Angewandte Chemie International Edition

A layered magnet is formed from the reaction (see H-tube apparatus; bottom) of tetracyanoethylene (TCNE; left) and [Fe(CO)₅] (right). The structural elucidation described by P. W. Stephens, J. S. Miller, and co-workers in their Communication on page 1521 ff. reveals that magnetic layers of [TCNE]^.− bonded to four high-spin Fe^II ions are connected by [C₄(CN)₈]²⁻, the diamagnetic σ dimer of [TCNE]^.−, which explains the higher than expected magnetization for this ferrimagnet.

Reduction of phenyl silyl acetylenes with lithium led to the unexpected formation of a dilithium dibenzopentalenide derivative together with the expected 1,4-dilithio-1,3-butadiene. The bulkiness of the silyl substituent of the phenyl silyl acetylene strongly affects its reduction mode. Further details may be found in the Communication by M. Saito and co-workers on page 1504 ff.

Guilty as charged; lock them up! Recent advances in the field of polymer vesicles are highlighted with particular focus on the temperature-induced, direct formation of vesicles in water from amphiphilic block copolymers and the structural “locking” of the resulting vesicles by formation of polyelectrolyte complexes (see picture).

Closer to nature: Biaryl motifs are common in organic molecules with important biological and physical properties. Carboxylic acids can now be used as aryl donors in palladium-catalyzed cross-coupling reactions to give biaryl compounds of high synthetic value (see scheme).

Did they or didn't they? In 1944, R. B. Woodward and W. von E. Doering reported the total synthesis of homomeroquinene and d-quinotoxine. On the basis of the conversion of d-quinotoxine into quinine reported by P. Rabe and K. Kindler in 1918, Woodward and Doering made the claim of the total synthesis of quinine (1). In 2000, G. Stork concluded that this claim was a myth. Previously unpublished archive material and numerous interviews throw new light onto this controversy.

On display: This model shows DNA (pink) annealed to a peptide nucleic acid (PNA; orange) containing several L-lysine γ side chains (^LKγ-PNA) in the middle of the PNA oligomer. The ^LKγ-PNA side chains project away from the nucleobase pairs (purple) and line the periphery of the duplex. This strategy can be used for the multifunctional display of various functional groups from the PNA residues without diminishing the binding affinity or selectivity to DNA.

Metal–H₂binding: A new tetrazolate-based metal–organic framework exhibits high H₂ uptake at low temperature and moderate pressure. The evacuation of coordinated solvent molecules from Cu²⁺ ions within the framework provides strong binding sites for H₂ molecules (see picture; Cu purple, C gray, N blue, Cl green).

Come together … over Re: Oxorhenium(VII) complexes catalyze the direct condensation of phosphoric acid with an alcohol to selectively give the corresponding phosphoric acid monoester on a 2–100-mmol scale (see scheme). This method should be useful for the industrially important synthesis of phosphoric acid monoesters.

The predicted endohedral icosahedral clusters Pu@Pb₁₂ (see picture; Pu blue, Pb yellow) and [Am@Pb₁₂]⁺ have an outermost 32-electron system corresponding to formally occupied 7s, 7p, 6d, and 5f actinide orbitals, each of which interacts with a Pb 6p-based orbital of the [Pb₁₂]²⁻ cage. This study provides the first example of a formal 32-electron principle, and 32 is not a false magic number.

It stacks up nicely: Exposure of dihydrogen sulfate salts of appropriately substituted cyclo[8]pyrroles to electron-deficient acceptor molecules gives discotic liquid crystals. The columnar mesophase structures are stabilized by electron-donor/electron-acceptor interactions (see picture; red: trinitrobenzene, green: cyclo[8]pyrrole cores, yellow: sulfate ions, gray: volume occupied by the substituents).

A buckyball sandwich: The depicted reaction produces cis-1 and cis-2 (see picture), in which the fullerene is sandwiched between two different clusters. Variable-temperature ¹H NMR spectra reveal that cis-1 and cis-2 are interconvertible and cis-2 exists as two isomers.

Ti-ght union: A highly regio- and stereoselective bimolecular coupling reaction is described for the union of substituted, unactivated olefins and internal alkynes (see scheme). The titanium-mediated coupling reaction proceeds with CC bond formation occurring distal to a pendent hydroxy group.

