Modifications of Rings B and C of Podocarpic Acid: Towards the Synthesis of Quassinoids Richard

Abstract

Attempts to alkylate products from Birch reductions of derivatives of podocarpic 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 reduction only. The enantiopure form of the bis(ethylene acetal) (15) of 19-norpodocarp-8-ene-3,12-dione, a potentially useful intermediate for quassinoid synthesis, has been prepared from the ketone (34). Functionality at C8 on the β-face has been successfully introduced by abnormal Reimer–Tiemann reactions of podocarpic acid (2) and its 13-methyl derivative (10). The saturated ketone (48) has been converted into an α,β-unsaturated ketone (18) which has potential for introducing functionality at C14.