The chemistry of fungi. Part 75. A partial elaboration of the rosane system from podocarpic acid

Abstract

In an approach to the synthesis of the rosane system [type (1)], 7-ethyl-O-methylpodocarpic acid (2; R¹= Et, R²= CO₂H) was converted by a Birch reduction into 7-ethyl-6-methoxy-1α,4aβ-dimethyl-1,2,3,4,4a,5,8,9,10,10aα-decahydrophenanthrene-1β-carboxylic acid (3; R = H). After esterification, the enolic methoxy-group was removed to yield the αβ-unsaturated 6-ketone (4), which was hydrogenated to the ketone (5; R = CO₂Me). Reduction of the derived ethylene acetal (7; R = CO₂Me) gave (7; R = CH₂OH), which was deacetalised and acetylated to yield the acetate (6; R = CH₂OAc). Alkylation of (6; R = CH₂OAc) with methyl-lithium–methyl iodide gave the ketone (8) which probably has the requisite C-13 (terpene numbering) stereochemistry of the rosane system.

Deoxypodocarpic acid (9) was reduced to the dihydrobenzenoid system (10), which was hydrogenated to the 8,9-olefin (11). A solution of (11) in sulphuric acid gave 1α,4bβ-dimethylperhydro(10aαH)phenanthrene-1β,4aβ-carbolactone (12)(cf. rosenonolactone).