Trifluoroselenoacetic acid, CF(3)C(O)SeH: preparation and properties

The hitherto unknown trifluoroselenoacetic acid was prepared through the reaction of trifluoroacetic acid with Woollins' reagent. The compound was fully characterized by mass spectrometry, (1)H, (19)F, (77)Se, and (13)C NMR, UV-visible, IR and Raman spectroscopy, and the boiling point at 46 °C was estimated from the vapor pressure curve. An IR matrix isolation study revealed the presence of two different syn-anti and anti-syn conformers. The IR spectra of the two stereoisomers have been assigned, aided by DFT, and ab initio calculations. The UV photolysis of Ar matrix isolated CF(3)C(O)SeH yielded CO, OCSe, CF(3)SeH, and CHF(3). Apart from CF(3)SeH, these products were also obtained by vacuum flash-pyrolysis (310 °C) of gaseous CF(3)C(O)SeH. Instead of CF(3)SeH, CF(2)Se, and HF were detected among the pyrolysis products. The different decomposition pathways of CF(3)C(O)SeH are discussed.     

Highly enantioselective organocatalytic α-amination reactions of aryl oxindoles: developing designer multifunctional alkaloid catalysts

An enantioselective α-amination of aryl oxindoles catalyzed by a dimeric quinidine has been developed. The reaction is general, broad in substrate scope, and affords the desired products in good yields with good to excellent enantioselectivities. This study provides the first examples of a general organocatalytic method for the creation of nitrogen-containing, tetrasubstituted chiral centers at C(3) of various aryl oxindoles. Furthermore, new catalysts and insights into structural elements of the catalysts that significantly influence enantioselectivities are disclosed.     

Evidence of site-specific fragmentation on thioacetic acid, CH3C(O)SH, irradiated with synchrotron radiation around the S 2p and O 1s regions

Site-specific fragmentations following S 2p and O 1s photoexcitation of thioacetic acid, CH3C(O)SH, have been studied by means of synchrotron radiation. Total ion yield (TIY) spectra were measured and multicoincidence techniques, which include photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO) time-of-flight mass spectrometry, were applied. The equivalent-core approximation was employed in order to estimate ionization transition values, and the observed peaks were tentatively assigned. A site-specific fragmentation is moderately observed by comparing the mass spectra collected at resonant energies around the inner and shallow inner shell S 2p and O 1s ionization edges. Beside H+ ion, the most abundant ions observed at the S 2p edge excitation were CH3CO+, SH+, S+, and CH3+. At the O 1s region the large CH3CO+ fragment was depressed, and small CHx+ (x = 0, 1, 2, 3), S+, and SH+ fragments were dominant. The dissociation dynamic for the main ion-pair production has been discussed. Two- and three-body dissociation channels have been observed in the PEPIPICO spectra, and the dissociation mechanisms were proposed.     

Synthesis and structural characterization of sterically crowded hydridotris(pyrazolyl)borato complexes: Unusual double 1,2-borotropic shift at a titanium centre

The potassium and thallium(I) derivatives of the hydrido-tris(3-Me₂Bz,5-Me-pyrazol-1-yl)borato ligand, K[Tp^Me2^Bz,Me] (1) and Tl[Tp^Me2^Bz,Me] (2), are reported. Their reactions with TiCl₄ under mild conditions afforded, after rearrangement of the ligand, recognized as a double 1,2-borotropic shift, the related Ti(IV) complex {hydrido-[bis(3-Me,5-Me₂Bz)(3-Me₂Bz,5-Me)-pyrazol-1-yl]borato}trichlorotitanium(IV), [Tp^Me2^Bz,Me∗∗] TiCl₃ (3). The ¹H- and ¹³C NMR spectra of the new compounds are discussed, the molecular structure of 3 has been determined by X-ray diffraction methods, the titanium centre has a pseudo-octahedral coordination, with the nitrogen and chloride ligands in a fac geometry. A possible mechanism of formation of 3 is proposed.     

Stereoselective uncatalyzed synthesis of 2,3-unsaturated-4-n-substituted-beta-O-glycosides by means of a new D-galactal-derived N-(mesyl)-aziridine

The reaction of the new D-galactal-derived allylic aziridine 1beta with O-nucleophiles (alcohols and monosaccharides) affords, in a high to complete beta-stereoselectivity, the corresponding 2,3-unsaturated-beta-O-glycosides bearing a beta-N-functionality at C4.     

