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Herein, we describe the investigation of electrochemical bromination of electron-rich arenes in a 200% cell. For this application, at first, the influence of an excess of supporting electrolyte (Bu 4 NBr) on chemical bromination was investigated. The application of >4.0 equiv of Bu 4 NBr proved to enhance the regioselectivity of the bromination process for O- and N-substituted arenes considerably. The linear paired electrolysis was then optimized upon these insights, and a number of electron-rich arenes could be brominated in high yields with excellent regioselectivity. The use of O 2 as a sacrificial starting material in combination with 2-ethylanthraquinone as a catalyst leads to the enhanced formation of H 2 O 2 at the cathode, resulting in current efficiencies >150% for a considerable number of examples.

The synthesis of unsymmetrical diorganyl selanes was accomplished under electrochemical conditions in an undivided cell utilizing a magnesium cathode and a carbon anode made out of aryl and alkyl iodides and diselanes. This electrochemical cross-electrophile coupling (eXEC) was accomplished using a simple nickel catalyst formed in situ out of Ni(acac) 2 and 2,2'-bipyridine in DMF at ambient temperatures. The reaction showed good functional group compatibility, and heteroaryl iodides, such as thiophene or pyridine derivatives, were well accepted.

Herein, we describe the application of a flow system for the generation of a soluble organo sodium compound and the transformation of this primary nucleophile with various Weinreb amides for the synthesis of alkyl-aryl ketones. Thereafter, the generation of secondary sodium intermediates, such as benzylic sodium nucleophiles or ortho -metalated sodium nucleophiles from various carbon pre-nucleophiles, is described. These transformations generated more complex ketones, and in this investigation the key aspect was to identify factors for the chemoselective and regioselective C-H deprotonation of concurring sites within the starting material. Finally, the direct synthesis of ketones from carboxylic acids and the organo sodium compound is described, revealing interesting aspects regarding the nucleophilicity and basicity of the alkyl sodium reagent.

The role of the inorganic substrate termination, within the organic-inorganic interface, has been well studied for systems that contain strong localised bonding. However, how varying the substrate termination affects coordination to delocalised electronic states, like that found in aromatic molecules, is an open question. Azupyrene, a non-alternant polycyclic aromatic hydrocarbon, is known to bind strongly to metal surfaces through its delocalised π orbitals, thus yielding an ideal probe into delocalised surface-adsorbate interactions. Normal incidence X-ray standing wave (NIXSW) measurements and density functional theory calculations are reported for the adsorption of azupyrene on the (111), (110) and (100) surface facets of copper to investigate the dependence of the adsorption structure on the substrate termination. Structural models based on hybrid density functional theory calculations with non-local many-body dispersion yield excellent agreement with the experimental NIXSW results. No statistically significant difference in the azupyrene adsorption height was observed between the (111) and (100) surfaces. On the Cu(110) surface, the molecule was found to adsorb 0.06 ± 0.04 Å closer to the substrate than on the other surface facets. The most energetically favoured adsorption site on each surface, as determined by DFT, is subtly different, but in each case involved a configuration where the aromatic rings were centred above a hollow site, consistent with previous reports for the adsorption of small aromatic molecules on metal surfaces.

The pre-electrolysis of LiClO 4 in acetonitrile in an undivided cell applying only "catalytic" amounts of current (e.g., 0.05 F) led to the formation of a strong acidic medium for the activation of benzylic ethers and acetals. The activated primary and secondary benzylic ethers and acetals could be converted with a range of carbon nucleophiles, such as allyl trimethylsilane, silyl enol ethers, and enol acetates, for the formation of new carbon-carbon bonds. A chemoselective reaction was observed when electron-deficient benzylic acetals were converted with allyl trimethylsilane to the monoallylated products, whereas an electron-rich benzylic acetal led to the double allylated product under activation of both ether groups.

