Electrochemical Radical Retro-Allylation of Homoallylic Alcohols with Sulfonyl Hydrazides

We report herein the first examples of electrochemical radical retro-allylation of homoallylic alcohols via the cleavage of the C(sp3)-C(sp3) bond. In this reaction, a variety of sulfonyl hydrazides were employed as the environmentally friendly radical sources via an electrochemical dehydrazination with the release of N2 and H2 as the byproducts, leading to sulfonyl allylic compounds in moderate to good yields. The reaction features metal- and base-free reaction conditions, broad functional group tolerance, and a broad substrate scope.

Glyoxylic Acid Monohydrate-Promoted Formation of the C-SO2 Bond Starting from Maleimides/Quinones and Sodium Sulfinates

By using glyoxylic acid monohydrate as a promoter, a wide range of substances containing a C-SO2 bond could be obtained from N-substituted maleimides or quinones and sodium sulfinates. The protocol features mild reaction conditions, short reaction time, and good atomic economics, which provides an alternative protocol for the α-sulfonylation of α,β-unsaturated ketones.

Ni-Catalyzed Hydrosulfonylation of Alkenes with Aromatic Iodides and K2S2O5

Hydrosulfonylation of alkenes with readily available aromatic iodides via a SO2-insetion strategy is presented. The combination of non-noble Ni catalysis with (iPr)3SiH as the final reductant enables the efficient formation of aryl and heteroaryl sulfinate intermediates, which undergo Michael-type additions to electron-deficient alkenes for initiating the hydrosulfonylation process. Moreover, the superiority of this protocol is demonstrated by broad substrate scope and good functional group compatibility.

Photoredox catalysis in alkene and alkyne alkylsulfonylations: the construction of Markovnikov selective α-sulfones

Photoredox alkene or alkyne alkylsulfonylation has been achieved with phthalimide esters and sulfinates providing unexpected α-sulfones. Mechanistic studies disclose that the preferential alkyl radical addition to the alkene or the Markovnikov hydrosulfonation of the alkyne should contribute to the formation of the β-alkylated α-sulfones. Moreover, the reaction is easy to operate covering quite large substrate scales including primary, secondary and tertiary alkyl groups and all sorts of terminal aryl alkenes or alkynes. Besides, the reaction was also suitable for the sulfonylation of several drug molecules.

Visible-Light Photoredox-Catalyzed Divergent 1,2-Diacylation and Hydroacylation of Alkenes with Carboxylic Acid Anhydride

A photoredox-catalyzed divergent 1,2-dicarbonylation and hydroacylation of alkenes with acid anhydride is presented. This approach offers a mild and efficient entry to 1,4-dicarbonyl compounds bearing all-carbon quaternary centers, exhibiting a broad substrate scope and high functional group compatibility. Hydrocarbonylaltion of alkenes can also be realized by simply introducing a proton source to the reaction system. Mechanism investigations support a radical addition/radical-polar crossover cascade.

Cu(ii)-mediated direct intramolecular cyclopropanation of distal olefinic acetate: access to cyclopropane-fused γ-lactones

Cyclopropane-fused ring scaffolds represent one of the most appealing structural motifs in organic chemistry due to their wide presence in bioactive molecules and versatility in organic synthesis. These skeletons are typically prepared from olefinic diazo compounds via transition-metal catalysed intramolecular carbenoid insertion, which suffers from prefunctionalization of starting materials and limited substrate scope. Herein, we disclose a practical copper-mediated direct intramolecular cyclopropanation of distal olefinic acetate to synthesize cyclopropane-fused γ-lactones and lactams. This cascade reaction is postulated to proceed through a hydrogen atom transfer event induced radical cyclization and copper-mediated cyclopropanation sequence. The protocol features high atom- and step-economy, excellent diastereoselectivity, broad tolerance of functional groups, and operational simplicity.

Rapid Synthesis of β-Chiral Sulfones by Ni-Organophotocatalyzed Enantioselective Sulfonylalkenylation of Alkenes

β-Chiral sulfones are substructures widespread in drug molecules and bioactive targets and serve as important chiral synthons in organic synthesis yet are challenging to access. Herein, a three-component strategy enabled by visible-light- and Ni-catalyzed sulfonylalkenylation of styrenes for the synthesis of enantioenriched β-chiral sulfones has been developed. This dual-catalysis strategy allows for one-step skeletal assembly along with the control of enantioselectivity in the presence of a chiral ligand, providing an efficient and straightforward access to enantioenriched β-alkenyl sulfones from easily available and simple starting materials. Mechanistic investigations reveal that the reaction undergoes a chemoselective radical addition over two alkenes followed by a Ni-intercepted asymmetric C_sp³-C_sp² coupling with alkenyl halides.

