Hydrophobic assembly of molecular catalysts at the gas-liquid-solid interface drives highly selective CO electromethanation.

Molecular catalysts offer tunable active and peripheral sites, rendering them ideal model systems to explore fundamental concepts in catalysis. However, hydrophobic designs are often regarded as detrimental for dissolution in aqueous electrolytes. Here we show that established cobalt terpyridine catalysts modified with hydrophobic perfluorinated alkyl side chains can assemble at the gas-liquid-solid interfaces on a gas diffusion electrode.

Accurate crystal structures and chemical properties from NoSpherA2.

The relationship between the structure and the properties of a drug or material is a key concept of chemistry. Knowledge of the three-dimensional structure is considered to be of such importance that almost every report of a new chemical compound is accompanied by an X-ray crystal structure - at least since the 1970s when diffraction equipment became widely available. Crystallographic software of that time was restricted to very limited computing power, and therefore drastic simplifications had to be made.

-Diels-Alder Reactions of In Situ-Generated Azoalkenes with Thioketones; Experimental and Theoretical Studies.

The -Diels-Alder reactions of in situ-generated azoalkenes with thioketones were shown to offer a straightforward method for an efficient and regioselective synthesis of scarcely known N-substituted 1,3,4-thiadiazine derivatives. The scope of the method was fairly broad, allowing the use of a series of aryl-, ferrocenyl-, and alkyl-substituted thioketones. However, in the case of N-tosyl-substituted cycloadducts derived from 1-thioxo-2,2,4,4-tetramethylcyclobutan-3-one and the structurally analogous 1,3-dithione, a more complicated pathway was observed.

Substitution Pattern-Controlled Fluorescence Lifetimes of Fluoranthene Dyes.

The absorption and emission properties of organic dyes are generally tuned by altering the substitution pattern. However, tuning the fluorescence lifetimes over a range of several 10 ns while barely affecting the spectral features and maintaining a moderate fluorescence quantum yield is challenging. Such properties are required for lifetime multiplexing and barcoding applications.

Pyridyl-Functionalized 1-Phosphabarrelene: Synthesis, Coordination Chemistry and Photochemical di-π-Methane Rearrangement.

The [4+2] cycloaddition of 2-(2'-pyridyl)-4,6-diphenyl-λ -phosphinine with the highly reactive dienophile hexafluoro-2-butyne has been studied and the first pyridyl-functionalized 1-phosphabarrelene was obtained and structurally characterized. Although monodentate CF -1-phosphabarrelenes show only a poor coordination ability, the chelating nature of the novel P,N-hybrid ligand gives access to various transition-metal complexes. Upon irradiation with UV light, the pyridyl-functionalized 1-phosphabarrelene undergoes a rather selective di-π-methane rearrangement in the coordination sphere of the metal center, leading to the formation of a complex based on a hitherto unknown pyridyl-functionalized 5-phosphasemibullvalene derivative.

Thyrotropin Receptor: Allosteric Modulators Illuminate Intramolecular Signaling Mechanisms at the Interface of Ecto- and Transmembrane Domain.

The large TSH-bound ectodomain of the thyrotropin receptor (TSHR) activates the transmembrane domain (TMD) indirectly via an internal agonist (IA). The ectodomain/TMD interface consists of a converging helix, a Cys-Cys-bridge-linked IA, and extracellular loops (ECL). To investigate the intramolecular course of molecular activation, especially details of the indirect activation, we narrowed down allosteric inhibition sites of negative allosteric modulator (NAM) by mutagenesis, homology modeling, and competition studies with positive allosteric modulator (PAM).

Naphthocage: A Flexible yet Extremely Strong Binder for Singly Charged Organic Cations.

We report a quite flexible naphthol-based cage (so-called "naphthocage") which adopts a self-inclusion conformation in its free state and is able to bind singly charged organic cations extremely strongly ( K > 10 M). Ion-selective electrodes prepared with this naphthocage show a super-Nernstian response to acetylcholine. In addition, the highly stable complex (10 M) between ferrocenium and the naphthocage can be switched electrochemically, which lays a basis for its application in stimuli-responsive materials.

