Hélio A. Stefani

Addition of hydrogen halides to acetylenic selenides. Synthesis of 1-halo-1-selenoalkenes

Abstract Acetylenic selenides react with HX (X=Cl, Br, I) at room temperature to give 1-halo-1-selenoalkenes in good yields. The 1-iodo-1-selenoalkenes were transformed into the corresponding vinylic organometallics (M=Zn, Cu, Cr).

Nucleophilic Addition of Potassium Alkynyltrifluoroborates to d-Glucal Mediated by BF3·OEt2: Highly Stereoselective Synthesis of α-C-glycosides

A convenient, mild and highly stereoselective method for C-glycosidation (alkynylation) of D-glucal with various potassium alkynyltrifluoroborates, mediated by BF3x OEt2 and involving oxonium intermediates, preferentially provides the alpha-acetylene glycoside products with good yields.

3,4-DIHYDROPYRIMIDIN-2(1H)-ONES: FAST SYNTHESIS UNDER MICROWAVE IRRADIATION IN SOLVENT FREE CONDITIONS

Abstract Microwave irradiation has been used to accelerate the synthesis of the Biginelli compounds, in one-pot reaction between β-keto esters, aryl aldehydes, and urea. These solvent-free reactions show that it is possible to prepare these compounds in a short time reaction and with good yield and easily isolable.

Alkynyl sulfides and selenides from alkynyl bromides and diorganoyl chalcogenides promoted by copper(I) iodide

Abstract Alkynyl sulfides and selenides were obtained in good yields by reacting alkynyl bromides with diorganoyl disulfides and diselenides in hexamethylphosphoric triamide (HMPA) in the presence of copper (I) iodide.

Synthesis and anti-inflammatory activity of acetylenic thiophenes

A series of acetylenic thiophene derivatives have been synthesized via Pd-catalyzed coupling reaction of 2-(butyltelluro)thiophene with a variety of terminal alkynes. These compounds showed good anti-inflammatory activity in the carrageenin-induced paw edema assay on rats.

New acetylenic furan derivatives: synthesis and anti-inflammatory activity

Abstract A series of acetylenic furan derivatives have been synthesized via Pd-catalyzed coupling reactions of 2-(alkyltelluro)furan with several terminal alkynes. These compounds showed good anti-inflammatory activity in the carrageenin-induced rat paw edema assay. This represents a new and efficient method for the synthesis of pharmacologically active compounds.

Sonogashira cross-coupling reaction of organotellurium dichlorides with terminal alkynes

The Sonogashira cross-coupling reaction of vinylic and heteroaromatic tellurium dichlorides has been explored, yielding the corresponding enynes and 2-alkynyl substituted heteroaromatic compounds. The reaction was carried out with PdCl2/CuI as catalysts and triethylamine as base, using methanol as solvent. The reaction proceeded under mild conditions and the cross-coupled products were obtained in good yields and in a stereoconservative manner.

Addition of tellurium tetrabromides and alkyl and aryl tellurium tribromides to terminal acetylenes

Abstract The addition of tellurium tetrabromides and alkyl and aryl tellurium tribromides to terminal acetylenes gives rise to thecorresponding bis(b-bromovinyl)tellurium dibromides and (b-bromovinyl)organyl tellurium dibromides which, by treatment withNaBH 4 , leads to formation of the reduced tellurides.

Preparation of the Principal Classes of Organic Tellurium Compounds

This chapter discusses diorganyl tellurides and ditellurides, organyltellurium trichlorides and diorganyltellurium dichlorides, which were the first classes of compounds investigated at the beginning of tellurium (Te) organic chemistry. Diorganyl tellurides, compounds with two organic groups linked to a Te atom, constitute the most abundant and familiar class of organic Te compounds. The organic groups of the most differentiated types can be identical or different, giving rise to symmetrical or unsymmetrical tellurides. The main routes to symmetrical diorganyl tellurides involve the direct reaction of nucleophilic telluride dianions with alkylating or arylating reagents. Otherwise, the electrophilic Te tetrahalides react with arylmagnesium reagents, giving diaryl tellurides. Diorganyl ditellurides are prepared by three routes: alkylation or arylation of the ditelluride dianion; oxidation of tellurolate anions; and reduction of the corresponding organyltellurium trichlorides. Organyltellurium trichlorides and diorganyltellurium dichlorides are prepared starting from the electrophilic tellurium tetrachloride by (1) condensation reactions with active methylene compounds; (2) addition to a C=C bond; (3) electrophilic substitution in aromatic hydrocarbons; and (4) reaction with organomercury chlorides. This chapter explores the preparation of principal classes of organic Te compounds in detail.

Expanding cyclitol structural diversity by biocatalysis and metalocatalysis. A click chemistry approach

The palladium catalyzed cross-coupling reaction of phenyltrifluoroborate with a chemoenzymatically derived bromoazidoconduritol, combined with 1,3-dipolar cycloaddition, with a variety of alkynes is described. Fourteen new compounds were synthesized in moderate to good yields. The click chemistry reaction can be effected by using sodium ascorbate and CuSO4 · 5H2O as catalyst in toluene–H2O at room temperature.