Terpenoids-LXXXI: transformation products of elemol and eudesmol and synthesis of elemanones and selinanones

Abstract

Tetrahydroelemol and dihydroeudesmol undergo dehydration on treatment with traces of perchloric acid in acetic acid. The resulting hydrocarbons when subjected to (i) epoxidation followed by BF₃-etherate treatment, (ii) hydroboration-oxdiation followed by further oxidation with Jones chromic acid reagent give elemanones and selinanones respectively. From the reaction mixtures (-) elemane-8-one (VIII) and (-) selinane-8-one (XXIII) can be separated in pure states via their semicarbazones. (±) Elemane-8-one can be obtained by hydrogenation of pyrogermacrone. The hindered ketones elemane-6-one (VII) and selinane-6-one (XXII) or their corresponding alcohols could not be obtained in the pure state. Stereochemistry of the various products have been discussed and their ORD curves examined.