Arylative Desulfonation of Diarylmethyl Phenyl Sulfone with Arenes Catalyzed by Scandium Triflate

Organocatalytic asymmetric synthesis of axially and centrally chiral heterotriarylmethanes by a Friedel-Crafts reaction

A highly enantioselective Friedel-Crafts reaction between C2-unsubstituted naphthyl-indoles and racemic 3-methylated-3H-pyrrolides catalyzed by chiral phosphoric acids has been developed. This reaction provides an efficient and facile route to a series of heterotricyclic triarylmethanes containing axially chiral naphthyl-indole and centrally chiral pyrrole moieties under mild conditions. Moreover, biological evaluation discovered one of these products with promising antitumor activity, and demonstrates its potential application in medicinal chemistry.

2H-Thiazolo[4,5-d][1,2,3]triazole: synthesis, functionalization, and application in scaffold-hopping

This manuscript unveils the synthesis of 2H-thiazolo[4,5-d][1,2,3]triazole (ThTz), an unprecedented [5-5]-fused heteroaromatic system, and established a scalable synthetic procedure for producing large quantities of the ThTz ring bearing a sulfone group on the thiazole ring. The sulfone moiety proves to be a versatile reactive tag, facilitating diverse transformations such as SNAr reactions, metal-catalyzed couplings, and radical-based alkylations. Furthermore, functionalization of the triazole ring highlights the potential of this newly developed heteroaromatic compound as a valuable heteroaryl building block, promoting scaffold hopping strategies in medicinal chemistry.

Regiodivergent synthesis of sulfone-tethered lactam-lactones bearing four contiguous stereocenters

Sulfone-tethered lactones/amides/amines display a diverse spectrum of biological activities, including anti-psychotic and anti-hypertensive. Sulfones are also widely present in functional materials and fragrances. We therefore reasoned that a regiodivergent and stereocontrolled strategy that merges the sulfone, lactone, and lactam motifs would likely lead to the discovery of new pharmacophores and functional materials. Here, we report mild conditions for the sulfonyllactonization of γ-lactam-tethered 5-aryl-4(E)-pentenoic acids. The annulation is highly modular, chemoselective, and diastereoselective. With respect to regioselectivity, trisubstituted alkenoic acids display a preference for 5-exo-trig cyclization whereas disubstituted alkenoic acids undergo exclusive 6-endo-trig cyclization. The lactam-fused sulfonyllactones bear angular quaternary as well as four contiguous stereocenters. The products are post-modifiable, especially through a newly developed Co-catalyzed reductive cross-coupling protocol.

Dehydroxylative Sulfonylation of Alcohols

Described here is the R₃P/ICH₂CH₂I-promoted dehydroxylative sulfonylation of alcohols with a variety of sulfinates. In contrast to previous dehydroxylative sulfonylation methods, which are usually limited to active alcohols, such as benzyl, allyl, and propargyl alcohols, our protocol can be extended to both active and inactive alcohols (alkyl alcohols). Various sulfonyl groups can be incorporated, such as CF₃SO₂ and HCF₂SO₂, which are fluorinated groups of interest in pharmaceutical chemistry and the installation of which has received increasing attention. Notably, all reagents are cheap and widely available, and moderate to high yields were obtained within 15 min of reaction time.

Transition-Metal-Free Synthesis of Polyfluoro-Polyarylmethanes via Direct Cross-Coupling of Polyfluoroarenes and Benzyl Chlorides

The transition-metal-free direct cross-coupling between polyfluoroarenes and benzyl chlorides is reported. In this strategy, a variety of polyfluoro di-, tri- and tetra-arylmethanes was efficiently prepared with good to excellent yields in the presence of Mg turnings via a one-pot procedure. Significantly, this method provides a general approach for the synthesis of polyfluorinated polyarylmethanes.

