Palladium catalyzed oxidation of renewable terpenes with molecular oxygen: oxidation of α-bisabolol under chloride-free conditions

Abstract

The palladium/p-benzoquinone catalyzed aerobic oxidation of α-bisabolol, a bio-renewable substrate with strong therapeutic potential available from various essential oils, has been developed. The reaction gives three main products arising from the oxidation of the sterically encumbered trisubstituted double bonds of the substrate, either endocyclic or exocyclic or both. Novel poly-functionalized sesquiterpenoids obtained with high combined selectivity from the oxidation of α-bisabolol are potentially useful as components of synthetic perfumes, cosmetics and pharmaceuticals. The system promotes an efficient dioxygen-coupled catalytic turnover in the absence of auxiliary redox-active co-catalysts under superatmospheric oxygen pressure. Alternatively, the reaction can be performed at atmospheric pressure in the presence of catalytic amounts of copper acetate as an electron transfer mediator for the regeneration of BQ during the catalytic cycle.