Dienamine-Induced Divinylcyclopropane-Cycloheptadiene Rearrangements.

Sigmatropic rearrangements constitute an important group of pericyclic reactions. In contrast to cycloaddition reactions, examples of catalytic variants of electrocyclic reactions and sigmatropic rearrangements are still scarce in the chemical literature. Herein, we report the first organocatalytic Cope rearrangement of in situ-generated divinylcyclopropanes.

Microwave-Assisted Synthesis of Mono- and Disubstituted 4-Hydroxyacetophenone Derivatives via Mannich Reaction: Synthesis, XRD and HS-Analysis.

An efficient microwave-assisted one-step synthetic route toward Mannich bases is developed from 4-hydroxyacetophenone and different secondary amines in quantitative yields, via a regioselective substitution reaction. The reaction takes a short time and is non-catalyzed and reproducible on a gram scale. The environmentally benign methodology provides a novel alternative, to the conventional methodologies, for the synthesis of mono- and disubstituted Mannich bases of 4-hydroxyacetophenone.

Corannulenes with Electron-Withdrawing Substituents: Synthetic Approaches and Resulting Structural and Electronic Properties.

Corannulene is a multifaceted polyaromatic compound. It has many interesting properties; for example, it has a bowl-shaped molecular structure that, in addition, undergoes a dynamic inversion process. It has attracted much attention within the last decades.

Tuning the Electron Affinity and Stacking Properties of Corannulene by Introduction of Fluorinated Thioethers.

Trifluoromethylthio-substituted corannulene can be easily synthesized in good yield by the reaction of iodocorannulene with CuSCF . Oxidation with meta-chloroperbenzoic acid (mCPBA) yields the corresponding sulfonyl compound which exhibits the largest anodic shift of the redox potential caused by a single substituent. Similarly, four SCF , SC F and SeC F substituents are introduced in the 1,2,5,6-positions of corannulene starting with 1,2,5,6-tetraiodo- or 1,2,5,6-tetrabromocorannulene, respectively.

Synthesis of Enantioenriched Bromohydrins via Divergent Reactions of Racemic Intermediates from Anchimeric Oxygen Borrowing.

We report a chiral phosphoric acid catalyzed bromocyclization/regiodivergent reaction of racemic intermediates sequence, which is enabled by anchimeric oxygen borrowing. Different types of alkenes are applicable, and both enantiomers of the bromohydrin products were obtained in generally excellent yields and enantioselectivities. In addition, an example of enantioconvergent synthesis from the two isomeric products is presented.

Gallium Hydrides and O/N-Donors as Tunable Systems in C-F Bond Activation.

The gallium hydrides (iBu) GaH (1 a), LiGaH (1 b) and Me N⋅GaH (1 c) hydrodefluorinate vinylic and aromatic C-F bonds when O and N donor molecules are present. 1 b exhibits the highest reactivity. Quantitative conversion to the hydrodefluorination (HDF) products could be observed for hexafluoropropene and 1,1,3,3,3-pentafluoropropene, 94 % conversion of pentafluoropyridine and 49 % of octafluorotoluene.

Mechanistic Studies on the Organocatalytic α-Chlorination of Aldehydes: The Role and Nature of Off-Cycle Intermediates.

Herein we report the isolation and characterization of aminal intermediates in the organocatalytic α-chlorination of aldehydes. These species are stable covalent ternary adducts of the substrate, the catalyst and the chlorinating reagent. NMR-assisted kinetic studies and isotopic labeling experiments with the isolated intermediate did not support its involvement in downstream stereoselective processes as proposed by Blackmond.

To Anion-π or not to Anion-π: The Case of Anion-Binding to Divalent Fluorinated Pyridines in the Gas Phase.

