Competing reaction pathways from α-halo-α-protioalkyl aryl sulfoxides initiated by organometallic reagents

The reactions of syn-1-haloethyl p-chlorophenyl sulfoxides (halogen = Cl, Br) with main-group organometallic reagents (n-BuMgCl, MeLi, n-BuLi, s-BuLi, and t-BuLi) in THF and PhMe solvents were examined. Product distributions were analyzed to determine the extent of competing sulfoxide ligand exchange, halogen-metal exchange, and deprotonation reaction pathways. A combination of t-BuLi in PhMe was optimal for initiation of sulfoxide ligand exchange from syn-1-chloroethyl p-chlorophenyl sulfoxide.     

Reactions of some 2H-Chromenes and 2H-Thiochromenes with triazolinediones

Simple 2H-chromenes and 2H-thiochromenes form the [2+2]-adducts, tetrahydro[1]benzo(thio)pyrano[3,4-c] [1,2]diazeto[1,2-a][1,2,4]triazoles, with triazolinediones, whereas their 3- and 4-bromo and the corresponding cycloalkylamino derivatives undergo an overall etectrophilic substitution sequence.     

An unusual dichotomy in the regioselectivity of a metal catalyzed versus thermal ene reaction

A Pd(+2) catalyzed cyclization of a 1,6-enyne complements a thermal Alder ene reaction; a rationale invoking a remote binding site is proposed.     

Gold nanoparticles as dehydrogenase mimicking nanozymes for estradiol degradation

Small gold nanoparticles can mimic dehydrogenase activity to catalyze estradiol (E2) oxidation to estrone (E1), extending the range of nanozyme catalysis to environmentally and biologically important substrates.     

A reinvestigation of asymmetric induction in diels-alder reactions to chiral acrylates.

The chiral induction in the Diels-Alder addition $\text{1}$ → $\text{2}$, assessed reliably by ¹⁹F-NMR-spectroscopy of the endo-esters $\text{4}$, varied between 47 - 93% in favor of the 2-(R)-adducts $\text{2}$ depending on the auxiliary chiral group and the Lewis-acid catalyst.     

Preparation and lithium doping of gallium oxynitride by ammonia nitridation via a citrate precursor route

Gallium oxynitride, isostructural to hexagonal gallium nitride (h-GaN), was obtained by ammonia nitridation of a precursor prepared from the addition of citric acid to an aqueous solution of gallium nitrate. Gallium oxynitride produced at 750 °C had a small amount of gallium vacancies, and was formulated as (Ga_0.89□_0.11) (N_0.66O_0.34) where the symbol □ stands for gallium vacancy. Both the gallium vacancies and oxygen substituted for nitrogen were randomly distributed within the structure. The amount of vacancies decreased with nitridation temperatures in the range of 750-850 °C. Approximately, 10 at% Li⁺ was doped into the gallium oxynitride, using a similar preparation with the additional presence of lithium nitrate, resulted in the random substitution of Ga³⁺ in an atomic ratio of Li/Ga<1 at 750 °C. Oxygen was codoped with lithium and substituted nitrogen in the wurtzite-type crystal lattice. These substitutions reduced the electrical conductivity in the gallium oxynitride semiconductor. A new oxynitride, Li₂Ga₃NO₄, was also obtained with Li₂CN₂ impurity using similar preparations from a mixture of Li/Ga?1. The crystal structure was isostructural with h-GaN, and was refined as P6₃mc with a=0.31674(1) nm, and c=0.50854(2) nm. The Ga and Li occupancies at the 2b site were refined to be 0.6085 and 0.3915, respectively, assuming that the other 2b site was randomly occupied with 1/5O and 4/5N. When the new compound was washed for over 1 min for the removal of Li₂CN₂ impurities, it was decomposed to a mixture of α-GaOOH and α-LiGaO₂. The as-prepared product with Li/Ga=1 showed the highest intensity in yellow luminescence among the products under excitation at 254 nm.     

Synthesis of the ladybug alkaloids (±)-propyleine and (±)-isopropyleine. Modification of the published structure of propyleine

The total syntheses of the ladybug alkaloids (±)-propyleine and (±)-isopropyleine are described. Evidence that the alkaloid propyleine is actually a rapidly interconverting mixture of propyleine and a previously unknown isomer isopropyleine is presented.     

Adhesive transfer of thin viscoelastic films

Micellar suspensions of acrylic diblock copolymers are excellent model materials for studying the adhesive transfer of viscoelastic solids. The micellar structure is maintained in films with a variety of thicknesses, giving films with a well-defined structure and viscoelastic character. Thin films were cast onto elastomeric silicone substrates from micellar suspensions in butanol, and the adhesive interactions between these coated elastomeric substrates and a rigid indenter were quantified. By controlling the adhesive properties of the film/indenter and film/substrate interfaces we were able to obtain very clean transfer of the film from the substrate to the portion of the glass indenter with which the film was in contact. Adhesive failure at the film/substrate interface occurs when the film/indenter interface is able to support an applied energy release rate that is sufficient to result in cavity nucleation at the film/substrate interface. Cavity formation is rapidly followed by delamination of the entire region under the indenter. The final stage in the transfer process involves the failure of the film that bridges the indenter and the elastomeric substrate. This film is remarkably robust and is extended to three times its original width prior to failure. Failure of this film occurs at the periphery of the indenter, giving a transferred film that conforms to the original contact area between the indenter and the coated substrate.     

Structural and rate studies of the 1,2-additions of lithium phenylacetylide to lithiated quinazolinones: influence of mixed aggregates on the reaction mechanism

The 1,2-addition of lithium phenylacetylide (PhCCLi) to quinazolinones was investigated using a combination of structural and rate studies. (6)Li, (13)C, and (19)F NMR spectroscopies show that deprotonation of quinazolinones and phenylacetylene in THF/pentane solutions with lithium hexamethyldisilazide affords a mixture of lithium quinazolinide/PhCCLi mixed dimer and mixed tetramer along with PhCCLi dimer. Although the mixed tetramer dominates at high mixed aggregate concentrations and low temperatures used for the structural studies, the mixed dimer is the dominant form at the low total mixed aggregate concentrations, high THF concentrations, and ambient temperatures used to investigate the 1,2-addition. Monitoring the reaction rates using (19)F NMR spectroscopy revealed a first-order dependence on mixed dimer, a zeroth-order dependence on THF, and a half-order dependence on the PhCCLi concentration. The rate law is consistent with the addition of a disolvated PhCCLi monomer to the mixed dimer. Investigation of the 1,2-addition of PhCCLi to an O-protected quinazolinone implicates reaction via trisolvated PhCCLi monomers.     

Predissociation spectroscopy of the argon-solvated H5O2+ "zundel" cation in the 1000-1900 cm(-1) region

Predissociation spectra of the H5O2+.Ar(1,2) cluster ions are reported in the 1000-1900 cm(-1) region. The weakly bound argon atoms enable investigation of the complex in a linear action mode, and the resulting spectra are much simpler than those reported previously in this region [Asmis et al., Science 299, 1375 (2003) and Fridgen et al., J. Phys. Chem. A 108, 9008 (2004)], which were obtained using infrared multiphoton dissociation of the bare complex. The observed spectrum consists of two relatively narrow bands at 1080 and 1770 cm(-1) that are likely due to excitation of the shared proton and intramolecular bending vibrations of the two water molecules, respectively. The narrow linewidths and relatively small (60 cm(-1)) perturbation introduced by the addition of a second argon atom indicate that the basic "zundel" character of the H5O2+ ion survives upon complexation.