OXIDATIONS OF 12-DEOXY-13-METHOXY-PODOCARPA-8,11,13-TRIENE, 12-HYDROXY-13-METHOXY-PODOCARPA-8,11,13-TRIENE, 12-METHOXY-13-METHOXY-PODOCARPA-8,11,13-TRIENE, AND 12-HYDROXY-13-METHOXY-PODOCARPA-8,11,13-TRIENE DERIVATIVES

Methods for the oxidation of the aryl ring of derivatives of podocarpi c acid have been examined. Oxidation of methyl 12-hydroxypodocarpa-8,1 1,13-trien-19-oate (2) with phenyliodonium diacetate in various solven ts gives 8 beta-substituted dienones. An 8 beta-chloro dienone is form ed during oxidation of the phenol (2) with t-butyl hypochlorite. Oxida tion of (2) with dimethyldioxiran gives mainly the 7-ketone (13) but a lso affords the novel epsilon-lactone (26), while treatment with ruthe nium tetraoxide also affords products of benzylic oxidation. Oxidation of methyl podocarpa-8,11,13-trien-19-oate (4) with m-chloroperbenzoic acid affords a B-ring lactone (29) and, unexpectedly, a 6 alpha-chlor o 7-ketone (30). The action of cerium(Iv) ammonium nitrate on (2) give s nitro derivatives rather than oxidation products. Oxidation of methy l -hydroxy-13-methoxypodocarpa-8,11,13-trien-19-oate (22) with m-chlor operbenzoic acid gives a low yield of a 7-oxo derivative (17) while tr eatment with ozone gives an unusual alpha,beta-unsaturated gamma-lacto ne (31), the hydroxy lactone (33), the unsaturated keto ester (34), an d the substituted furan (35). Oxidation of (22) with Fremy's salt give s products of ring B oxidation. The structure of (31) has been confirm ed by X-ray crystallography.