Dithionite-Involved Multicomponent Coupling for Alkenyl and Alkyl Tertiary Sulfones

Unlock the C-N Bond Amidation of Enaminones: Metal-Free Synthesis of Enamides by Water-Assisted Transamidation

The C-N bond transamidation of primary amides with N,N-dimethyl enaminones has been efficiently realized by heating in the presence of trifluoromethanesulfonic acid (TfOH). The method enables the practical synthesis of valuable enamides without the use of any metal reagent. In addition, this transamidation protocol can also be expanded to the reactions of sulfonamides, and the late-stage functionalization on sulfonamide drugs such as Celecoxib and Valdecoxib has been verified. Moreover, the participation of water in assisting the transamidation process has been identified by the isotope labeling experiments using D2O, disclosing a new possibility in designing catalytic tactic to other transamidation reactions.

A Redox-neutral Nickel-catalysed Sulfonylation of (Hetero)aryl Boronic Acids with 2-Chlorothiazoles

A redox-neutral nickel-catalysed sulfonylation for arylsulfone synthesis was developed. (Hetero)aryl boronic acids reacted with potassium metabisulfite (K2 S2 O5 ) and readily available 2-chlorothiazoles in the presence of air-stable Ni(OTf)2 and 4,4-di-tert-butyl bipyridine (dtbpy) as a commercially available ligand to produce the corresponding 2-sulfonylthiazoles in moderate to excellent yields. This practical protocol tolerates a wide range of substrates including boronic acids and 2-chloro(benzo)thiazoles without additional bases, allowing the direct synthesis of functional arylsulfones.

Photoredox Catalysis-Enabled Sulfination of Alcohols and Bromides

Sulfinates are important lynchpin intermediates in pharmaceutical production; however, their synthesis via photoredox catalysis is challenging because of their facile oxidation. We herein disclose a photocatalytic strategy for the direct conversion of alcohols and alkyl bromides into alkyl sulfinates. These transformations are enabled by the utilization of easily oxidized radical precursors─namely, alcohol N-heterocyclic carbene adducts and N-adamantyl aminosupersilane─that facilitate efficient synthesis of the oxidatively labile sulfinate products. A broad range of functional groups are amenable to the reported transformations, providing rapid access to sulfonamides, sulfonyl halides, sulfones, and sulfonic acids. The utility of these methods is further demonstrated via the late-stage diversification of natural products and drugs into pharmaceutically relevant sulfonamides and "clickable" sulfonyl fluorides. In summary, this work illustrates the potential of novel radical precursors to expand the breadth of photoredox transformations.

Alkyltin fluorides as alkylating reagent in aminoalkylation of maleimides

Alkyltin fluoride is a frequently used electrophilic stannylation reagent via the cleavage of the Sn-F bond in traditional organic synthetic chemistry. Herein, we report the unprecedented copper-catalyzed aminoalkylation of maleimides using alkyltin fluoride as alkylating reagent through cleavage of the C-Sn bond via a radical pathway. Excellent functional group tolerance, use of O₂ as green oxidant and late-stage modification of some drug intermediates are the standout features of the current toolbox. Mechanistic studies reveal that alkyltin fluorides are capable of producing alkyl radicals in a Cu/O₂ catalytic system.

Photocatalytic synthesis of alkyl-alkyl sulfones via direct C(sp3)-H bond functionalization

We report a highly efficient one-pot, three-component strategy for the construction of alkyl-alkyl sulfones through a photoinduced TBADT-catalyzed C(sp³)-H sulfonylation of unactivated hydrocarbon compounds. A wide range of commercially available hydrocarbon compounds and bioactive molecules can be successfully applied to the catalytic system, affording the corresponding alkyl-alkyl sulfones in good to excellent yields (>50 examples, up to 87% yield).

Generation and Use of Glycosyl Radicals under Acidic Conditions: Glycosyl Sulfinates as Precursors

We herein report a method that enables the generation of glycosyl radicals under highly acidic conditions. Key to the success is the design and use of glycosyl sulfinates as radical precursors, which are bench-stable solids and can be readily prepared from commercial starting materials. This development allows the installation of glycosyl units onto pyridine rings directly by the Minisci reaction. We further demonstrate the utility of this method in the late-stage modification of complex drug molecules, including the anticancer agent camptothecin. Experimental studies provide insight into the reaction mechanism.

