Insect pheromone components: Use of 13C NMR spectroscopy for assigning the configuration of CC double bonds of monoenic or dienic pheromone components and for quantitative determination of Z/E mixtures

Several insect sex pheromone components and structural analogues have been characterized by ¹³C NMR spectroscopy. The evaluation of the difference between the chemical shift values of the allytic carbons present in the diunsaturated pheromone components and those of the carbons having the same position on the n-alkane chain of the corresponding saturaated compounds was used to assign the configuration of the CC double bonds present into such dienic compounds. The technique avoids the need to use the nuclear Overhausser effect; it allows quantitative evaluation, with good accuracy, of the stereoisomeric composition of mixtures of synthetic monoenic or dienic pheromone components such as (Z)- and (E)-9-tetraceden-1-yl acetate and (Z)- and (E)-9,11-dodecadien-1-yl acetate.     

Liquid-vapor and liquid-liquid phase equilibria of the Brodholt-Sampoli-Vallauri polarizable water model

Liquid-vapor and liquid-liquid phase equilibria of the polarizable Brodholt-Sampoli-Vallauri water model have been investigated by Gibbs ensemble Monte Carlo computer simulations. The coexisting liquid and vapor densities and energy of vaporization of the model is found to be in a reasonable agreement with experimental data in the entire temperature range of liquid-vapor coexistence. The critical temperature and density of the model are found to be 615 K and 0.278 gcm(3), respectively, close to the experimental values of 647.1 K and 0.322 gcm(3). In the supercooled state two distinct liquid-liquid coexistence regions are observed. The existence of liquid-liquid phase separation of a polarizable water model is demonstrated for the first time.     

Hurwitz theory and the double ramification cycle

This survey grew out of notes accompanying a cycle of lectures at the workshop Modern Trends in Gromov–Witten Theory, in Hannover. The lectures are devoted to interactions between Hurwitz theory and Gromov–Witten theory, with a particular eye to the contributions made to the understanding of the Double Ramification Cycle, a cycle in the moduli space of curves that compactifies the double Hurwitz locus. We explore the algebro-combinatorial properties of single and double Hurwitz numbers, and the connections with intersection theoretic problems on appropriate moduli spaces. We survey several results by many groups of people on the subject, but, perhaps more importantly, collect a number of conjectures and problems which are still open.     

On the applicability of multireference second-order perturbation theory to study weak magnetic coupling in molecular complexes

The performance of multiconfigurational second-order perturbation techniques is established for the calculation of small magnetic couplings in heterobinuclear complexes. Whereas CASPT2 gives satisfactory results for relatively strong magnetic couplings, the method shows important deviations from the expected Heisenberg spectrum for couplings smaller than 15-20 cm(-1). The standard choice of the zeroth-order CASPT2 Hamiltonian is compared to alternative definitions published in the literature and the stability of the results is tested against increasing level shifts. Furthermore, we compare CASPT2 with an alternative implementation of multiconfigurational perturbation theory, namely NEVPT2 and with variational calculations based on the difference dedicated CI technique.     

Nucleus- and side-chain fluorinated 3-substituted indoles by a suitable combination of organometallic and radical chemistry

Regioselectively fluoro-, trifluoromethyl- and trifluoromethoxy-substituted 3-methyleneindolines have been prepared using a four-step procedure involving metalation/bromination of fluorinated Boc-protected anilines, N-propargylation of the resulting o-bromoarylcarbamate and reductive radical cyclization of the product with tributyltin hydride/AIBN. 3-Methyleneindolines, as valuable, versatile intermediates, can be transformed into highly functionalized 3-substituted indoles by ene-type reactions using different enophiles. Thus, fluoro-, trifluoromethyl- and trifluoromethoxy-substituted diethyl 2-hydroxy-2-[(1H-indol-3-yl)methyl]malonates, ethyl 2-hydroxy-3-(1H-indol-3-yl)propionates and ethyl 2-hydroxy-3-(1H-indol-3-yl)-2-trifluormethylpropionates were obtained in 77-86% yield by simply heating the corresponding tert-butyl 3-methyleneindoline-1-carboxylate with an equimolar amount of diethyl ketomalonate, ethyl glyoxalate and ethyl 3,3,3-trifluoropyruvate, respectively, at 100 °C, without solvent, for 0.5-4 h.     

