Collision-induced dissociations of substituted benzyl anions: Deprotonated 2-Phenyl-1,3-dithiane

Deprotonated 2-phenyl-1,3-dithiane undergoes competitive losses of H˙, C₃H₆ C₂H₄S, C₃H₄S, C₇H₆S, C₁₀H₁₀ and C₁₀H₁₀S upon collisional activation. The elimination of H occurs from the phenyl ring. The loss of C₃H₆ occurs by simple cleavage of the dithiane ring. All other processes involve specific proton transfer followed by either cleavage or internal nucleophilic displacement.     

MEASUREMENT OF CELL LYSIS BY LIGHT SCATTERING

Abstract— A method is presented which is capable of continuously monitoring the degree of hemolysis in erythrocyte suspensions too dilute to be monitored by conventional light transmission techniques. Scattered light is used to non-destructively assess hemolysis in sparse monolayers which are particularly well suited to many photohemolytic studies. The small angle scattering (<10°), measured here, shows a transient decline as cells settle in a culture dish and then is constant if no lysis occurs. Lysis is indicated by a decrease in scattered light to < 20% of initial intensity when lysis is complete. The light used to monitor lysis is restricted to wavelengths longer than 700 nm which is outside the absorption band of many. photosensitizers of current interest, and is a wavelength range at which light scattering is relatively independent of changes in cell volume. In photohemolytic studies with phloxine B lysis values from light scattering are shown to correlate well with lysis values from hemoglobin release. An apparatus is described which is capable of periodically measuring lysis in eight suspensions without intervention by the experimenter.     

Effect of crystal packing on the structures of polymeric metallocenes

The pressure dependencies of the crystal structures of the polymeric metallocenes lithium cyclopentadienide (LiCp) and potassium cyclopentadienide (KCp) have been determined by synchrotron X-ray powder diffraction. The decrease of the volume of LiCp by 34% up to a pressure of p = 12.2 GPa and of KCp by 23% at p = 5.3 GPa as well as the bulk moduli of K = 7.7 GPa for LiCp and 4.9 GPa for KCp indicate a high compressibility for these compounds. The crystal structures of KCp have been determined up to p = 3.9 GPa. An increase of the bend angle is found from 45 degrees at p = 0 GPa up to 51 degrees at p = 3.9 GPa. This variation is completely explained by a model invoking attractive K+ Cp- interaction and repulsive nonbonded carbon-carbon interactions. It is proposed that the bend angle in the polymeric alkali metal metallocenes is the result of the optimization of the crystal packing.     

An anion-dependent switch in selectivity results from a change of C-H activation mechanism in the reaction of an imidazolium salt with IrH5(PPh3)2

Changing the counteranion along the series Br, BF4, PF6, SbF6 in their ion-paired 2-pyridylmethyl imidazolium salts causes the kinetic reaction products with IrH5(PPh3)2 to switch from chelating N-heterocyclic carbenes (NHCs) having normal C2 (N path) to abnormal C5 binding (AN path). Computational work (DFT) suggests that the AN path involves C-H oxidative addition to Ir(III) to give Ir(V) with little anion dependence. The N path, in contrast, goes by heterolytic C-H activation with proton transfer to the adjacent hydride. The proton that is transferred is accompanied by the counteranion in an anion-coupled proton transfer, leading to an anion dependence of the N path, and therefore of the N/AN selectivity. The N path goes via Ir(III), not Ir(V), because the normal NHC is a much less strong donor ligand than the abnormal NHC. PGSE NMR experiments support the formation of ion-pair in both the reactants and the products. 19F,1H-HOESY NMR experiments indicate an ion-pair structure for the products that is consistent with the computational prediction (ONIOM(B3PW91/UFF)).     

Olefin oxygenation by the hydroperoxide adduct of a nonheme manganese(IV) complex: epoxidations by a metallo-peracid produces gentle selective oxidations

The reactive intermediates and mechanisms of oxygenation of olefins by manganese complexes were investigated by treating olefins with newly synthesized [MnIV(Me2EBC)(OH)2](PF6)2 in the presence and absence of peroxide and by studying its catalytic epoxidation reaction in normal aqueous solution and, individually, with isotopically labeled H218O, 18O2, and H218O2. The manganese oxo species is not the reactive intermediate for the oxygen transfer process mediated by this manganese complex. A novel manganese(IV) peroxide intermediate, MnIV(Me2EBC)(O)(OOH)+, was captured by mass spectrometry and is proposed as the intermediate that oxygenates olefins in this catalytic system.     

Secondary metabolites of the coelenterate echinopora lamellosa

The marine coelenterate Echinopora lamellosa (class Anthozoa, family Scleractinidae) was found to contain a number of unprecedented secondary metabolites which were isolated and identified as smilagenin (I), neodunol methyl ether (II), glycyrrhetic acid (III), 3β-acetoxyglycyrrhetic acid (IV), and 3β-acetoxy-11-deoxoglycyrrhetic acid (V). The structure of neodunol methyl ether was confirmed and its absolute configuration determined by the x-ray diffraction method.     

Hyperfine structure of the 625 nm band in the a 3Πu ← X 1 Σg transitions of Na2

Hyperfine structures of transitions in the a ³Π_u ← X¹Σ_g system of Na₂ have been accurately measured by Doppler-free laser excitation spectroscopy in a collimated molecular beam. The hyperfine patterns are quantitatively explained and the reduced matrix elements of the magnetic dipole hf interaction determined from a least-squares fit to the measured line positions.     

Synthesis of anticonvulsant activity of some 2-phenylcarbamoyl-1,2-diazabicyclo[2.2.2]octanes

A number of aryl isocyanates were adducted to 1,2-diazabicyclo[2.2.2]octane and afforded 2-phenyl-carbamoyl-1,2-diazabicyclo[2.2.2]octanes. Some of the products displayed anticonvulsant activity.     

An efficient synthesis of cyercene A

An efficient approach to the total synthesis of the marine derived polypropionate cyercene A is described. A key feature of the synthesis is the development of methodology for the diastereoselective Wadsworth-Emmons type condensation of a functionalised γ-pyrone unit.     

A general method for the preparation of 4- and 6-azaindoles

Nitropyridines reacted with an excess of vinyl Grignard reagent to produce 4- or 6-azaindoles. Improved yields were obtained when a halogen atom was present at the position alpha to the nitrogen atom in the pyridine ring.