocarbazoles. The mechanistic study reveals that this special selectivity is realized by the addition of a sulfonyl radical to the 3,4-dihydrocabazole intermediate via dehydrogenative desaturation of tetrahydrocarbazoles. This approach features readily available starting materials, high regioselectivity, broad substrate scope, and attractive synthetic utility.

Visible-Light-Induced Cascade Cyclization of 1-(2-(Arylethynyl)benzoyl)indoles into Sulfonated Benazepino[1,2-a]indolones

1-(2-(Arylethynyl)benzoyl)indoles were developed as an innovative scaffold for radical cascade cyclization under visible-light and mild conditions, enabling efficient synthesis of sulfonated benazepino[1,2-a]indolones. This method operates at room temperature and demonstrates broad substrate compatibility and scalability, with promising potential for sunlight-driven reactions.

Photocatalytic Sulfonylation: Innovations and Applications

Photosynthesis, converting sustainable solar energy into chemical energy, has emerged as a promising craft to achieve diverse organic transformations due to its mild reaction conditions, sustainability, and high efficiency. The synthesis of sulfonated compounds has drawn significant attention in the pharmaceuticals, agrochemicals, and materials industries due to the unique structure and electronic properties of the sulfonyl groups. Over the past decades, many photocatalytic sulfonylation reactions have been developed. In this review, the recent advances in photocatalyzed sulfonylation have been reviewed since 2020, with a primary focus on discussing reaction design and mechanism.

Catalyst-free regioselective sulfonylation of phenoxazine with sulfonyl hydrazides in H2O/HFIP

A facile catalyst-free sulfonylation of phenoxazine with sulfonyl hydrazides was efficiently developed in H2O/HFIP without any catalyst. This metal- and catalyst-free protocol is suitable for aromatic and aliphatic reagents to afford the corresponding sulfones in moderate to high yields. A gram-scale experiment was performed to assess the practicability of the method.

Shining light for organophotocatalysed site-selective sulfonylation of anilides

The site-selective sulfonylation of C(sp2)-H bonds of anilide and quinoline amide derivatives has been developed using organophotocatalysis. This mild and sustainable protocol, which operates at room temperature, precludes the requirement for any metal-based catalyst or photocatalyst and oxidant, which are the challenges associated with existing methodologies. Furthermore, the generation of aryl sulfonyl radicals from commercially available aryl sulfonyl chlorides has been achieved through the use of Rose Bengal as an organophotocatalyst, an approach that was previously unexplored. The detailed mechanistic investigation unveiled the underlying mechanism for site-selective sulfonylation at both the proximal and distal positions, thereby establishing a straightforward approach for building valuable aryl sulfone scaffolds.

Visible-Light Induced Radical Addition-Elimination Reaction for Constructing Allylic Sulfones from Sulfonyl Chlorides and Allyl Bromides

Allyl sulfones are commonly present in bioactive compounds and organic building blocks. This work introduces a photocatalytic radical addition-elimination reaction involving readily accessible sulfonyl chlorides and allyl bromides. It delivers structurally diverse allylic sulfones in moderate to excellent yields, showcasing a high tolerance to functional groups. Notably, this method operates under mild reaction conditions without the need for oxidants, stoichiometric reducing metals, or additives.

Rhodium-Catalyzed Regio- and Enantioselective Allylic Sulfonylation from Sulfonyl Hydrazides

A highly regio- and enantioselective allylic sulfonylation has been developed with rhodium and bisoxazolinephosphine (NPN*) ligands from racemic branched allylic carbonates and readily available sulfonyl hydrazides under neutral conditions. Branch-selective allylic sulfones with a >20:1 branch:linear ratio and >99% ee could be synthesized in ≤96% yield. Both Z and E linear allylic carbonates could also be converted into the same chiral branched allylic sulfones with high regio- and enantioselectivities.

Radical bicyclization of 1,6-enynes with sulfonyl hydrazides by the use of TBAI/TBHP in the aqueous phase

A novel 5-exo-dig/6-endo-trig bicyclization of 1,6-enynes with sulfonyl hydrazides in the aqueous phase using the cheap and available tetrabutylammonium iodide (TBAI)-tert-butyl hydroperoxide (TBHP) combined system is reported. The resulting reaction of diverse nitrogen- and oxygen-polyheterocycles displays high chemical selectivity, high step-economy, and a moderate substrate scope. Moreover, iodosulfonylation can be realized by modulating the structure of the 1,6-enynes.

