• Cover image
    Issue
    Volume 52, Issue 48
    12455-12744
    November 25, 2013

Cover Pictures

Free Access

Cover Picture: Stereoselective Synthesis of Vinyl Triflones and Heteroaryl Triflones through Anionic O→Cvinyl and N→Cvinyl Trifluoromethanesulfonyl Migration Reactions (Angew. Chem. Int. Ed. 48/2013)

  • First Published: 04 November 2013
Six transformations in one pot allow the stereoselective synthesis of various di‐ and trisubstituted vinyl triflones, and several heteroaryl triflones from gem‐dibromovinyl substrates. In their Communication on page 12628 ff., N. Shibata et al. explore the key steps of this procedure. The cover picture shows a “Japanese‐style painting” by Mami Shibata (a Tama Art University student), named “Kaze” (“breeze” in English). The six transformations in one pot proceed very smoothly, like birds in a breeze.
Free Access

Inside Cover: Double‐Decker‐Type Dinuclear Nickel Catalyst for Olefin Polymerization: Efficient Incorporation of Functional Co‐monomers (Angew. Chem. Int. Ed. 48/2013)
  • First Published: 07 November 2013
A dinuclear nickel complex with a new double‐decker structure, and its catalytic properties are described by D. Takeuchi, K. Osakada, et al. in their Communication on page 12536 ff. The complex promotes the copolymerization of ethylene with bifunctional monomers such as terminal dienes and unsaturated carboxylic esters. The close positioning of the nickel centers supported by the rigid macrocyclic ligand enhances the coordination of the bifunctional monomers and stabilize the growing polymer end.
Free Access

Inside Back Cover: Identification of the HcgB Enzyme in [Fe]‐Hydrogenase‐Cofactor Biosynthesis (Angew. Chem. Int. Ed. 48/2013)
  • First Published: 12 November 2013
One reaction step of the biosynthesis of [Fe]‐hydrogenase‐cofactor is elucidated by S. Shima et al. in their Communication on page 12555 ff. A structural genomics approach, in combination with model reactions and thorough product analysis by X‐ray crystallography of the protein–product complexes, revealed that HcgB is the enzyme that catalyzes guanylylpyridinol formation from a 2,4‐dihydroxypyridine derivative and guanosine triphosphate.
Free Access

Back Cover: S2 Fluorescence Dynamics of meso‐Aryl‐Substituted Subporphyrins (Angew. Chem. Int. Ed. 48/2013)

  • First Published: 18 November 2013
The S2 fluorescence and the photophysical behavior of the higher excited states of subporphyrins are described by A. Osuka, D. Kim, et al. in their Communication on page 12632 ff. The S2 fluorescence of subporphyrins had not been described to date. Similarly, the Big Dipper is recognized as an asterism of seven stars. However, the eighth star, Alcor, definitely exists, although its close proximity to the star Mizar renders it more difficult to resolve.

Graphical Abstract

News

Author Profile

Marina A. Petrukhina

  • First Published: 05 July 2013
“My favorite saying is “yes, we can!” I can never resist travelling to new places …︁” This and more about Marina A. Petrukhina can be found on page 12480.

News

Obituary

Book Review

Bioinspiration and Biomimicry in Chemistry. Reverse‐Engineering Nature. Edited by Gerhard F. Swiegers.
  • First Published: 08 November 2013
John Wiley and Sons, Hoboken, 2012. 508 pp., hardcover, € 122.00.—ISBN 978‐0470566671

Highlights

Cellular Transport

Intracellular Transport Mechanisms: Nobel Prize for Medicine 2013
  • First Published: 08 November 2013
How are biomolecules transported between cellular compartments? James E. Rothman, Randy W. Schekman, and Thomas C. Südhof made seminal contributions to answering this question with their research into the molecular mechanism of intracellular vesicle transport. For their achievements, the researchers were awarded the Nobel Prize in Physiology or Medicine on October 7, 2013.