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.

Inexpensive and bench stable diarylmethylium tetrafluoroborates as organocatalysts in the light mediated hydrosulfonylation of unactivated alkenes

In this paper, we present the synthetic potential of diarylmethylium tetrafluoroborates as catalysts for the visible light promoted hydrosulfonylation of unactivated alkenes. For the first time, these salts, which are bench stable and easily preparable on a multi-gram scale, were employed as organocatalysts. Interestingly, a catalyst loading of only 1 mol% allowed sulfone products to be efficiently obtained from good-to-excellent yields with high functional-group tolerance and scalability up to 15 mmol of alkene. The mechanistic study, both experimental and computational, presented here, revealed an alternative mechanism for the formation of the key sulfonyl radical. Indeed, the photoactive species was proved not to be the diarylcarbenium salt itself, but two intermediates, a stable S-C adduct and an ion couple, that were formed after its interaction with sodium benzenesulfinate. Upon absorbing light, the ion couple could reach an excited state with a charge-transfer character which gave the fundamental sulfonyl radical. A PCET (proton-coupled electron transfer) closes the catalytic cycle reforming the diarylcarbenium salt.

Lighting Up the Organochalcogen Synthesis: A Concise Update of Recent Photocatalyzed Approaches

This review describes the recent advances in photocatalyzed reactions to form new carbon–sulfur and carbon–selenium bonds. With a total of 136 references, of which 81 articles are presented, the authors introduce in five sections an updated picture of the state of the art in the light-promoted synthesis of organochalcogen compounds (from 2019 to present). The light-promoted synthesis of sulfides by direct sulfenylation of C–C π-bonds; synthesis of sulfones; the activation of Csp2–N bond in the formation of Csp2–S bonds; synthesis of thiol ester, thioether and thioacetal; and the synthesis of organoselenium compounds are discussed, with detailed reaction conditions and selected examples for each protocol.

Switchable In Situ SO2 Capture and CF3 Migration of Enol Triflates with Peroxyl Compounds under Iron Catalysis

Switchable in situ SO₂ capture and CF₃ migration of enol triflates with peroxyl compounds under iron catalysis are presented. By regulating the structure of peroxides, a variety of keto-functionalized dialkyl sulfones and α-trifluoromethyl ketones were selectively synthesized in good yields under mild conditions.

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.

Hydrosulfonylation of Alkenes with Sulfonyl Imines via Ir/Cu Dual Photoredox Catalysis

Sulfonamides exhibit the advantages of wide prevalence, excellent prefunctionalization capability, and broad functional group compatibility. We report here utilizing sulfonyl imines as sulfonyl radical precursors for hydrosulfonylation of activated alkenes via visible-light irradiation. By preinstallation of functional groups into the sulfonamides and subsequent hydrosulfonylation, a variety of complex sulfones were synthesized with good efficiency under Ir/Cu dual photoredox catalysis. Additionally, this protocol expands the research in late-stage N-S bond modification in sulfonamides.

Photocatalytic Late-Stage Functionalization of Sulfonamides via Sulfonyl Radical Intermediates

A plethora of drug molecules and agrochemicals contain the sulfonamide functional group. However, sulfonamides are seldom viewed as synthetically useful functional groups. To confront this limitation, a late-stage functionalization strategy is described, which allows sulfonamides to be converted to pivotal sulfonyl radical intermediates. This methodology exploits a metal-free photocatalytic approach to access radical chemistry, which is harnessed by combining pharmaceutically relevant sulfonamides with an assortment of alkene fragments. Additionally, the sulfinate anion can be readily obtained, further broadening the options for sulfonamide functionalization. Mechanistic studies suggest that energy-transfer catalysis (EnT) is in operation.

Transition-Metal-Free Radical-Triggered Hydrosulfonylation and Disulfonylation Reaction of Substituted Maleimides with Sulfonyl Hydrazides

A convenient and practical hydrosulfonylation and disulfonylation of substituted maleimides was realized using sulfonyl hydrazides as the sulfur reagent and tert-butyl hydroperoxide as the oxidant. The advantages of the reactions include mild and transition-metal-free reaction conditions, good functional group tolerance, and readily available starting materials. The radical species-induced pathway is also demonstrated by mechanistic studies.

