Radical Hydro-Fluorosulfonylation of Unactivated Alkenes and Alkynes.

Recently, radical fluorosulfonylation is emerging as an appealing approach for the synthesis of sulfonyl fluorides, which are highly in demand in various disciplines, particularly in chemical biology and drug discovery. Here, we report the first establishment of radical hydro-fluorosulfonylation of alkenes, which is enabled by using 1-fluorosulfonyl 2-aryl benzoimidazolium (FABI) as an effective redox-active radical precursor. This method provides a new and facile approach for the synthesis of aliphatic sulfonyl fluorides from unactivated alkenes, and can be further applied to the late-stage modifications of natural products and peptides, as well as ligation of drugs in combination with click chemistry. Remarkably, this system could enable the radical hydro-fluorosulfonylation of alkynes, affording valuable alkenylsulfonyl fluoride products with a rare, high Z-selectivity, which are normally less stable and more challenging to synthesize in comparison with the E-configured products.

Photoredox catalytic radical fluorosulfonylation of olefins enabled by a bench-stable redox-active fluorosulfonyl radical precursor.

Sulfonyl fluorides have attracted considerable and growing research interests from various disciplines, which raises a high demand for novel and effective methods to access this class of compounds. Radical flurosulfonylation is recently emerging as a promising approach for the synthesis of sulfonyl fluorides. However, the scope of applicable substrate and reaction types are severely restricted by limited known radical reagents. Here, we introduce a solid state, redox-active type of fluorosulfonyl radical reagents, 1-fluorosulfonyl 2-aryl benzoimidazolium triflate (FABI) salts, which enable the radical fluorosulfonylation of olefins under photoredox conditions. In comparison with the known radical precursor, gaseous FSO2Cl, FABI salts are bench-stable, easy to handle, affording high yields in the radical fluorosulfonylation of olefins with before challenging substrates. The advantage of FABIs is further demonstrated in the development of an alkoxyl-fluorosulfonyl difunctionalization reaction of olefins, which forges a facile access to useful ß-alkoxyl sulfonyl fluorides and related compounds, and would thus benefit the related study in the context of chemical biology and drug discovery in the future.

Electrochemical Oxo-Fluorosulfonylation of Alkynes under Air: Facile Access to ß-Keto Sulfonyl Fluorides.

Radical fluorosulfonylation is emerging as an appealing approach for the synthesis of sulfonyl fluorides, which have widespread applications in many fields, in particular in the context of chemical biology and drug development. Here, we report the first investigation of FSO2 radical generation under electrochemical conditions, and the establishment of a new and facile approach for the synthesis of ß-keto sulfonyl fluorides via oxo-fluorosulfonylation of alkynes with sulfuryl chlorofluoride as the radical precursor and air as the oxidant. This electrochemical protocol is amenable to access two different products (ß-keto sulfonyl fluorides or α-chloro-ß-keto sulfonyl fluorides) with the same reactants. The ß-keto sulfonyl fluoride products can be utilized as useful building blocks in the synthesis of various derivatives and heterocycles, including the first synthesis of an oxathiazole dioxide compound. Furthermore, some ß-keto sulfonyl fluorides and derivatives exhibited notably potent activities against Bursaphelenchus xylophilus and Colletotrichum gloeosporioides.

Introducing A New Class of Sulfonyl Fluoride Hubs via Radical Chloro-Fluorosulfonylation of Alkynes.

Sulfonyl fluorides have widespread applications in many important fields, including ligation chemistry, chemical biology, and drug discovery. Therefore, new methods to increase the synthetic efficiency and expand the available structures of sulfonyl fluorides are highly in demand. Here, we introduce a new and powerful class of sulfonyl fluoride hubs, ß-chloro alkenylsulfonyl fluorides (BCASF), which can be constructed via radical chloro-fluorosulfonyl difunctionalization of alkynes under photoredox conditions. BCASF molecules exhibit versatile reactivities and well undergo a series of transformations at the chloride site while keeping the sulfonyl fluoride group intact, including reduction, Suzuki coupling, Sonogashira coupling, as well as nucleophilic substitution with various nitrogen, oxygen, and sulfur nucleophiles. By using BCASF as a synthetic hub, a wide range of sulfonyl fluorides becomes readily accessible, such as cis alkenylsulfonyl fluorides, dienylsulfonyl fluorides, and ynenylsulfonyl fluorides, which are challenging or even not possible to synthesize before with the known methods. Moreover, further application of BCASF to the late-stage modification of peptides and drugs is also demonstrated.

