Showing papers in "Letters in Organic Chemistry in 2007"

Improved Synthesis of Benzotriazoles and 1-Acylbenzotriazoles by Ultrasound Irradiation

Abstract: Univ Sao Paulo, Lab Sintese Mol Bioativas, Dept Farm, Fac Ciencias Farmaceut, BR-05508300 Sao Paulo, Brazil

Ionic Liquid/Silica Sulfuric Acid Promoted Fast Synthesis of a Biginelli-Like Scaffold Reaction

Abstract: Biginelli-like scaffolds were synthesized in good yields by a three-component condensation reaction of 5,5-dimethyl-1,3-cyclohexanedione, an aldehyde and urea, N-methylurea or thiourea in 1-butyl-3- methylimidazolium bromide ((bmim)Br) as ionic liquid (IL) in the presence of silica sulfuric acid (SSA) as solid acid catalyst at 100 °C within less than 2 hours.

Aza-Michael addition of amines to activated alkenes catalyzed by Silica supported perchloric acid under a solvent-free condition ¶

Abstract: An efficient aza-Michael addition of amines to a series of α,β-unsaturated ketones, carboxylic esters, nitriles and chalcones has been carried out using perchloric acid supported over silica gel (HClO4-SiO2) at room temperature in high yields under solvent-free reaction conditions.

Vanadium-Substituted Keggin Type Heteropolyacid are Used for the Selective Oxidation of Sulfides to Sulfoxides and Sulfones Using Hydrogen Peroxide

Abstract: Fil: Romanelli, Gustavo Pablo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Investigacion y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigacion y Desarrollo en Ciencias Aplicadas; Argentina

Montmorillonite K10 Catalyzed Selective Oxidation of Sulfides to Sulfoxides Using Hydrogen Peroxide

Abstract: A clean and highly selective oxidation of sulfides to sulfoxides with 35% hydrogen peroxidecatalyzed by Montmorillonite K10 in methanol is described. A series of structurally different sulfides wereoxidized selectively at room temperature in excellent yields. This reaction is very simple and proceeds withoutover-oxidation under mild condition, and shows many advantages over the existing methodologies. Usingthis procedure, sulfides bearing functional groups such as hydroxyl, methoxy, amino, nitrile, aldehyde, andolefinic double bond remained intact. Keywords: Montmorillonite K10, hydrogen peroxide, sulfide, sulfoxide, catalyzed sulfoxidation.Convenient synthesis of organic sulfoxides is achallenging research in synthetic organic chemistry becauseof the importance of the sulfoxides as intermediates inchemically and biologically active compounds [1].Oxidation of sulfides is a very useful route for preparation ofsulfoxides and several oxygenating reagents as well ashalogenating ones are available. This type of transformationby various oxidation methods has been extensively reviewed[2]. However, in conventional oxidation methods undesir-able overoxidation to sulfone [3], and in halogenatingreactions the C-S bond cleavage, formation of halo-derivatives or halogenation of aromatic ring are quitefrequent competing reactions [4]. Besides the extendedreaction period, most of the oxidation methods useexpensive, hazardous peracids and toxic heavy metal or rareoxidant that are difficult to prepare and detract their practicalapplication in many cases. The selective oxidation ofsulfides to sulfoxides has also been developed usingtransition metal catalyzed sulfoxidation with hydrogenperoxide and derivatives [5], and metal Schiff basecomplexes in combination with a variety of oxidant havebeen used as catalysts for this purpose [6]. Furthermore, anenzymatic catalysis has also been reported [7]. However themajor shortcoming of all heme-dependent peroxidases andSchiff base-metal complexes is their low operation stabilitydue to facile oxidative degradation of heterocyclic orporphyrine ring. Heterogeneous catalyzed oxidativetransformations by solid supports have gained popularityduring the past decades thanks to distinct advantages ofselectivity, mildness and operational simplicity. Anincreasingly popular category of supported catalysts andreagents have been developed in an effort to achieve facile,efficient, cheap and selective methods [8]. In the course ofour studies on selective oxidative organic transformations [9,10], and using solid support mediated reaction [11], and toelaborate safer and simpler oxidation process, we haveinvestigated the role of natural clays in catalytic oxidation ofsulfides to corresponding sulfoxides using hydrogenperoxide. So far, the capability of hydrogen peroxide as anefficient oxidant has been studied considerably both fromenvironmental and economical viewpoints. It is ideal wasteavoiding oxidant and its aqueous solution shows safety inusage, storage and handling [12, 13]. But, as mentioned inthe literature, without activation with a catalyst, it has to beused in controlled manner to avoid over-oxidation to sulfone[14]. Drabowicz [15] reported that for selective oxygenationof sulfides to sulfoxides by hydrogen peroxide in theabsence of catalyst, the reaction time was extremely long andsome other functional groups were easily destroyed. This isthe first report of the clay catalyzed selective oxidation ofsulfides to sulfoxides using 35% H

Enantiospecific Synthesis of (-)-Radicamine B

Abstract: Radicamine B 2, the enantiomer of natural radicamine B 5, was synthesized via a chiral nitrone derived from D-xylose in 10 steps with an overall yield of 15%.

