The Synthesis of (+)-Pisiferol and (+)-Pisiferal

Abstract Reduction of abieta-8,11,13,-trien-6-one with lithium aluminium hydride, followed by treatment with lead tetraacetate and iodine, affored 6β,20-epoxyabieta-8,11,13-triene. This was converted into a separable mixture of abieta-8,11,13-trien-20-ol (13) and 5βH-abieta-8,11,13-trien-20-ol (14) by a series of reactions; ether cleavage with acetic p-toluenesulfonic anhydride, catalytic hydrogenation, and reduction with lithium aluminium hydride. Acetylation of 13 and 14 gave the corresponding acetates, 20-acetoxyabieta-8,11,13-triene (11) and 20-acetoxy-5βH-abieta-8,11,13-triene (12). Friedel-Crafts acylation of 11 with acetyl chloride in the presence of anhydrous aluminium chloride afforded 20-acetoxy-12-acetylabieta-8,11,13-triene, which was converted into pisiferol by oxidation with m-chloroperbenzoic acid and subsequent treatment with lithium aluminium hydride. The synthetic pisiferol was oxidized with Jones reagent to give pisiferal. Similarly, 5βH-abieta-8,11,13-triene-12,20-diol was synthesized from 12. Conversion of the cis A/B ring junctions in 12 into the trans ones is also described.