Computational Chemistry

Solving Chemical Problems with a Mixture of Quantum‐Mechanical and Molecular Mechanics Calculations: Nobel Prize in Chemistry 2013
  • First Published: 07 November 2013
The significance of computer simulations in such varied fields as chemistry, biophysics, structural biology, and materials science is emphasized by the award of the Nobel Prize in Chemistry 2013 to three of the most important pioneers of computational chemistry. Computer simulations are widely used today to interpret experimental results, to test hypotheses, and as inspiration for experiments.

Essay

Homogenous Catalysis

Oligomerization of Ethylene to α‐Olefins: Discovery and Development of the Shell Higher Olefin Process (SHOP)
  • First Published: 15 October 2013

Luck, talent, and hard work: Currently, over a million tons of α‐olefins are manufactured per annum using the Shell Higher Olefin Process (SHOP). The discovery of the process was the result of correct model conceptions and lucky coincidence. W. Keim, one of the main participants in the development of SHOP, gives a personal account of the events.

Minireview

Nucleic Acid Modifications

Artificial Genetic Sets Composed of Size‐Expanded Base Pairs
  • First Published: 07 November 2013
Expanded horizons: Stretched nucleobases, which are larger than the bases of the natural Watson–Crick architecture, lead to the development of artificial genetic sets. These systems have properties that are useful for understanding fundamental biochemical questions as well as for the development of new biotechnological, biomedical, and nanostructural tools and methods.

Review

Redox‐Active Ligands

Complexes with Nitrogen‐Centered Radical Ligands: Classification, Spectroscopic Features, Reactivity, and Catalytic Applications
  • First Published: 08 November 2013
Radical character is found in many complexes with nitrogen ligands, as shown by studies of their electronic structure, spectroscopic features, and (catalytic) reactivity. The Review focuses on the reactivity of detectable aminyl ([M(.NR2)]), nitrene/imidyl ([M(.NR)]), and nitridyl radical complexes ([M(.N)]), and their application in the (catalytic) synthesis of nitrogen‐containing organic molecules such as aziridines and amines.

Communications

Molecular Electronics

Growth of Ultrathin Organic Semiconductor Microstripes with Thickness Control in the Monolayer Precision
  • First Published: 31 October 2013
Organic semiconductors: Growth of ultrathin (<15 nm), continuous, and microstructured organic semiconductor (OSC) films at monolayer precision is important for organic electronics and a challenging task. Uniform monolayer to hexalayer (ca. 1.6–12 nm; see picture) dendritic OSC microstripes at monolayer precision are grown by a dip‐coating process.

Copolymerization

Double‐Decker‐Type Dinuclear Nickel Catalyst for Olefin Polymerization: Efficient Incorporation of Functional Co‐monomers
  • First Published: 07 November 2013
A dinuclear Ni complex with a double‐decker structure (see scheme) and a short Ni–Ni distance promotes the copolymerization of ethylene with functional monomers. Matching of the Ni–Ni distance with the co‐monomer structure resulted in polymers containing a high density of the co‐monomer unit.

Lithium‐Ion Batteries

A Lithium‐Rich Compound Li7Mn(BO3)3 Containing Mn2+ in Tetrahedral Coordination: A Cathode Candidate for Lithium‐Ion Batteries

  • First Published: 14 October 2013
Filled to capacity: Li7Mn(BO3)3 is lithium‐rich and fulfills the prerequisites for a high‐capacity cathode for Li‐ion batteries. It contains a framework of MnO4 tetrahedra (pink) and BO33− ions (B green, O red, Li black). By employing a nano‐composite to enhance electronic conductivity, a first charge capacity of 280 mAh g−1, and a specific energy of 1135 W h kg−1 are obtained within 4.7–1.7 V at a rate of 10 mA g−1.

