Synthetic studies on spirovetivane phytoalexins. V. A stereoselective total synthesis of (.+-.)-oxylubimin.

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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.