Calixarene-based chiral phase-transfer catalysts derived from cinchona alkaloids for enantioselective synthesis of α-amino acids

The synthesis of the first calixarene-based chiral phase-transfer catalysts derived from cinchona alkaloids has been achieved in two steps from p-tert-butylcalix[4]arene. The catalytic efficiency of the chiral calix[4]arenes 3a-c was evaluated by carrying out the phase-transfer alkylation of N-(diphenylmethylene)glycine ethyl ester with benzyl bromide. Various factors that affect the chemical yield and enantio selectivity were also examined. Benzylation of glycine imine 4 using calix[4]arene- based dimeric catalyst 3a as a chiral phase-transfer catalyst in toluene/CHCl3 mixture (7:3 v/v) at 0 degrees C gave the best enantioselectivities and yields in the presence of aqueous NaOH. (C) 2008 Elsevier Ltd. All rights reserved.