Chemistry of santonene. Part V. The stereochemistry of γ-metasantonin

Abstract

γ-Metasantonin (II) has been shown to have a cis-A/B ring fusion. Reduction of (II) gives a dihydro-derivative (V) and a single tetrahydro-derivative (VIa). Tetrahydrosantonenic acid (VIIa), when treated with acetic anhydride, affords an isomer (VIII) of (V), the triene (XII), and the enol acetate (XIII). Compound (VIII) on reduction affords a mixture of two alcohols (IXa) and (Xa). N.m.r. spectra are used to assign structures to the ketones and alcohols. When treated with acetyl chloride–acetic anhydride γ-metasantonin affords the enol acetate (XI).