A molecular beam laser-microwave double-resonance spectrometer for precise measurements of high temperature molecules

A laser-microwave double-resonance experiment has been developped basing on the principle of the known laser-rf double-resonance technique. This novel beam experiment allows high-resolution measurements of rotational transitions in a molecular ground state. The method was applied to the high-temperature radical CaCl to study the hyperfine structure of transitions between low-lying rotational states. Microwave scans yielded linewidths of 15–20 kHz limited only by time-of-flight broadening and residual Zeeman splitting.     

ZnCl2-mediated stereoselective addition of terminal alkynes to D-(+)-mannofuranosyl nitrones

[reaction: see text] An optimized process for the addition of terminal alkynes to chiral nitrones using ZnCl2 and NEt3 in toluene is reported. The new reaction protocol is facile to perform and cost-effective. The resulting optically active propargyl N-hydroxylamines are isolated in good to excellent yield and high diastereoselectivity.     

A modular approach to polyketide building blocks: cycloadditions of nitrile oxides and homoallylic alcohols

A general approach to the diastereoselective synthesis of Delta(2)-isoxazolines via magnesium-mediated, hydroxyl-directed diastereoselective nitrile oxide cycloadditions of homoallylic alcohols and monoprotected homoallylic diols is disclosed. A broad spectrum of aliphatic and aromatic nitrile oxides and a variety of homoallylic alcohols participate in the cycloaddition, thus expanding the scope of polyketide building blocks that can be accessed using this strategy.     

Solid-phase synthesis of photochromic spiropyrans

[reaction: see text] A convenient solid-phase synthesis of spiropyrans is described. A succinate linker was employed, which allows base-catalyzed cleavage of the desired photochromophore derivatized with a succinimide. Excellent yields and purities were obtained for the compounds that comprise a library of 23 spiropyrans. Opening of the succinimide ring in spiropyran could be realized under mild conditions.     

2-microlocal analysis of martingales and stochastic integrals

Recently, a new approach in the fine analysis of sample paths of stochastic processes has been developed to predict the evolution of the local regularity under (pseudo-)differential operators. In this paper, we study the sample paths of continuous martingales and stochastic integrals. We proved that the almost sure 2-microlocal frontier of a martingale can be obtained through the local regularity of its quadratic variation. It allows to link the Hölder regularity of a stochastic integral to the regularity of the integrand and integrator processes. These results provide a methodology to predict the local regularity of diffusions from the fine analysis of its coefficients. We illustrate our work with examples of martingales with unusual complex regularity behaviour and square of Bessel processes.