Functionalization of the naturally occurring linalool and nerol by the palladium catalyzed oxidation of their trisubstituted olefinic bonds

Abstract

Linalool and nerol, bio-renewable terpenic alkenyl alcohols found in many essential oils, were selectively oxidized by molecular oxygen in the presence of the chloride-free Pd(OAc)₂/p-benzoquinone catalytic system. An efficient dioxygen-coupled catalytic turnover was achieved in the absence of auxiliary electron-transfer mediators under 5–10 atm of oxygen pressure. In both substrates, only one of two olefinic bonds was involved in the interaction with palladium, whereas the other one remained intact. Primary allylic acetates were formed as major reaction products: 8-linalyl acetate and 8-neryl acetate from linalool and nerol, respectively. In the case of linalool, the intramolecular cyclization product (known as herboxide), also resulted from the oxidation of the internal double bond, was also formed in significant amounts. All monoterpenic compounds obtained in the present work are natural products found in exotic plants or grape wines and are potentially useful as fragrance ingredients due to their pleasant scents.