Two one-pot routes from iodoarenes to diaryliodonium triflates have been developed in the sustainable solvent ethyl acetate. The first method yields the recently reported aryl(dimethylisoxazolyl)iodonium triflates, circumventing the need for stepwise synthesis of this chemoselective arylating reagent. The second method gives other types of diaryliodonium salts, and the scalability of the protocols was exhibited with two >45 mmol scale-ups with impressively low E-factors.

Although functionalized cyclopropenes have found uses in many applications, their synthesis has been severely limited. Now, a hypervalent iodine reagent, in conjunction with gold catalysis, has been utilized to control their reactivity, allowing efficient formation of cyclopropenyl alkynes/alkenes.

The combination of mechanochemistry and hypervalent iodine chemistry has rarely been reported, despite the numerous advantages offered by this enabling technology. With this in mind, this study addresses the key issue of transforming hypervalent iodine-mediated, solution-based reactions into the mechanochemical realm, accompanied by benchmarking and sustainability studies of the different types of reactions. Interestingly, several reagents displayed quite different reactivity and regioselectivity under mechanochemical conditions.

The study of different forms of nanocellulose is a fast-growing field with many advantages. As a biobased polymer, it holds strong promise to replace petrochemical solid supports that need to be phased out. While there are already a plethora of nanocellulose applications, e.g., in the fields of material science, engineering, and water treatment, there is a surprising lack of reports concerning their applications in catalysis and organic chemistry. A crucial property of nanocellulose is its well-defined surface structure, which enables surface modifications to reach useful solid-supported catalysts and reagents. In this perspective, we explore the use of unmodified and modified variants of nanocellulose in organic chemistry. We further propose that the use of mechanochemistry could be a future application to increase the activity and eliminate the requirement for aqueous media due to nanocellulose’s dispersion issues.

The transition-metal free S-vinylation of thiophenols by vinylbenziodoxolones (VBX) constituted an important step forward in hypervalent iodine-mediated vinylations, highlighting the difference to vinyliodonium salts and that the reaction outcome was influenced by the substitution pattern of the benziodoxolone core. In this study, we report several new classes of hypervalent iodine vinylation reagents; vinylbenziodazolones, vinylbenziodoxolonimine and vinyliodoxathiole dioxides. Their synthesis, structural and electronic properties are described and correlated to the S-vinylation outcome, shedding light on some interesting facets of these reagents.

Herein, we disclose a convenient protocol for the α-diarylation of carbon nucleophiles to yield heavily functionalized quaternary products. Diaryliodonium salts are utilized to transfer both aryl groups under transition-metal-free conditions, which enables an atom-efficient and high-yielding method with broad functional group tolerance. The methodology is amenable to a wide variety of carbon nucleophiles and can be utilized in late-stage functionalization of complex arenes. Furthermore, it is compatible with a new class of zwitterionic iodonium reagents, which gives access to phenols with an ortho-quaternary center. The diarylated products bear an ortho-iodo substituent that can be utilized in further transformations, including the formation of novel, functionalized six-membered cyclic iodonium salts.

Our group has reported several one-pot protocols for the synthesis of diaryliodonium salts, which have been recognized as attractive multi-purpose reagents in areas ranging from organic synthesis to materials chemistry. Over the years, we have identified limitations in the published protocols concerning synthesis of mixed electron-rich and electron-poor, as well as highly electron-poor diaryliodonium salts, as the corresponding starting materials are either too reactive or too unreactive. In this update, we discuss the underlying limitations concerning the stability and reactivity of the involved reagents and provide strategies to overcome these challenges through updated synthetic protocols. 

ortho-Functionalized azobenzenes are much sought after molecular switches, as they may be tuned to absorb in the visible range of light and the (Z)-isomers can have high thermal half-lives. To enable straightforward access to these targets, we have developed a synthetic route via novel ortho-substituted azobenzene-functionalized diaryliodonium salts. Selective transfer of the azobenzene moiety to O-, N-, C- and S-nucleophiles under mild, transition metal-free conditions gives access to an unprecedented range of ortho-substituted azobenzenes. The photoswitching properties of the reagents were investigated and the structure was determined by X-ray crystallography.

ORIGIN

Hypervalent bromine(III) reagents exhibit superior electrophilic reactivity compared with their iodine analogs. Recently, Wencel-Delord and coworkers described a strategy for the synthesis of cyclic bromonium salts and their utility as efficient arylating agents via aryne intermediates in the presence of a weak base.

REACTION MECHANISM

Aryl transfer reactions involving hypervalent halogen(III) reagents enable access to functionalized nucleophiles, and efficient methodology for arylations with diaryliodonium salts has been developed for a range of nucleophiles. Diarylbromonium salts are much less utilized, mainly due to instability and synthesis problems. However, transition metal-free C–O and C–N couplings involving cyclic bromonium(III) salts were recently reported under mild conditions. With carboxylates, exclusive meta- or ortho- selectivity was observed depending on the ring substitution pattern. The use of amine nucleophiles resulted in moderate to high regioselectivity in favor of the meta-substituted products.The reaction was found to proceed by deprotonation of bromonium salt A with simultaneous β-elimination of the excellent bromine(III) leaving group, leading to aryne B. Subsequent meta-selective nucleophilic attack by carboxylate C generates anionic intermediate D, which is either protonated by a new molecule of A in a possible autocatalytic process, or by the formed bicarbonate, releasing product E.Bromonium salts display greater reactivity and electrophilicity than the iodine analogs. Arylation of carboxylic acids with the latter proceeds regiospecifically at increased temperatures, whereas aryne formation is quite uncommon. Aryne intermediates have been utilized in cycloadditions and mechanistic studies from our group suggest that aryne formation also takes place in transition metal-free O-arylations of aliphatic alcohols with electron-rich diaryliodonium salts, resulting in regioisomeric product mixtures. Cyclic diaryliodonium salts are less reactive and their transformations generally require transition metal catalysis, as exemplified by the ortho-functionalization with carboxylic acids.

We report an efficient radical-mediated C-C coupling through photoredox-catalyzed reactions of 4-alkyl-dihydropyridines (DHPs) and vinylbenziodoxol(on)es (VBX, VBO). This transition-metal-free and mild photocatalytic method has excellent functional group tolerance and affords vinylated products in good yields, with complete retention of the alkene configuration. The utility of the methodology is demonstrated by the diastereoselective synthesis of C-vinyl glycosides. Preliminary mechanistic studies suggest that the C-C bond formation is stereospecific and proceeds through a concerted radical coupling transition state.