Beyond Kolbe and Hofer–Moest: Electrochemical Synthesis of Carboxylic Anhydrides from Carboxylic Acids

Herein we report a conceptually new non‐decarboxylative electrolysis of carboxylic acids to obtain their corresponding anhydrides as highly valuable reagents in organic synthesis. All carbon atoms of the starting material are preserved in the product in an overall redox‐neutral reaction. In a broad substrate scope of carboxylic acids the anhydrides are generated with high selectivity, which demonstrates the versatility of the developed method. Beneficially, no dehydrating reagents are required in comparison to conventional methods and the synthesis is based on uncritical starting materials using graphite and stainless steel as very inexpensive and eco‐friendly electrode materials.     

Alkyliodines in High Oxidation State: Enhanced Synthetic Possibilities and Accelerated Catalyst Turn-Over

In contrast to aryliodine(III) compounds, which have matured into a particularly attractive class of oxidants in modern synthesis, the synthetic potential of related alkyliodine(III) derivatives has remained widely underestimated. This is surprising since several unique synthetic possibilities arise directly from the low stability of their central carbon–iodine bond. In this respect, these high-oxidation-state iodine compounds resemble environmentally benign variants of the prominent metal counterparts such as those derived from palladium, nickel and copper. This Concept article summarizes the general reactivity trends in alkyliodine(III) chemistry and discusses selected examples of their strategic use as highly reactive, transient species in organic synthesis and homogeneous catalysis.     

Iodine Catalysis for C(sp3)–H Fluorination with a Nucleophilic Fluorine Source

Iodine catalysis was developed for aliphatic fluorination through light-promoted homolytic C−H bond cleavage. The intermediary formation of amidyl radicals enables selective C−H functionalization via carbon-centered radicals. For the subsequent C−F bond formation, previous methods have typically been limited by a requirement for electrophilic fluorine reagents. We here demonstrate that the intermediary instalment of a carbon–iodine bond sets the stage for an umpolung, thereby establishing an unprecedented nucleophilic fluorination pathway.     

Pyridinic Nanographenes by Novel Precursor Design

In this work we present the solution-synthesis of pyridine analogues to hexa-peri-hexabenzocoronene (HBC)—which might be called superpyridines—via a novel precursor design. The key step in our strategy was the pre-formation of the C−C bonds between the 3/3’ positions of the pyridine and the adjacent phenyl rings—bonds that are otherwise unreactive and difficult to close under Scholl-conditions. Apart from the synthesis of the parent compound we show that classical pyridine chemistry, namely oxidation, N-alkylation and metal-coordination is applicable to the π-extended analogue. Furthermore, we present basic physical chemical characterizations of the newly synthesized molecules. With this novel synthetic strategy, we hope to unlock the pyridine chemistry of nanographenes.     

Synthetic and Structural Study of peri-Substituted Phosphine-Arsines

A series of phosphorus-arsenic peri-substituted acenaphthene species have been isolated and fully characterised, including single crystal X-ray diffraction. Reactions of EBr₃ (E = P, As) with iPr₂PAcenapLi (Acenap = acenaphthene-5,6-diyl) afforded the thermally stable peri-substitution supported donor–acceptor complexes, iPr₂PAcenapEBr₂ 3 and 4. Both complexes show a strong P→E dative interaction, as observed by X-ray crystallography and ³¹P NMR spectroscopy. DFT calculations indicated the unusual As∙∙∙As contact (3.50 Å) observed in the solid state structure of 4 results from dispersion forces rather than metallic interactions. Incorporation of the excess AsBr₃ in the crystal structure of 3 promotes the formation of the ion separated species [iPr₂PAcenapAsBr]⁺Br⁻ 5. A decomposition product 6 containing the rare [As₆Br₈]^2– heterocubane dianion was isolated and characterised crystallographically. The reaction between iPr₂PAcenapLi and EtAsI₂ afforded tertiary arsine (BrAcenap)₂AsEt 7, which was subsequently lithiated and reacted with PhPCl₂ and Ph₂PCl to afford cyclic PhP(Acenap)₂AsEt 8 and acyclic EtAs(AcenapPPh₂)₂ 9.     

Thermal and dielectric properties of oriented liquid crystalline polysiloxane doped with azo‐dye

Investigations of dielectric relaxation and thermal properties of mixtures composed of liquid crystalline side‐chain polysiloxane and low molecular mass azo‐dye have been carried out. The dyes have been chosen to solublize well in the polymer matrix at concentrations up to 0.08 mol fraction. The dielectric relaxation experiments have shown the presence of separate processes attributed to reorientational motions of mesogenic side groups and dye molecules. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 369–377, 1999     

On the Beavers–Joseph Interface Condition for Non-parallel Coupled Channel Flow over a Porous Structure at High Reynolds Numbers

Transport in Porous Media - Stereolithographic 3D printing is of paramount interest for researchers studying porous media because it is possible to use resins with a wide range of physical and...