A chemical conversion of penicillin sulfoxides into 6,7-epi-1-oxocephams

Penicillin sulfoxides were converted into 6,7-epi-1-oxocephams by a simple and efficient method. The oxidation of 1,2-seco-Δ²-cephem with osmium tetroxide provided 1,2 diol 5 which was then converted to the chloro-β-lactams 6. Treatment of 6 with tin (II) chloride or silver tetrafluoroborate afforded 6,7-epi-1-oxocephams 2,3. Several reactions were attempted to obtain 1-oxo-exomethylene cephalosporins 13,15 from the oxazoline 11 prepared from the exomethylene cephalosporin 8.