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

As the "chemical chameleon", sulfonyl-containing compounds and their variants have been merged with various types of reactions for the efficient construction of diverse molecular architectures by taking advantage of their incredible reactive flexibility. Currently, their involvement in radical transformations, in which the sulfonyl group typically acts as a leaving group via selective C-S, N-S, O-S, S-S, and Se-S bond cleavage/functionalization, has facilitated new bond formation strategies which are complementary to classical two-electron cross-couplings via organometallic or ionic intermediates. Considering the great influence and synthetic potential of these novel avenues, we summarize recent advances in this rapidly expanding area by discussing the reaction designs, substrate scopes, mechanistic studies, and their limitations, outlining the state-of-the-art processes involved in radical-mediated desulfonylation and related transformations. With a specific emphasis on their synthetic applications, we believe this review will be useful for medicinal and synthetic organic chemists who are interested in radical chemistry and radical-mediated desulfonylation in particular.

Transition Metal-Catalyzed Cross-Couplings of Benzylic Sulfone Derivatives

In recent years, the use of organosulfones as a new class of cross-coupling partner in transition-metal catalyzed reactions has undergone significant advancement. In this personal account, our recent investigations into desulfonylative cross-coupling reactions of benzylic sulfone derivatives catalyzed by Pd, Ni, and Cu catalysis is described. Combined with the facile α-functionalizations of sulfones, our methods can be used to form valuable multiply-arylated structures such as di-, tri-, and, tetraarylmethanes from readily available substrates. The reactivity of sulfones can be increased by introducing electron-withdrawing substituents such as 3,5-bis(trifluoromethyl)phenyl and trifluoromethyl groups, which enable more challenging cross-coupling reactions. Reactive intermediates including Cu-carbene complexes were identified as key intermediates in sulfone activation, representing new types of C-SO₂ bond activation processes. These results indicate sulfones are powerful functional groups, enabling new catalytic desulfonylative transformations.

Chemo-, regio- and stereoselective synthesis of monofluoroalkenes via a tandem fluorination-desulfonation sequence

A widely applicable approach for the synthesis of Z-monofluoroalkenes from readily available alkyl triflones and NFSI has been reported. The reaction proceeded under mild conditions, affording mono-fluorinated alkenes in good to excellent yields with excellent chemo- regio- and stereoselectivity. The mechanism may involve electrophilic fluorination of triflones followed by the highly stereoselective concerted bimolecular elimination (E2) of CF3SO2H.

Base promoted gem-difluoroolefination of alkyl triflones

A new synthesis of gem-difluoroalkenes from readily available alkyl triflones and difluorocarbene precursors such as TMSCF₂Br has been reported. The reaction, regardless of electronic effect, gives gem-difluoroalkenes in good to excellent yields. The mechanism may involve deprotonation of triflones, nucleophilic addition, and the elimination of SO₂CF₃.

Transition-Metal-Free Synthesis of Polyfunctional Triarylmethanes and 1,1-Diarylalkanes by Sequential Cross-Coupling of Benzal Diacetates with Organozinc Reagents

A variety of functionalized triarylmethane and 1,1-diarylalkane derivatives were prepared via a transition-metal-free, one-pot and two-step procedure, involving the reaction of various benzal diacetates with organozinc reagents. A sequential cross-coupling is enabled by changing the solvent from THF to toluene, and a two-step SN 1-type mechanism was proposed and evidenced by experimental studies. The synthetic utility of the method is further demonstrated by the synthesis of several biologically relevant molecules, such as an anti-tuberculosis agent, an anti-breast cancer agent, a precursor of a sphingosine-1-phosphate (S1P) receptor modulator, and a FLAP inhibitor.

A Titanium-Catalyzed Reductive α-Desulfonylation

A titanium(III)-catalyzed desulfonylation gives access to functionalized alkyl nitrile building blocks from α-sulfonyl nitriles, circumventing traditional base-mediated α-alkylation conditions and strong single electron donors. The reaction tolerates numerous functional groups including free alcohols, esters, amides, and it can be applied also to the α-desulfonylation of ketones. In addition, a one-pot desulfonylative alkylation is demonstrated. Preliminary mechanistic studies indicate a catalyst-dependent mechanism involving a homolytic C-S cleavage.

A multi-component reaction of electron-rich arenes, potassium metabisulfite, aldehydes and aryldiazonium tetrafluoroborates

A multi-component reaction of electron-rich arenes, potassium metabisulfite, aldehydes and aryldiazonium tetrafluoroborates under mild conditions is reported, leading to a range of (arylsulfonyl)methylbenzenes in moderate to good yields.

