Phase transfer catalyzed asymmetric alkylations of imine glycinamides

Recent advances in asymmetric phase-transfer catalysis

The use of chiral nonracemic onium salts and crown ethers as effective phase-transfer catalysts have been studied intensively primarily for enantioselective carbon-carbon or carbon-heteroatom bond-forming reactions under mild biphasic conditions. An essential issue for optimal asymmetric catalysis is the rational design of catalysts for targeted reaction, which allows generation of a well-defined chiral ion pair that reacts with electrophiles in a highly efficient and stereoselective manner. This concept, together with the synthetic versatility of phase-transfer catalysis, provides a reliable and general strategy for the practical asymmetric synthesis of highly valuable organic compounds.

The regioselective α-alkylation of the benzophenone imine of glycinamide, alaninamide, and related derivatives

The benzophenone imine of glycinamide was alkylated using ion pair extraction (RX, 10% aq. NaOH, Bu4NHSO4 (1 equiv.), CH2Cl2, rt) to give the α-monosubstituted products, which were then alkylated a second time using stronger basic conditions (KO-t-Bu, THF, 0 °C, RX). Crystal structures of the Schiff bases of glycinamide, an α-monosubstituted and an α,α-disubstituted product were reported.Key words: benzophenone imines, Schiff bases, alkylation, ion pair extraction (IPE), phase-transfer catalysis (PTC), anhydrous base, X-ray crystal structures.