Rearrangement of the Angular Methyl Group in Dehydroabietic Acid Derivatives.

The rearrangement of the angular methyl group in dehydroabietic acid derivatives was examined. Treatment of 12-methoxy-5, 8, 11, 13-abietatetraene (25) with boron trifluoride etherate afforded 12-methoxy-5β-methyl-10-norabieta-1(10), 8, 11, 13-tetraene (26). On the other hand, 12-methoxy-7-oxo-5, 8, 11, 13-abietatetraene (27) provided three naphthalene derivatives, 28, 29 and 30, on treatment with sulfuric acid in acetic anhydride. Methyl 7-oxo-5, 8, 11, 13-abietatetraen-18-oate (5) was reduced with sodium borohydride in the presence of cerium(III) chloride heptahydrate and the resulting alcohol (32) was further treated with p-toluensulfonic acid monohydrate to give methyl 5β-methyl-10-norabieta-1(10), 6, 8, 11, 13-pentaen-18-oate (33). On the other hand, under similar conditions, 7-oxo-5, 8, 11, 13-abietatetraene (11) and its 12-methoxy derivative (27) were transformed into the naphthalene derivatives, 35 and 37, respectively, via the corresponding alcohols, 34 and 36.