Catalysts For Asymmetric Synthesis Research Articles

ChemInform Abstract: Chiral Lewis Acids as Efficient Catalysts in Asymmetric Synthesis

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Synthesis and use of enantiomerically pure tert-leucine

Abstract Owing to its bulky, inflexible and hydrophobic tert -butyl side chain, tert -leucine (Tle) finds increased use in templates or catalysts in asymmetric synthesis as well as in peptidic medicinal compounds. ( S )-Tle, available through a large-scale enzymatic reductive amination process, has been incorporated into a variety of anti-AIDS and -cancer compounds. With two new routes to ( R )-Tle coming available, the number of applications of both ( R )- and ( S )-Tle can be expected to increase considerably.

Polymer-Supported Chiral Catalysts in Asymmetric Synthesis

Abstract By far the best method of synthesis of chiral organic compounds from prochiral substrates is through the use of chiral catalysts or enzymes. This approach has several advantages, the most important of which is that either the enzyme is naturally occurring or the catalyst can be easily generated from a naturally occurring chiral material. If resolution needs to be accomplished, it is carried out with small amounts of catalyst rather than with large quantities of product. Thus from a catalytic amount of chiral material large quantities of one enantiomeric product can be generated.

Reduction asymetrique catalysee par des complexes de metaux de transition IV. synthese d'amines chirales au moyen d'un complexe de rhodium et d'isopropylidene dihydroxy-2,3 bis(diphenylphosphino)-1,4 butane (diop)

A chiral rhodium complex with (+)-diop as ligand is used as a catalyst in asymmetric synthesis leading to amines and N-acyl derivatives. Two kinds of reactions are investigated: asymetric hydrogenation of enamides and hydrosilylation of imines. Good optical yields are observed in the synthesis of N-acetyl α-phnenylethylamine (e.e. 45%) and N-acetyl α-phenylpropylamine (e.e. 83%). A strong solvent effect is observed, which can reverse the absolute configuration of tN-acetyl-α-phenylethylamine obtained by reduction of its enamide precursor. N-Benzyl-α-phenyl ethylamine is prepared by hydrosilylation with 65% optical purity. An asymmetric synthesis of 1,2,3,4-tetrahydropapaverine (e.e 38%) and related compounds is described.