Photosensitized Vicinal Sulfonylamination of Alkenes with Oxime Ester and DABCO·(SO2)2

A metal-free photosensitized three-component reaction of oxime esters, alkenes, and DABCO·(SO₂)₂ was developed. This protocol could accommodate a wide substrate scope, including activated and unactivated alkenes and aryl and aliphatic carboxylic acid oxime esters, delivering a broad range of β-amino sulfones in moderate to high yields. The insertion of SO₂ as a linker moiety allows the manipulation of the functionality in the reaction process, expanding the utility of oxime esters as bifunctional reagents.

Rh(III)-catalyzed [4 + 1] cyclization of aryl substituted pyrazoles with cyclopropanols via C-H activation

A rhodium-catalyzed formal [4 + 1]-cyclization reaction of aryl substituted pyrazoles with cyclopropanols via C-H bond activation/cyclization processes to selectively construct a series of carbonyl functionalized pyrazolo[5,1-a]isoindoles is described. The reaction features good functional group compatibility and a broad substrate scope with respect to both cyclization components with up to 84% yields. Mechanistic studies indicated that the C-H cleavage might be the rate-determining step in this transformation.

Mechanochemical synthesis of aromatic sulfonamides

A three-component Pd-catalysed aminosulfonylation reaction of K₂S₂O₅ and amine with aryl bromides or aromatic carboxylic acids was developed. This strategy was developed to utilise mechanical energy and accommodate primary as well as secondary aliphatic and aromatic amines to provide a new shortcut to a wide range of sulfonamides. Studies on the scope and limitations of the reaction indicated its tolerance of a vast range of functional groups and many structural patterns. The reactions were scaled up to gram quantities.

Switchable Divergent Synthesis in Gold-Catalyzed Difunctionalizations of o-Alkynylbenzenesulfonamides with Aryldiazonium Salts

Gold-catalyzed difunctionalizations of o-alkynylbenzenesulfonamides with aryldiazonium salts are reported herein. Upon irradiation with the blue LEDs, benzosultam products were formed via aminoarylation accompanied by the release of N₂. Without irradiation, aryldiazonium salts were engaged as efficient electrophiles, facilitating electrophilic deaurations of the vinyl-Au(I) intermediates, followed by tautomerization to give the N-aryl-substituted α-imino (E)-hydrazones. The regioselectivities of 6-endo-dig and 5-exo-dig cyclizations were excellent.

Deaminative metal-free reaction of alkenylboronic acids, sodium metabisulfite and Katritzky salts

A convenient and efficient approach to (E)-alkylsulfonyl olefins via a metal/light-free three-component reaction of alkenylboronic acids, sodium metabisulfite and Katritzky salts is described. This alkylsulfonylation proceeds smoothly with a broad substrate scope, leading to diverse (E)-alkylsulfonyl olefins in moderate to good yields. During the process, excellent functional group tolerance is observed and sodium metabisulfite is used as the source of sulfur dioxide. Mechanistic studies show that the alkyl radical generated in situ from Katritzky salt via a single electron transfer with alkenylboronic acid or DIPEA is the key step for providing an alkyl radical intermediate, which undergoes further alkylsulfonylation with sulfur dioxide.

A sequential Ugi–Smiles/transition-metal-free endo-dig Conia–ene cyclization: the selective synthesis of saccharin substituted 2,5-dihydropyrroles

A convenient, transition-metal-free access to a series of unprecedented saccharin substituted 2,5-dihydropyrroles is reported.

A Direct and an Efficient Regioselective Synthesis of 1,2-Benzothiazine 1,1-dioxides, β-Carbolinones, Indolo[2,3-c]pyran-1-ones, Indolo[3,2-c]pyran-1-ones, Thieno[2,3-c]pyran-7-ones and Pyrano[3',4':4,5]imidazo[1,2-a]pyridin-1-ones via Tandem Stille/Heterocyclization Reaction

A general regioselective one-pot synthesis of 1,2-benzothiazine 1,1-dioxides from 2-iodo benzenesulfonamide moieties and allenylstannanes is described using a domino Stille-like/Azacyclization reaction. The conditions developed also opened a novel access to β-carbolinones, indolopyranones, thienopyranones and pyrano-imidazopyridines.

