Asymmetric Hydroxylation of (S,S)-(+)-Pseudoephedrine Phenylacetamide Enolates

Enantioenriched α-hydroxy acids and esters have been synthesized by oxidation of (S,S)-(+)- pseudoephedrine arylacetamide enolates with different reagents. We have found that the oxidation of these enolates proceeds with good yields and diastereoselectivities and, interestingly, we have also noticed that the use of different oxidation reagents allows the selective preparation of any of the two possible epimers of the target α-hydroxy amides. We have also optimized a mild procedure for the removal of the chiral auxiliary and therefore for the obtention of enantioenriched α-hydroxy acids, which were also easily converted into the corresponding α-hydroxy esters. The developed methodology becomes a promising field of research due to the potentiality of the reaction, which a priori should allow the stereodivergent synthesis of a wide variety of α-hydroxy carbonyl compounds.