Phenols, anilines, and malonates have been arylated under metal-free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new “anti-ortho effect” has been identified in the arylation of malonates. Several “dummy groups” have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal-free reagents.

This review summarizes the development of user-friendly, recyclable and easily separable heterogeneous catalysts for C–H activation during the last decade until December 2015.

cyclizations · homogeneous catalysis · oxidation · seleniumApplications of selenium reagents in organic chemistry have developed rapidly over the past years, and comprehensive reviews on this area have appeared.[1] Rather new, however, is the use of selenium-based catalysts in organic synthesis. We highlight new developments in organoselenium catalysis and in particular the use of selenium electrophiles and organoselenium compounds in carbonylation reactions and the oxidation of alkenes and carbonyl compounds. The use of organoselenium ligands for metal-catalyzed processes is not covered here; the topic has been reviewed recently elsewhere.[1f] Also their potential as efficient mimetics for selenoenzymes will not be discussed. [2] In this Highlight we will focus on the catalytic use of selenium electrophiles for selenenylations and halogenations as well as the use of perseleninic acids as catalytic oxidants for various substrates.The use of electrophilic selenium reagents is a very versatile strategy for functionalizing alkenes 1. To avoid the use of stoichiometric amounts of selenium reagents, researchers have sought for analogous catalytic methods. Selenenylation-deselenenylation sequences involve two steps: the initial selenofunctionalization is followed by oxidation of the organoselenium moiety in 2, which allows the regeneration of the reagent through b elimination giving 3 or substitution to provide 4 (Scheme 1). Various reagents can be used to activate the selenide moiety in 2 to undergo elimination or substitution. The most explored approach involves oxidation with an excess of persulfate.[3] The oxidant is initially responsible for the generation of the electrophilic selenenylating agent from the corresponding diselenide and then for the oxidation of the selenium moiety in 2 allowing the regeneration of the catalyst. This approach proved to be useful for functionalizations such as hydroxylations, alkoxylations, and cyclizations, and when chiral nonracemic diselenides were used, interesting levels of stereoselectivity were reached. [3] Depending on the substrate 5, either an addition-elimination sequence to yield 6 or a cyclization-elimination sequence to give 7 is possible by using an electrochemical procedure (Scheme 2).[4] The reaction is initiated by anodic oxidation of bromide to bromine. The latter reacts with the diselenide to afford the arylselenenyl bromide, which promotes the selenofunctionalization. Subsequent elimination of the selenium moiety via a tetravalent selenium compound gives the products 6 or 7 and regenerates the arylselenenyl bromide. Alternatively, hypervalent iodine reagents such as [bis(trifluoroacetoxy)iodo]benzene can be used as oxidants, in combination with catalytic amounts (5 mol %) of diselenides, to effect the conversion of butenoic acids 5 (R = H) to the corresponding butenolides 7 in yields of up to 95 %.[5] In a diselenide-catalyzed dihydroxylation of alkenes with ammonium persulfate as the oxidant both nucleophiles are hydroxy groups and diols of type 4 (Nu = Nu' =...

Palladium-catalyzed cross-coupling reactions are indispensable tools in molecular syntheses with numerous applications in academia and for the practitioners in the chemical and pharmaceutical industries.

A survey of papers exploring the scope of click chemistry in the area of π-conjugated polymers for organic electronics is given.

Transition metal-catalyzed C–H activation has emerged as an increasingly powerful strategy in molecular syntheses and a particularly attractive alternative to classical methods of cross-couplings. During the recent years, significant focus has been dedicated to further improve the sustainable nature of the C–H activation approach. As solvents represent a major portion of organic pollution caused by chemical syntheses, a range of nontoxic, biobased, sustainable solvents have been developed to substitute for common organic reaction media. In this review, we present a general perspective of biomass-derived solvents for transition metal-catalyzed C–H activation reactions and their unique potential for chemical syntheses up to January 2019.

Key aspects for the development of a greener synthesis and the use of the organoselenium compounds.

The first general and efficient diphenyl diselenide-catalyzed dihydroxylation of double bonds is presented. Hydrogen peroxide can be used as the oxidizing agent, affording generally good yields and high diasteroselectivity.