Regiospecific Cleavage of S-N Bonds in Sulfonyl Azides: Sulfonyl Donors

Sulfonyl azides have been widely used as sulfonamido, diazo, and azido donors, as well as all-nitrogen 1,3-dipoles donors in synthetic chemistry. Here, the sulfonyl azides were used as efficient sulfonyl donors, which is very unusual. Trifluoromethanesulfonic acid-induced formation of the sulfonyl cation reactive species from sulfonyl azides was developed and used for the first time to couple various inactivated arenes to prepare sulfones at ambient temperature.

Synthesis of β-Sulfonyl Amides through a Multicomponent Reaction with the Insertion of Sulfur Dioxide under Visible Light Irradiation

A multicomponent reaction of styrenes, aryldiazonium tetrafluoroborates, sulfur dioxide, nitriles, and water in the presence of a photocatalyst at room temperature is performed. This vicinal aminosulfonylation of styrenes with the insertion of sulfur dioxide under visible light irradiation proceeds efficiently with excellent chemoselectivity, giving rise to the corresponding β-sulfonyl amides in moderate to good yields.

Synthesis of 3-(Methylsulfonyl)benzo[ b]thiophenes from Methyl(2-alkynylphenyl)sulfanes and Sodium Metabisulfite via a Radical Relay Strategy

A radical relay strategy for the generation of 3-(methylsulfonyl)benzo[ b]thiophenes through a reaction of methyl(2-alkynylphenyl)sulfanes with sodium metabisulfite in the presence of a photocatalyst under visible light irradiation is developed. This photoinduced sulfonylation proceeds efficiently under mild conditions by using a catalytic amount of sodium methylsulfinate as an initiator. During the reaction process, the methyl radical generated in situ is the key intermediate, which undergoes a radical relay with the combination of sulfur dioxide to afford methylsulfonyl-containing compounds.

Rhodium-catalyzed direct C–H bond alkynylation of aryl sulfonamides with bromoalkynes

This protocol selectively provides a straightforward route to prepare ortho-(1-alkynyl) benzenesulfonamides or six-membered benzosultams by using different silyl protected bromoalkynes.

Regioselective synthesis of polycyclic sulfones via radical-induced three-component bicyclization cascades

New radical-triggered three-component bicyclization cascades of 2-alkynylaryldiazonium tetrafluoroborates with a sulfur dioxide surrogate DABCO·(SO₂)₂ and internal alkynes have been reported for the first time, leading to 49 examples of polycyclic sulfones with moderate to good yields.

Visible-light promoted one-pot synthesis of sulfonated spiro[4,5]trienones from propiolamides, anilines and sulfur dioxide under transition metal-free conditions

A novel visible-light promoted sulfonylation/ipso-cyclization of N-arylpropiolamides with aromatic amines and DABCO·(SO₂)₂ to synthesize various sulfonated spiro[4,5]trienones is reported.

Substituted Hantzsch esters as radical reservoirs with the insertion of sulfur dioxide under photoredox catalysis

A three-component reaction between 4-substituted Hantzsch esters, DABCO·(SO₂)₂, and vinyl azides in the presence of photoredox catalysts under visible light irradiation is developed. A range of (Z)-2-(alkylsulfonyl)-1-arylethen-1-amines is obtained in moderate to good yields with good regioselectivity and stereoselectivity.

Double SO2 Insertion into 1,7-Diynes Leading to Functionalized Naphtho[1,2-c]thiophene 2,2-dioxides

A novel metal-free double SO₂ insertion/multicomponent bicyclization cascade of benzene-linked 1,7-diynes has been established by treatment with aryldiazonium tetrafluoroborates and DABCO-bis(sulfur dioxide) under redox-neutral conditions, providing a range of dual sulfone-containing naphtho[1,2-c]thiophene 2,2-dioxides with generally high stereoselectivity. The reaction pathway is proposed to proceed through the sequence of arylsulfonyl-radical-induced 6-exo-dig/5-endo-trig bicyclization, H-abstraction, and diazotization.

Transition-metal-free, visible-light-induced oxidative cross-coupling for constructing β-acetylamino acrylosulfones from sodium sulfinates and enamides

A visible-light-induced, Rose Bengal catalyzed photoredox process for synthesizing β-acetylamino acrylosulfones has been discovered.

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.

Thiosulfonylation of alkenes with the insertion of sulfur dioxide under non-metallic conditions

A three-component reaction of 1-(2-allylaryl)thioureas, sulfur dioxide, and aryldiazonium tetrafluoroborates under mild conditions is realized, leading to sulfonated [3,1]-benzothiazepines in good yields. High efficiency is observed for this non-metallic transformation.

