Synthesis and application of chiral beta-amino disulfides as ligands for the enantioselective addition of diethylzinc to aldehydes

A new class of chiral beta-amino disulfides was synthesized from readily available and inexpensive starting materials by a straightforward method and their abilities as ligands were examined in the enantioselective addition of diethylzinc to aldehydes. Enantiomeric excesses of up to 99% have been obtained using 0.5 mol % of the chiral catalysts.

Mild and efficient one-pot synthesis of chiral beta-chalcogen amides via 2-oxazoline ring-opening reaction mediated by indium metal

A simple and efficient procedure for the synthesis of beta-seleno and beta-thio amides via the ring-opening reaction of chiral 2-oxazolines in the presence of indium metal has been developed. Features of this method include the following: (i) easily and accessible starting materials; (ii) indium metal is more stable and less expensive then its respective salts; (iii) useful to excellent yields of beta-chalcogen amides derivatives. (C) 2008 Elsevier B. V. All rights reserved.

Phase transitions of frozen camu-camu (Myrciaria dubia (HBK) McVaugh) pulp: Effect of cryostabilizer addition

Camu-camu is a tropical fruit with very high vitamin C content and commercialized as frozen pulp. Enthalpies of freezing, temperatures of the onset of ice melting, and glass transition temperatures of the maximally freeze-concentrated phase (T`(g)) of camu-camu pulp and of samples containing maltodextrin (DE20) and sucrose were measured by differential scanning calorimetry. Maltodextrin exhibited the largest freeze stabilization potential, increasing T`(g) from -58.2 degrees C (natural pulp) to -39.6 degrees C when 30% (w/w) maltodextrin DE 20 was added. Sucrose showed negligible effect on T`(g) but enhanced considerably the freezing point depression and less amount of ice was formed.

Analysis of experimental interlocking blocks of concrete with addition of residues of process the tires retreading production

Analysis of experimental interlocking blocks of concrete with addition of residues of process the tires retreading production. With the population growth in recent years, industry in general has adjusted itself to resulting demand. the industry of tire retreading generates residues that have been discarded without any control. this adds to environmental pollution and promotes the proliferation of vectors harmful to health, aiming to find an application for this type of residues, this study presents experimental results to interlocking concrete block pavements, with addition of residues tires, interlocking blocks were built up and we determined, through laboratory tests, the need to set the mark that provide greater return regarding analyzed characteristics, there are four types of dosage of concrete with residues tires. We accomplished tests of compression strength, water absorption and resistance to impact. Through the preliminary results, we verified that are satisfactory, confirming the possibility of applying this type of interlocking block in environments with low demand, which would bring the economy of natural sources of aggregates, beyond ecological benefits through the reuse of residues from retreading of tires.

Influence of ceria addition on thermal properties and local structure of bismuth germanate glasses

Bismuth germanate glasses are interesting materials due to their physical properties and their unique structural characteristics caused by the coordination changes of bismuth and germanium atoms. Glasses of the bismuth germanate system were prepared by melting/molding method and were investigated concerning their thermal and structural properties. The structural analysis of the samples was carried out by micro-Raman and Fourier transform infrared spectroscopes. It was observed that the glass structure is formed basically by GeO(4) tetrahedral units also having the formation of the GeO(6) octahedral units. BiO(2) was considered a network former by observing the presence of octahedral BiO(6) and pyramidal BiO(3) groups in the local structure of the samples. An absorption band observed at 1103 cm(-1) in the IR spectrum of the undoped glass was attributed to the Bi-O-Ge and/or Bi-O-Bi linkage vibration. The said band shifted to lower wavenumbers after the CeO(2) addition thus reflecting changes in the glass network. Cerium oxide was an efficient oxidant agent to prevent the darkening of the glasses which was probably associated to the reduction of Bi ions. However, CeO(2) was incorporated as a local network modifier in the glass structure even at concentrations of 0.2 mol%. (C) 2010 Elsevier B.V. All rights reserved.

Reactions of 1,2.,5-thiadiazole 1,1-dioxide derivatives with nitrogen nucleophiles. Part IV. Addition of alpha-diamines

alpha-diamines, such as ethylendiamine and o-phenylendiamine, add to 3,4-aryl-disubstituted 1,2,5-thiadiazole 1,1-dioxides to give dihydropyrazines or quinoxalines, respectively and sulfamide. The new compound acenaphtho [5,6-b]-2,3-dihydropyrazine was synthesized and characterized. The addition of ethylendiamine to 3,4-diphenyl-1,2,5-thiadiazoline 1,1-dioxide gives 3,4-disubstituted thiadiazoildine 1,1-dioxide, dihydropyrazines, or pyrazines, depending on the reaction condition used. The reactions were followed by cyclic voltammetry and NMR spectroscopy which, in some cases, allowed the detection of the thiadiazolidine intermediate. Copyright (c) 2008 John Wiley & Sons, Ltd.

