Highly Stereoselective Reactions of γ-Sulfinyl Carbanions with Achiral Imines

Abstract

Lithium 2-p-tolylsulfinylbenzyl carbanions react with different N-substituted imines affording 1,2-diaryl ethyl (and propyl) amines with a high stereoselectivity control at both benzyllic (only dependent of the sulfur configuration) and iminic carbons. The anti:syn ratio, ranging between > 96: < 4 and < 2: > 98, dependent on the electronic density at nitrogen.     

Generation of nanoparticles with adjustable size and controlled stoichiometry: recent advances

We present a bottom-up fabrication route based on the sputtering gas aggregation source that allows the generation of nanoparticles with controllable and tunable chemical composition while keeping the control of the cluster size. We demonstrate that the chemical composition of the particles can be monitored by the individual adjustment of the working parameters of the magnetrons inserted in a gas aggregation zone. Such control of the parameters leads to a fine control of the ion density of each target material and hence to the control of the chemical composition of the nanoparticles. In particular, we show through X-ray photoemission, atomic force microscopy, and high-resolution transmission electron microscopy that it is possible to generate bimetallic (AgAu) and trimetallic (AgAuPd) alloy nanoparticles with well-defined and tunable stoichiometries from three targets of pure Ag, Au, and Pd. The proposed route for the generation of nanoparticles opens new possibilities for the fabrication of nanoparticles using a physical method that, for some applications, could be complementary to the chemical methods.     

Expanding the scope of arylsulfonylacetylenes as alkynylating reagents and mechanistic insights in the formation of Csp2-Csp and Csp3-Csp bonds from organolithiums

We describe the unexpected behavior of the arylsulfonylacetylenes, which suffer an "anti-Michael" addition of organolithiums producing their alkynylation under very mild conditions. The broad scope, excellent yields, and simplicity of the experimental procedure are the main features of this methodology. A rational explanation of all these results can be achieved by theoretical calculations, which suggest that the association of the organolithiums to the electrophile is a previous step of their intramolecular attack and is responsible for the unexpected "anti-Michael" reactions observed for substituted sulfonylacetylenes.     

Role of quaternary ammonium salts as new additives in the enantioselective organocatalytic β-benzylation of enals

We report herein the efficiency of quaternary ammonium salts as co-catalysts in organocatalytic Michael reactions involving iminium activation of α,β-unsaturated aldehydes. The enantioselective formal benzylation of these substrates has been optimized and used to rationalize the role of the ammonium salts in these processes.     

Ultrasound-assisted extraction of pesticides from olive branches: a multifactorial approach to method development

A rapid and simple method has been developed for the analysis in olive branches of two insecticides currently used in olive pest control, dimethoate and α-cypermethrin. The effects of analytical conditions on pesticide recovery and the optimal extraction conditions were evaluated by means of a factorial design. The use of this chemometric tool in analytical method development allows the identification of the principal and interaction effects of the extraction conditions on the recovery of pesticides. It also gives information about the location of pesticide maximum recovery with minimal experimental investment. Extraction was carried out with an ultrasonic bath and the experimental conditions studied included the volume of extractant, the time of extraction, the number of extraction steps and the sample weight. The sample was further cleaned up using a Florisil solid-phase extraction cartridge. For the overall extraction procedure, recoveries of 99 % for α-cypermethrin and 90 % for dimethoate from the spiked samples were found for 1 g of sample extracted three times with 35 mL hexane, sonicating for 2 min in each step. The complete process including ultrasonic extraction and filtration will not require more than 15–20 min, in contrast with several hours for conventional liquid–solid extraction techniques. The proposed method allows a high sample throughput, as commonly required in monitoring studies.     

Regiochemical control in asymmetric Diels-Alder cycloadditions of enantiopure (S)S-(p-tolylsulfinyl)-1,4-benzoquinones with Dane''s diene

Enantiopure sulfinylquinones (+)-2 and (+)-3 reacted with Dane's diene 1 under thermal and ZnBr₂ Lewis acid conditions with reversal regiochemistry but similar π-facial diastereoselectivity to afford, after spontaneous elimination of the sulfinyl group, tetracyclic derivatives 4–9.     

How the electrode potential controls the selection rules of the charge transfer mechanism of SERS

This communication reports, for the first time, the dependence of the SERS intensities under resonant CT conditions (SERS-CT) on the electrode potential. SERS-CT intensities have been estimated from the properties of S(0)-CT(i) transitions ranging between 200-1200 nm of selected [Ag(n)-pyridine](q) and [Ag(n)-pyrazine](q) complexes.