Targeting the aryl hydrocarbon receptor with a novel set of triarylmethanes

The aryl hydrocarbon receptor (AhR) is a chemical sensor upregulating the transcription of responsive genes associated with endocrine homeostasis, oxidative balance and diverse metabolic, immunological and inflammatory processes, which have raised the pharmacological interest on its modulation. Herein, a novel set of 32 unsymmetrical triarylmethane (TAM) class of structures has been synthesized, characterized and their AhR transcriptional activity evaluated using a cell-based assay. Eight of the assayed TAM compounds (14, 15, 18, 19, 21, 22, 25, 28) exhibited AhR agonism but none of them showed antagonist effects. TAMs bearing benzotrifluoride, naphthol or heteroaromatic (indole, quinoline or thiophene) rings seem to be prone to AhR activation unlike phenyl substituted or benzotriazole derivatives. A molecular docking analysis with the AhR ligand binding domain (LBD) showed similarities in the binding mode and in the interactions of the most potent TAM identified 4-(pyridin-2-yl (thiophen-2-yl)methyl)phenol (22) compared to the endogenous AhR agonist 5,11-dihydroindolo[3,2-b]carbazole-12-carbaldehyde (FICZ). Finally, in silico predictions of physicochemical and biopharmaceutical properties for the most potent agonistic compounds were performed and these exhibited acceptable druglikeness and good ADME profiles. To our knowledge, this is the first study assessing the AhR modulatory effects of unsymmetrical TAM class of compounds.

Regioselective molybdenum-catalyzed allylic substitution of tertiary allylic electrophiles: methodology development and applications

The first molybdenum-catalyzed allylic sulfonylation of tertiary allylic electrophiles is described. The method employs a readily accessible catalyst (Mo(CO)₆/2,2′-bipyridine, both are commercially available) and represents the first example of the use of a group 6 transition metal-catalyst for allylic sulfonylation of substituted tertiary allylic electrophiles to form carbon–sulfur bonds. This atom economic and operationally simple methodology is characterized by its relatively mild conditions, wide substrate scope, and excellent regioselectivity profile, thus unlocking a new platform to forge sulfone moieties, even in the context of late-stage functionalization and providing ample opportunities for further derivatization through traditional Suzuki cross-coupling reactions.

The first general example of Mo-catalyzed allylic sulfonylation of tertiary allylic electrophile provides an efficient way to forge sulfone moieties, and providing ample opportunities for further transformation through traditional Suzuki cross-coupling.

TBAB-Catalyzed 1,6-Conjugate Sulfonylation of para-Quinone Methides: A Highly Efficient Approach to Unsymmetrical gem-Diarylmethyl Sulfones in Water

A highly efficient sulfonylation of para-quinone methides with sulfonyl hydrazines in water has been developed on the basis of the mode involving a tetrabutyl ammonium bromide (TBAB)-promoted sulfa-1,6-conjugated addition pathway. This reaction provides a green and sustainable method to synthesize various unsymmetrical diarylmethyl sulfones, showing good functional group tolerance, scalability, and regioselectivity. Further transformation of the resulting diarylmethyl sulfones provides an efficient route to some functionalized molecules.

Metal free highly efficient C–N bond formation through 1,6-addition: synthesis and photophysical studies of diaryl methyl amino acid esters (DMAAEs)

A transition-metal free, proficient strategy for the one-pot synthesis of diverse diaryl methyl amino acid esters (DMAAEs) has been established from the easily accessible chiral amino acid esters and para-quinone methides (QMs) in very good to excellent yields.

Tritylium assisted iodine catalysis for the synthesis of unsymmetrical triarylmethanes

The combined Lewis acid catalytic system, generated from molecular iodine and tritylium tetrafluoroborate effectively catalyzed the Friedel-Crafts (FC) arylation of diarylmethyl sulfides providing an efficient access to various unsymmetrical triarylmethanes. The addition of tritylium and iodine created a more active catalytic system to promote the cleavage of sulfidic C-S bonds.

Metal-free iodine-promoted direct synthesis of unsymmetrical triarylmethanes

Completely unsymmetrical triarylmethanes were prepared in a one-pot reaction via o-QM intermediates generated in situ.

