New Approach for Complete Reversal of Enantioselectivity Using a Single Chiral Source

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Attempt for obtaining both enantiomers in high enantiomeric excess is attractive and important challenges, because it is often the case that each enantiomer exhibits different bioactivity. This review summarizes some approaches to realize complete reversal of enantioselectivity by changing various conditions. Our new approach to achieve reversal of enantioselection in the reaction of enantioselective addition of diketene to aldehydes affording optically active 5-hydroxy-3-ketoesters in high optical yield using Schiff bases containing oxazoline moiety derived from L-serine, was achieved. Starting from one chiral center (in this case from L-serine), we obtained two chiral Schiff base possessing oxazoline moieties, each of which recognized different enantioface of aldehydes in the addition reaction of diketene to aldehydes in high level (up to 93% ee R and 89% ee (S), respectively). This is the first example of complete reversal of enantioselection from the single chirality of L-serine.