Formation of enantiomeric 4-oxa-2,6-diazabicyclo[3.2.0]hept-2-en-7-onest from methyl 6α- and 6β-phenoxyacetamidopenicillanates

Methyl 6a-phenoxyacetamidopenicillanate was transformed by reaction with chloramine T or (dichloroiodo)benzene into methyl 3-methyl-2-[(1R,5S)-3-phenoxyrnethyl-7-oxp-4-oxa-2,6-diazabicyclo[3.2.0]hept-2- en-6-yl]but-2-enoate. The (1S,5R)-isomer was prepared by the reaction of (dichloroiodo)benzene with methyl 6ß-phenoxyacetamidopenicillanate. Differences in the reactivities of the 6a- and 6ß-acylaminopenicillanates towards chloramine T and (dichloroiodo) benzene are noted.