Abstract
Stereoselective conversion of l-abietic acid (1) to d-phyllocladene (16) was achieved by the use of two carbon units of the isopropyl group in 1 for the formation of its D-ring. Catalytic hydrogenation of methyl 13-methoxycarbonylmethyl-7-oxopodocarpa-8, 11, 13-trien-15-oate (2), derived from 1, over ruthenium oxide, followed by oxidation, gave stereoselectively methyl 13β-methoxycarbonylmethyl-7-oxopodocarpan-15-oate (4), without loss of the 7-oxygen function. Although attempts of cyclization reaction of methyl 7-hydroxy-13β-(2'-hydroxyethyl)-podocarpan-15-oate (6) to methyl 15-hydroxy-7-oxo-17-norphyllocladan-18-oate (7) were fruitless, the formation of the D-ring from methyl 13β-carboxymethyl-7-oxopodocarpan-15-oate (5) was accomplished by polyphosphoric acid-AcOH treatment to give methyl 7, 15-dioxo-17-norphyllocladan-18-oate (9) in high yield. Selective removal of the 7-oxygen function of 9, via monothioketalization, yielded methyl 15-oxo-17-norphyllocladan-18-oate (11), which was further converted to methyl 17-norphylloclad-15-en-18-oate (14). Hydroboration of 14, followed by oxidation, gave methyl 16-oxo-17-norphyllocladan-18-oate (15) accompanied with 11.