Photoredox-catalyzed intermolecular azidosulfonylation of alkenes with DABCO·(SO2)2, trimethylsilyl azide and thianthrenium salts

Synthesis of β-azido alkylsulfones through a photoredox-catalyzed azido sulfonylation of alkenes with DABCO·(SO2)2, trimethylsilyl azide and alkyl thianthrenium salts is developed.

Iron-Catalyzed Sulfonylthiocyanation of α,β-Unsaturated Amides/Esters via the Insertion of Sulfur Dioxide

An iron-catalyzed four-component sulfonylthiocyanation between α,β-unsaturated amides/esters, TMSNCS, aryldiazonium tetrafluoroborates, and sulfur dioxide (from SOgen) is demonstrated. This protocol is characterized by mild reaction conditions, good functional group compatibility, broad substrate scope, and good to excellent yields, providing a feasible method for the preparation of β-thiocyanated sulfone compounds. The preliminary mechanism investigation shows that a radical pathway may be involved in the process.

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.

CF3SO2Na-Mediated Five-Component Carbonylation of Triarylboroxines with TMSCF3 and THF/LiOH/NaI to Give Aroyloxyalkyl Iodides

Herein, we developed an efficient and transition-metal-free multicomponent coupling reaction for the synthesis of aroyloxyl alkyl iodides. In the reaction among 2,4,6-triarylboroxines, THF, TMSCF₃, LiOH, and NaI, five-component reactions could be precisely controlled by modulating CF₃SO₂Na, supplying one type of aroyloxyl alkyl iodides in moderate to high yields. The reaction exhibits good functional group tolerance and a wide substrate scope and can be easily transformed into other useful compounds. The mechanism is proposed on the basis of the control experiments.

Photocatalyzed Decarboxylative Thiolation of Carboxylic Acids Enabled by Fluorinated Disulfide

Thiolation of carboxylic acids using a disulfide reagent having tetrafluoropyridinyl groups is described. The light-mediated process is performed using an acridine-type photocatalyst. Primary, secondary, tertiary, and heteroatom-substituted carboxylic acids can be thiolated, and the method can be applied to the late-stage modification of a range of naturally occurring compounds and drugs. The fluorinated pyridine fragment is believed to enable the C-S bond formation. The resulting sulfides were used as redox-active radical precursors.

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.

Expeditious and Efficient ortho-Selective Trifluoromethane-sulfonylation of Arylhydroxylamines

A metal- and oxidant-free, practical and efficient method for the synthesis of highly versatile and synthetically useful ortho-trifluoromethanesulfonylated anilines from arylhydroxylamines and trifluoromethanesulfinic chloride was developed. This rapid transformation proceeded smoothly with good yields and excellent ortho-selectivity in the absence of any metals or ligands. Mechanistically, the reaction comprised a noncanonical O-trifluoromethanesulfinylation of the arylhydroxylamine, and the subsequent [2,3]-sigmatropic rearrangement to afford ortho-trifluoromethanesulfonylated aniline derivatives. The practical application of this reaction was demonstrated by further conversion into a series of functional molecules under different reaction conditions.

Sulfinates from Amines: A Radical Approach to Alkyl Sulfonyl Derivatives via Donor-Acceptor Activation of Pyridinium Salts

Synthetically versatile alkyl sulfinates can be prepared from readily available amines, using Katritzky pyridinium salt intermediates. In a catalyst-free procedure, primary, secondary, and benzylic alkyl radicals are generated by photoinduced or thermally induced single-electron transfer (SET) from an electron donor-acceptor (EDA) complex, and trapped by SO₂ to generate sulfonyl radicals. Hydrogen atom transfer (HAT) from Hantzsch ester gives alkyl sulfinate products, which are used to prepare a selection of medicinal chemistry relevant sulfonyl-containing motifs.