Lanthanum Trichloride (LaCl3): An Efficient Catalyst for Conjugate Addition of Amines to Electron-Deficient Olefins

Abstract: Electron-poor alkenes undergo rapid conjugate addition with a wide range of amines in the presence of lanthanum trichloride at room temperature to produce the corresponding 2-amino compounds in excellent yields.

Thia-michael addition reactions in water using 3-[Bis(alkylthio) methylene]pentane-2,4-diones as odorless and efficient thiol equivalents

Abstract: 3-[Bis(ethylthio)methylene]pentane-2,4-dione (1a) and 3-[bis(benzylthio)methylene]pentane-2,4-dione (1b) have been investigated as non-thiolic and odorless thiol equivalents in thia-Michael addition reactions. In the presence of aqueous p-dodecyl benzenesulfonic acid (DBSA), compound (1) was cleaved and the generated thiols underwent facile conjugate addition to alpha,beta-unsaturated ketones 2 in-situ, affording the corresponding beta-keto sulfides (3) in good yields.

Selenium-Containing Heterocycles From Isoselenocyanates: Synthesis of Ethyl 4-Oxo-2-amino-4,5-dihydroselenophene-3-carboxylates

Abstract: Aryl and alkyl isoselenocyanates 2 react with ethyl γ-chloroacetoacetate (1) in the presence of triethylamine to give the corresponding 4-oxo-2-amino-4,5-dihydroselenophene-3-carboxylates 4a-f in moderate to good yields.

Synthesis of 3-(Azolylmethylene)Chroman-4-ones via Addition of Indoles and N-Methylpyrrole to 3-(Polyfluoroacyl)Chromones

Abstract: Reactions of 3-(polyfluoroacyl)chromones with indole and N-methylindole in refluxing pyridine and N- methylpyrrole under solvent-free conditions proceed at the C(2) atom of the chromone system with pyrone ring opening and subsequent cyclization to 2-hydroxy-3-(indol-3-ylmethylene- or pyrrol-2-ylmethylene)-2-(polyfluoroalkyl)chroman- 4-ones in good yields. Treatment of these compounds with morpholine gives trans-indolyl(pyrrolyl)chalcones. The synthetic utility of 2-unsubstituted 3-formyl- and 3- acylchromones derives primarily from the reactivity of their three electron-deficient centers at C-2, C-4, and the 3-formyl or 3-acyl groups. The majority of the reactions with these compounds are nucleophilic additions with concomitant opening of the pyrone ring leading to various types of het- erocyclic products (1-3). In contrast to well studied 3- formyl- (4-8) and 3-acylchromones (9,10), no data on the chemical properties of 3-(polyfluoroacyl)chromones 1 have been documented. This is quite surprising, especially be- cause chromones containing an electron-withdrawing R F CO group in the 3-position should contain the highly electro- philic C(2) atom, which is usually attacked by nucleophilic reagents. 3-Polyfluoroacyl substituted chromones, despite their po- tential interest as building blocks in organic synthesis for the construction of more complex polyfluoroalkyl-containing heterocycles have not received much attention, probably owing to the lack of general methods for the preparation of these compounds. We have recently developed a simple and convenient synthesis of 3-(polyfluoroacyl)chromones 1 from 2-hydroxy-2-(polyfluoroalkyl)chroman-4-ones and diethoxy- methyl acetate and found that their reactions with primary

Synthesis and Antitumor Activities of 3-Substituted 1-(5-formylfurfuryl)indolin-2-one Derivatives

Abstract: Forty-two 3-substituted 1-(5-formylfurfuryl)indolin-2-ones were synthesized and most of these compounds ex- hibited potent inhibitory activities against P. oryzae (MIC = 0.78-25 μg/mL) and human intestinal Caco-2 cells (IC50 = 0.19-9.42 μM). Eight compounds selected for further screening also showed inhibitory activities (IC50 = 1.84-10.32 μM) against human lung adenocarcinoma cells (SPC-A1).

Polyvinylpolypyrrolidone-Bromine Complex, Mild and Efficient Polymeric Reagent for Selective Deprotection and Oxidative Deprotection of Silylethers

Abstract: Mild and convenient method for deprotection and direct oxidative deprotection of silyl ethers to the corresponding hydroxy and carbonyl compounds is described using polyvinylpolypyrrolidone-bromine complex (PVPP-Br2). Selective oxidative deprotection of benzylic silyl ethers in the presence of primary aliphatic alcohols was also achieved at room temperature.