General approach for the stereocontrolled construction of the β-lactam ring in amino acid-derived 4-alkyl-4-carboxy-2-azetidinones

The first general approach toward the asymmetric synthesis of 4-alkyl-4-carboxy-2-azetidinones derived from amino acids is described. The stereoselective construction of the β-lactam ring was achieved through base-mediated intramolecular cyclization of the corresponding Nα-chloroacetyl derivatives bearing (+)- or (−)-10-(N,N-dicyclohexylsulfamoyl)isoborneol as chiral auxiliary (ee up to 82%).We thank the Comisión Interministerial de Ciencia y Tecnología (SAF 2000-0147) for financial support. G.G.-N. is a predoctoral fellow from the Ministerio de Ciencia y Tecnología, Spain