In recent years the use of cinchona alkaloids as effective organocatalysts has been realised. The commercial availability and easy modification of these privileged structures
establish them as attractive compounds for use in synthesis. For these reasons we were eager to apply cinchona alkaloid catalysis to the enantioselective synthesis of two important classes of molecule, p-amino acids and aziridines.
(A) Synthesis of fi-Alkylaspartates via fi-Lactone Ring-Opening
The cinchona alkaloid-catalysed reaction of ethyl glyoxylate with substituted ketenes, formed in situ from acid chloride precursors, gives as-disubstituted p-lactones in moderate yield and high enantiomeric excess. Glyoxylate has rarely been used in the amine-catalysed ketene cycloaddition and this chemistry allowed for the direct installation of an ester functionality into the product. Subsequent azide ring opening,
reduction and ester hydrolysis allow access to chiral p-alkyl aspartates.
(B) Synthesis of Aziridines from a,/J-Unsaturated Ketone Derivatives Our group has developed an organocatalytic reaction which furnishes unprotected aziridines in good yield from a,(3-unsaturated ketone derivatives. Screening of chiral
tertiary amines derived from the cinchona alkaloid motif allowed reasonable levels of enantioselectivity to be achieved. The substrate scope of the reaction was probed to incorporate a range of different alkene derivatives.