Total Synthesis of (+/-)-Pisiferic Acid, Methyl (+/-)-Pisiferate, and (+/-)-Pisiferol

Article abstract of DOI:10.1246/bcsj.55.1599

Acid catalyzed cyclization of 4-(3-isopropyl-4-methoxyphenethyl)-3,5,5-trimethyl-2-cyclohexen-1-one afforded 12-methoxyabieta-8,11,13-trien-2-one and its cis-isomer.Both compounds were further converted into 12-methoxyabieta-8,11,13-trien-2β-ol, which was treated with lead tetraacetate in the presence of iodine to yield 2β,20-epoxy-12-methoxyabieta-8,11,13-triene.Ether cleavage of the 2β,20-epoxy compound with acetyl p-toluenesulfonate, followed by catalytic hydrogenation, afforded 20-acetoxy-12-methoxyabieta-8,11,13-triene (23).This was then converted into methyl 12-methoxyabieta-8,11,13-trien-20-oate (27) via methyl 12-methoxy-7-oxoabieta-8,11,13-trien-20-oate.Demethylation of 27 with AlBr3-EtSH gave pisiferic acid, but with AlCl3EtSH 27 was partially demethylated to give methyl pisiferate.The acetate 23 was also converted into pisiferol by demethylation and reduction