Oxidation of Terpenoids with a Cyclohexanone Fragment by Performic Acid

Abstract

Performic acid is a reactive, inexpensive, and available reagent for Baeyer–Villager oxidation of ketones that is used infrequently in the chemistry of cyclic terpene ketones, e.g., only for the oxidation of isocaranone [1] and allobetulone [2]. The goal of the present work was to expand the scope of this reagent for the oxidation of terpenoids with a cyclohexanone fragment. We found that Baeyer–Villager oxidation of 28-oxoallobetulin-3-one (1), carvomenthone (2), and menthone (3) by performic acid occurred regioand stereospecifically to give lactones 5–7, respectively. Oxidation of isomenthone (4) by H2O2–HCOOH caused racemization of the asymmetric center with the isopropyl substituent (probably due to keto–enol tautomerism under acidic conditions) to give a mixture of diastereomeric lactones 7 and 8 (1:1), in contrast with diastereospecific m-chloroperbenzoic acid [3].