1,720,968 research outputs found
Naplephos: a modular library of chiral phosphines based on glucose for highly enantioselective asymmetric catalysis
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Rational design of pseudo-enantiomeric libraries of ligands based on pyranoses for application in asymmetric catalysis
No full textThis review deals with the solution given by synthetic chemists to overcome the problem of access to both enantiomers of a given process when carbohydrates are used as ligands. Indeed, although sugars are stereochemically rich compounds, and derived from one of the most abundant renewable material, their use in asymmetric catalysis has been limited by the fact that most of them have D-configuration.
This review explains the concept of pseudo-enantiomeric ligands, and collects examples based on pyranoses, by describing their relevant use in asymmetric catalysis
Carbohydrates as building blocks of privileged ligands
No full text“Privileged ligands” are chiral auxiliaries of wide applicability in asymmetric catalysis. In the previous decades, their effective three-dimensional structures have often been reproduced by using building blocks from a “chiral pool”, such as the carbohydrates. This strategy has provided unique ligand moieties which combine the performance of “privileged ligands” with increased flexibility and accessibility. This review gives an overviewof the research within this field, giving emphasis to the best results obtained with each ligand type
New tagged naplephos ligands for asymmetric allylic substitutions undertraditional and unconventional conditions
No full textCarbohydrated-based pyridine-2-carboxamides for Mo-catalyzed asymmetric allylic alkylations
No full textBis(pyridine-2-carboxamides) were prepared from 1,2-diamines obtained from alpha-D-ghlcose and alpha-D-mannose. The ligands were assessed in molybdenum-catalyzed asymmetric allylic alkylations (AAA) by using both methyl (E)-3-phenyl-2-propenyl and methyl rac-1-phenyl-2-propenyl carbonates and dimethyl malonate as nucleophile under microwave irradiation. High enantioselectivity (99 % ee) and high regioselectivity (49:1 in favour of the branched isomer) were observed in reactions of the linear achiral substrate in the presence of 10 mol-% of a catalyst prepared from a ligand derived from glucose. Somewhat lower enantioselectivity (up to 96 % ee) was observed in reactions with the branched racemic carbonate by using the same ligand. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)</p
A novel and robust homogeneous supported catalyst for biodiesel production
No full textA homogeneous supported catalyst based on Zn(II) was prepared by anchoring complex [Zn(OAc)2(N,N0-chelate)] on silica, where N,N0-chelate is a suitably functionalised di-imine ligand. The complex was able to promote the esterification and transesterification of acidic vegetable oils at
160 °C within two hours. The catalyst could be also easily recovered and immediately re-cycled
TOTALLY RECYCLABLE CATALYSTS FOR ESTERIFICATION REACTIONS
No full textThe invention relates to a catalytic esterification process for the synthesis of an ester of a fatty acid using zinc oxide (ZnO) or zinc(ll) based salts with basic anions, as totally and immediately recyclable catalysts for esterification reactions. The process includes the esterification of fatty acids (C4-C22) with mono-alcohols (C6-C22) and poly-alcohols (C3-C12) (di-hydroxy, tri-hydroxy, tetra-hydroxy, penta-hydroxy) obtaining the corresponding acyl-derivatives
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