Contact Electrification

Water–Solid Surface Contact Electrification and its Use for Harvesting Liquid‐Wave Energy
  • First Published: 07 October 2013
Electrical wave mechanics: A newly designed triboelectric nanogenerator is based on the contact electrification between a patterned polydimethylsiloxane pyramid array and water. Cost‐effective and simple, the prototype triboelectric nanogenerator shows the potential to harvest energy from liquid waves and serve as chemical and temperature sensors.

Self‐Assembly

A Supramolecular Gel from a Quadruple Zwitterion that Responds to Both Acid and Base
  • First Published: 02 October 2013
Four arms: A quadruple zwitterion based on a pentaerythritol core forms thermoreversible gels in DMSO driven by the formation of ion‐paired dimers between the zwitterionic units. Furthermore, it exhibits reversible gel–sol transitions in response to both acid and base.

Cofactor Biosynthesis

Identification of the HcgB Enzyme in [Fe]‐Hydrogenase‐Cofactor Biosynthesis
  • First Published: 07 November 2013
[Fe]‐Hydrogenase requires the iron guanylylpyridinol (FeGP) cofactor for activity. The function of HcgB, an enzyme in the biosynthesis of the FeGP cofactor, was predicted by structural genomics and confirmed by model reactions and various analytical methods: HcgB catalyzes the terminal guanylyltransferase reaction for the formation of guanylylpyridinol. GMP=guanosine monophosphate.

Synthetic Methods

Open Access

Selective Reduction of Barbituric Acids Using SmI2/H2O: Synthesis, Reactivity, and Structural Analysis of Tetrahedral Adducts

  • First Published: 09 October 2013
Making a mark: Since the 1864 landmark discovery by Adolf von Baeyer, barbituric acids have played a prominent role in organic synthesis. Herein, the first chemoselective monoreduction of barbituric acids to the corresponding hemiaminals is described. The method delivers mono‐ and bicyclic hemiaminal products by a general single‐electron‐transfer polarity reversal mechanism.

Helical Structures

Structural Characterization of α/β‐Peptides having Alternating Residues: X‐ray Structures of the 11/9‐Helix from Crystals of Racemic Mixtures
  • First Published: 02 October 2013
Twisted (crystal)sisters: The structures of the α/β‐peptide 11/9‐helix were determined by single‐crystal X‐ray crystallography. The racemic compounds adopt centrosymmetric crystal packing, and display fully folded 11/9‐helical conformations. The helical parameters of the 11/9‐helix are analogous to those of the 310‐helix, despite different hydrogen‐bonding types.

Pigment Discoloration

Formation of Metallic Mercury During Photodegradation/Photodarkening of α‐HgS: Electrochemical Evidence
  • First Published: 02 October 2013
The red pigment α‐HgS tends to blacken in the presence of light and chloride ions. Hypotheses exist for the decomposition and discoloration, including formation of β‐HgS (black) or of metallic mercury, but these have not been detected on naturally or synthetically degraded HgS paint. Electrochemical experiments now demonstrate the formation of metallic mercury in the presence of light and chloride ions.

Imaging Agents

PEGylation and Zwitterionization: Pros and Cons in the Renal Clearance and Tumor Targeting of Near‐IR‐Emitting Gold Nanoparticles
  • First Published: 09 October 2013
Got it PEGged: PEGylation and zwitterionization have distinct effects on the pharmacokinetic and tumor‐targeting properties of luminescent gold nanoparticles (AuNPs), although both strategies lead to effective renal clearance. High tumor‐targeting efficiency and specificity were obtained with PEGylated AuNPs, whereas rapid tumor detection was more readily achieved with zwitterionic AuNPs. HD=hydrodynamic diameter, GS=glutathione.

Electrocatalysis

Biomimetic Synthesis of an Ultrathin Platinum Nanowire Network with a High Twin Density for Enhanced Electrocatalytic Activity and Durability
  • First Published: 02 October 2013
Structure‐enhanced catalytic activity: An ultrathin platinum multiple‐twinned nanowire network is shown to be an efficient electrocatalyst (see picture). This material has a higher electrochemical surface area and exhibits a much improved activity toward both the oxygen reduction reaction and the methanol oxidation reaction relative to commercial Pt/C catalysts.

