Directed Cp*RhIII-Catalyzed Fluorosulfonylvinylation of Arenes

Synthesis of 2-arylethenesulfonyl fluorides and isoindolinones: Ru-catalyzed C-H activation of nitrones with ethenesulfonyl fluoride

A novel strategy for the synthesis of 2-arylethenesulfonyl fluorides from nitrones and ethenesulfonyl fluoride (ESF) by the activation of the C-H bond using an inexpensive and readily available Ru-catalyst has been developed. In this process, the directing group can be concomitantly converted to an amide group. Interestingly, changing the substituent of the nitrogen of nitrones from a tert-butyl to a methyl group resulted in the formation of cyclic isoindolinones. Detailed mechanistic studies are also presented.

Synthesis and 18F Labeling of Alkenyl Sulfonyl Fluorides via an Unconventional Elimination Pathway

A successful Cu-catalyzed addition of both Cl and SO₂OCF₂H groups into alkenes allows us to discover the unusual reactivity of the SO₂OCF₂H group. As opposed to common sulfonic esters (RSO₂-O-R'), in which the R' group is highly electrophilic, the SO₂ moiety demonstrates higher electrophilicity in RSO₂-OCF₂H. The unexpected reactivity is further developed not only as a synthetic tool for well-functionalized alkenyl sulfonyl fluorides but also for the first ¹⁸F labeling of alkenyl sulfonyl fluorides.

Advances in the site-selective C-5, C-3 and C-2 functionalization of chromones via sp2 C-H activation

In this work, site-selective C-H activation at C-5, C-3 and C-2 positions of chromones for the introduction of structural diversity to the chromone scaffold was studied. The keto group of the chromone moiety acts as the directing group for the selective functionalization of chromones at the C-5 position. Furthermore, the C-H functionalization at the electron-rich C-3 position of the chromone can be achieved using electrophilic coupling partners. The C-H functionalization at the C-2 position can be possible using nucleophilic coupling partners. The direct functionalization methods provide a better pathway for the generation of C-5, C-3 and C-2-substituted chromones with good atom economy than that of classical pre-functionalized reaction protocols.

Sulfonyl fluorides as targets and substrates in the development of new synthetic methods

The advent of sulfur(VI)-fluoride exchange (SuFEx) processes as transformations with click-like reactivity has invigorated research into electrophilic species featuring a sulfur-fluorine bond. Among these, sulfonyl fluorides have emerged as the workhorse functional group, with diverse applications being reported. Sulfonyl fluorides are used as electrophilic warheads by both medicinal chemists and chemical biologists. The balance of reactivity and stability that is so attractive for these applications, particularly the resistance of sulfonyl fluorides to hydrolysis under physiological conditions, has provided opportunities for synthetic chemists. New synthetic approaches that start with sulfur-containing substrates include the activation of sulfonamides using pyrilium salts, the deoxygenation of sulfonic acids, and the electrochemical oxidation of thiols. Employing non-sulfur-containing substrates has led to the development of transition-metal-catalysed processes based on palladium, copper and nickel, as well as the use of SO₂F₂ gas as an electrophilic hub. Selectively manipulating molecules that already contain a sulfonyl fluoride group has also proved to be a popular tactic, with metal-catalysed processes again at the fore. Finally, coaxing sulfonyl fluorides to engage with nucleophiles, when required, and under suitable reaction conditions, has led to new activation methods. This Review provides an overview of the challenges in the efficient synthesis and manipulation of these intriguing functional groups.

Recent advances in rhodium-catalysed cross-dehydrogenative-coupling between two C(sp2)-H bonds

Rhodium-catalysed cross-dehydrogenative coupling (CDC) has received considerable attention in recent years. This modern technology has been considered as an attractive synthetic tool for selective C−C bond formation due to (1)...

Desulfonative Suzuki-Miyaura Coupling of Sulfonyl Fluorides

Sulfonyl fluorides have emerged as powerful "click" electrophiles to access sulfonylated derivatives. Yet, they are relatively inert towards C-C bond forming transformations, notably under transition-metal catalysis. Here, we describe conditions under which aryl sulfonyl fluorides act as electrophiles for the Pd-catalyzed Suzuki-Miyaura cross-coupling. This desulfonative cross-coupling occurs selectively in the absence of base and, unusually, even in the presence of strong acids. Divergent one-step syntheses of two analogues of bioactive compounds showcase the expanded reactivity of sulfonyl fluorides to encompass both S-Nu and C-C bond formation. Mechanistic experiments and DFT calculations suggest oxidative addition occurs at the C-S bond followed by desulfonation to form a Pd-F intermediate that facilitates transmetalation.

Radical-mediated vicinal addition of alkoxysulfonyl/fluorosulfonyl and trifluoromethyl groups to aryl alkyl alkynes

The addition of sulfonyl radicals to alkenes and alkynes is a valuable method for constructing useful highly functionalized sulfonyl compounds. The underexplored alkoxy- and fluorosulfonyl radicals are easily accessed by CF₃ radical addition to readily available allylsulfonic acid derivatives and then β-fragmentation. These substituted sulfonyl radicals add to aryl alkyl alkynes to give vinyl radicals that are trapped by trifluoromethyl transfer to provide tetra-substituted alkenes bearing the privileged alkoxy- or fluorosulfonyl group on one carbon and a trifluoromethyl group on the other. This process exhibits broad functional group compatibility and allows for the late-stage functionalization of drug molecules, demonstrating its potential in drug discovery and chemical biology.

