Chemistry - A European Journal

A viable alternative to existing organometallic bases for use in organic synthesis is offered by Mg bisamides. The reactivity and selectivity of these bases has led to them becoming increasingly used in a number of applications including regio-, stereo- and enantioselective organic transformations (see picture).

The novel giant wheel alkoxide [Mn₁₉O₁₂(moe)₁₄(moeH)₁₀]⋅MOEH (MOE = OC₂H₂OCH₃, see figure) was prepared by metathesis from MnCl₂ and KMOE. All Mn atoms are divalent, and antiferromagnetic exchange is observed. The compound is a very suitable precursor for the synthesis of Mn-containing ceramics in the sol-gel process.

The definitive assignment of the structure of aeruginosins 298-A and B has been established by the total syntheses of putative structures containing L-Leu and the real natural peptides incorporating D-Leu. The synthesis of the new nonproteinogenic bicyclic α-amino acid L-Choi (see scheme) from L-tyrosine opens up synthetic routes to other members of this family of serine protease inhibitors.

For the first time, the formation of a mixed sodium amide/n-butyl sodium complex (see figure) was observed when the chiral amine (R)-methyl(1-phenyl-2-pyrrolidinoethyl)[¹⁵N]amine was added to a large excess of nBuNa. Addition of nBuLi resulted in a formation of a new mixed sodium/lithium amide.

Photochromic diarylethenes that have p-phenylene-substituted benzothiophene aryl groups with and without nitronyl nitroxide radicals at both ends of the molecules were synthesized. Both photocyclization and photocycloreversion quantum yields of the diarylethene with nitronyl nitroxide radicals were found to increase with the increase in the π-conjugated chain length. Photoswitching of the magnetic interaction between two nitronyl nitroxide radicals (see scheme) was studied in terms of ESR spectroscopy.

Incorporation of an extra annulus of aromatic residues into resorcin[4]arenes provides molecules that demonstrate remarkable ion-channel mimicking behaviour in biological membranes through interdigitation of long lower rim alkyl substituents (schematically depicted). Conductimetric studies reveal outstanding selectivity for transport of potassium over sodium.

New prototypes of molecular-level machines have been prepared from catenanes that undergo “co-conformational” switching upon reduction of the two bipyridinium units (see scheme). These [2] and [3]catenanes have either one or two dialkylammonium sites, together with two bipyridinium recognition sites, in the π-electron-deficient ring component and incorporate π-electron-rich aromatic polyethers as their other macrocyclic ring component(s).

Perfluorination of an aromatic ring causes a dramatic change in the way it interacts with other functional groups. The electron-withdrawing fluorines lead to a net positive charge on the face of the π-system and so edge-to-face aromatic interactions (see figure) that involve pentafluorophenyl are found to be repulsive.

The short terminal S−N bond characterizes the products from the reaction of ArNSNSiMe₃ with [(Me₂N)₃S]⁺[Me₃SiF₂]⁻ (TASF) as arylthiazylamides Ar−N̄−S̄≡N|⁻ (see structure). A bonding model is proposed which accounts for the influence of the acceptor strength and/or the twisting of the aryl group on the bond lengths.

A linear free-energy relationship has been established between the gas-phase acidity of (oligo)chlorobenzenes and their rates of sec-butyllithium promoted metalation (see scheme, ΔΔG=0.125 (±0.015)×ΔΔG. This proportionality of thermodynamic and kinetic data is the more remarkable as the effects of individual chlorine atoms are not additive but are attenuated upon cumulation. This trend is confirmed by MP2 calculations.

A very efficient method for the preparation of five- and six-membered ring systems in high yields can be achieved through the cobalt(I)-mediated cycloisomerization of 1,n-enynes (see scheme). By a judicious choice of the substitution, cyclobutene, produced from a cobaltacyclopentene, was isolated.

