Coherence transfer delay optimisation in PSYCOSY experiments

PSYCOSY is an f1 broadband homonuclear decoupled version of the COSY nuclear magnetic resonance pulse sequence. Here, we investigate by a combination of experimental measurements, spatially distributed spin dynamics simulations, and analytical predictions the coherence evolution delay necessary in PSYCOSY experiments to ensure intensity discrimination in favour of the correlations typically arising from short range (ⁿJ, n ≤ 3) ¹H–¹H couplings and show that, in general, a coherence evolution delay of around 35 ms is optimum.     

Conformational analysis of some C2-symmetric cyclic peptides containing tetrahydrofuran amino acids

Cyclic oligomers of tetrahydrofuran amino acids, cyclo-(Taa1-Leu-Val)2 (left), cyclo-(Taa2-Leu-Val)2 (middle), and cyclo-(Taa2-Phe-Leu)2 (right), displayed well-defined intramolecularly hydrogen-bonded structures with distorted "beta-beta corner" motifs similar to the tennis ball seam.     

Organocatalytic Asymmetric Mannich Cyclization of Hydroxylactams with Acetals: Total Syntheses of (−)‐Epilupinine, (−)‐Tashiromine,and (−)‐Trachelanthamidine

An asymmetric, organocatalytic, one‐pot Mannich cyclization between a hydroxylactam and acetal is described to provide fused, bicyclic alkaloids bearing a bridgehead N atom. Both aliphatic and aromatic substrates were used in this transformation to furnish chiral pyrrolizidinone, indolizidinone, and quinolizidinone derivatives in up to 89 % yield and 97 % ee. The total syntheses of (?)‐epilupinine, (?)‐tashiromine, and (?)‐trachelanthamidine also achieved to demonstrate the generality of the process.     

The palladium-catalyzed cross-coupling reaction of carboxylic anhydrides with arylboronic acids: a DFT study

The mechanism of the cross-coupling of phenylboronic acid with acetic anhydride, a viable model of the widely used Suzuki reaction, has been studied by DFT calculations at the BP86/6-31G level of theory. Two alternative catalytic cycles have been investigated, one starting from a neutral Pd(0)L(2) complex, the other from an anionic "Jutand-type" [Pd(0)L(2)X](-) species. The reaction profiles are in good agreement with the experimental findings, as both pathways require only moderate activation energies. Both pathways are dominated by cis-configured square-planar palladium(II)diphosphine intermediates. Despite careful investigations, we did not find in this model reaction any evidence for five-coordinate palladium(II) intermediates, which are commonly believed to cause the profound effects of counterions in palladium-catalyzed transformations. Instead, our calculations suggest that the higher catalytic activity of anionic complexes, such as [Pd(PMe(3))(2)OAc](-), may arise from their stronger ability to coordinate to carbon electrophiles. The transmetalation sequence is the same for both catalytic cycles, involving the dissociation of one phosphine ligand from the palladium. In the decisive transition state, in which the phenyl group is transferred from boron to palladium, the acetate base is found to be in a bridging coordination between these two atoms.     

Cerium(IV) ammonium nitrate catalyzed synthesis of α-dehydro-β-amino esters

α-Dehydro-β-amino esters have been synthesized regioselectively from acetates of Baylis-Hillman adducts with amines in the presence of a catalytic amount of ceric ammonium nitrate (CAN) in good yield. The regioselectivity does not differ with respect to the polarity of the solvent.     

Nanocrystals,Nanorods and other Nanostructures of Nickel,Ruthenium, Rhodium and Iridium prepared by a Simple Solvothermal Procedure

The solvothermal decomposition of nickel acetate in n-octylamine medium at 250 °C gives rise to nickel nanostructures while in a hydrocarbon medium NiO nanostructures are obtained. It has been possible to obtain nickel nanorods of 12–15 nm diameter by this means. By carrying out the reaction at a slightly higher temperature, ultra-thin single-crystalline sheets of nickel are obtained. The nanorods and the thin sheets, with the FCC structure, are both ferromagnetic at room temperature, with the nanorods exhibiting high coercivities. It has been possible to obtain ruthenium, rhodium and iridium nanostructures by carrying out the decomposition of the respective metal acetylacetonates in a hydrocarbon (decalin or toluene) or an amine (n-octylamine or oleylamine) around 300 °C. Nanorod formation is favored by linear long-chain amines. The method described by us to prepare the nanostructures of nickel, ruthenium, rhodium and iridium is simple and straightforward compared to the literature procedures, the preparation of single-crystalline thin sheets of nickel by such a solution route being noteworthy. The nanostructures prepared in the amine media could be readily dispersed in hydrocarbon solvents. Dedicated to Professor Dr. Günther Schmid     

Transmetallation reactions of a lithium disilenide

The first magnesium, copper and zinc disilenides were prepared via transmetallation reactions of a lithium disilenide and structurally characterised. The copper and zinc derivatives show red-shifted UV/vis absorptions due to admixture of metal d-orbitals to the highest occupied molecular orbital.