René Miranda

Preparation of Benzylidene Barbituric Acids Promoted by Infrared Irradiation in Absence of Solvent

Abstract Several benzaldehydes were condensed with barbituric acid under infrared irradiation, in absence of solvent, affording the corresponding 5-benzylidene barbituric acids.

Knoevenagel Condensation Catalyzed by a Mexican Bentonite Using Infrared Irradiation

Abstract Diethyl malonate undergoes condensation with aromatic aldehydes without solvents. in the presence of a Mexican bentonite using infrared irradiation as the energy source, to give the benzylidenemalonate compounds in fair yield.

Infrared irradiation: Effective promoter in the formation of N-benzylideneanilines in the absence of solvent

Abstract Infrared irradiation promoted the formation of a series of Schiff bases in the condensation reaction between benzaldehydes and anilines, in the absence of solvent. Benzaldehydes and anilines, containing either electron‐withdrawing or electron‐releasing groups, were assessed to identify any substituent effect on the formation of the Schiff bases. This methodology is characterized by ease of set‐up and work‐up, and the reaction yields were comparable with those obtained in the methods reported previously. Moreover, this new procedure is environmentally benign because no solvent was employed in the transformations.

Oxidative Cleavage of Aldo and Keto Oximes with Chromyl Chloride Adsorbed on Silica and Bentonite Earth

Abstract A number of Aldo, Keto and O-Acetyl oximes have been deblocked using chemisorbed Chromyl chloride on Bentonite and Silica Gel. A comparative study between the Chromyl chloride in solution and supported is also given.

Infrared Assisted Production of 3,4-Dihydro-2(1H)-pyridones in Solvent-Free Conditions

A green approach for the synthesis of a set of ten 4-aryl substituted-5-alcoxy carbonyl-6-methyl-3,4-dihydro-2(1H)-pyridones using Meldrum’s acid has been devised, the absence of solvent and the activation with infrared irradiation in addition to a multicomponent protocol are the main reaction conditions. The transformations proceeded with moderated yields (50–75%) with a reasonable reaction rate (3 h). It is worth noting that two novel molecules of the new class of the bis-3,4-dihydropyridones were also obtained. In addition, a comparison without the use of infrared irradiation was performed.

Characterization of a bentonitic clay and its application as catalyst in the preparation of benzyltoluenes and oligotoluenes

Abstract The preparation of oligomeric toluenes catalyzed with a bentonitic clay, using thermal energy and ultrasound, was performed and evaluated. When ortho and para benzyltoluenes were studied, the oligomerization reaction was found to be dependent of the catalyst amount, reaction time, temperature and the presence of pyridine as competitive inhibitor. A proposal for the molecular structure calculation analysis at semiempirical AM1 level was proposed based on the regioselectivity and in the oligomerization pathway. Furthermore, a detailed study to characterize the clay was performed, thus several physicochemical properties of the clay were determinated by means of: 29 Si and 27 Al MAS–NMR, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, IR spectrophotometry, thermal analysis (DTA, TG-DTG), and adsorption techniques (N 2 -BET).

Role of lactone ring in structural, electronic, and reactivity properties of aflatoxin B1: a theoretical study.

This study involved quantum mechanical calculations to explain the chemical behavior of the lactone ring of aflatoxin B1, which is a carcinogenic hazardous compound. The aflatoxin B1 compound, produced by the fungi Aspergillum flavus, was studied with the B3LYP/6-311+G(d,p) method; its reactivity properties were accounted for by means of the calculated geometrical and electronic parameters. The results obtained indicate that the fused A, B, C, and D rings of aflatoxin adopt a continuous planar conformation. The carbon atom of the lactone group presents a highly electrophilic character, since the population analysis yields a high positive charge for this atom, whereas high negative charges were recorded for both oxygen sites of that group. Thus, in an acidic aqueous medium, the oxygen atoms could be protonated and the carbon site may suffer a nucleophilic attack by water. Accordingly, the OC−O bond length has been lengthened substantially. So it was demonstrated that the lactonic ring of aflatoxin B1 is hydrolyzed under acidic conditions by an acid-acyl bimolecular mechanisms, AAC2, suggesting the deletion of its carcinogenic properties.

