Azetidinone intermediates for the synthesis of cephem ring systems. Part 1. Chemical shift non-equivalence of the allylic methylene protons

Abstract

The chemical shift non-equivalence of the allylic methylene groups CH₂Br and CH₂SPh, present in some azetidinone intermediates useful for the synthesis of cephem ring systems, affords a valuable criterion for establishing the stereochemistry of the double bond. The synthetic procedures used for the preparation of the compounds examined are described.