Cu-catalyzed arylcarbocyclization of alkynes with diaryliodonium salts through C-C bond formation on inert C(sp3)-H bond

Lewis-Acid-Mediated Intramolecular Cyclization of 4-Aryl-5-allyl-1,2,3-triazoles to Substituted Cyclopentene Derivatives

4-Aryl-5-allyl-N-fluoroalkyl-1,2,3-triazoles available by a three-component reaction of fluoroalkyl azides, copper acetylides, and allyl halides underwent aluminum halide-mediated transformation to N-(4-halo-2-aryl-cyclopentenyl) imidoyl halides by cyclization of vinyl cation intermediates, followed by halide capture. Utilization of the cyclic products was demonstrated by the synthesis of N-alkenyl amides, amidines, isoquinolines, and tetrazoles or by the subsequent modification of the cyclopentene ring.

Diverse reactivity of the gem-difluorovinyl iodonium salt for direct incorporation of the difluoroethylene group into N- and O-nucleophiles

The synthesis of gem-difluoroethylene compounds remains a difficult task in organic synthesis. Here, the direct difluoroethylation reactions of N- and O-nucleophiles including amides and acids were realized with a hypervalent iodine reagent: gem-difluorovinyl iodonium salt (DFVI). The reactions were accomplished via a neighbouring group rearrangement. The gem-difluorovinyl iodonium salt was found to display diverse reactivity due to its unique electronic effect and was applied to the incorporation of difluoroethylene group, including difluorovinylation of carboxylic acids, difluorovinylation and 1,3-cyclic fluorovinylation of amides and 1,1-cyclic difluoroethylation of amines.

Vinyl cation-mediated intramolecular hydroarylation of alkynes using pyridinium reagents

Once considered to be exotic species of limited synthetic utility, vinyl cations have recently been shown to be highly versatile intermediates in a variety of processes. Here, we report a method for the synthesis of aryl-substituted benzocycloheptenes and -hexenes using the hydrotriflate salt of an electron-poor pyridine as a uniquely efficient proton source for a vinyl cation mediated Friedel-Crafts cyclization. The mild conditions made possible by this reagent allowed a range of simple and functionalized alkynes bearing pendant aryl groups to serve as suitable substrates for this scalable and convenient protocol.

Copper-Catalyzed Chemo-, Regio-, and Stereoselective Multicomponent 1,2,3-Trifunctionalization of Internal Alkynes

Herein, we report the first diaryliodonium salts promoted multicomponent 1,2,3-trifunctionalization of alkynes, where both the acetylenic bond and the adjacent nonactivated propargylic C(sp³)-H bond were functionalized synergistically to generate α-arylated enones with high chemo-, regio-, and stereoselectivity. A broad spectrum of diaryliodonium salts and internal alkynes could be utilized in this protocol, and a diverse collection of highly substituted and stereochemically defined linear and cyclic complex structures could be elaborated from the enone products.

Photocatalytic Sulfonylcarbocyclization of Alkynes Using SEt as a Traceless Directing Group: Access to Cyclopentenes and Indenes

Cyclopentenes and indenes are important structural scaffolds in synthetic, medical, and material chemistry. Cyclization of alkynes via remote C-H functionalization is an appealing approach to construct these motifs due to its high efficiency and step-economy. Herein, a traceless directing group strategy was designed to reverse the regioselectivity of radical addition which enabled an unprecedented photocatalytic sulfonylcarbocyclization of terminal alkynes by forming C-C bond on inert C(sp³ )-H bond. It offers a facile access to decorated cyclopentenes and indenes under mild conditions. The resultant products could be converted into a set of valuable molecular scaffolds, including a key intermediate of AM-6226. Mechanistic experiments suggest a radical cascade pathway comprising a Markovnikov-type sulfonylation, 1,5-hydrogen atom transfer, 5-endo-trig cyclization, and β-elimination. This study lays further groundwork for the use of anti-Baldwin 5-endo-trig radical cyclization in rapidly assembling five-membered carbocycles.