Liquid Coordination Complexes

Liquid Coordination Complexes Formed by the Heterolytic Cleavage of Metal Halides
  • First Published: 11 October 2013
Confused complexes: Reaction of a range of donor molecules with AlCl3 or GaCl3, gives mobile liquids with very high metal contents. They contain statistically distributed mixtures of anionic, cationic, and neutral complexes in equilibrium. These liquid coordination complexes (LCCs), have high conductivity, tunable Lewis acidity, and low vapor pressure.

Ligand–Protein Complexes

Dissociation Kinetics of a Binary Complex in Solution by Protein Displacement
  • First Published: 07 October 2013
Kinetics determined by NMR: Whereas most measurements of kinetic parameters of a ligand–protein complex use displacement of the ligand, protein displacement can give accurate off‐rates in solution (see picture). Analytical and simulation results are given for the apparent off‐rate obtained by protein displacement.

Bioconjugation

Rapid, Stable, Chemoselective Labeling of Thiols with Julia–Kocieński‐like Reagents: A Serum‐Stable Alternative to Maleimide‐Based Protein Conjugation
  • First Published: 02 October 2013
Exquisite chemoselectivity for cysteine has been found for methylsulfonylphenyloxadiazole compounds under various buffer conditions. Furthermore, the resulting protein conjugates have superior stability to cysteine–maleimide conjugates in human plasma (HSA=human serum albumin, MBP‐C‐HA=maltose‐binding protein). This new thiol‐click reaction offers a new approach to generate stable protein conjugates and Pegylated proteins.

G‐Quadruplexes

Real‐Time Optical Detection of Stabilized Artificial G‐Quadruplexes Under Confined Conditions
  • First Published: 02 October 2013
The color of self‐assembly: Porous silicon (pSi) can be used as a scaffolding matrix to stabilize G‐quadruplexes under confined conditions. When G‐quadruplexes were infused into the pores, a change in the film color was observed, so that confinement and stabilization of the G‐quadruplexes can be easily observed.

Rotational Dynamics

Modulating the Rotation of a Molecular Rotor through Hydrogen‐Bonding Interactions between the Rotator and Stator
  • First Published: 02 October 2013
Two molecular rotors were synthesized (see picture). An investigation of the rotator rotation based on the imaginary parts of the complex dielectric constant (ε′′) for each molecular rotor at various frequencies and temperatures revealed that the rotation of the mono‐component molecular rotor could be modulated through hydrogen‐bonding interactions between the rotator and the stator.

Mesoporous Materials

Crystallization of Tungsten Trioxide Having Small Mesopores: Highly Efficient Photoanode for Visible‐Light‐Driven Water Oxidation
  • First Published: 07 October 2013
Small mesopores are more efficient: A mesoprous oxide semiconductor (tungsten trioxide) having small mesopores was crystallized at high temperature (550 °C) by a simple one‐step procedure. The highly crystalline mesoporous WO3 has an extremely high surface area which improves the visible‐light‐driven photoelectrochemical performance of water oxidation (see picture) relative to WO3 having interparticle mesopores.

Fullerides

Counterintuitive Anisotropy of Electron Transport Properties in KC60(THF)5⋅2 THF Fulleride

  • First Published: 02 October 2013
Spin and charge transport: The electronic and structural properties obtained from KC60(THF)5⋅2 THF single crystals are reported (see picture). An important finding is the presence of one‐dimensional electric conductivity and the observation of counterintuitive anisotropy for electron transport.

Vapor Sensing

Three‐Dimensional Solvent‐Vapor Map Generated by Supramolecular Metal‐Complex Entrapment
  • First Published: 02 October 2013
Whodunit? [Re(phen)(CO)3Cl] (phen=1,10‐phenanthroline) has been entrapped within a faujasite zeolite. For this material, changes in the photoluminescence intensity, wavelength, and lifetime are observed upon exposure to solvent vapors. Every solvent vapor produces a unique combination of photophysical parameters that can be used as a fingerprint of the vapor.

