Asymmetric Phase-transfer Catalysts Research Articles

Combining chiral elements: a novel approach to asymmetric phase-transfer catalyst design

A new dicationic asymmetric phase-transfer catalyst, designed by combining chiral elements, is described. Catalytic testing using standard glycine imino ester alkylations shows good yields and moderate enantioselectivities.

The synthesis and applications of asymmetric phase-transfer catalysts derived from isomannide and isosorbide

We report herein the synthesis of various derivatives of isomannide and isosorbide. Alkylation on N-(diphenylmethylene)glycine tert-butyl ester show the new catalysts to be effective phase-transfer catalysts with moderately good enantioselectivity. The effect of exo and endo substituents on the enantioselectivity of alkylation reaction have also been studied.

Synthesis and competency of a tartrate-derived dicationic solid–liquid phase-transfer catalyst

A new asymmetric phase-transfer catalyst is described, along with a new, flexible synthetic scheme using a tartaric acid chloride. Alkylations and Michael reactions on a glycine imino ester show the new catalyst to be an effective phase-transfer catalyst with limited enantioselectivity.

Identification of a highly effective asymmetric phase-transfer catalyst derived from α-methylnaphthylamine

A library of quaternary ammonium salts has been generated via reaction of simple chiral amines with a series of conformationally dynamic biphenyl units. Screening of this library against the alkylation of a glycine imine has led to the identification of a highly effective asymmetric phase-transfer catalyst derived from α-methylnaphthylamine.

ChemInform Abstract: A Practical Asymmetric Synthesis of α-Methyl α-Amino Acids Using a Chiral Cu-Salen Complex as a Phase-Transfer Catalyst.

Abstract The asymmetric C -alkylation of N -benzylidene alanine methyl ester has been achieved using a copper(II) (salen) complex as an asymmetric phase transfer catalyst and provides a practical synthesis of α-methyl α-amino acids with up to 86% enantiomeric excess.

A practical asymmetric synthesis of α-methyl α-amino acids using a chiral Cu–salen complex as a phase transfer catalyst

The asymmetric C-alkylation of N-benzylidene alanine methyl ester has been achieved using a copper(II) (salen) complex as an asymmetric phase transfer catalyst and provides a practical synthesis of α-methyl α-amino acids with up to 86% enantiomeric excess.

Asymmetric phase transfer catalysts derived from the cinchona alkaloids

Since the first reported use of asymmetric phase transfer catalysts (PTC) derived from the cinchona alkaloids in 1989, the present third generation N-9-anthracenylmethyl quaternary salts 1 and 2 have been shown to catalyse a number of reactions, affording optically active products with high ee's. The high enantioselectivity of these salts is due to their well-defined geometries, where three of the four tetrahedron faces around the quaternary nitrogen cation are effectively blocked by the other components of the structure, leaving one relatively open face allowing intimate contact with the counterion of the substrate. This complex can then be attacked enantioselectively. Effective mising of phases during reaction is necessary, but more recently, catalysts 1(b) and 2(b) have been successfully employed with Schwesinger bases, in homogeneous solution, yielding similar ee's.

A new class of asymmetric phase-transfer catalysts derived from Cinchona alkaloids — Application in the enantioselective synthesis of α-amino acids

A new class of Cinchona alkaloid-derived quaternary ammonium phase-transfer catalysts bearing a N-anthracenylmethyl function are presented. These catalysts show high stereocontrol in the asymmetric alkylation of a benzophenone-derived glycine-imine, and application of this process to the enantioselective synthesis of a range of α-amino acid esters (e.e. 67–94%) is investigated.