An unprecedented method for vicinal addition of alkoxysulfonyl/fluorosulfonyl and trifluoromethyl groups to aryl alkyl alkynes has been developed to afford useful alkenylsulfonate esters and alkenylsulfonyl fluorides.

A general approach to nitrile- and sulfonyl fluoride-substituted cyclopropanes

Both cis and trans relative configurations of functionalized cyano cyclopropane bearing sulfonyl fluoride moiety were accessed by Corey-Chaykovsky cyclopropanation reactions. This protocol used mild conditions, and obtained good yields with excellent functional group compatibility. Further application of this class of compounds in SuFEx reactions and cyano reductions were also successfully achieved in good yields.

Rhodium-Catalyzed Redox-Neutral Olefination of Aryldiazenes with Acrylate Esters via C-H Activation and Transfer Hydrogenation

Rh(III)-catalyzed redox-neutral C-H olefination of aryldiazenecarboxylates has been realized using arylate esters as the olefinating reagents. This reaction proceeds under mild and redox-neutral conditions, resulting in integration of C-H activation and transfer hydrogenation. The chemoselectivity complements that of previously reported rhodium-catalyzed coupling of the same substrates.

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.

A Simple Protocol for the Stereoselective Construction of Enaminyl Sulfonyl Fluorides

A clickable connective hub 1-bromo-2-triazolethane-1-sulfonyl fluoride BTESF (1) was developed and successfully applied for the fluorosulfonylvinylation of a host of primary and secondary cyclic or acyclic amines including amino acids and pharmaceuticals. Further antimicrobial experiments revealed that vinyl sulfonyl fluoride functionalized norfloxacin (3ak), ciprofloxacin (3am), and lomefloxacin (3an) exhibited 4-fold improved antimicrobial activity against Gram-positive bacteria compared to their parent drugs.

Copper-catalyzed mild desulfonylation of vinyl sulfonyl molecules

The first Cu-catalyzed chemical selective desulfonylation of vinyl sulfonyl molecules to olefins was developed using B₂pin₂–water as the reductant.

Rh-Catalyzed Highly Enantioselective Synthesis of Aliphatic Sulfonyl Fluorides

Rh-catalyzed, highly enantioselective (up to 99.8% ee) synthesis of aliphatic sulfonyl fluorides was accomplished. This protocol provides a portal to a class of novel 2-aryl substituted chiral sulfonyl fluorides, which are otherwise extremely difficult to access. This asymmetric synthesis has the feature of mild conditions, excellent functional group compatibility, and wide substrate scope (51 examples) generating a wide array of structurally unique chiral β-arylated sulfonyl fluorides for sulfur(VI) fluoride exchange (SuFEx) click reaction and drug discovery.

Synthetic and Mechanistic Studies of a Versatile Heteroaryl Thioether Directing Group for Pd(II) Catalysis

A weakly coordinating monodentate heteroaryl thioether directing group has been developed for use in Pd(II) catalysis to orchestrate key elementary steps in the catalytic cycle that require conformational flexibility in a manner that is difficult to accomplish with traditional strongly coordinating directing groups. This benzothiazole thioether, (BT)S, directing group can be used to promote oxidative Heck reactivity of internal alkenes providing a wide range of products in moderate to high yields. To demonstrate the broad applicability of this directing group, an arene C-H olefination method was also successfully developed. Reaction progress kinetic analysis provides insights into the role of the directing group in each reaction, which is supplemented with computational data for the oxidative Heck reaction. Furthermore, this (BT)S directing group can be transformed into a number of synthetically useful functional groups, including a sulfone for Julia olefination, allowing it to serve as a "masked olefin" directing group in synthetic planning. In order to demonstrate this synthetic utility, natural products (+)-salvianolic acid A and salvianolic acid F are formally synthesized using the (BT)S directed C-H olefination as the key step.

Utilizing Carbonyl Coordination of Native Amides for Palladium-Catalyzed C(sp3 )-H Olefination

PdII -catalyzed C(sp3 )-H olefination of weakly coordinating native amides is reported. Three major drawbacks of previous C(sp3 )-H olefination protocols, 1) in situ cyclization of products, 2) incompatibility with α-H-containing substrates, and 3) installation of exogenous directing groups, are addressed by harnessing the carbonyl coordination ability of amides to direct C(sp3 )-H activation. The method enables direct C(sp3 )-H functionalization of a wide range of native amide substrates, including secondary, tertiary, and cyclic amides, for the first time. The utility of this process is demonstrated by diverse transformations of the olefination products.

Rh-Catalyzed Annulative Insertion of Terminal Olefin onto Pyridines via a C-H Activation Strategy Using Ethenesulfonyl Fluoride as Ethylene Provider

A Rh(III)-catalyzed annulative insertion of ethylene onto picolinamides was achieved, providing a portal to a class of unique pyridine-containing molecules bearing a terminal olefin moiety for diversification. Application of this method for modification of Sorafenib was also accomplished.

The growing applications of SuFEx click chemistry

SuFEx (Sulfur Fluoride Exchange) is a modular, next generation family of click reactions, geared towards the rapid and reliable assembly of functional molecules.