Copper-catalyzed radical Heck type cyclization: a three-component reaction of DABCO·(SO2)2, aryldiazonium tetrafluoroborates and dienes toward sulfonated benzo- seven-membered nitrogen heterocycles

A three-component reaction of the sulfur dioxide surrogate of DABCO·(SO₂)₂, aryldiazonium tetrafluoroborates and dienes has been developed, affording a series of sulfonated nitrogen heterocycles.

The triple role of rongalite in aminosulfonylation of aryldiazonium tetrafluoroborates: synthesis of N-aminosulfonamides via a radical coupling reaction

A novel synthesis strategy of N-aminosulfonamides has been reported which uses rongalite as a radical initiator, a SO₂ surrogate and a reducing reagent simultaneously.

C–H bond sulfonylation of anilines with the insertion of sulfur dioxide under metal-free conditions

2-Sulfonylanilines are generated in moderate to good yields through a three-component reaction of anilines, DABCO·(SO₂)₂, and aryldiazonium tetrafluoroborates under mild conditions. No metal catalysts or additives are needed for this transformation.

Stereoselective synthesis of sulfonated 1-indenones via radical-triggered multi-component cyclization of β-alkynyl propenones

New radical-triggered multi-component cyclizations of β-alkynyl propenones have been developed, leading to 50 examples of sulfonated 1-indenones with generally good yields and high levels of stereoselectivity.

Synthesis of sulfonated naphthols via C–H bond functionalization with the insertion of sulfur dioxide

A three-component reaction of naphthols, sulfur dioxide, and aryldiazonium tetrafluoroborates catalyzed by iron(iii) chloride through a radical process via direct C–H functionalization is developed, leading to diverse sulfonated naphthols in good yields.

Generation of sulfonated isobenzofuran-1(3H)-ones under photocatalysis through the insertion of sulfur dioxide

Generation of sulfonated isobenzofuran-1(3H)-ones starting from 2-vinylbenzoic acids, aryldiazonium tetrafluoroborates, and DABCO˙(SO₂)₂ under photocatalysis in the presence of visible light is achieved. Additionally, the method can be extended to 4-phenylpent-4-enoic acid and 5-phenylhex-5-enoic acid.

Synthesis of 6-(sulfonylmethyl)phenanthridines through a reaction of aryldiazonium tetrafluoroborates, sulfur dioxide, and vinyl azides

Synthesis of 6-(sulfonylmethyl)phenanthridines through a three-component reaction of aryldiazonium tetrafluoroborates, a sulfur dioxide surrogate of DABCO·(SO₂)₂, and vinyl azides under metal- and additive-free conditions is achieved.

Intramolecular oxysulfonylation of alkenes with the insertion of sulfur dioxide under photocatalysis

Intramolecular oxysulfonylation of alkenes with the insertion of sulfur dioxide promoted by visible light is developed, leading to sulfonated tetrahydrofurans and related compounds in moderate to good yields.

A copper-catalyzed sulfonylative C–H bond functionalization from sulfur dioxide and aryldiazonium tetrafluoroborates

Sulfonylative C–H bond functionalization through a copper-catalyzed three-component reaction of 8-aminoquinoline amides, DABCO·(SO₂)₂ and aryldiazonium tetrafluoroborates is developed. Excellent selectivity in the para-position is observed.

Generation of sulfonated 1-isoindolinones through a multicomponent reaction with the insertion of sulfur dioxide

A four-component reaction of 2-vinylbenzoic acids, aryldiazonium tetrafluoroborates, sulfur dioxide, and nitriles under photocatalysis in the presence of visible light is developed, leading to sulfonated 1-isoindolinones in moderate to good yields.

Palladium-Catalyzed Direct C-H Functionalization of Indoles with the Insertion of Sulfur Dioxide: Synthesis of 2-Sulfonated Indoles

A palladium-catalyzed direct C-H bond sulfonylation of indoles with the insertion of sulfur dioxide is achieved through a three-component reaction of 1-(pyridin-2-yl)indoles, DABCO·(SO₂)₂, and aryldiazonium tetrafluoroborates under mild conditions. Diverse 2-sulfonated indoles are generated by using 10 mol % of palladium(II) bromide as the catalyst at room temperature. This synthetic approach is efficient by merging palladium catalysis and insertion of sulfur dioxide via a radical process. 2-Pyrimidinyl can be used as the directing group well as for the C-H bond sulfonylation. Additionally, the directing group can be easily removed.