Alpha- vs ortho-lithiation of N-alkylarylaziridines: probing the role of the nitrogen inversion process

The lithiation reaction of monophenyl- and diphenylaziridines has been investigated in detail in an effort to understand why the former undergo exclusively or mainly ortho-lithiation while the latter are lithiated exclusively at the alpha-position. Evidence is reported that ruled out the possibility that the alpha-lithiation, observed for the diphenylaziridines, is the result of an ortho- to alpha-translocation phenomenon, thus substantiating a direct alpha-deprotonation process. The role of the aziridine nitrogen lone-pair has been considered: dynamics at the aziridine nitrogen as well as complex-induced proximity effects seem to be responsible for the observed regioselectivity in both monophenyl and diphenylaziridines. It turns out that, by tuning the reaction conditions for the lithiation of trans-1-alkyl-2-methyl-3-phenylaziridines, it is possible to generate with high regioselectivity alpha- and/or ortho-lithiated aziridines, which can be stereoselectively functionalized by electrophilic trapping. A regioselective ortho-functionalization of diphenylaziridines is made possible by halogen- or tin-lithium exchange and by deprotonation of bis-deuterated aziridines.     

Scale‐up of Microwave‐Assisted Polymerizations in Batch Mode: The Cationic Ring‐Opening Polymerization of 2‐Ethyl‐2‐oxazoline

Summary: The use of microwave heating in polymer science is a rapidly growing field of research leading to faster and cleaner polymerization procedures. However, the majority of the investigations are performed at small scales (≈1 mL), which is far away from potential commercial applications of microwave‐assisted polymerizations. In addition, it has been shown in organic chemistry that microwave‐assisted reaction protocols can be directly scaled without the need for process optimization. In this contribution, we have investigated the direct scaling of microwave‐assisted polymerization procedures under pressure conditions using the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline as the model system. This polymerization was performed at scales ranging from 4.0 mmol (1 mL) to 1.0 mol (250 mL) in different microwave synthesizers covering both monomode and multimode devices.

Scale‐up of microwave‐assisted polymerizations in batch mode: the cationic ring‐opening polymerization of 2 ethyl‐2‐oxazoline.     

Stabilisation of the Secondary Structure of Chitosan Gels during the Preparation of Composites

Summary: Zeolite-chitosan composites have been prepared by encapsulation of zeolites by a gelling solution of chitosan or by in-situ synthesis of zeolites inside a chitosan gel. The preparation of the composite implies modifications of both components. Zeolites are dealuminated by the acid solution in which chitosan is dissolved and the morphology of the chitosan fibrils is stabilized by iniorganic species issued from the dealumination of the zeolites or from their synthesis medium. Zeolite-bearing chitosan xerogels present surface area and porosity similar to the textural properties of chitosan aerogels.     

A Study of Graphene‐Based Copper Catalysts: Copper(I) Nanoplatelets for Batch and Continuous‐Flow Applications

The use of graphene derivatives as supports improves the properties of heterogeneous catalysts, with graphene oxide (GO) being the most frequently employed. To explore greener possibilities as well as to get some insights into the role of the different graphenic supports (GO, rGO, carbon black, and graphite nanoplatelets), we prepared, under the same standard conditions, a variety of heterogeneous Cu catalysts and systematically evaluated their composition and catalytic activity in azide–alkyne cycloadditions as a model reaction. The use of sustainable graphite nanoplatelets (GNPs) afforded a stable Cu^I catalyst with good recyclability properties, which are compatible with flow conditions, and able to catalyze other reactions such as the regio‐ and stereoselective sulfonylation of alkynes (addition reaction) and the Meerwein arylation (single electron transfer process).