A series of mono- and divalent fluorinated pyridine derivatives is investigated by electrospray ionization (tandem) mass spectrometry and quantum chemical calculations with respect to their capability to bind anions in the gas phase. The pyridine derivatives differ not only in valency, but also with regard to the degree of fluorination of the pyridine rings, the positions of the fluorine atoms, the rigidity of the spacers connecting the two pyridines in the divalent compounds, and the relative configuration. While the monovalent compounds did not form anion complexes, the divalent analogues exhibit anion binding even to weakly coordinating anions such as tetrafluoroborate.

Synthesis of (+)-Vitepyrroloid A and (+)-Vitepyrroloid B by Late-Stage Ni-Catalyzed C(sp2)-C(sp3) Cross-Electrophile Coupling.

A concise and scalable five-step synthesis of vitepyrroloids A and B, two cytotoxic labdane diterpenoid alkaloids from Vitex trifolia, is reported. The presented approach features a Ni-catalyzed cross-electrophile coupling between a (+)-sclareolide-derived alkyl iodide and 3-bromo-2-cyanopyrrole.

Selective Synthesis of Perfluoroalkylated Corannulenes and Investigation of their Structural, Dynamic and Electrochemical Behavior.

Herein we report general methods allowing the synthesis of various perfluoroalkylated corannulenes with a specific substitution pattern. Variable temperature NMR spectroscopic investigations revealed dynamic behavior which was analyzed by line shape analysis. The activation parameters of these dynamic processes were determined.

Organocatalytic C-F Bond Activation with Alanes.

Hydrodefluorination reactions (HDF) of per- and polyfluorinated olefins and arenes by cheap aluminum alkyl hydrides in non-coordinating solvents can be catalyzed by O and N donors. TONs with respect to the organocatalysts of up to 87 have been observed. Depending on substrate and concentration, high selectivities can be achieved.

Synthesis of Thelepamide via Catalyst-Controlled 1,4-Addition of Cysteine Derivatives and Structure Revision of Thelepamide.

The first enantioselective total synthesis and structural reassignment of (-)-thelepamide, a cytotoxic tetraketide-amino acid from the marine worm Thelepus crispus, is reported. A convergent approach provides access to all thelepamide diastereomers in six steps from four simple building blocks. Key features of the synthesis include the application of Melchiorre's organocatalytic thia-Michael reaction and a sonication-assisted assembly of an unprecedented N,O-acetal-hemiacetal moiety.

Synthesis and Structure Revision of Dichrocephones A and B.

Herein, we report the first enantioselective synthesis of dichrocephones A and B, which are cytotoxic triquinane sesquiterpenes with a dense array of stereogenic centers within a strained polycyclic environment. Key features include the application of a catalytic asymmetric Wittig reaction, followed by stereoselective functionalization of the propellane core into a pentacyclic intermediate. Double reductive ring cleavage yielded the proposed structure of dichrocephone A.

Closing the Gap: Structural Evidence for the Missing Hexabromide Dianion [Br ].

The formation and experimental characterization of the first hexabromide dianion is presented. This dianion fills the last remaining gap in the series of polybromides from the tribromide [Br ] to the undecabromide [Br ] . The experimental results are compared to quantum-chemical calculations.

Palladium-Catalyzed Directed Halogenation of Bipyridine N-Oxides.

The palladium-catalyzed directed C-H halogenation of bipyridine N-oxides was investigated. Using NCS or NBS (N-chloro- or N-bromosuccinimide) and 5 mol % Pd(OAc) in chlorobenzene (0.10 molar) at 110 °C, pyridine-directed functionalization took place and 3-chloro- or 3-bromobipyridine N-oxides were obtained in high yields.

Direct Experimental Evidence for Halogen-Aryl π Interactions in Solution from Molecular Torsion Balances.

We dissected halogen-aryl π interactions experimentally using a bicyclic N-arylimide based molecular torsion balances system, which is based on the influence of the non-bonded interaction on the equilibria between folded and unfolded states. Through comparison of balances modulated by higher halogens with fluorine balances, we determined the magnitude of the halogen-aryl π interactions in our unimolecular systems to be larger than -5.0 kJ mol , which is comparable with the magnitude estimated in the biomolecular systems.