Abstract The reactivity of Δ 3-and Δ 2-3-bromomethylcephems toward carboxylate nucleophiles has been studied. The Δ 3-bromomethylcephem 1, less reactive than the Δ 2- analogue 4, is converted in high yields into 3-acyl-oxymethyl-3-cephems 2a-d, generally with no isomerization of the double bond, only within a narrow range of conditions. In particular, the Δ 3-7-aminocephalosporanic acid (7-ACA) derivative 2a has been obtained ...
