Assembly maps,K-theory, and hyperbolic groups

Following Connes and Moscovici, we show that the Baum-Connes assembly map forK _*(C*v) is rationally injective when is word-hyperbolic, implying the Equivariant Novikov conjecture for such groups. Using this result in topologicalK-theory and Borel-Karoubi regulators, we also show that the corresponding generalized assembly map in algebraicK-theory is rationally injective.     

Janis Stradins: An outstanding electrochemist and expert in the history of science

Journal of Solid State Electrochemistry - Janis Stradins (10.12.1933 – 29.11.2019) was a well-known expert in molecular electrochemistry, ESR spectroscopy and physical organic chemistry, as...     

Stereoselective hydrogenations of aryl-substituted dienes

The carbene complex can mediate hydrogenations of dienes with up to 20:1.0 diastereoselectivity and 99% ee; the scope and limitations of these reactions were investigated.     

Preparation of sigma- and pi-allylcopper(III) intermediates in SN2 and SN2' reactions of organocuprate(I) reagents with allylic substrates

The first pi-allyl complexes of CuIII have been prepared and characterized by using rapid injection nuclear magnetic resonance spectroscopy (RI-NMR). The prototype, (eta3-allyl)dimethylcopper(III), was prepared by injection of allyl chloride into a THF-d8 solution of iodo-Gilman reagent, Me2CuLi.LiI (A), spinning in the probe of an NMR spectrometer at -100 degreesC. A sigma-allyl ate complex, lithium (eta1-allyl)trimethylcuprate(III), was prepared in high yield by including 1 equiv of tributylphosphine in the reaction mixture or by using allyl acetate as the substrate. Cyano ate complex, lithium cis-(eta1-allyl)cyanodimethylcuprate(III) was obtained in high yield by injecting allyl chloride or allyl acetate into the cyano-Gilman reagent, Me2CuLi.LiCN (B), in THF-d8 at -100 degrees C. Reactions of A with allylic substrates show a definite dependence on leaving group (chloride vs acetate), whereas those of B do not. Moreover, these reagents have different regioselectivities, which in the case of A vary with temperature. Finally, the exclusive formation of cis-cyano sigma-allyl CuIII intermediates in both the 1,4-addition of B to alpha-enones and its SN2alpha reaction with allylic substrates now makes sense in terms of pi-allyl intermediates in both cases, thus unifying the mechanisms of these two kinds of conjugate addition.     

An efficient and practical system for the catalytic oxidation of alcohols, aldehydes, and alpha,beta-unsaturated carboxylic acids

Upon exposure to commercial bleach (approximately 5% aqueous sodium hypochlorite), nickel(II) chloride or nickel(II) acetate is transformed quantitatively into an insoluble nickel species, nickel oxide hydroxide. This material consists of high surface area nanoparticles (ca. 4 nm) and is a useful heterogeneous catalyst for the oxidation of many organic compounds. The oxidation of primary alcohols to carboxylic acids, secondary alcohols to ketones, aldehydes to carboxylic acids, and alpha, beta-unsaturated carboxylic acids to epoxy acids is demonstrated using 2.5 mol % of nickel catalyst and commercial bleach as the terminal oxidant. We demonstrate the controlled and selective oxidation of several organic substrates using this system affording 70-95% isolated yields and 90-100% purity. In most cases, the oxidations can be performed without an organic solvent, making this approach attractive as a "greener" alternative to conventional oxidations.     

Rapid-injection NMR study of iodo- and cyano-Gilman reagents with 2-cyclohexenone: observation of pi-complexes and their rates of formation

Rapid-injection is a very useful technique for the preparation of temperature-sensitive and air-sensitive compounds in the cold, nitrogen-filled probe of an NMR spectrometer. We have used this method to prepare solutions of pi-complexes from 2-cyclohexenone and prototypical cuprates Me2CuLi.LiI and Me2CuLi.LiCN, and we have assigned structures on the basis of 1H and 13C NMR. In each case two pi-complexes were observed, and in the former, their rates of formation were measured by rapid-injection 1H NMR and EXSY spectroscopy. These results provide insights into the normal and anomalous conjugate addition reactions of organocuprates.