Stereoselective Synthesis of Substituted (Z)-N-Allyl Sulfonamides via a Palladium-Catalyzed Three-Component Tandem Reaction

This paper reports the efficient synthesis of substituted (Z)-N-allyl sulfonamides via a palladium-catalyzed three-component tandem reaction of N-buta-2,3-dienyl sulfonamides with iodides and sulfonyl hydrazide or sulfinic acid sodium salt as nucleophiles. Pd(PPh₃)₄ (2.5 mol %), K₂CO₃, and THF were used as the optimal catalyst, base, and solvent, respectively. The substituted (Z)-N-allyl sulfonamides were obtained in a 30-83% overall yield. Mechanistic investigations revealed that the formation of the single (Z)-isomer was controlled by the formation of a six-membered palladacycle intermediate.

Practical synthesis and biological screening of sulfonyl hydrazides

A methodology for the synthesis of sulfonyl hydrazides mediated by hypervalent iodine is described. Taking advantage of the umpolung properties of hypervalent iodine reagents, the polarity of sodium sulfinate salts is reversed, and a key intermediate is generated and reacted with mono- and disubstituted hydrazines. To highlight the practical utility of this protocol, a diverse range of sulfonyl hydrazides were synthesized in yields up to 62%. Furthermore, a gram-scale reaction was performed, showing the robustness of the procedure. Mechanistic studies, including DFT calculations, were performed and the bioactivity of the generated compounds was evaluated.

Easy access to α-carbonyl sulfones using cross-coupling of α-aryl-α-diazoesters with sulfonyl hydrazides

A facile synthesis of α-carbonyl sulfones has been accomplished by the cross-coupling of α-aryl-α-diazoesters with sulfonyl hydrazides in the presence of CuI and DBU. The reaction employs inexpensive and bench stable sulfonyl hydrazides as a sulfonyl source, and facilitates the migratory insertion with α-aryl-α-diazoesters under mild reaction conditions.

The Application of Sulfonyl Hydrazides in Electrosynthesis: A Review of Recent Studies

Sulfonyl hydrazides are viewed as alternatives to sulfinic acids and their salts or sulfonyl halides, which are broadly used in organic synthesis or work as active pharmaceutical substances. Generally, sulfonyl hydrazides are considered good building blocks and show powerful value in a diverse range of reactions to construct C-S bonds or C-C bonds, and even C-N bonds as sulfur, carbon, or nitrogen sources, respectively. As a profound synthetic tool, the electrosynthesis method was recently used to achieve efficient and green applications of sulfonyl hydrazides. Interestingly, many unique and novel electrochemical syntheses using sulfonyl hydrazides as radical precursors have been developed, including cascade reactions, functionalization of heterocycles, as well as a continuous flow method combining with electrochemical synthesis since 2017. Accordingly, it is necessary to specifically summarize the recent developments of electrosynthesis with only sulfonyl hydrazides as radical precursors to more deeply understand and better design novel electrochemical synthesis reactions. Herein, electrosynthesis research using sulfonyl hydrazides as radical precursors since 2017 is reviewed in detail based on the chemical structures of products and reaction mechanisms.

A Bi(OTf)3-Promoted Hydrosulfonylation of Alkenes with Sulfonyl Hydrazides: An Approach to Branched Sulfones

The Bi(OTf)₃-promoted hydrosulfonylation of alkenes with sulfonyl hydrazides to produce branched sulfones is reported, in which various branched sulfones (>40 examples) have been prepared in moderate to good yields. The gram-scale reaction and synthesis of the experimental inhibitor precursor showed the potential application. A preliminary mechanistic study revealed that double-bond migration to form the α,β-conjugated alkene is crucial for this transformation.

Copper-catalyzed C-3 benzylation of quinoxalin-2(1H)-ones with benzylsulfonyl hydrazides

An unprecedented use of benzylsulfonyl hydrazides as benzylating agents has been demonstrated in the direct C-3 benzylation of quinoxalin-2(1H)-ones. A range of benzylsulfonyl hydrazides participated in the C-3 benzylation of quinoxalin-2(1H)-ones with CuCN as the catalyst and DTBP as the oxidant, delivering structurally diverse 3-benzylquinoxalin-2(1H)-ones in moderate to good yields.