Clay-mediated cyclooligomerization of olefin oxides: a one-pot route to crown ethers

The catalytic synthesis of substituted 1,3-dioxolanes, 1,4-dioxanes, 9-crown-3, 12-crown-4 and 15-crown-5 ethers, from alkyl oxiranes and a montmorillonite type clay is discussed.

Green Approach—Multicomponent Production of Boron—Containing Hantzsch and Biginelli Esters

Multicomponent reactions are excellent methods that meet the requirements of green chemistry, by reducing the number of steps, and consequently reducing purification requirements. Accordingly, in this work, 11 novel hybrid-boron-containing molecules, namely eight 1,4-dihydropyridines and three 3,4-dihydropyrimidinones, derived from formylphenylboronic acids (ortho, meta and para), were obtained using a green approach, involving H-4CR and B-3CR practices, in the presence of ethanol, which is a green solvent, and using three comparatively different modes of activation (mantle heating, yield 3%–7% in 24 h, Infrared Radiation (IR) irradiation, yield 12%–17% in 12 h, and microwave irradiation, yield 18%–80%, requiring very low reaction times of 0.25–0.33 h). In addition, as a green-approach is offered, a convenient analysis, of the 12 green chemistry principles for the overall procedure was performed. Finally, since all the products are new, characterizations were carried out using common analytic procedures (1H, 11B, and 13C NMR, FAB+MS, HRMS, and IR). The accurate mass data of unexpected ions related to interactions between thioglycerol and the expected products, in the FAB+-mode, enabled unequivocal characterization of the target molecules.

QSAR, docking, dynamic simulation and quantum mechanics studies to explore the recognition properties of cholinesterase binding sites

A set of 84 known N-aryl-monosubstituted derivatives (42 amides: series 1 and 2, and 42 imides: series 3 an 4, from maleic and succinic anhydrides, respectively) that display inhibitory activity toward both acetylcholinesterase and butyrylcholinesterase (ChEs) was considered for Quantitative structure-activity relationship (QSAR) studies. These QSAR studies employed docking data from both ChEs that were previously submitted to molecular dynamics (MD) simulations. Donepezil and galanthamine stereoisomers were included to analyze their quantum mechanics properties and for validating the docking procedure. Quantum parameters such as frontier orbital energies, dipole moment, molecular volume, atomic charges, bond length and reactivity parameters were measured, as well as partition coefficients, molar refractivity and polarizability were also analyzed. In order to evaluate the obtained equations, four compounds: 1a (4-oxo-4-(phenylamino)butanoic acid), 2a ((2Z)-4-oxo-4-(phenylamino)but-2-enoic acid), 3a (2-phenylcyclopentane-1,3-dione) and 4a (2-phenylcyclopent-4-ene-1,3-dione) were employed as independent data set, using only equations with r(m(test))²>0.5. It was observed that residual values gave low value in almost all series, excepting in series 1 for compounds 3a and 4a, and in series 4 for compounds 1a, 2a and 3a, giving a low value for 4a. Consequently, equations seems to be specific according to the structure of the evaluated compound, that means, series 1 fits better for compound 1a, series 3 or 4 fits better for compounds 3a or 4a. Same behavior was observed in the butyrylcholinesterase (BChE). Therefore, obtained equations in this QSAR study could be employed to calculate the inhibition constant (Ki) value for compounds having a similar structure as N-aryl derivatives described here. The QSAR study showed that bond lengths, molecular electrostatic potential and frontier orbital energies are important in both ChE targets. Docking studies revealed that despite the multiple conformations obtained through MD simulations on both ChEs, the ligand recognition properties were conserved. In fact, the complex formed between ChEs and the best N-aryl compound reproduced the binding mode experimentally reported, where the ligand was coupled into the choline-binding site and stabilized through π-π interactions with Trp82 or Trp86 for BChE and AChE, respectively, suggesting that this compound could be an efficient inhibitor and supporting our model.