Autocatalytic Synthesis of Thioesters via Thiocarbonylation of gem-Difluoroalkenes

S-Arylation of Thioic S-Acid Using Thianthrenium Salts via Photoactivation of Electron Donor-Acceptor Complex

Thioesters make up an important class of bioactive compounds. Due to their chemoselectivity, they have been widely used in the synthesis of a wide range of complex bioactive molecules and natural products. At present, chemists have developed a variety of methods for the preparation of thioester compounds. However, these methods usually require the use of transition metal catalysis or harsh reaction conditions. The strategy of synthesizing thioester compounds via visible light-induced electron donor-acceptor (EDA) complex reactions avoids the problems associated with conventional methods through the development of photocatalysis. Here we report a sustainable method for thiocarbonylating aryl sulfonium salts via a visible light-induced EDA complex process without transition metals.

Visible Light-Accelerated Palladium-Catalyzed Thiocarbonylation Using Oxalic Acid Monothioester with Aryl/Alkenyl Sulfonium Salts

Herein, we present a decarboxylative thiocarbonylation of aryl and alkenyl sulfonium salts with oxalic acid monothioethers (OAMs), which can be achieved by visible light-accelerated palladium catalysis. Sulfonium salts are widely available, and OAM is an easily accessible and stored reagent; this mild reaction method can also be used for the synthesis of different types of thioester compounds. The reaction represents a new application of visible light-accelerated palladium catalysis in catalytic decarboxylative cross-couplings.

Amine-Induced Selective C-C Bond Cleavage of 2,2,2-Trifluoroethyl Carbonyls for the Synthesis of Ureas and Amides

An efficient and selective transformation of 2,2,2-trifluoroethyl carbonyls into ureas/amides with amines is reported. This protocol allows the selective cleavage of the C-C bond of 2,2,2-trifluoroethyl carbonyls under transition metal-free and oxidant-free conditions, which is in contrast to the analogous C-F or C-CF₃ bond functionalization. This reaction reveals the unexplored reactivity of 2,2,2-trifluoroethyl carbonyls and exhibits a broad substrate range and good functional group tolerance.

Na2S·9H2O Enabled Defluorodisulfuration and Hydrodefluorination of Perfluorobutyl Tetralones: Synthesis of Trifluoromethyl 1,2-Dithioles

An unprecedented defluorocyclization of perfluorobutyl tetralones with Na₂S·9H₂O was developed for the synthesis of trifluoromethyl 1,2-dithioles, which provided chemists novel access to biologically and pharmaceutically relevant organofluorides. Successive C(sp³)-F bond functionalization at the perfluoroalkyl chain is vital for the formation of four C-H/C-S/S-S bonds and a five-membered S-heterocycle assembly. Cheap, weakly toxic, and odorless inorganic sulfide Na₂S·9H₂O acts as both a disulfurating precursor and a hydrodefluorinating reagent in this tandem multi-bond-interconverting reaction.

Synthesis of C3-halo substituted bicyclo[1.1.1]pentylamines via halosulfoamidation of [1.1.1]propellane with sodium hypohalites and sulfonamides

Herein, we report a catalyst-free synthesis of C3-halo substituted bicyclo[1.1.1]pentylamines under mild conditions. The reaction involves the use of sodium hypohalites and sulfonamides to generate N-halosulfonamides in situ, which subsequently undergo radical addition with [1.1.1]propellane to yield the desired products with suitable functional group tolerance.

Synthesis of Imidized Cyclobutene Derivatives by Strain Release of [1.1.1]Propellane

Herein, we report the metal-free synthesis of imidized methylene cyclobutane derivatives via a strain-release driven addition reaction of [1.1.1]propellane. Using this strategy, the methylene cyclobutyl cation intermediate generated by protonation of [1.1.1]propellane was found to be trapped by nitriles to form a nitrilium ion intermediate, which subsequently reacted with carboxylic acids to produce imidized methylene cyclobutene derivatives via a Mumm-type rearrangement.

Synthesis of aryldifluoromethyl aryl ethers via nickel-catalyzed suzuki cross-coupling between aryloxydifluoromethyl bromides and boronic acids

As a unique organofluorine fragment, gem-difluoromethylated motifs have received widespread attention. Here, a convenient and efficient synthesis of aryldifluoromethyl aryl ethers (ArCF₂OAr') was established via Nickel-catalyzed aryloxydifluoromethylation with arylboronic acids. This approach features easily accessible starting materials, good tolerance of functionalities, and mild reaction conditions. Diverse late-stage difluoromethylation of many pharmaceuticals and natural products were readily realized. Notably, a new difluoromethylated PD-1/PD-L1 immune checkpoint inhibitor was conveniently synthesized and showed both improved metabolic stability and enhanced antitumor efficacy. Preliminary mechanistic studies suggested the involvement of a Ni(I/III) catalytic cycle.

