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Chemistry

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The chiral pool as a source of enantioselective catalysts and auxiliaries

Article Abstract:

An undertaking to compile and study the use of chiral molecules and their derivatives as enantioselective agents discovers that most of them are of natural origin. The project tabulates the chiral catalysts, modifiers, ligands and reagents according to their source types and lists the various reactions they are used on as well as the highest optical yields obtained therefrom. A structural correlative analysis of the most effective chiral ligands points to the ligand atom, chelate size, type of backbone and number and location of asymmetric centers as factors shaping enantioselective efficiency.

Ligands, Ligands (Chemistry), Chemical tests and reagents, Reagents

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Cyclohexyl-based chiral auxiliaries

Article Abstract:

The use of cyclohexyl-based chiral auxiliaries, particularly 8-phenylmenthol, trans-2-phenylcyclohexanol and their derivatives,allows asymmetric induction with levels of control exceeding 1000:1 and diastereomeric yields commonly above 90%. The two auxiliaries are reusable and readily obtained from pulegone and cyclohexene, respectively. While they have been successfully used in nucleophilic, electrophilic, redox and rearrrangementreactions, the highest levels of control achieved from them are in nucleophilicaddition at the beta-stereocenter of glyoxylates involving Grignards and alkenes.

Cyclohexane, Alicyclic compounds

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Enantioselective addition of organozinc reagents to aldehydes

Article Abstract:

Chiral catalysts and ligands allow the enantioselective addition of organozinc reagents to aldehydes. The catalysts (or ligands) may be homogeneoussuch as amino alcohols, piperazines and oxazoborolidines, or heterogeneous onesbound to polymers, alumina or silica gel. In both cases, secondary alcohols of high optical purity are obtained, with the highest marks for C-C bond formationgoing to polymer-bound catalysts. Diastereoselective addition results from the use of an achiral catalyst with racemic chiral aldehydes while enantioselectiveaddition results when chiral catalysts are used.

Usage, Polymers, Silica gel, Organometallic compounds, Aluminum oxide, Aldehydes, Alcohols, Zinc compounds

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