Defects play a critical role for the functionality and performance of materials, but the understanding of the related effects is often lacking, because the typically low concentrations of defects make them difficult to study. A prominent case is the topological defects in two-dimensional materials such as graphene. The performance of graphene-based (opto-)electronic devices depends critically on the properties of the graphene/metal interfaces at the contacting electrodes. The question of how these interface properties depend on the ubiquitous topological defects in graphene is of high practical relevance, but could not be answered so far. Here, we focus on the prototypical Stone-Wales (S-W) topological defect and combine theoretical analysis with experimental investigations of molecular model systems. We show that the embedded defects undergo enhanced bonding and electron transfer with a copper surface, compared to regular graphene. These findings are experimentally corroborated using molecular models, where azupyrene mimics the S-W defect, while its isomer pyrene represents the ideal graphene structure. Experimental interaction energies, electronic-structure analysis, and adsorption distance differences confirm the defect-controlled bonding quantitatively. Our study reveals the important role of defects for the electronic coupling at graphene/metal interfaces and suggests that topological defect engineering can be used for performance control.

The first example for the electrochemical cis-dichlorination of alkenes is presented. The reaction can be performed with little experimental effort by using phenylselenyl chloride as catalyst and tetrabutylammoniumchloride as supporting electrolyte, which also acts as nucleophilic reagent for the S N 2-type replacement of selenium versus chloride. Cyclic voltammetric measurements and control experiments revealed a dual role of phenylselenyl chloride in the reaction. Based on these results a reaction mechanism was postulated, where the key step of the process is the activation of a phenylselenyl chloride-alkene adduct by electrochemically generated phenylselenyl trichloride. Like this, different aliphatic and aromatic cyclic and acyclic alkenes were converted to the dichlorinated products. Thereby, throughout high diastereoselectivities were achieved for the cis-chlorinated compounds of >95 : 5 or higher., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Indium tribromide catalysed the transfer hydrogenation from dihydroaromatic compounds, such as the commercially available γ-terpinene, to enones, which resulted in the cyclisation to trisubstituted furan derivatives. The reaction was initiated by a Michael addition of a hydride nucleophile to the enone subunit followed by a Lewis-acid-assisted cyclisation and the formation of a furan-indium intermediate and a Wheland intermediate derived from the dihydroaromatic starting material. The product was formed by protonation from the Wheland complex and replaced the indium tribromide substituent. In addition, a site-specific deuterium labelling of the dihydroaromatic HD surrogates resulted in site specific labelling of the products and gave useful insights into the reaction mechanism by H-D scrambling., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The acyl nitroso Diels-Alder reaction of 1,3-dienes with electrochemically oxidised hydroxamic acids is described. By using alternating current electrolysis, their typical electro-induced decomposition could be suppressed in favour of the 1,2-oxazine cycloaddition products. The reaction was optimised using Design of Experiments (DoE) and a sensitivity test was conducted. A mixture of triethylamine/hexafluoroisopropanol served as supporting electrolyte in dichloromethane, thus giving products of high purity after evaporation of the volatiles without further purification. The optimised reaction conditions were applied to various 1,3-dienes and hydroxamic acids, giving up to 96 % isolated yield., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

An electrochemical synthesis of organic polysulfides through sulfur insertion from elemental sulfur to disulfides or thiols is introduced. The highly economic, low-sensitive and low-priced reaction gives a mixture of polysulfides, whose distribution can be influenced by the addition of different amounts of carbon disulfide as co-solvent. To describe the variable distribution function of the polysulfides, a novel parameter, the "absorbance average sulfur amount in polysulfides" (SAP) was introduced and defined on the basis of the "number average molar mass" used in polymer chemistry. Various organic polysulfides were synthesized with variable volume fractions of carbon disulfide, and the yield of each polysulfide was determined by quantitative 13 C NMR. Moreover, by using two symmetrical disulfides or a disulfide and a thiol as starting materials, a mixture of symmetrical and asymmetrical polysulfides could be obtained., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The transfer-hydrogenation as well as the regioselective and regiodivergent addition of H-D from regiospecific deuterated dihydroaromatic compounds to a variety of 1,1-di- and trisubstituted alkenes was realised with InBr 3 in dichloro(m)ethane. In comparison with the previously reported BF 3 ⋅Et 2 O-catalysed process, electron-deficient aryl-substituents can be applied reliably and thereby several restrictions could be lifted, and new types of substrates could be transformed successfully in hydrodeuterogenation as well as deuterohydrogenation transfer-hydrogenation reactions., (© 2021 The Authors. Published by Wiley-VCH GmbH.)

