Asymmetric Synthesis of the Both Enantiomers of α-Hydroxy Acids by the Diastereoselective Reduction of Chiral α-Keto Amides with (Complex) Metal Hydrides in the Presence of Metallic Salt

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Abstract
Effects of the metallic salts and the reducing reagents in the diastereoselective reduction of chiral α-keto amides derived from (S)-proline methyl ester were examined. Lithium borohydride afforded (S)-α-hydroxy acids, whereas diisobutylaluminum hydride afforded (R)-isomers. In the presence of lithium bromide, reduction with LiBH4 afforded (S)-mandelic acid in over 80% e.e.