Highly enantioselective monoalkylation of p-chlorobenzaldehyde imine of glycine tert-butyl ester under mild phase-transfer conditions

The selective monoalkylation of glycine tert-butyl ester aldimine Schiff base 3 has been realized in high chemical yield with excellent enantioselectivity under mild liquid–liquid phase-transfer conditions by the use of binaphthyl-derived chiral quaternary ammonium bromides 7 and 8 as catalysts. This achievement demonstrates that 3 can be used as a cost-effective substrate for the preparation of optically active α-alkyl-α-amino acid derivatives by chiral phase-transfer catalysis.

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(S)-2-Amino-3-(1-naphthyl)propionic acid tert-butyl esterC17H21NO2Ee 99%[α]D26=+33.6 (c 1.04, CHCl3)Source of chirality: catalytic asymmetric reactionAbsolute configuration: S

(S)-2-Benzoylaminobutyric acid tert-butyl esterC15H21NO3Ee 99%[α]D29=+42.9 (c 1.00, CHCl3)Source of chirality: catalytic asymmetric reactionAbsolute configuration: S