Aerobic oxidation of naturally occurring α-bisabolol catalyzed by palladium(II) salts as sole catalysts

• α-Bisabolol is a bio-renewable substrate occurring in high concentrations in essential oils of various plants, for example, chamomile.
• Novel selective oxidations of α-bisabolol with dioxygen using palladium salts as sole catalysts and non-acidic non-corrosive methanol or dimethylacetamide as solvents have been developed.
• Poly-functionalized sesquiterpenic compounds obtained in these reactions are potentially useful as fragrance ingredients and synthetic intermediates.

α-Bisabolol, a sesquiterpene found in various essential oils, has numerous direct commercial uses in cosmetic and therapeutic formulations. In the present work, we report two novel liquid-phase processes for the catalytic oxidation of α-bisabolol with dioxygen, in which palladium salts (PdCl2 or Pd(OAc)2) are employed as sole catalysts. The addition of co-catalysts conventionally used for the re-oxidation of reduced palladium species or special ligands for their stabilization is not required. The reactions occur in non-acidic solvents, i.e., aqueous methanol or dimethylacetamide, and give exclusively the products derived from the interaction of the acyclic olefinic bond with palladium, whereas the other olefinic bond remains intact. The method allows to perform the green and simple synthesis of poly-functionalized compounds potentially useful for fine chemical industry as fragrance ingredients and synthetic intermediates, starting from a bio-renewable substrate.

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