[Interesting new rearrangements of the cephalosporin antibiotics]

Abstract

On the course of the preparation of new cephalosporin derivatives with potential HLE inhibiting activity, three new rearrangements were observed. When a 7 beta-aminocephem sulfone (prepared in situ from 2) was diazotized in methanolic HClO4 solution with HNO2, the triazole 3 was prepared in good yield. On the other hand, the 2 alpha-bromocephem 6 rearranged to two different products, depending on the solvent used. When it was allowed to stay in acetonitrile for 7 days, the bromopyrrol 8 was the product, while in acetone, THF or DMF the aromatic side chain brominated product 7 was obtained. In both cases the inverse polarity of the C-2-Br bond and the easily resulting bromonium ion can be regarded responsible for the rearrangements.