Pyrene derivatives play a prominent role in organic electronic devices, including field effect transistors, light emitting diodes, and solar cells. The flexibility in the desired properties has previously been achieved by variation of substituents at the periphery of the pyrene backbone. In contrast, the influence of the topology of the central π-electron system on the relevant properties such as the band gap or the fluorescence behavior has not yet been addressed. In this work, pyrene is compared with its structural isomer azupyrene, which has a π-electron system with non-alternant topology. Using photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy, and other methods, it is shown that the electronic band gap of azupyrene is by 0.72 eV smaller than that of pyrene. The difference of the optical band gaps is even larger with 1.09 eV, as determined by ultraviolet-visible absorption spectroscopy. The non-alternant nature of azupyrene is also associated with a more localized charge distribution. Further insight is provided by density functional theory (DFT) calculations of the molecular properties and ab initio coupled cluster calculations of the optical transitions. The concept of aromaticity is used to interpret the major topology-related differences., (© 2021 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

The generation of bromine by oxidation of bromide anions at the anode and reduction of molecular oxygen at the cathode to hydrogen peroxide resulted in the overall formation of two molecules of Br 2 (=four electron oxidation) by passing just two electrons through the solution. The bromine was used for the bromination of alkenes and thereby a linear paired electrolysis was attained which resulted in current efficencies of up to 200 %. Also, the diiodination of cyclohexene as well as the electrophilic aromatic bromination of an electron-rich arene were realised both in 168 % current efficiencies., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

This review will outline the recent advances in chemo-, regio-, and stereoselective (cross-) dimerization of terminal alkynes to generate 1,3-enynes using different types of iron and cobalt catalysts with altering oxidation states of the active species. In general, the used ligands have a crucial effect on the stereoselectivity of the reaction; e.g., bidentate phosphine ligands in cobalt catalysts can generate the E -configured head-to-head dimerization product, while tridentate phosphine ligands can generate either the Z -configured head-to-head dimerization product or the branched head-to-tail isomer. Furthermore, the hydroalkynylation of silyl-substituted acetylenes as donors to internal alkynes as acceptors will be discussed using cobalt and nickel catalysts., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Weber and Hilt.)

The synthesis of 1,3-oxazoles from symmetrical and unsymmetrical alkynes was realized by an iodonium cation-pool electrolysis of I 2 in acetonitrile with a well-defined water content. Mechanistic investigations suggest that the alkyne reacts with the acetonitrile-stabilized I + ions, followed by a Ritter-type reaction of the solvent to a nitrilium ion, which is then attacked by water. The ring closure to the 1,3-oxazoles released molecular iodine, which was visible by the naked eye. Also, some unsymmetrical internal alkynes were tested and a regioselective formation of a single isomer was determined by two-dimensional NMR experiments., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

A diastereoselective hydroalkynylation of terminal alkynes to form the head-to-head dimerization products by two different cobalt-phosphine catalyst system is reported. The use of the bidentate ligand dppp and additional triphenylphosphine led to the selective formation of the (E)-1,3-enynes (E:Z>99:1) in good to excellent yields, while the tridentate ligand TriPhos led to the corresponding (Z)-1,3-enynes in moderate to good yields with excellent stereoselectivities (up to E:Z=1:99). Both pre-catalysts are easy to handle, because of their stability under atmospheric conditions. The optimized reaction conditions were identified by the Design of Experiments (DoE) approach, which has not been used before in cobalt-catalysed reaction optimisation. DoE decreased the number of required reactions to a minimum., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The electrochemical, oxidative Umpolung reaction of silyl enol ethers utilizing simple iodide salts for the synthesis of α-amino ketones is described. The products were isolated in excellent yields of up to 100%, and various functionalized starting materials were accepted in an undivided electrochemical cell design. Moreover, a sensitivity assessment to ensure an improved reproducibility of the reaction and cyclic voltammetry experiments were performed to postulate a plausible reaction mechanism on their basis.