Solvent-mediated switching between oxidative addition and addition–oxidation: access to β-hydroxysulfides and β-arylsulfones by the addition of thiols to olefins in the presence of Oxone

Solvent-switching allows formation of either β-hydroxy-2-arylethyl aryl sulfides or 2-arylethyl aryl sulfones exclusively in thiol–ene ‘click’ reactions conducted with Oxone.

Atom-Economical, Catalyst-Free Hydrosulfonation of Densely Functionalized Alkenes: Access to Oxindole Containing Sulfones

An atom-economical hydrosulfonation of densely functionalized alkenes under catalyst-free conditions is described. Alkenes possessing hydroxy-oxindole moiety underwent hydrosulfonation on treatment with arylsulfinic acids in green media to afford the resulting...

Oxidative thiocyanation of allylic alcohols: an easy access to allylic thiocyanates with K2S2O8 and NH4SCN

A practical method for the synthesis of allylic thioacyanates from allylic alcohols was disclosed employing K2S2O8 as the oxidant and NH4SCN as the thiocyanate source.

Recent Progress and Emerging Technologies towards a Sustainable Synthesis of Sulfones

Sulfones play a pivotal role in modern organic chemistry. They are highly versatile building blocks and find various applications as drugs, agrochemicals, or functional materials. Therefore, sustainable access to this class of molecules is of great interest. Herein, the goal was to provide a summary on recent developments in the field of sustainable sulfone synthesis. Advances and existing limitations in traditional approaches towards sulfones were reviewed on selected examples. Furthermore, novel emerging technologies for a more sustainable sulfone synthesis and future directions were discussed.

Radical 1,5-Chloropentafluorosulfanylation of Unactivated Vinylcyclopropanes and Transformation into α-SF5 Ketones

The radical 1,5-chloropentafluorosulfanylation of vinyl cyclopropanes (VCPs) initiated by Et₃B/O₂ affords allylic pentafluorosulfanyl/homoallylic chloride products through the ring-strain release of the cyclopropane. The VCP substitution pattern was investigated. The utility of this reaction was illustrated in post-transformation of the C═C bond by ozonolysis, giving access to valuable α-SF₅ carbonyl compounds.

Recent progress in the radical α-C(sp3)-H functionalization of ketones

The direct use structurally simple ketones as α-ketone radical sources for α-C(sp³)-H functionalization is a sustainable and powerful approach for constructing complex and multifunctional chemical scaffolds with diverse applications. The reactions of α-ketone radicals with alkenes, alkynes, enynes, imides, and imidazo[1,2-a]pyridines have broadened the structural diversity and complexity of ketones. Through chosen illustrative examples, we outline the recent progress in the development of methods that enable the radical α-C(sp³)-H functionalization of ketones, with an emphasis on radical initiation systems and possible mechanisms of the transformations. The application of these strategies is illustrated by the synthesis of several biologically active molecules and drug molecules. Further subdivision is based on substrate type and reaction type.

Visible Light as the Key for the Formation of Carbon–Sulfur Bonds in Sulfones, Thioethers, and Sulfonamides: An Update

This review summarizes the most relevant advancements made in the photocatalyzed synthesis of sulfones, thioethers, and sulfonamides from 2017 to the beginning of 2021. Synthetic strategies towards the construction of sulfur–carbon bonds are discussed together with the proposed reaction mechanisms. Interestingly, sulfur-based functional groups, which are of fundamental importance for the pharmaceutical field, can be assembled by photocatalysis in an easy and straightforward way under milder reaction conditions employing less toxic and expensive sulfur sources in comparison with common strategies.

1 Introduction

2 Sulfones

2.1 Sodium Sulfinates and Sulfinic Acids

2.2 Sulfonyl Halides

2.3 Sulfonyl Hydrazones

2.4 Sulfur Dioxide Surrogates

2.5 Miscellaneous

3 Thioethers

4 Sulfonamides

5 Conclusions

Self-Sufficient Class VII Cytochromes P450: From Full-Length Structure to Synthetic Biology Applications

Members of class VII cytochromes P450 are catalytically self-sufficient enzymes containing a phthalate dioxygenase reductase-like domain fused to the P450 catalytic domain. Among these, CYP116B46 is the first enzyme for which the 3D structure of the whole polypeptide chain has been solved, shedding light on the interaction between its domains, which is crucial for catalysis. Most of these enzymes have been isolated from extremophiles or detoxifying bacteria that can carry out regio- and enantioselective oxidation of compounds of biotechnological interest. Protein engineering has generated mutants that can perform challenging organic reactions such as the anti-Markovnikov alkene oxidation. This potential, combined with the detailed 3D structure, forms the basis for further directed evolution studies aimed at widening their biotechnological exploitation.