Cu-catalyzed [2 + 2 + 1] cascade annulation of vinyl iodonium salts with elemental sulfur/selenium for the modular synthesis of thiophenes and selenophenes

The Cu-catalyzed [2 + 2 + 1] regioselective synthesis of thiophenes/selenophenes was realized from aryl-vinyl iodonium salts and elemental sulfur/selenium.

Preparation and Synthetic Application of Naproxen-Containing Diaryliodonium Salts

The synthesis of naproxen-containing diaryliodonium salts has been realized from naproxen methyl ester and ArI(OH)OTs activated by trimethylsilyl trifluoromethanesulfonate (TMSOTf) in a solvent mixture comprising dichloromethane and 2,2,2-trifluoroethanol (TFE). Those iodonium salts have been successfully used in the functionalization of an aromatic ring of naproxen methyl ester, including fluorination, iodination, alkynylation, arylation, thiophenolation, and amination and esterification reactions. Moreover, further hydrolysis of the obtained 5-iodo-naproxen methyl ester afforded 5-iodo-naproxen.

Remote methylene C(sp3)–H functionalization enabled by organophosphine-catalyzed alkyne isomerization

Non classical EWG-activated arylalkynes as C1 units in organophosphine catalyzed diverse remote sp3 C–H functionalization.

Synthesis of Spirocyclic Compounds by a Ring-Expansion/Cationic Cyclization Cascade Reaction of Chlorosulfate Derivatives

A novel cascade reaction to prepare spirocarbocyclic compounds from chlorosulfate derivatives has been developed. The process involves an unusual thermal elimination of the chlorosulfate moiety, a ring-expansion reaction, and a subsequent cationic cyclization reaction. Despite the relatively complex skeletal rearrangement, the reaction described here is featured by its operational simplicity, being just a thermal process that does not require additional reagents, catalysts, or additives.

Mechanistic Study on Gold-Catalyzed Cycloisomerization of Dienediynes Involving Aliphatic C-H Functionalization and Inspiration for Developing a New Strategy to Access Polycarbocycles

Previously, we developed a gold-catalyzed cycloisomerization of dienediynes to synthesize the fused 6,7,5-tricyclic compounds. This reaction involves aliphatic C-H functionalization under mild conditions with high regio- and diastereoselectivities. Herein, we present a combined density functional theory (DFT) and experimental study to understand its mechanism. The reaction starts with a 6-endo-dig cyclization to generate a cis-1-alkynyl-2-alkenylcyclopropane. Then, a Cope rearrangement takes place to give a seven-membered-ring allene intermediate, whose central carbon atom possesses vinyl cation character and thus is highly reactive toward aliphatic C-H insertion. After the C-H insertion, two successive [1,2]-hydride shifts then occur to give the tricyclic product and to complete the catalytic cycle. Notably, steric effect induced by the bulky ligand is found to be important for the diastereocontrol in the C-H insertion step. DFT calculations suggested that the malonate-tethered substrate utilized in our previous work may undergo an undesired 5-exo-dig cyclization under gold catalysis, which could be the reason why the desired fused 6,7,5-tricarbocyclic product was not generated. These mechanistic insights then guided us to design substrates with a shortened carbon tether in the present work to inhibit the exo-dig cyclization so that the tandem cyclopropanation/Cope rearrangement/C-H functionalization could occur to construct polycarbocycles containing a seven-membered ring. This prediction was supported by new experiments, providing a new strategy to access fused 5,7,5-tricyclic and 5,7,6,6-tetracyclic carbocycles. In addition, how the substituents affect the chemoselectivity was also investigated.

