Fast and green microwave-Assisted conversion of essential oil allylbenzenes into the corresponding aldehydes via alkene isomerization and subsequent potassium permanganate promoted oxidative alkene group cleavage

Abstract

Essential oil allylbenzenes from have been converted quickly and efficiently into the corresponding benzaldehydes in good yields by a two-step "green" reaction pathway based on a solventless alkene group isomerization by KF/Al2O3 to form the corresponding l-arylpropene and a subsequent solventless oxidation of the latter to the corresponding benzaldehyde by KMnO4/CuSO4-5H2O. The assistance by microwave irradiation results in very short reaction times (<15 minutes). The green conversion of eugenol (4-allyl-2-methoxyphenol) into vanillin (4-hydroxy-3-methoxybenzaldehyde) has been carried out in a similar way, requiring however two additional microwave-assisted synthetic steps for acetylation of the hydroxy group prior to the oxidation reaction, and for the final deacetylation of vanillin acetate (4-acetoxy-3-methoxybenzaldehyde) by KF/Al2O3 under solvent-free conditions, respectively. © 2009 by the authors.