Formal Total Synthesis of Spirangien A

A formal total synthesis of the spiroketal containing cytotoxic myxobacteria metabolite spirangien A (<b>1</b>) is described. The approach utilizes a late introduction of the C20 alcohol that mirrors the biosynthesis of this compound. The key steps involved a high yielding cross metathesis reaction between enone <b>6</b> and alkene <b>7</b> to give <i>E</i>-enone <b>4</b> and a Mn-catalyzed conjugate reduction α-oxidation reaction to introduce the C20 hydroxyl group. Acid treatment of the α-hydroxyketone <b>4</b> gave spiroketal <b>19</b> which was converted into known spirangien A (<b>1</b>) advanced intermediate spiroketal <b>3