Transformations of penicillins: novel ring-opening reactions of a penicillin-derived sulphimide

Abstract

(2S,4R,6S,7S)-Methyl 3,3-dimethyl-8-oxo-7-phenoxacetamido-5-p-tolysulphonyl-4-thia-1,5-diazabicyclo-[4.2.0]octane-2-carboxylate S-p-tolysulphonylimide was thermolysed in refluxing toluene to afford quantitatively (3S,4S)-1-(1-methoxycarbonyl-2-methylprop-2-enyl)-3-phenoxyacetamido-4-[N-(p-tolysulphonylaminothio)-p-tolysulphonylamino]azetidin-2-one, by a β-elimination mechanism. Treatment of the monocyclic azetidinone with triphenylphosphine afforded methyl N-(α-phenoxyacetamido-β-p-tolylsulphonylacryloyl)-βγ-didehydrovalinate, which underwent addition of alcohols to the enamine double bond to form gem-alkoxy-amine dipeptides. The reduction of both the monocyclic azetidinone and the enamine dipeptide with sodium borohydride is described.