ON THE STEREOSELECTIVITY OF THE REACTION OF N-(9-PHENYLFLUOREN-9-YL)ASPARTATE ENOLATES WITH ELECTROPHILES - SYNTHESIS OF ENANTIOMERICALLY PURE 3-HYDROXY, 3-AMINO, AND 3-HYDROXY-3-METHYLASPARTATES

We have developed efficient and stereoselective preparations of enantiomerically pure (3R)- and (3S)-N-Pf-3-hydroxy- and N-Pf-3-aminoaspartates by reaction of N-Pf-aspartate enolates with electrophilic hydroxylating or aminating reagents. The stereoselectivity of the hydroxylation and amination reactions was shown to be dependent on the structure of the enolate (which is strongly affected by the presence of strong metal complexing agents) and whether the electrophile is able to complex the enolate counterion in the transition state of the reaction. We have also developed a regioselective preparation of enantiomerically pure N-Pf-3-hydroxy-3-methylaspartates, albeit with only modest stereoselectivity.