Elton L. Borges

Organochalcogen compounds from glycerol: synthesis of new antioxidants.

We describe here a simple method for the synthesis of glycerol derivatives containing an organochalcogen unit (Se, Te and S) using NaBH4 and PEG-400 as a solvent. The new methodology was used to synthesize a range of new organochalcogen compounds in good yields. Furthermore, four of synthesized compounds were evaluated for their antioxidant activity using different assays, such as 2-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, nitric oxide (NO) and hydroxyl radical (OH) scavenging, ferric ion reducing antioxidant power (FRAP), ferrous ion chelating, superoxide dismutase-like activity and inhibition of linoleic acid lipid peroxidation. The new organotellurium 2,2-dimethyl-4-(phenyltellanylmethyl)-1,3-dioxolane 3 j showed antioxidant activity and was more effective in inhibition of induced lipid peroxidation compared to solketal 4. Selenium and sulfur analogs 3a and 3m and solketal 4 did not present antioxidant effect. These findings suggest that 2,2-dimethyl-4-(phenyltellanylmethyl)-1,3-dioxolane 3 j is a promising antioxidant and that its activity is influenced by the presence of the tellurium atom on the structure.

Addition of thiols to phenylselenoalkynes using KF/Alumina under solvent-free conditions

We present herein the results of a simple and efficient protocol for the hydrothiolation of phenylselenoalkynes promoted by KF/Al2O3 using solvent-free conditions. This improved method furnishes selectively the corresponding (Z)-1-phenylseleno-2-organylthio-1-alkenes in reasonable to good yields starting from selenoalkynes and aliphatic or aromatic thiols. The presence of the phenylselenium group in the alkyne directed the regiochemistry of the thiol addition. The catalytic system can be reused up to 4 times without previous treatment.

Synthesis of enantiomerically pure bis(2,2-dimethyl-1,3-dioxolanylmethyl)chalcogenides and dichalcogenides

Herein we describe the reaction between the nucleophilic species of chalcogenium (sulfur, selenium and tellurium) and (R)- and (S)-solketal tosylates to prepare enantiomerically pure bis-1,3-dioxolanylmethyl chalcogenides and dichalcogenides in short reaction times and good yields. Furthermore, the new diselenide 4a was evaluated in the Michael reaction with acrylonitrile, giving (R)-3-[(2,3-dihydroxypropyl)selanyl]propanenitrile 6b after two steps.

Atom-Economic Synthesis of Functionalized Octahydroacridines from Citronellal or 3-(Phenylthio)-citronellal

Abstract Here we present a simple, solvent-free, one-pot, hetero-Diels–Alder reaction of (R)-citronellal or 3-(phenylthio)-citronellal with arylamines using solid-supported catalyst (SiO2/ZnCl2). This general, efficient, and improved method is selective, affording preferentially new trans-fused 3-(phenylthio)-octahydroacridines (S-OHAs) in good yields. The use of microwave irradiation facilitates the procedure and accelerates the reaction.

Green Hydroselenation of Aryl Alkynes: Divinyl Selenides as a Precursor of Resveratrol

A simple and efficient protocol to prepare divinyl selenides has been developed by the regio- and stereoselective addition of sodium selenide species to aryl alkynes. The nucleophilic species was generates in situ, from the reaction of elemental selenium with NaBH4, utilizing PEG-400 as the solvent. Several divinyl selenides were obtained in moderate to excellent yields with selectivity for the (Z,Z)-isomer by a one-step procedure that was carried out at 60 °C in short reaction times. The methodology was extended to tellurium, giving the desired divinyl tellurides in good yields. Furthermore, the Fe-catalyzed cross-coupling reaction of bis(3,5-dimethoxystyryl) selenide 3f with (4-methoxyphenyl)magnesium bromide 5 afforded resveratrol trimethyl ether 6 in 57% yield.

Glycerol as Precursor of Organoselanyl and Organotellanyl Alkynes

Herein we describe the synthesis of organoselanyl and organotellanyl alkynes by the addition of lithium alkynylchalcogenolate (Se and Te) to tosyl solketal, easily obtained from glycerol. The alkynylchalcogenolate anions were generated in situ and added to tosyl solketal in short reaction times, furnishing in all cases the respective products of substitution in good yields. Some of the prepared compounds were deprotected using an acidic resin to afford new water-soluble 3-organotellanylpropane-1,2-diols. The synthetic versatility of the new chalcogenyl alkynes was demonstrated in the iodocyclization of 2,2-dimethyl-1,3-dioxolanylmethyl(2-methoxyphenylethynyl)selane 3f, which afforded 3-iodo-2-(2,2-dimethyl-1,3-dioxolanylmethyl) selenanylbenzo[b]furan in 85% yield, opening a new way to access water-soluble Se-functionalized benzo[b]furanes.

Selective synthesis of 4-thiomethyl-1,3-dioxolan-2-ones under microwave irradiation using an environmentally benign KF/Al2O3/PEG-400 system

We describe a simple and rapid method for selective synthesis of 4-thiomethyl-1,3-dioxolan-2-ones promoted by KF/Al2O3 using PEG-400 as solvent under microwave irradiation. The protocol employs 3-O-tosyl glycerol 1,2-carbonate 1 and a diverse array of thiols 2 to afford corresponding 4-thiomethyl-1,3-dioxolan-2-ones 3 in good yield and short reaction time compared with conventional heating methods. Moreover, selective synthesis of 1,3-bis-arylthiopropan-2-ol 4 by a stoichiometric and temperature-controlling reaction is presented.

Synthesis of Organosulfur and Organoselenium Derivatives from Castor Oil

Aiming to meet some principles of Green Chemistry, this article describes the synthesis of new organochalcogenium compounds derived from a renewable source. For this purpose, methyl (Z)-12-[(p-toluenesulfonyl)oxy]methyl-9-octadecenoate was initially prepared in two steps from castor bean oil. It was used in the synthesis of (Z)12-organylchalcogenoctadec-9-enoates by nucleophilic substitution with chalcogenolate ions. This is an efficient synthetic route for the synthesis of various new, semi-synthetic sulfides and selenides in good yields.

Síntese de Sulfetos e Selenetos Derivados do Óleo de Mamona

Este artigo descreve a sintese de novos compostos organocalcogenios derivados de fonte renovavel, atendendo alguns dos principios da Quimica Verde. Para isto, utilizando o oleo de mamona como material de partida, foi preparado inicialmente o ( Z )-12-[ ( p- toluenossulfonil)oxi]-9-octadecenoato de metila, intermediario chave para a sintese dos ( Z )-12-organoilcalcogenoctadec-9-enoatos de alquila via substituicao nucleofilica com ions calcogenolatos (tiolatos ou selenolatos). Esta rota sintetica se mostrou eficiente para a sintese de varios sulfetos e selenetos ineditos com bons rendimentos. DOI: 10.5935/1984-6835.20140006