Isomerisation of benzyl 6-phenoxyacetoxypenicillanates and their S-oxides

Abstract

The preparation of benzyl 6α- and 6β-phenoxyacetoxypenicillanate and their (S)- and (R)-S-oxides is described. No epimerisation was observed when benzyl 6α- or 6β-phenoxyacetoxypenicillanate or benzyl 6α- or 6β-trimethylsiloxypenicillanate was treated with 1,5-diazabicyclo[4.3.0]non-5-ene (DBN). Benzyl 6β-phenoxyacetoxypenicillanate (S)-S-oxide was transformed into the 6α-isomer with DBN as catalyst; the converse reaction was not observed. With both isomers in these experiments, the phenoxyacetoxy side chain was hydrolysed to a large extent.