(R)-2-Phenylglycine as a Chiral Auxiliary in the Asymmetric Synthesis of 2-Azetidinones

Abstract

The chlorozinc enolate of ethyl-[(2, 2,5,5-tetramethyl-1-aza-2,5-disila)cyclopentyl]-acetate was reacted with the ZnCl{2} complex of N-benzylidene-2-phenylglycine methyl ester in THF at -70 }o{C. After removal of the protecting silyl moiety (3S, 4S, @aR)-1-(methoxycarbonyl)(phenyl)methyl-3-amino-4-phenyl-2-azetidinone was obtained in 73% yield with >97% d.e.. By treatment with aqueous ammonia complete epimerization at the @a-position was accomplished. The (3S, 4S, @aS) enantiomer was crystallized from THF and the absolute configuration was determined by X-Ray crystallography.