Olivanic acids and related compounds: total synthesis of (±)-PS-5 and (±)-6-epi PS-5

The trans- and cis-substituted β-lactam isomers of p-nitrobenzyl 3-(2-acetamidoethylthio)-6-ethyl-7-oxo-1-azabicyclo[3.2.0]heptane-2-carboxylate can be oxidised with iodobenzene dichloride–pyridine under anhydrous conditions to give the 3,4-unsaturated esters, which after isomerisation and deprotection afford the sodium salts of (±)-PS-5 and (±)-6-epi PS-5.