Oxidation and isomerisation of colupulone; the separation and structures of two transformation products

Abstract

Colupulone (2) when boiled under aerobic conditions in acid (pH 5.4) buffer is transformed in good yield to, amongst other products, two non-polar tricyclic ketones, 8-hydroxy-4,4-dimethyl-3-isopropyl-7-(3-methylbut-2-enyl)-9-(2-methylpropionyl)tricyclo[5,3,1,0^1,5]undecane-10,11-dione (12) and its didehydro-derivative (13), separable by silver nitrate–silicic acid chromatography. The minor product (13) may be obtained more conveniently by treatment of colupulone (2) with lead tetra-acetate.