Modification of the 4-phenylbutyl side chain of potent 3-benzazepine-based GluN2B receptor antagonists

Excitotoxicity driven by overactivation of NMDA receptors represents a major mechanism of acute and chronic neurological and neurodegenerative disorders. Negative allosteric modulators interacting with the ifenprodil binding site of the NMDA receptor are able to interrupt this ongoing neurodamaging process. Starting from the potent 3-benzazepine-1,7-diol 4a novel NMDA receptor antagonists were designed by modification of the N-(4-phenylbutyl) side chain. With respect to developing novel fluorinated PET tracers, regioisomeric fluoroethoxy derivatives 11, 12, 14, and 15 were synthesized. Analogs 19 and 20 with various heteroaryl moieties at the end of the N-side chain were prepared by Sonogashira reaction and nucleophilic substitution. The fluoroethyl triazole 37 was obtained by 1,3-dipolar cycloaddition. In several new ligands, the flexibility of the (hetero)arylbutyl side chain was restricted by incorporation of a triple bond. The affinity towards the ifenprodil binding site was tested in an established competition assay using [³H]ifenprodil as radioligand. Introduction of a fluoroethoxy moiety at the terminal phenyl ring, replacement of the terminal phenyl ring by a heteroaryl ring and incorporation of a triple bond into the butyl spacer led to considerable reduction of GluN2B affinity. The phenol 15 (K_i = 193 nM) bearing a p-fluoroethoxy moiety at the terminal phenyl ring represents the most promising GluN2B ligand of this series of compounds. With exception of 15 showing moderate σ₂ affinity (K_i = 79 nM), the interaction of synthesized 3-benzazepines towards the PCP binding site of the NMDA receptor, σ₁ and σ₂ receptors was rather low (K_i > 100 nM).

DFT calculations on the mechanism of copper-catalysed tandem arylation-cyclisation reactions of alkynes and diaryliodonium salts

We present a computational mechanistic study on the copper(III)-catalysed carboarylation-ring closure reactions leading to the formation of functionalised heterocycles. We have performed DFT calculations along selected routes and compared their free energy profiles. The calculations considered two viable options for the underlying mechanism which differ in the order of the oxazoline ring formation and the aryl transfer steps. In our model transformation, it was found that the reaction generally features the aryl transfer-ring closing sequence and this sequence shows very limited sensitivity to the variation of the substituent of the reactants. On the basis of the mechanism the origin of the stereoselectivity is ascribed to the interaction of the Cu ion with the oxazoline oxygen driving the ring-closure step selectively.

Copper-catalyzed tandem arylation–cyclization of 2-alkynylaryl isothiocyanates with diaryliodonium salts: an efficient synthesis of thiochromeno[2,3-b]indoles

A Cu-catalyzed arylation–cyclization approach is developed for the synthesis of thiochromeno[2,3-b]indoles through the S-arylation, 5-endo-trig cyclization, and Friedel–Crafts-type cyclization sequence.

Acid-promoted bicyclization of arylacetylenes to benzobicyclo[3.2.1]octanes through cationic rearrangements

Acid-promoted site- and stereo-selective bicyclization of alkynes to benzobicyclo[3.2.1]octanes was realized with atom- and step-economy. The reaction proceeded through two C–C bonds formed on remote alkyl C–H bonds via twice long-distance cationic rearrangement.

Copper-catalyzed intramolecular aryl-bicyclization of diynes with diaryliodonium salts via vinyl cations

A novel protocol for the synthesis of polycyclic compounds from linear diynes and diaryliodonium salts has been realized.

Arylation with Diaryliodonium Salts

This chapter focuses on recent developments in metal-free and metal-catalyzed arylations with diaryliodonium salts (diaryl-λ3-iodanes). Synthetic routes to diaryliodonium salts are briefly described, and chemoselectivity trends with unsymmetric iodonium salts are discussed.

Cu-catalyzed intramolecular aryl-etherification reactions of alkoxyl alkynes with diaryliodonium salts via cleavage of a stable C–O bond

Cu-catalyzed aryl-etherification reactions of alkoxyl alkynes with diaryliodonium salts are realized to produce oxo-heterocyclesviacleavage of a stable C–O bond.