ASYMMETRIC-SYNTHESIS OF N-(ETHOXYCARBONYL)-BETA-METHYLPHENYLALANINE ESTERS

Amination of the silyl ketene acetal of methyl (R)-3-phenylbutanoate ( 3) by photolysis with ethyl azidoformate gave the derivative of (2R,3S )-beta-methylphenylalanine (4) with a low diastereomeric excess in spi te of the resident chirality. Using the silyl ketene acetal 6, also be aring an Oppolzer's chiral auxiliary, the (2R,3S)-beta-methylphenylala nine derivative (7) was obtained with a higher diastereomeric excess i ndicating a matching effect. It was possible to obtain the (2S,3S)-bet a-methylphenylalanine derivative (10) as the major product, starting f rom 9 bearing the enantiomeric chiral auxiliary.