Synthetic Studies on Spirovetivane Phytoalexins. V. : A Stereoselective Total Synthesis of (±)-Oxylubimin

Abstract

(±)-Oxylubimin (4), the most highly oxygenated spirovetivane phytoalexin, was synthesized stereoselectively from a key intermediate, (2RS, 5RS, 9SR, 10RS)-9-hydroxy-6, 10-dimethyl-2-pivaloyloxyspiro[4.5]dec-6-en-8-one (3). Its methoxymethyl ether (8) was reduced with NaBH₄ and CeCl₃·7H₂O to give predominantly the desired alcohol (9a) (9a/9b=6.4). The alcohol (9a) was successfully transformed into oxylubimin (4) via several steps, involving introduction of a bis(ethoxycarbonyl)methyl group at the C₂, catalytic hydrogenation of the C₆-C₇ double bond, and pyridinium chlorochromate oxidation of the hydroxymethyl group at C₆.