Asymmetric Catalysis

Organocatalytic Asymmetric Conjugate Addition of Aldehydes to Nitroolefins: Identification of Catalytic Intermediates and the Stereoselectivity‐Determining Step by ESI‐MS
  • First Published: 02 October 2013
Looking back: The asymmetric organocatalytic 1,4‐addition of aldehydes to nitroolefins was studied by ESI‐MS. Analysis of the back reaction starting from quasienantiomeric mass‐labeled 1,4‐adducts (see scheme) provided conclusive evidence for an enamine rather than an enol mechanism, and allowed identification of the enantioselectivity‐determining step.

Synthetic Methods

3‐Methyl‐4‐oxa‐5‐azahomoadamantane: Alkoxyamine‐Type Organocatalyst for Alcohol Oxidation
  • First Published: 11 October 2013
Strong, silent type: A novel alkoxyamine‐type organocatalyst has been discovered for alcohol oxidation (see scheme). The alkoxyamine exhibits a high catalytic activity for the oxidation of alcohols to afford the corresponding carbonyl compounds in high yield by oxidative transformation into an oxoammonium ion, which is proposed to serve as an active species.

Stereoselective Synthesis of Vinyl Triflones and Heteroaryl Triflones through Anionic O→Cvinyl and N→Cvinyl Trifluoromethanesulfonyl Migration Reactions

  • First Published: 15 October 2013
Six transformations, one pot: Various di‐ and trisubstituted vinyl triflones, as well as several heteroaryl triflones, were stereoselectively synthesized from easily accessible gem‐dibromovinyl substrates (see scheme, Boc=tert‐butoxycarbonyl). The highlights of this synthetic method lie in the remote O→Cvinyl or N→Cvinyl triflyl migrations and the one‐pot, three‐step protocol.

Subporphyrins

S2 Fluorescence Dynamics of meso‐Aryl‐Substituted Subporphyrins

  • First Published: 25 October 2013
S2 Fluorescence: Subporphyrins are intriguing compounds, but the behavior of their higher excited states has not been studied thus far. The S2 fluorescence of subporphyrins has now been investigated; internal conversion from the S2 to the S1 state was revealed to occur within approximately 300 fs. The two transition dipole moments of the degenerate S2 states are orthogonally oriented despite the C3 symmetry of the subporphyrin.

Photochemistry

Concerted Two‐Electron Transfer and High Selectivity of TiO2 in Photocatalyzed Deoxygenation of Epoxides

  • First Published: 07 October 2013
No two ways about it: In the photocatalytic deoxygenation of epoxides, the TiO2 particle concertedly transfers two stored electrons to generate a carbanion intermediate, which dissociates to the alkene product. This pathway ensures the higher alkene and stereoselectivity of the photocatalytic deoxygenation than those involving a single‐electron transfer.

Asymmetric Catalysis

Enantioselective Copper‐Catalyzed [3+3] Cycloaddition of Azomethine Ylides with Azomethine Imines
  • First Published: 02 October 2013
The more dipoles, the merrier: An asymmetric [3+3] cycloaddition of azomethine ylides derived from imines 1 with azomethine imines 2 in the presence of a chiral ferrocenylphosphine–copper catalyst afforded highly functionalized heterocyclic products 3 in high yield with excellent enantio‐ and diastereoselectivity (see scheme; DBU=1,8‐diazabicyclo[5.4.0]undec‐7‐ene). The 1,3‐dipolar reaction partners can be readily prepared from aldehydes.