Base-promoted synthesis of diarylsulfones from sulfonyl hydrazines and diaryliodonium salts

An efficient and concise method for the synthesis of diverse substituted sulfones was developed with high selectivity. Using n-PrOH as the solvent, diaryl sulfones are formed even on a gram scale via metal-free coupling from sulfonyl hydrazines with symmetrical or unsymmetrical diaryliodonium salts.

Radical coupling reactions of hydrazines via photochemical and electrochemical strategies

Hydrazines are versatile building blocks in organic synthesis.

A new method for C(sp2)-H sulfonylmethylation with glyoxylic acid and sodium sulfinates

We herein describe a C4 sulfonylmethylation of pyrazol-5-amines with glyoxylic acid and sodium sulfinates. The reaction only needed to add water as the solvent, and it featured mild reaction condition,...

Sulfonyl radical triggered selective iodosulfonylation and bicyclization of 1,6-dienes

A novel sulfonyl radical triggered selective iodosulfonylation and bicyclization of 1,6-dienes has been described for the first time. High selectivity and efficiency, mild reaction conditions, excellent functional group compatibility, and broad substrate scope are the attractive features of this synthetic protocol, which provides a unique platform for precise radical cyclization.

The bioactivity of benzenesulfonyl hydrazones: A short review

The synthesis and biological activity evaluation of benzenesulfonyl hydrazones is quite frequently encountered in scientific literature. This class of compounds is very interesting due to the wide spectrum of potential applications in the field of medicinal chemistry. The benzenesulfonyl hydrazones possess mainly antibacterial, antifungal, anticancer, antidepressant properties, activity against Alzheimer's disease, insecticidal activity and ability to inhibit the activity of enzymes. This review is an attempt to gather the literature findings on the most promising bioactive benzenesulfonyl hydrazones.

Novel 2,4,6-Trimethylbenzenesulfonyl Hydrazones with Antibacterial Activity: Synthesis and In Vitro Study

This research describes the synthesis and in vitro antimicrobial activity study of a series of 2,4,6-trimethylbenzenesulfonyl hydrazones. Twenty-five hydrazones (2-26) were synthesized on the basis of condensation reaction. The in vitro bioactivity study confirmed the potential application of obtained derivatives as antimicrobial agents. Among the tested compounds, the highest activity was discovered for derivative 24, which possessed minimal inhibitory concentration (MIC) ranging from 7.81 to 15.62 µg/mL against Gram-positive reference bacterial strains. Synthesized benzenesulfonyl hydrazones can be applied as potential ligands for the synthesis of bioactive metal complexes.

Recent advances for the synthesis of chiral sulfones with the sulfone moiety directly connected to the chiral center

The recent development of strategies for the asymmetric synthesis of chiral sulfones with sulfone moieties directly connected to the stereocenters.

Nitriles as radical acceptors in radical cascade reactions

The application of the cyano group as a radical acceptor in the cascade reactions for the construction of various important heterocycles and carbocycles was summarized.

Transition-metal-free sulfonylations of methylthiolated alkynones to synthesize 3-sulfonylated thioflavones

A set of transition-metal-free NaI/TBHP-mediated sulfonylation cyclization reactions of methylthiolated alkynones with sulfonyl hydrazides was developed, by which various 3-sulfonylated thioflavones were prepared under mild reaction conditions.

Iodine-mediated aminosulfonylation of alkenyl sulfonamides with sulfonyl hydrazides: synthesis of sulfonylmethyl piperidines, pyrrolidines and pyrazolines

An aminosulfonylation of alkenyl sulfonamides was reported. Using iodine as the catalyst, TBHP as the oxidant, and sulfonyl hydrazides as the sulfonyl radical sources, a variety of sulfonylmethyl piperidines, pyrrolidines and pyrazolines were obtained in moderate to excellent yields.

Electrochemical Alkoxysulfonylation Difunctionalization of Styrene Derivatives Using Sodium Sulfinates as Sulfonyl Sources

An eco-friendly method for the synthesis of β-alkoxy sulfones via electrochemical alkoxysulfonylation reaction of styrenes with sodium sulfinates as sulfonyl sources has been established. The reaction is conducted in an undivided cell at room temperature and tolerates a wide scope of styrenes, sodium sulfinates, and alcohols. The reaction does not need any chemical oxidants and transition-metal catalysts, which provides a new and green access to β-alkoxy sulfones.