María del Mar Afonso

(S)-2-methyl-5-(prop-1-en-2-yl)cyclopent-1-ene-1-carbaldehyde (2) is a component of the essential oils of several plants and has also been used in many syntheses, usually of terpenes. Although the preparation of compound 2 has been reported several times, no side products have been reported previously. In this Short Note, we present the identification of one such side product. This new compound (3) arises from a vinylogous aldol autocondensation, occurring after the formation of 2, even when the reaction runs for a short time. However, it can diminish the yield of 2 when the reaction is allowed to continue for a longer time.

Vinylallenes have been used in Diels–Alder reactions with a variety of dienophiles. However, vinylallenes activated at the allenic part of the molecule have been reacted only with carbon–carbon double bonds. We prepared siloxy vinylallenes by the base-induced equilibrium of silyl-protected allyl-propargyl alcohols. We found that these systems react with imines to form cycloadducts with total regio and facial selectivity, but only moderate endo:exo selectivity. The cycloadducts obtained were transformed into indolizidine derivatives. The reaction was studied computationally using DFT and compared to the reaction of siloxydienes. It was found that the main difference between those systems is the higher nucleophilicity of the siloxydienes compared to the siloxy vinylallenes.

(R)-3,3,6-trimethyl-3,3a,4,5-tetrahydro-1H-cyclopenta[c]furan was obtained by the acid cyclization of the alcohol (S)-(2-methyl-5-(prop-1-en-2-yl)cyclopent-1-en-1-yl)methanol, which, in turn, is obtained from (R)-limonene. The structure of the new compound was established using NMR spectroscopy (¹H, ¹³C, COSY, HSQC, and HMBC spectra) and high-resolution mass spectrometry. The chemical shifts of the proton and carbon atoms were calculated at the DFT level with a high correlation between the calculated and experimental values.

The 5,8-disubstituted indolizidines are the largest family of indolizidines isolated from the skin of amphibians. These compounds exhibit interesting biological activities such as noncompetitive blockers of nicotinic receptors. In this paper, we present a short, simple, and general synthesis of these alkaloids based on the hetero Diels–Alder reaction between suitable monoactivated dienes and Δ¹-pyrroline as the dienophile. The selectivity of the process is explained based on computational studies. Concise synthesis of the indolizidine alkaloid 181B from a hetero Diels–Alder reaction was accomplished in four steps.

The application of nanotechnology has been an important tool in the development of sustainable analytical procedures which have been developed in agreement with the principles of sustainability and green chemistry. In this sense, such materials have been widely applied in the area of food analysis providing important improvements in terms of specificity, efficiency, and simplicity. Besides, in recent years, the discovery of other innovative materials developed in the framework of green chemistry, such as deep eutectic solvents (DESs), has gained special attention from the scientific community for whom the design and successful application of sustainable strategies is a huge challenge. In this sense, the recent combination of nanomaterials and DESs have resulted in the performance of suitable approaches in the area of food sciences bringing about interesting alternatives in food analysis. The aim of this review article is to revise the application of nanomaterials combined with DESs in food analysis, paying special attention to the synthesis and characterization steps, as well as to the performance of the most recent approaches developed in the field for the analysis of food commodities.

Vinylallenes have been synthesized and used as reagents for many years. However, the number of reviews covering the advances in the chemistry of vinylallenes are scarce. Most of the information lies in general reviews about allenes or in reviews dedicated to specific areas of research. Today, vinylallenes are used in the synthesis due to the special characteristics of this moiety, a diene with a non-conjugated double bond and the capacity to generate axial chirality. In this review, the most relevant publications involving vinylallenes, published in the last fifteen years, are compiled. The review includes new or improved synthetic methods and the reactivity of vinylallenes prepared by classical or new methods. The reactions of vinylallenes have been classified as Nazarovtype processes, cycloaddition reactions, and reactions in which vinylallenes are key intermediates, usually non-isolated but essential for the process to occur. Other types of reactivity are also included.

In this work, we studied carbon paste electrodes (CPEs) with two kinds of binders: mineral oil or ionic liquids (IL) derived from N-substituted octyl pyridinium bis(trifluoromethylsulfonyl)imide with the substituents H-, CH₃-, CN- and CF₃-. The work aims to study this series of IL and determine a possible effect of the substituent of the cation in the behavior of the IL as a binder of graphite for obtaining IL-CPEs. The electrochemical response and the electrical behavior were measured by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Surprisingly, the substituent does not affect the cyclic voltammetry response because in all the cases, high resistance and high capacitive currents were obtained. The best response in terms of conductivity is obtained by CPE. In the case of impedance measurements, the substituent does not cause differences, and in all the cases, the IL-CPEs show nearly the same responses. CPE shows lower capacitance and higher resistance for diffusion compared to the IL-CPEs due to his lower porosity. The high resistance showed by the IL-CPEs by cyclic voltammetry can be attributed to poorly intermolecular forces among graphite, water, electrolyte, and ILs as demonstrated by theoretical calculations.

A microdispersive solid‐phase extraction method has been developed using multiwalled carbon nanotubes of 110–170 nm diameter and 5–9 μm length for the extraction of a group of nine phthalic acid esters (i.e., bis(2‐methoxyethyl) phthalate, bis‐2‐ethoxyethyl phthalate, dipropyl phthalate, butylbenzyl phthalate, bis‐2‐n‐butoxyethyl phthalate, bis‐isopentyl phthalate, bis‐n‐pentyl phthalate, dicyclohexyl phthalate, and di‐n‐octyl phthalate) from tap water as well as from different beverages commercialized in plastic bottles (mineral water, lemon‐ and apple‐flavored mineral water, and an isotonic drink). Determination was carried out by high‐performance liquid chromatography coupled to mass spectrometry. The extraction procedure was optimized following a step‐by‐step approach, being the optimum extraction conditions: 50 mL of each sample at pH 6.0, 80 mg of sorbent, and 25 mL of acetonitrile as elution solvent. To validate the methodology, matrix‐matched calibration and a recovery study were developed, obtaining determination coefficients >0.9906 and absolute recovery values between 70 and 117% (with relative standard deviations < 17%) in all cases. The limits of quantification of the method were between 0.173 and 1.45 μg/L. After the evaluation of the matrix effects, real samples were also analyzed, finding butylbenzyl phthalate in all samples (except in apple‐flavored mineral water), though at concentrations below its limit of quantification of the method.