The conversion of racemic α-cyclocitral into 3-(3-isopropyl-4-methoxyphenethyl)-4,4-dimethyl-2-methylenecyclohexanone (2) was carried out in five steps via 3-(3-isopropyl-4-methoxyphenethyl)-2,4,4-trimethyl-1-cyclohexene. An intramolecular cyclization of 2 with polyphosphoric acid produced the corresponding two tricyclic ketones possessing cis- and trans-A/B ring junctions. Each of these ketones was further converted into 12-mesyloxy-9(10→20)-abeo-abieta-1(10),8,11,13-tetraene in four steps. The mesylate was reduced with lithium aluminium hydride to give (±)-pisiferin.

No abstract

No abstract

In order to elucidate the absolute configuration of C-15 in natural ar-abietatrien-12,16-oxide, (15R)-12,16-epoxy-8,11,13-abietatriene (1a) and its (15S)-epimer (1b) have been synthesized. Treatment of (15R)-8,11,13-abietatriene-12,16-diol with a mixture of chloromethyl methyl ether, dicyclohexano-18-crown-6, and potassium carbonate afforded 1a as a minor product and (15R)-12-methoxymethyl ether as a major product. The latter was further converted into 1a. A similar treatment of (15S)-8,11,13-abietatriene-12,16-diol gave 1b. Catalytic hydrogenations of 12,16-epoxy-8,11,13,15-abietatetraene, methyl 12,16-epoxy-8,11,13,15-abietatetraen-19-oate (5), and methyl 12,16-epoxy-8,11,13,15-abietatetraen-18-oate (7) afforded the corresponding (15R)-dihydrobenzofuran derivatives and their (15S)-epimers. Conversions of the hydrogenation products from 5 and 7 into 1a and 1b were also carried out. The synthetic 1a was identical with natural ar-abietatrien-12,16-oxide.

The oxidation of methyl (+)-13β-abiet-8-en-18-oate with Collins reagent yielded nine oxidation products. Their structures were elucidated on the basis of spectroscopic and chemical data to be methyl (−)-14-hydroxy-7-oxoabieta-8,11,13-trien-18-oate (1% yield), methyl (−)-11,14-dioxoabieta-8,12-dien-18-oate (1%), methyl (+)-11-oxo-13β-abiet-8-en-18-oate (18%), methyl (−)-8α,9α-epoxy-7-oxo-13β-abietan-18-oate (2%), methyl (+)-7-oxoabieta-8,11,13-trien-18-oate (2%), methyl (+)-11,14-dihydroxy-7-oxoabieta-8,11,13-trien-18-oate (2%), methyl (+)-7,11-dioxo-13β-abiet-8-en-18-oate (17%), methyl (+)-14-oxo-13β-abiet-8-en-18-oate (15) (4%), and methyl (+)-7-oxo-13β-abiet-8-en-18-oate (23%) respectively. It is noteworthy that oxygenation occurs not only at the C-7 and C-11 positions but also at the C-14 position. The oxygenated products obtained in this studies could be useful intermediates for the synthesis of the oxidized diterpenoids of abietane skeleton. To exemplify this, 15 was converted to methyl suaveolate and suaveolol. Hydrolysis of the former yielded suaveolic acid, thus confirming its absolute configuration to be 4R, 5R, 10S, 13S, and 14S.