An interesting rearrangement: Management of functional groups in derivatives of indoles enables a rearrangement to take place which provides the pentacyclic ring system found in phalarine (see scheme, CSA=camphorsulfonic acid, Ts=toluene-4-sulfonyl). Studies into the mechanism proved valuable for the total synthesis of phalarine and provided insight into the chemistry of indoles in general.

End of the expedition … for now: Completion of the first total synthesis of phalarine from an advanced rearrangement product brought up interesting obstacles to overcome. Use of the Gassman oxindole synthesis and subsequent manipulations led to the racemic natural product (see scheme, Ts=toluene-4-sulfonyl).

The right way round: Peribysin E, a naturally occurring adhesion inhibitor, has been synthesized and, as a result, its absolute configuration reassigned. The natural and nonnatural enantiomers can be reached starting from (R)- or (S)-carvone, respectively. A key step is the ring contraction of 1 to 2 (see scheme, TBS=tert-butyldimethylsilyl, TES=triethylsilyl).

Stringing them along: The pores of a mesoporous silica particle were filled with guest molecules and then blocked by threading cyclodextrin molecules (CDs) onto the surface-grafted polyethylenimine (PEI) chains at pH 11. At pH 5.5, the guest molecules can be released from the pores of the particle by reversible dethreading of the CDs from the PEI chains.

Fast switches: Eigen and Weller's classic diffusion reaction model for aqueous acid–base neutralization reactions is used to interpret the proton-transfer dynamics between pyranine and trichloroacetate. Upon mutual diffusion of the acid and base to form an encounter reaction complex, solvent switches mediate the proton transfer between acid and base and provide a general framework for all observed dynamic features (see picture; ROH=acid, B=base).

A functional reassignment: BtrD, a protein encoded in the butirosin gene cluster, functions as a deacetylase rather than a nucleotidyltransferase as previously reported. BtrD was found to selectively catalyze the conversion of 2′-N-acetylparomamine to paromamine, strongly suggesting that butirosin's neosamine moiety originates from uridine diphospho(UDP)-N-acetylglucosamine (see picture).

Uniform polymerization sites with high activity can be created by treating a Phillips-type Cr^II/SiO₂ catalyst with CH₂Cl₂ (as shown schematically in the picture) under well-defined conditions. A mechanism is proposed in which CH₂Cl₂ increases the catalytic activity of a small fraction of Cr sites while poisoning the remainder.

Maxing out at six: The maximum bond order that can be achieved between two equal atoms in the periodic system is six. The picture shows the potential energy curves for the diatoms Cr₂, Mo₂, and W₂, where the latter two are sextuply bonded molecules (d=internuclear distance in atomic units).

It'see rie: A new method for quantitative measurement of ee values is described. The method exploits the unique electrooptic properties of the chiral smectic A liquid-crystal phase and is potentially applicable to the high-throughput (>10⁶ determinations per day) measurement of ee values for any chiral analyte.

Extreme chemistry: The carbon nitride imide C₂N₂(NH) is synthesized from the single-source precursor 1-cyanoguanidine under high-pressure and high-temperature conditions in a laser-heated diamond-anvil cell. Characterization of single crystals recovered at ambient conditions reveals that the new compound adopts a defect wurtzite structure (see picture).

A strong correlation is found between the propensity of individual amino acids to induce peptide-bond cleavage in the gas phase (P_AA–XX) and their structure-forming propensity (P_S, red) and H-bond-accepting propensity (P_H, blue). Thus, the same fundamental parameter, carbonyl group basicity, governs the formation of secondary protein structures in solution and directs fragmentation in the gas phase.

Inversion versus retention: A palladium-catalyzed annulation with enantioenriched secondary alkyl iodides gives mechanistic insight into the stereochemistry of this CH bond functionalization reaction (see scheme) involving a proposed Pd^II/Pd^IV catalytic cycle.

Shells within shells: Simply varying the concentration of the cetyltrimethylammonium bromide surfactant in a template process leads to single-, double-, triple-, and quadruple-shelled Cu₂O hollow spheres (see TEM image). Thus, the vesicle-directed synthesis of inorganic multishelled hollow spheres is feasible.

