Highly enantioselective phase-transfer catalytic alkylation in the preparation of non-natural alpha-amino acids via solid phase synthesis using aldimine linker

A new Merrifield-resin-derived glycinimine tert-butyl ester (9) was prepared and applied to the enantioselective synthesis of non-natural alpha-amino acids. High enantioselectivities (86 to99% ee) were accomplished by employing the aldimine linker under phase-transfer alkylation conditions, using 50% aqueous CsOH in toluene/chloroform (7:3) at 0 degrees C in the presence of N-(9-anthracenylmethyl)-O(9)-allylcinchonidium bromide (10 mol %).