Oxidation of methyl podocarpate and methyl 12-hydroxyabietan-8,11,13-trien-18-oate with thallium(III) perchlorate

Abstract

On oxidation with thallium(III) perchlorate in aqueous perchloric acid, methyl podocarpate (5) yielded two products which were identified on the basis of spectral data as the p-quinol (8) and the aryl ketone (7a) which resulted from oxidation at C-7 remote from the aromatic ring c. When methyl 12-hydroxyabietan-8,11,13-trien-18-oate (6) was treated with the same reagent, a similar benzylic oxidation occurred yielding two aromatic compounds which spectroscopic analysis showed to be the aryl ketone (11) and the lactone (12) with a rearranged skeleton. The structure and stereochemistry of the latter product were established unequivocally by an X-ray crystallographic analysis. Possible mechanisms for the formation of compounds (7a), (11), and (12) are proposed.