Memory of chirality in the enantioselective synthesis of β-lactams derived from amino acids.: Influence of the reaction conditions

The asymmetric induction observed during cyclisation of N-benzyl-N-chloroacetyl-(L)-Phe derivatives to the corresponding S-enriched 2-azetidinones, ascribed to chirality memory, can be controlled by the appropriate choice of the base and solvent. Using the organic base BTPP, the ee values obtained in different solvents showed a good correlation with the AN solvent parameter, except for NMP. It seems that a combination of the solvent properties, rather than individual parameters, and the presence of enolate aggregates are decisive for final enantiomer distribution.