Defect-free BaSO₄nanofilaments are formed in aqueous solution with poly(acrylate) and partially monophosphonated poly(ethylene oxide)-block-poly(methacrylic acid) from amorphous nanoparticles through vectorially directed aggregation and particle fusion. The filaments are single crystals of about 30 nm in diameter but up to several hundred μm in length and form bundles with morphological complexity (see picture).

Formation of highly substituted enantiomerically enriched pyrrolidin-2-one derivatives by means of a [3+2] cycloaddition of Fischer carbene complexes with functionalized azomethine ylides followed by oxidation is described for the first time. This methodology is further employed to prepare (+)-Rolipram (see scheme).

A tetraphosphaquadricyclane and an exceptional 1,2-adduct are formed from the addition of phosphinidene [PhPW(CO)₅] to a 1,3,5-triphosphabenzene (see scheme). Ab initio and X-ray structure analyses give insights into their formation pathways, which differ from the corresponding additions reported for Arduengo carbenes and silylenes.

Diazaphospholanes are formed with high diastereoselectivity from the addition of [PhPW(CO)₅] to PhPC=N-(CH₂)_n-N=CHPh (n=2,3,4) diimines, through intramolecular 1,3-dipolar cycloadditions of P,N ylide intermediates. Azaphosphiridines are only formed by intermolecular [1+2] additions. The diazaphospholanes hydrolyze to P,N-heterocycles (see formulae).

Thulium diiodide is able to reduce unsaturated cyclic hydrocarbons that have a reduction potential more positive than −2.0 V. Reduction of cyclooctatetraene or acenaphthylene in THF with thulium diiodide afforded [(η⁸-C₈H₈)TmI(thf)₂] (1) and the rac-ansa-metallocene complex [(η⁵-C₁₂H₈)₂TmI(thf)] (2) (see [Eq. (1)]), respectively.

Immobilisation of both Pd and Fe porphyrins in the same membrane of Nafion creates a new composite system, in which the Pd complex induces the O₂-mediated oxidation of cyclohexene to the allylic hydroperoxide and the iron porphyrin works as a thermal catalyst for specific oxygenations of cycloalkenes. The quantum yield θ is 1.1 and the turnover number is 4×10³ with respect to the iron porphyrin.

A unique doubly braided [2]catenane (see figure), as well as simple rings or singly braided [2]catenanes, form easily and selectively by self-assembly on reaction of a flexible dialkynyldigold(I) precursor [X(4-C₆H₄OCH₂CCAu)₂] with 1,4-bis(diphenylphosphino)butane. The hinge group X determines the preferred topological isomer.

A methodology for combinatorial solid-phase glycopeptide library synthesis and analysis was developed on polar polyethylene glycol (PEG)-based resins (see scheme). Solid-phase glycosylation of peptide side-chain hydroxy groups and on-bead product analysis by nanoprobe MAS-NMR are demonstrated. Unexpected preference for tyrosine glycosylation on PEG resins was observed.

The gas-phase molecular structures of 1,3λ⁴δ²,2,4-benzodithiadiazine and 5,6,7,8-tetrafluoro-1,3λ⁴δ²,2,4-benzodithiadiazine have been investigated by ab initio calculations and electron diffraction. The results clearly illustrate the differences that exist between the solid-state structure and that of the free molecule, in the absence of packing effects.

Lipophilic rhenium complexes can be synthesized in excellent yields in water by using β-CD to solubilize the ligands. The influence of the reaction time and temperature on the complex configuration has been investigated in depth. Using a β-CD dimer, it is possible to specifically template the formation of a single configuration (see figure).

A chain of calixarene capsules encapsulating aquo-bridged sodium atoms characterizes the anion (see picture) of a crystalline supramolecular complex formed by reaction of sodium p-sulfonatocalix[4]arene and scandium(III) tris-triflate. In the presence of [18]crown-6 a two-dimensional coordination polymer is formed through Sc^III–calixarene interactions, with host–guest interactions between the calixarenes and crown ether molecules effectively imparting a third dimension to the network.