Discovery of a novel one-step RuO4-catalysed tandem oxidative polycyclization/double spiroketalization process. Access to a new type of polyether bis-spiroketal compound displaying antitumour activity

Four novel C₃₀ polyether bis-spiroketals, displaying selective inhibition of the BT474 breast-derived cancer cell line, have been obtained from squalene through an unprecedented one-step, RuO₄-catalysed, cascade process characterised by a tandem oxidative pentacyclization/double oxidative spiroketalization sequence. Preliminary studies indicate that the Ru-mediated spiroketalization steps proceed with retention of configuration at the forming spirocentres. A similarity with the oxidative behaviour of PCC has been disclosed.     

Catalysis and inhibition of ligand substitution in palladium(II) square-planar complexes: effects of DNA.

The kinetics of substitution, by thiourea, of ethylenediamine (en) or N,N'-dimethylethylenediamine (Me(2)en) coordinated to palladium(II) in the complexes [Pd(4,4'-R(2)bpy)(en)](PF(6))(2) (bpy = 2,2'-bipyridine; R = H or Me), [Pd(en)(2)](PF(6))(2) and [Pd(Me(2)en)(2)](PF(6))(2) have been studied at 25 degrees C, pH 7 and various ionic strength values, in the presence of calf thymus DNA. The rate of the reaction in water depends on ionic strength, pH, and nucleophile concentration; at fixed pH and ionic strength the k(obsd) values are correlated to the square of the thiourea concentration. This rate law is not altered by the presence of DNA, but the rate of reaction is influenced, depending on the nature of ancillary ligand, L-L, bound to palladium. DNA inhibits the substitution process when L-L is bpy or 4,4'-Me(2)bpy and catalyzes the same reaction when L-L is en or Me(2)en. These opposite kinetic effects can be related to the noncovalent interactions of the various complexes with the DNA double helix. Inhibition of the reactivity of the complexes [Pd(4,4'-R(2)bpy)(en)](2+) is due to protection of the reaction center from nucleophile attack by DNA. Acceleration of the reaction when L-L is en or Me(2)en is related to the dependence of the rate of reaction on pH. If, due to the higher activity of water under the electric field of phosphate groups, hydronium ion concentration on DNA surface is higher than in the bulk solution, the enzyme-like dependence of the rate of reaction on [DNA] is due to progressive accumulation of the complexes around the double helix. Regardless of the complexes' nature, the rate constant values obtained in DNA at pH 7 correspond to values determined in water at pH 5. This pH value on the DNA surface, lower by about two units with respect to the bulk solution, is in good agreement with theoretical predictions. Acceleration of ethylenediamine substitution has been observed for all of the complexes studied in the presence of sodium polyvinylsulfonate.     

Effects of Field Fluctuations,Losses, and Aberrations on the Sensitivity of a Michelson GW Antenna Using Squeezed Radiation

The sensitivity of an interferometric gravitational wave (GW) antenna operating above a few hundred Hertz is shot-noise limited. Sub-shot-noise sensitivity can be achieved by superimposing squeezed light on the laser field. The benefits of this approach are reduced in nonideal interferometers having fringe visibility less than unity, as pointed out by Gea-Banacloche and Leuchs and recently discussed by Chickarmane. Here, we consider an interferometer described by a set of coefficients V_l^(k), V_sq^(k), V_lsq^(k) depending on the misalignment, mismatching, and aberrations of the optical systems, as well as on the asymmetry of the beam splitter and the two-arm losses. Due to the presence of terms proportional to the product of laser times squeezed fields, we have taken into account the amplitude fluctuations of a_l. A simple model of the squeezed vacuum light, produced by a degenerate optical parametric oscillator (OPO), is used for calculating the dependence of the spectral density of the output of a GW antenna on the fluctuations of the OPO-cavity resonance frequency, the pump amplitude fluctuation, and the nonlinear-crystal-temperature drift. A set of figures η_sq± and r_lsq±⁽²⁾ are introduced for describing the effects of the amplitude fluctuations and the relative line width γ_la on the spectral density of the quadrature phase operator X = a_la_sq⁺ h.c.