Modifications of rings B and C of podocarpic acid: Towards the synthesis of quassinoids

Attempts to alkylate products from Birch reductions of derivatives of podoc arpic acid are reported. Attempted reductive silylation of ring c of methyl 12-methoxypodocarpa-8,11,13-trien-19-oate (5) gives products of C4 ester r eduction only. The enantiopure form of the bis(ethylene acetal) (15) of 19- norpodocarp-8-ene-3,12-dione, a potentially useful intermediate for quassin oid synthesis, has been prepared from the ketone (34). Functionality at C8 on the beta-face has been successfully introduced by abnormal Reimer-Tieman n reactions of podocarpic acid (2) and its 13-methyl derivative (10). The s aturated ketone (48) has been converted into an alpha,beta-unsaturated keto ne (18) which has potential for introducing functionality at C14.