Radical Fluorosulfonylation: Accessing Alkenyl Sulfonyl Fluorides from Alkenes.

Sulfonyl fluorides have widespread applications in many fields. In particular, their unique biological activity has drawn considerable research interest in the context of chemical biology and drug discovery in the past years. Therefore, new and efficient methods for the synthesis of sulfonyl fluorides are highly in demand. In contrast to extensive studies on FSO2+ -type reagents, a radical fluorosulfonylation reaction with a fluorosulfonyl radical (FSO2. ) remains elusive so far, probably owing to its instability and difficulty in generation. Herein, the development of the first radical fluorosulfonylation of alkenes based on FSO2 radicals generated under photoredox conditions is reported. This radical approach provides a new and general access to alkenyl sulfonyl fluorides, including structures that would otherwise be challenging to synthesize with previously established cross-coupling methods. Moreover, extension to the late-stage fluorosulfonylation of natural products is also demonstrated.

Decarboxylative Thiolation of Redox-Active Esters to Thioesters by Merging Photoredox and Copper Catalysis.

Thioesters and related thiols are critically important to biological systems and also widely employed in the synthesis of pharmaceutically important molecules and polymeric materials. However, known synthetic methods often suffer from the disadvantage of being specific only to certain substrates. Herein, we describe a facile decarboxylative thioesterification of alkyl acid derived redox-active esters by merging photoredox catalysis and copper catalysis. This reaction is applicable to a wide range of carboxylic acids, as well as natural products and drugs, allowing for the synthesis of various thioesters with diverse structures, including tertiary ones that are not accessible via traditional nucleophilic substitution from tertiary halides. Moreover, product utilization is demonstrated with a direct transformation of thioesters to sulfonyl fluorides.

Palladium(II)-Catalyzed Enantioselective Arylation of Unbiased Methylene C(sp3 )-H Bonds Enabled by a 2-Pyridinylisopropyl Auxiliary and Chiral Phosphoric Acids.

Enantioselective functionalizations of unbiased methylene C(sp3 )-H bonds of linear systems by metal insertion are intrinsically challenging and remain a largely unsolved problem. Herein, we report a palladium(II)-catalyzed enantioselective arylation of unbiased methylene ß-C(sp3 )-H bonds enabled by the combination of a strongly coordinating bidentate PIP auxiliary with a monodentate chiral phosphoric acid (CPA). The synergistic effect between the PIP auxiliary and the non-C2 -symmetric CPA is crucial for effective stereocontrol. A broad range of aliphatic carboxylic acids and aryl bromides can be used, providing ß-arylated aliphatic carboxylic acid derivatives in high yields (up to 96 %) with good enantioselectivities (up to 95:5 e.r.). Notably, this reaction also represents the first palladium(II)-catalyzed enantioselective C-H activation with less reactive and cost-effective aryl bromides as the arylating reagents. Mechanistic studies suggest that a single CPA is involved in the stereodetermining C-H palladation step.

Site-Selective δ-C(sp3 )-H Alkylation of Amino Acids and Peptides with Maleimides via a Six-Membered Palladacycle.

The site-selective functionalization of unactivated C(sp3 )-H bonds remains one of the greatest challenges in organic synthesis. Herein, we report on the site-selective δ-C(sp3 )-H alkylation of amino acids and peptides with maleimides via a kinetically less favored six-membered palladacycle in the presence of more accessible γ-C(sp3 )-H bonds. Experimental studies revealed that C-H bond cleavage occurs reversibly and preferentially at γ-methyl over δ-methyl C-H bonds while the subsequent alkylation proceeds exclusively at the six-membered palladacycle that is generated by δ-C-H activation. The selectivity can be explained by the Curtin-Hammett principle. The exceptional compatibility of this alkylation with various oligopeptides renders this procedure valuable for late-stage peptide modifications. Notably, this process is also the first palladium(II)-catalyzed Michael-type alkylation reaction that proceeds through C(sp3 )-H activation.

Palladium-Catalyzed Remote Aryldifluoroalkylation of Alkenyl Aldehydes.

A palladium-catalyzed three-component reaction between fluoroalkyl bromides, arylboronic acids, and alkenyl aldehydes has been developed and provides facile access to 5-, 6-, or 7-difluoroalkylated ketones under very mild reaction conditions. The resultant products can be smoothly converted into CF2 -containing tetrahydronaphthalenes by a novel silver-catalyzed intramolecular decarboxylative cyclization of 5-aryl-2,2-difluoropentanoic acids.