Photoinduced Cascade C-N/C═O Bond Formation from Bromodifluoroalkyl Reagents, Amines, and H2O via a Triple-Cleavage Process

A green, sustainable, and straightforward method for the synthesis of unsymmetrical oxalamides via photoinduced C-N/C═O bond formation of bromodifluoroacetamide, amine, and H₂O through a triple-cleavage process has been developed. In addition, this approach also provides access to the known bioactive compounds, and a feasible reaction mechanism is proposed. Moreover, the advantages of this transformation, including mild reaction conditions, a broad substrate scope, and operational simplicity, make this protocol attractive for further applications.

Visible-Light-Mediated α-Ketoacylations of NH-Sulfoximines with gem-Difluoroalkenes

A photochemical approach for the preparation of α-keto-N-acyl sulfoximines from NH sulfoximines and gem-difluoroalkenes has been developed. In the presence of NBS, the reactions proceed in air without the need of a photocatalyst or additional oxidant. Results of mechanistic studies suggest that the two oxygens in the products stem from water and dioxygen.

Synthesis of Tetrasubstituted Alkenyl Nitriles via Cyanocarbene Addition of [1.1.1]Propellane

Herein, we report the metal-free synthesis of methylenecyclobutane containing tetrasubstituted alkenyl nitriles via a strain-release driven addition reaction of [1.1.1]propellane under mild conditions. Using this strategy, TMSN3 was shown to...

Access to α,α-difluoro(arylthio)methyl oxetanes from α,α-difluoro(arylthio)methyl ketones and trimethylsulfoxonium halides: scope, mechanism and applications

A general and practical method for the synthesis of α,α-difluoro(arylthio)methyl oxetanes is reported that occurs by the reaction of α,α-difluoro(arylthio)methyl ketones with trimethylsulfoxonium halides. This reaction undergoes the sequential Corey-Chaykovsky...

Photocatalytic Activation of Elemental Sulfur Enables a Chemoselective Three-Component Thioesterification

A mild and chemoselective three-component thioesterification using olefins, α-ketoacids, and elemental sulfur has been developed. The photocatalytic activation of elemental sulfur, a cheap and abundant sulfur source, enables the rapid installation of a sulfur atom into molecules, reactions that ordinarily would require the use of reactive and malodorous sulfur-containing compounds such as thiols and thioacids. This novel reaction is characterized by high yields and a broad substrate scope, which enables the introduction of thioester moieties into complex molecules including a steroid, a peptide, and a nonprotected glycoside. Mechanistic studies indicated that the success of this transformation depends on the multiple roles played by the elemental sulfur, including those of a sulfurizing agent, a terminal oxidant, and a HAT mediator.

Sc(OTf)3-Catalyzed C2-Selective Cyanation/Defluorination Cascade of Perfluoroalkylated 3-Indolylmethanols and Application to the Synthesis of 3-Fluoro(perfluoroalkyl)-β-carbolines

An unprecedented Sc(OTf)₃-catalyzed C2-selective cyanation/defluorination cascade of perfluoroalkylated 3-indolylmethanols with TMSCN is described, which provides a novel and practical strategy for the synthesis of structurally diverse 3-(2-cyano)-indolyl substituted gem-difluoroalkenes and β-fluoro-β-perfluoroalkylalkenes. The reaction features excellent regio- and stereoselectivity and broad substrate scope. Notably, the obtained gem-difluoroalkenes and β-fluoro-β-perfluoroalkylalkenes could be easily transformed into 3-fluoro(perfluoroalkyl)-β-carbolines with excellent efficiency simply by treating them with Grignard reagents or DIBAL-H under mild reaction conditions.

Highly Stereoselective Intramolecular Carbofluorination of Internal α,β-Ynones Promoted by Selectfluor

Herein, we report a metal-free intramolecular carbofluorination protocol for the synthesis of tetrasubstituted monofluoroalkenes from internal α,β-ynones and Selectfluor with both high stereoselectivity and broad functional group tolerance. The chelation between tetrafluoroborate anion and the oxygen present in the aldehyde group rendered the reaction highly stereoselective, with the tetrafluoroborate serving as the direct fluorine source. Therefore, with addition of sodium tetrafluoroborate, Selectfluor could be reused several times without sacrificing reactivity.