The preparation of 9-substituted Delta 5-octenolides: Synthesis of 8-deoxy-pseudo-ascidiatrienolide C

Two routes have been explored for the preparation of the title 9 membered lactones. Lactonisation of a hydroxy acid bearing an embryonic unsaturated side chain followed by palladium-catalysed chain extension was shown to be problematic. The preferred procedure, which involved prior formation of the complete carbon skeleton followed by lactonisation using Mukaiyama conditions, was employed to prepare 8-deoxy-pseudo-Ascidiatrienolide C. The efficiency of the lactonisation process is particularly notable.