Uranium Siloxides

Controlled Thermolysis of Uranium (Alkoxy)siloxy Complexes: A Route to Polymetallic Complexes of Low‐Valent Uranium
  • First Published: 09 October 2013
Decomposition into higher species: Intramolecular UIII‐mediated homolytic CO bond cleavage in UIII (alkoxy)siloxy complexes at low temperature and subsequent reduction with KC8 led to unprecedented polymetallic complexes containing siloxy, silanediolate, and silanetriolate ligands (see example: U green, Si yellow, K blue, O red). Such compounds may be useful precursors to uranium ceramics relevant for catalysis and the storage of spent nuclear fuel.

Synthetic Methods

Bis(amino)cyclopropenylidenes as Organocatalysts for Acyl Anion and Extended Umpolung Reactions
  • First Published: 02 October 2013
Back to BACs: In the pursuit of novel carbene organocatalysts, bis(amino)cyclopropenylidenes (BACs) were explored as alternatives to N‐heterocyclic carbenes. They were effective in catalyzing the Stetter reaction, and displayed unique advantages over the commonly used thiazolylidenes and triazolylidenes. They also mediated extended umpolung reactions of enals. In addition, chiral analogues can be accessed readily for applications in enantioselective catalysis.

Enantioselective Functionalization of Radical Intermediates in Redox Catalysis: Copper‐Catalyzed Asymmetric Oxytrifluoromethylation of Alkenes
  • First Published: 16 October 2013
Something radical: An efficient enantioselective oxytrifluoromethylation of alkenes has been developed using a copper catalyst system. Mechanistic studies are consistent with a metal‐catalyzed redox radical addition mechanism in which a CO bond is formed by the copper‐mediated enantioselective trapping of a prochiral alkyl radical intermediate derived from the initial trifluoromethyl radical addition.

Hydrogen Storage

Immobilization of Aluminum Borohydride Hexammoniate in a Nanoporous Polymer Stabilizer for Enhanced Chemical Hydrogen Storage
  • First Published: 02 October 2013
Caught in a trap: The well‐distributed Al(BH4)3⋅6 NH3/PSDB (PSDB=poly(styrene‐co‐divinylbenzene)) nanocomposite was synthesized by the stabilization of volatile Al(BH4)3 within a porous polymer and subsequent treatment with ammonia. This material showed a hydrogen‐storage performance that was significantly improved over that of its bulk counterpart. Partial regeneration using hydrazine in ammonia is also described.

Asymmetric Catalysis

Highly Enantioselective Dearomatizing Formal [3+3] Cycloaddition Reactions of N‐Acyliminopyridinium Ylides with Electrophilic Enol Carbene Intermediates

  • First Published: 02 October 2013
Extrusion of dinitrogen from enol diazoacetates with a RhII catalyst generates metal enol carbenes. Subsequent vinylogous addition of these to N‐acyliminopyridinium ylides results in an effective formal [3+3] cycloaddition to give highly substituted 1,2,3,6‐tetrahydropyridazines in up to 98 % ee and high yield.

Heterocycle Synthesis

Palladium‐Catalyzed Synthesis of Benzofurans and Coumarins from Phenols and Olefins
  • First Published: 11 October 2013
Triple CH functionalization: Palladium‐catalyzed synthesis of benzofurans and coumarins by reacting phenols and unactivated olefins is described. The reaction comprises sequential CH functionalization and shows diverse functional group compatibility. Preliminary mechanistic studies shed light into the possible mechanisms.

Reductive Bond Cleavage

Selective Reductive Cleavage of Inert Aryl CO Bonds by an Iron Catalyst
  • First Published: 07 October 2013
Breaking point: An effective reductive cleavage of inert aryl CO bonds with an inexpensive iron catalyst has been developed. During this process, the reduction of the arene rings was not observed. This catalytic system also enabled the selective cleavage of the β‐O‐4 linkage of lignin model compounds under an atmosphere of hydrogen, thus offering an opportunity for the depolymerization of lignin.