Pyridine-catalyzed desulfonative borylation of benzyl sulfones

Herein, we report the transition-metal free, pyridine-catalyzed desulfonative borylation of benzyl sulfones with bis(pinacolato)diboron (B₂pin₂).

Synthesis of new mixed-bistriarylmethanes and novel 3,4-dihydropyrimidin-2(1H)one derivatives

Formylated-triarylmethanes were realized as ideal precursors for the design and synthesis of mixed-bistriarylmethanes and 3,4-dihydropyrimidin-2(1H)one-triarylmethane hybrid derivatives.

Fluorinated Alcohol-Promoted Reaction of Chlorohydrocarbons with Diverse Nucleophiles for the Synthesis of Triarylmethanes and Tetraarylmethanes

This article reports an efficient synthesis of triarylmethanes and tetraarylmethanes from chlorohydrocarbons with miscellaneous nucleophiles in fluorinated alcohols, featuring metal-free, wide substrate scope, excellent functional group tolerance, and mild reaction conditions.

Carbene-catalyzed enantioselective oxidative coupling of enals and di(hetero)arylmethanes

Di(hetero)arylmethane is a unique structural motif for natural and synthetic functional molecules. To date, it remains challenging to functionalize the diaryl methyl sp3 carbon-hydrogen bond directly in an enantioselective manner. This is likely due to the relatively inert nature of the carbon-hydrogen bond and the difficult enantiofacial discrimination of two sterically similar aryl substituents. Here we disclose an N-heterocyclic carbene-catalyzed direct oxidative coupling of enals and di(hetero)arylmethanes. Our method allows for highly enantioselective transformation of diaryl methanes and quick access to benzimidazole fused lactams.

A Novel Sc(OTf)3 -Catalyzed (2+2+1)-Cycloannulation/Aza-Friedel-Crafts Alkylation Sequence toward Multicyclic 2-Pyrrolines

The rapid assembly of molecular complexity continues to be at the forefront of novel reaction development. In the pursuit of that goal, we herein report a novel Sc(OTf)₃ -catalyzed, one-pot multicomponent reaction that furnishes complex multicyclic 2-pyrrolines with excellent overall yields and perfect diastereocontrol. This process is based on our previously established (2+2+1)-cycloannulation of in situ generated 1-azaallyl cations, 1,3-dicarbonyls and primary amines. The newly formed and highly reactive aminal moiety is readily substituted with indoles and pyrroles both as external and internal π-nucleophiles to provide densely functionalized N-heterocycles with four new σ-bonds and two vicinal quaternary stereogenic centers. In addition, DFT calculations have been conducted to further characterize the intermediate 1-azaallyl cations.

Catalyst-Free 1,6-Conjugate Addition/Aromatization/Sulfonylation of para-Quinone Methides: Facile Access to Diarylmethyl Sulfones

An efficient, catalyst-free strategy to construct diarylmethyl sulfones via 1,6-conjugate addition/aromatization/sulfonylation reaction of para-quinone methides with sulfonyl hydrazides under mild and environmentally benign conditions has been developed. The established protocol provided a highly chemo- and regioselectivity synthesis of a diverse array of novel diarylmethyl sulfones with excellent yields, and the reaction could be scaled up.

Unmasking Dipole Character of Acyl Ketene Dithioacetals via a Cascade Reaction with Arynes: Synthesis of Benzo[b]thiophenes

An unusual strategy toward novel substituted benzo[b]thiophenes has been developed. The generation of arynes in the presence of acyl ketene dithioacetals resulted in a cascade reaction involving [3 + 2] cycloaddition, and a dealkylative arylation of a thioether moiety to afford 2,3-disubstuted benzo[b]thiophenes. This route represents an expeditious approach to benzothiophenes that employs acyl ketene dithioacetals as dipoles.

Polycyclic heteroaromatic ring construction driven by silver/cobalt co-catalyzed desulfonylative and defluorinative fragment-recombination of enol nonaflates with amidines

A novel Ag(i)/Co(ii) co-catalyzed tandem fragmentation and recombination reaction commencing from detachable nonaflates and amidines has been developed.

Stereocontrolled glycoside synthesis by activation of glycosyl sulfone donors with scandium(iii) triflate

Activation of armed glycosyl sulfone donors, using scandium(iii) triflate under microwave irradiation, provides a selective preparation of α-mannosides.