Synthesis of new fluorous modular chiral ligand derivatives from amino alcohols and application in enantioselective carbon-carbon bond-forming alkylation reactions

N-Trifluoracyl beta-chalcogeno amides and N-perfluoracyl beta-thio amide ligands were prepared by a simple and efficient reaction sequence. These new ligands were evaluated in palladium-catalyzed alkylation of rac-(E)-1,3-diphenyl-2-propenyl acetate in the presence of dimethyl malonate and an enantioselectivity of up to 99% was obtained. After catalysis, the fluorous ligand can be easily recovered by liquid-liquid extraction and reused without loss in the activity. (C) 2010 Elsevier Ltd. All rights reserved.

Enantioselective transesterification catalysis by Candida antarctica lipase immobilized on superparamagnetic nanoparticles

Lipase B from Candida antarctica can be directly immobilized onto functionalized superparamagnetic nanoparticles, preserving its enzymatic activity in the enantioselective transesterification of secondary alcohols, with excellent results in terms of enantiomeric discrimination. The immobilized enzyme can be easily recovered with a magnet, allowing its reuse with negligible loss of activity. (C) 2009 Elsevier Ltd. All rights reserved

Tellurium in organic synthesis: the enantioselective synthesis of the pheromone blend components of Mayetiola destructor, Drosophila mulleri and Contarinia pisi

The components of the pheromone blend of Mayetiola destructor, Drosophila mulleri, and Contarinia pisi were synthesized in high enantiomeric excess (99% ee) from a common enantiopure dianion prepared from an enantiopure hydroxytelluride. (C) 2009 Elsevier Ltd. All rights reserved.

Improving the enantioselective bioreduction of aromatic ketones mediated by Aspergillus terreus and Rhizopus oryzae: the role of glycerol as a co-solvent

The improvement of the enzymatic performance of Aspergillus terreus and Rhizopus oryzae in enantioselective bioreductions by using glycerol as a co-solvent has been studied. In the most of the bioreductions, glycerol has demonstrated its potential for improved conversions (up to >99%) and enantioselectivities (up to >99%) when compared to reactions in aqueous or other aqueous-organic media (THF, diethyl ether, toluene, DMSO and acetonitrile). Moreover, high isolated yields of the desired chiral alcohols have been obtained on a preparative scale showing the great potential of this green solvent in biocatalysis. (C) 2009 Elsevier Ltd. All rights reserved.

Lipase-Catalyzed Highly Enantioselective Kinetic Resolution of Boron-Containing Chiral Alcohols

The first application of enzymes as catalysts to obtain optically pure boron compounds is described. The kinetic resolution of boron-containing chiral alcohols via enantioselective transesterification catalyzed by lipases was studied. Aromatic, allylic, and aliphatic secondary alcohols containing a boronate ester or boronic acid group were resolved by lipase from Candida antartica (CALB), and excellent E values (E > 200) and high enantiomeric excesses (up to >99%) of both remaining substrates and acetylated product were obtained.

Stereoselective Nucleophilic Addition of Potassium Alkyltrifluoroborates to Cyclic N-Acyliminium Ions: a Simple and Mild Approach to Chiral 5-Alkyl-pyrrolidin-2-ones

The stereoselective nucleophilic addition of potassium alkyltrifluoroborates to cyclic N-acyliminium ions derived from N-benzyl-3,4,5-triacetoxy-pyrrolidin-2-one, which affords 5-substituted-pyrrolidin-2-ones, is described. The products are obtained in moderate to good yields and are produced predominantly as the anti diastereomer.

Mechanistic study of the addition reaction of TeCl(4) to alkynes: Participation of TeCl(3) centered-radical

The mechanism of the addition reaction of TeCl(4) to alkynes was indirectly established by the detection of TeCl(3) centered radicals using EPR spin trapping, ESI-MS and ESI-MS/MS characterization. Crown Copyright (C) 2008 Published by Elsevier B. V. All rights reserved.

Tellurium in organic synthesis: a new approach to trisubstituted gamma-butyrolactones with trans-trans relative stereochemistry. Total enantioselective synthesis of (-)-Blastmycinolactol, (+)-Blastmycinone, (-)-NFX-2, and (+)-Antimycinone

The total synthesis of (-)-Blastmycinolactol, (+)-Blastmycinone, (-)-NFX-2, and (+)-Antimycinone was accomplished in few steps in high yields and ee, starting from enantiomerically enriched (S)-Z-vinylic hydroxytellurides. (C) 2010 Published by Elsevier Ltd.

Catalytic Enantioselective alpha-Arylation of Carbonyl Compounds

Enantioselective creation of benzylic quaternary centers still is a continuous challenge to many synthetic organic chemists. Among the existing methods for installation of this type of center, the direct asymmetric alpha-arylation of carbonyl compounds is very attractive due to the ready availability of the coupling substrates. Herein, we present some new tools to the catalytic asymmetric alpha-arylation of carbonyl compounds that overcame many of the drawbacks posted in previous methods for this type of reaction.