Structure and Synthesis of (+)-Shonanol

Article abstract of DOI:10.1246/bcsj.54.2099

The structure of shonanol was restudied and found to be 12-hydroxyabieta-2,8,11,13-tetraen-1-one (1) by the following synthesis.A Grignard reaction of methyl (+)-12-methoxyabieta-8,11,13-trien-18-oate with phenylmagnesium bromide, followed by treatment with lead tetraacetate and calcium carbonate afforded a mixture of Δ³-, Δ⁴-, and Δ⁴⁽¹⁸⁾-19-nor compounds.This was oxidized with selenium dioxide to give (+)-12-methoxy-19-norabieta-4(18),8,11,13-tetraen-3α-ol.This alcohol was converted to (+)-12-methoxyabieta-5,8,11,13-tetraen-3-one (6) by the known procedure.Reduction of 6 with lithium aluminium hydride, followed by catalytic hydrogenation, yielded (+)-12-methoxyabieta-8,11,13-trien-3β-ol (8) and a small amount of its cis isomer.The compound (8) was then converted to (+)-12-methoxyabieta-1,8,11,13-tetraen-3-one (12) by a series of reactions: oxidation with pyridinium chlorochromate, bromination with pyridinium tribromide, and dehydrobromination with lithium carbonate and lithium bromide.Demethylation of 12 with boron tribromide gave (+)-12-hydroxyabieta-1,8,11,13-tetraen-3-one.Oxidation of 12 with alkaline hydrogen peroxide, followed by treatment with hydrazine hydrate, gave (+)-12-methoxyabieta-2,8,11,13-tetraen-1α-ol; this was oxidized with Jones reagent to give the corresponding 1-oxo compound.The 1-oxo compound was finally demethylated with boron tribromide to yield (+)-1, whose spectra were identical with those of natural shonanol.