Modular Synthesis

Open Access

Palladium‐Catalyzed Three‐Component Diaryl Sulfone Synthesis Exploiting the Sulfur Dioxide Surrogate DABSO
  • First Published: 02 October 2013
SO(2) efficient: A three‐component palladium‐catalyzed coupling of aryl lithium compounds; sulfur dioxide (provided by the easy‐to‐handle solid surrogate, DABSO); and aryl, heteroaryl, and alkenyl (pseudo)halides yields a diverse library of sulfones. An electron‐poor XantPhos‐type ligand suppresses aryl–aryl exchange and is key to obtaining high yields.

Free‐Radical Scavengers

Atypical Structural and π‐Electron Features of a Melanin Polymer That Lead to Superior Free‐Radical‐Scavenging Properties
  • First Published: 07 October 2013
The black we wear: Why nature selected 5,6‐dihydroxyindole‐2‐carboxylic acid (DHICA) to synthesize (photo)protective eumelanin pigments is an enigma. Synthetic DHICA eumelanin has now been shown to be a highly efficient free‐radical scavenger in the solid state, which is due to a conformationally interrupted π‐electron network associated with atypical optical, paramagnetic, and aggregation properties.

Mechanochemical Activation

An Orders‐of‐Magnitude Increase in the Rate of the Solid‐Catalyzed CO Oxidation by In Situ Ball Milling
  • First Published: 23 September 2013
Shaken, not stirred: CO oxidation was carried out continuously in a shaker ball mill. During milling, the reaction rate increases dramatically, but drops rapidly to zero when the mill is stopped. Compared to a conventional experiment in a plug‐flow reactor, the rate of a ball‐mill reaction catalyzed by Cr2O3 is three orders of magnitude higher at room temperature and one order of magnitude higher at 100°C.

Water Splitting

Hematite‐Based Water Splitting with Low Turn‐On Voltages
  • First Published: 07 October 2013
Power up: The photoelectrochemical performance of hematite in a water‐splitting device was improved significantly through surface modification with amorphous NiFeOx (see graph showing the large cathodic shift observed; FTO=fluorine‐doped tin oxide). The measured photovoltage increased from 0.24 to 0.61 V, which yielded a record‐low turn‐on potential of 0.62 V (versus the reversible hydrogen electrode, RHE).

Photochemistry

A Visible‐Light‐Mediated Synthesis of Carbazoles
  • First Published: 07 October 2013
The photosynthetic preparation of N‐aryl‐ and N‐alkyl‐bearing carbazoles utilizes continuous flow, visible light, and an in situ formed Cu‐based sensitizer (see picture). The method is mild and efficient, and allows the straightforward synthesis of a variety of carbazoles with different substituents, heterocycles, and complex carbon architectures.

Asymmetric Catalysis

Enantioselective Copper‐Catalyzed Conjugate Addition of Trimethylaluminum to β,γ‐Unsaturated α‐Ketoamides: Efficient Access to γ‐Methyl‐Substituted Carbonyl Compounds
  • First Published: 11 October 2013
Picture perfect: By using the reagent trimethylaluminium and β,γ‐unsaturated α‐ketoamides, 1,4‐adducts were obtained with perfect 1,4‐regioselectivity and good to excellent yields and ee values. The potential synthetic utility of the methodology was highlighted by preparation of γ‐methyl‐substituted carbonyls, key synthons to many natural products. binap=2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl, TC=thiophene carboxylate.

Hydroamination

Diversity‐Oriented Synthesis of Hydrazine‐Derived Compounds from Amino Isocyanates Generated In Situ
  • First Published: 07 October 2013
Behind the mask: Nitrogen‐substituted isocyanates are rare and their synthetic potential is virtually untapped. Simple masked precursors can form amphoteric amino isocyanate intermediates in situ, and allows the synthesis of complex hydrazine derivatives upon addition with amines. This reactivity was used in a cascade substitution/hydroamination sequence, and in the assembly of azadipeptide analogues.

