Alkylation of N′-[(S)-1′-phenylethyl]-N-(diphenylmethylene)glycinamide using a phase transfer catalyst (PTC) for practical asymmetric syntheses of α-amino acid derivatives
The chiral auxiliary mediated stereoselective alkylation reaction of N′-[(S)-1′-phenylethyl]-N-(diphenylmethylene)glycinamide (1) using a phase transfer catalyst (PTC) is described. Alkylation of 1 using 18-crown-6 as a PTC for liquid-solid extraction of KOH in toluene gives best results. This methodology provides a practical protocol for the preparation of a variety of enantio-enriched unnatural α-amino acid derivatives up to 83:17 enantiomeric ratio.