Skeletal Rearrangements of Ring C Aromatic Diterpenoids

Abstract

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).