Reaction of 7-oxototara-8,11,13-trien-13-yl acetate (3) with acetic anhydride-perchloric acid affords the γ-pyrone (8) in addition to the previously reported acetyl derivative (4). Baeyer–Villiger oxidations of the ketones (3) or (5) have given starting material or complex mixtures, but the ε-lactone (9) and the rearranged product (11) were isolated from two experiments with (3). Oxidation of 13-methoxytotara-8,11,13-triene (2) with Jones reagent gives the 7-oxo derivative (5) and a low yield of a ring B opened substituted p-benzoquinone (13). Pathways to (11) and (13) are proposed.
The structure of a naphthalene derivative obtained by rearrangement of 13-methoxytotara-5,8,11,13-tetraen-7α-ol (2) has been revised to 5-(5′-isopropyl-6′-methoxy-2′-methyl-1′-naphthyl)-2-methylpent-2-ene (7). A minor oxidation product of 13-methoxytotara-8,11,13-triene (4) has been identified as 4-methoxy-3,3-dimethyl-7-(1′,3′,3′-trimethyl-2′-oxocyclohexanyl)isobenzofuran-1(3H)-one (16) and its structure confirmed by X-ray crystallography. Methyl 12-methoxypodocarpa-8,11,13-trien-19-oate (12) has been converted into an intermediate used in the synthesis of the linear diterpenoid umbrosone [3-(1′-hydroxy-1′-methylethyl)-5,5,9-trimethyl-5,6,7,8-tetrahydroanthracene-1,2-dione] (15).