Outstanding catalytic activity for the selective oxidation of acrolein (see picture) is observed with a crystalline metal oxide, Mo₃VO_x (x≤11.1). The catalyst is synthesized from a solution containing pentagonal units of {Mo(Mo₅O₂₇)} (blue), which further react with molybdenum and vanadium species (red) to form a 3D metal oxide.

The Full Monty? Stripping a catalyst down to its bare essentials gives a neutral iridium complex containing only one monodentate phosphoramidite ligand that is an efficient catalyst for the enantioselective hydrogenation of α-dehydroamino acids (see picture).

Between the lines: Functionalized single-walled carbon nanotubes (SWNTs) can be aligned in the hexagonal columnar mesophase of discotic liquid crystals (DLCs). The thermophysical properties of SWNT–DLC composites indicate inclusion of SWNTs in the supramolecular order of DLCs (see picture).

The degree of bulkiness of the silyl substituent strongly affects the reduction mode of phenyl silyl acetylenes. For example, the treatment of phenyl(triisopropylsilyl)acetylene with lithium led to the unprecedented formation of a dilithium dibenzopentalenide together with the expected 1,4-dilithio-1,3-butadiene (see scheme), whereas the reduction of phenyl(tert-butyldimethylsilyl)acetylene gave only the corresponding 1,4-dilithio-1,3-butadiene.

Charging ahead: Adaptive functional nanowires can be used for magnetoswitchable bioelectrocatalysis. This control is accomplished by changing the surface orientation of two-segment gold/nickel nanowires, which are functionalized with glucose oxidase (GOx), in connection to a surface-bound ferrocene (Fc) electron-transfer mediator (see picture).

From A to B: The decalin moiety of azadirachtin, which includes the fully functionalized AB ring system (see picture), was synthesized stereoselectively in only 23 steps. Key steps include an intramolecular Diels–Alder reaction, a decarboxylation, a Claisen rearrangement, and finally a tandem radical cyclization.

Out of the blue: The convergent asymmetric total synthesis of the antitumor antibiotic (−)-cribrostatin 4 from the blue sponge Cribrochalina features asymmetric Staudinger and Pictet–Spengler reactions to form the tetrahydroisoquinoline moiety. These reactions were followed by a reductive opening/elimination of a tricyclic β-lactam and a Pictet–Spengler cyclization to access the unsaturated pentacyclic core.

The wages of spin: Insight into the elusive structure of [V(TCNE)_x]-based magnets is provided by the structural analysis of the title compound (T_c≈100 K; TCNE=tetracyanoethylene; z≈0.3), in which {Fe^II(μ₄-[TCNE])^.−} layers are bridged by diamagnetic TCNE dimers μ₄-[C₄(CN)₈]²⁻ (see picture; Fe gold; C black; N blue). Strong intralayer spin coupling between the Fe^II centers leads to the observed magnetic ordering.

A simple solution process without the assistance of surfactant, catalyst, or template under ambient conditions in air has been used to prepare single-crystal hollow microtubes with a rectangular cross section from [2-(p-dimethylaminophenyl)ethenyl]phenylmethylenepropanedinitrile (DAPMP). The DAPMP microtubes (see picture for SEM images) show remarkably strong frequency-doubling nonlinear optical properties.

Piecing it all together with palladium: Two- and three-component cascade processes that are promoted by a multifunctional Pd catalyst lead to indoles in a highly efficient manner (see scheme). The key step is the Pd-catalyzed α-arylation of imines with o-dihalobenzene derivatives.

Double or nothing: The bissesquiterpene (+)-aquaticol was synthesized by biomimetic oxidative dearomatization of 1 via an orthoquinol intermediate that undergoes spontaneous and selective dimerization; only like diastereomers react. The remarkable double diastereofacial differentiation observed is explained in terms of a double hyperconjugative “Cieplak–Fallis” effect expressed in a C₂-symmetric bispericyclic transition state.

Zero, one, or three? The role of Au⁰, Au^I, and Au^III cations in the heterogeneous gold catalyst Au/CeO₂ was investigated with the copper-free Sonogashira cross-coupling reaction of iodobenzene and phenyl acetylene (see picture). Reactions carried out under both heterogeneous and homogeneous conditions using distinct Au⁰, Au^I, and Au^III species reveal that Au^I is the active species for the cross-coupling reaction.