Nanocrystal Sensors

Polyhedral Au–Pd Core–Shell Nanocrystals as Highly Spectrally Responsive and Reusable Hydrogen Sensors in Aqueous Solution
  • First Published: 07 October 2013
Absorption signals absorption: The surface plasmon resonance absorption band of tetrahexahedral, octahedral, and cubic Au–Pd core–shell nanocrystals with gold nanocrystal cores was strongly red shifted upon hydrogen absorption into the Pd shell. This reversible spectral shift makes the nanocrystals promising recyclable hydrogen‐gas sensors. Hydrogen absorption could even be detected visually with smaller core–shell octahedra (see picture).

Organocatalysis

Catalytic Enantioselective Michael Addition of α‐Aryl‐α‐Isocyanoacetates to Vinyl Selenone: Synthesis of α,α‐Disubstituted α‐Amino Acids and (+)‐ and (−)‐Trigonoliimine A
  • First Published: 11 October 2013
Be like Mike: The title reaction in the presence of the catalyst 1 afforded Michael adducts in excellent yields and enantioselectivities. The adducts were readily converted into α,α′‐disubstituted α‐amino acids. The enantioselective total synthesis of both (+)‐ and (−)‐trigonoliimine A was accomplished using one of the Michael adducts derived from this methodology. M.S.=molecular sieves.

Cross‐Coupling

Copper(I)‐Catalyzed Alkylation of Aryl‐ and Alkenylsilanes Activated by Intramolecular Coordination of an Alkoxide
  • First Published: 09 October 2013
Let's coordinate: Copper(I)‐catalyzed cross‐coupling of alkenyl‐ and arylsilanes with primary alkyl iodides as well as allylic and benzylic halides as C(sp3)X electrophilic coupling partners has been realized by intramolecular activation through alkoxide coordination. This alkylation tolerates a range of functional groups including a free hydroxy group. IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene.

Ammonia Synthesis

The Haber–Bosch Process Revisited: On the Real Structure and Stability of “Ammonia Iron” under Working Conditions
  • First Published: 09 October 2013
In situ neutron diffraction was used to study the structural properties of an industrial ammonia synthesis catalyst under working conditions similar to those of the Haber–Bosch process. Despite favorable thermodynamics, no indications of reversible bulk nitridation of the iron catalyst was observed in a self‐generated ammonia concentration of 12 vol % at 425 °C and 75 bar after 88 h on stream.

Heterocycle Synthesis

Metal‐Free Oxidative Cyclization of Alkynyl Aryl Ethers to Benzofuranones
  • First Published: 07 October 2013
Readily available phenols can be converted into substituted aryl alkynyl ethers, which react with an N‐oxide as an oxidant and catalytic amounts of a Brønsted acid to provide benzofuranones. If non‐terminal alkynyl ethers are applied, a 1,2‐hydride shift takes place and phenyl acrylates are obtained. Thus activated alkynes can serve as α‐oxy carbene precursors even in the absence of a metal catalyst.

Polyinterhalides

Iodine–Iodine Bonding makes Tetra(diiodine)chloride, [Cl(I2)4]−, Planar

  • First Published: 02 October 2013
All square: The polyinterhalide [Cl(I2)4]− is square‐planar in the crystal structure of [(H5O2)(I2b15c5)2][Cl(I2)4] (I2b15c5=diiodobenzo‐15‐crown‐5), although it would be tetrahedral in the gas phase. Along with other effects, such as electrostatic attractions between the cationic and planar anionic layers, iodine–iodine bonding with σ‐hole interactions plays a considerable role is stabilizing the square‐planar configuration.

β‐Peptides

Solid‐State NMR Spectroscopy

The Conformation of the Prion Domain of Sup35 p in Isolation and in the Full‐Length Protein
  • First Published: 09 October 2013
The whole is not the sum of the parts: Fibrils form both from the full‐length Sup35 prion protein and also from its isolated NM domain. A conformation analysis of both shows that Sup35NM and fragments thereof, which are often used as convenient models for prion fibril assembly, have a very different conformation of the prion domains.