An electrochemical iodine-mediated transformation of enamino-esters for the synthesis of 2H-azirine-2-carboxylates is presented. In addition, a thermic conversion of azirines to 4-carboxy-oxazoles in quantitative yield without purification was described. Both classes 2H-azirines-2-carboxylates and the 4-carboxy-oxazoles are substructures in natural products and therefore are of considerable interest for synthetic and pharmaceutical chemists. The optimization was not performed in a conventional manner with a one-factor-at-a-time process but with a Design of Experiments (DoE) approach. Beside a broad substrate scope the reaction was also employed to a robustness screen, a sensitivity assessment, and complemented with mechanistic considerations from cyclic voltammetry experiments., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The cobalt-catalyzed hydrovinylation reaction and the Alder-ene reaction generate acyclic 1,4-dienes, which were investigated in the selenium dioxide oxidation to afford further functionalized dienes prone for follow-up reactions. The chemoselective allylic oxidation of ester-functionalized 1,4-dienes occurs at the most electron-rich double bond. The steric demand of the electron-rich, alkyl-substituted double bond determines the reaction pathway, whether the double bond transposition toward the conjugated 1,3-diene or the allylic oxidation is faster. As reaction products, 2,4-diene-6-ols or divinyl ketones were obtained.

Cyclic α-(ortho-iodophenyl)-β-oxoesters were converted in a ring-expanding transformation to furnish benzannulated cycloalkanone carboxylic esters. The reaction sequence started by electrochemical reduction of the iodoarene moiety. In a mechanistic rationale, the resulting carbanionic species was adding to the carbonyl group under formation of a strained, tricyclic benzocyclobutene intermediate, which underwent carbon-carbon bond cleavage and rearrangement of the carbon skeleton by retro-aldol reaction. The scope of the reaction sequence was investigated by converting cyclic oxoesters with different ring sizes yielding benzocycloheptanone, -nonanone and -decanone derivatives in moderate to good yields. Furthermore, acyclic starting materials and cyclic compounds carrying additional substituents on the iodophenyl ring were submitted to this reaction sequence. The starting materials for this transformation are straightforwardly obtained by conversion of β-oxoesters with phenyliodobis(trifluoroacetate)., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

A novel approach of electrolysis using alternating current was applied in the sulfur-sulfur bond metathesis of symmetrical disulfides towards unsymmetrical disulfides. As initially expected, a statistical distribution in disulfides was obtained. Furthermore, the influence of electrode polarisation by alternating current was investigated on a two-disulfide matrix. The highly dynamic nature of this chemistry resulted in the creation of dynamic disulfide libraries by expansion of the matrices, consisting of up to six symmetrical disulfides. In addition, mixing of matrices and stepwise expanding of a matrix by using alternating current electrolysis were realised., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The regioselective and regiodivergent addition of H-D to a variety of 1,1-diarylalkenes was realized utilizing selectively deuterated dihydroaromatic compounds, which were generated by cobalt catalysis. The reaction was initiated by catalytic amounts of BF 3 ·Et 2 O by abstracting hydride or deuteride ions from the respective dihydroaromatic reducing agents and led to a highly regioselective incorporation of deuterium and hydrogen at the desired positions of the starting material.

Various two-dimensional (2D) carbon allotropes with nonalternant topologies, such as pentaheptites and phagraphene, have been proposed. Predictions indicate that these metastable carbon polymorphs, which contain odd-numbered rings, possess unusual (opto)electronic properties. However, none of these materials has been achieved experimentally due to synthetic challenges. In this work, by using on-surface synthesis, nanoribbons of the nonalternant graphene allotropes, phagraphene and tetra-penta-hepta(TPH)-graphene, have been obtained by dehydrogenative C-C coupling of 2,6-polyazulene chains. These chains were formed in a preceding reaction step via on-surface Ullmann coupling of 2,6-dibromoazulene. Low-temperature scanning probe microscopies with CO-functionalized tips and density functional theory calculations have been used to elucidate their structural properties. The proposed synthesis of nonalternant carbon nanoribbons from the fusion of synthetic line-defects may pave the way for large-area preparation of novel 2D carbon allotropes.

The electrochemical carbon-carbon bond formation process between β-keto esters and silyl enol ethers was investigated utilizing manganese salts. The tricarbonyl compounds were generated in moderate to good yields under neutral conditions. Control experiments revealed that an electro-generated base at the cathode is important. Electroanalytical measurements with a Mn(TPA) complex suggested that the oxidation of the silyl enol ether is the first step in the oxidation process initiated by a corresponding Mn(IV) species.