Phosphotungstic Acid as a Versatile Catalyst for the Synthesis of Fragrance Compounds by α‐Pinene Oxide Isomerization: Solvent‐Induced Chemoselectivity

Abstract

The remarkable effect of the solvent on the catalytic performance of H3PW12O40, the strongest heteropoly acid in the Keggin series, allows direction of the transformations of alpha-pinene oxide (1) to either campholenic aldehyde (2), trans-carveol (3), trans-sobrerol (4 a), or pinol (5). Each of these expensive fragrance compounds was obtained in good to excellent yields by using an appropriate solvent. Solvent polarity and basicity strongly affect the reaction pathways: nonpolar nonbasic solvents favor the formation of aldehyde 2; polar basic solvents favor the formation of alcohol 3; whereas in polar weakly basic solvents, the major products are compounds 4 a and 5. On the other hand, in 1,4-dioxane, which is a nonpolar basic solvent, both aldehyde 2 and alcohol 3 are formed in comparable amounts. The use of very low catalyst loading (0.005-1 mol %) and the possibility of catalyst recovery and recycling without neutralization are significant advantages of this simple, environmentally benign, and low-cost method. This method represents the first example of the synthesis of isomers from alpha-pinene oxide, other than campholenic aldehyde, with a selectivity that is sufficient for practical usage.

Isomerization of styrene oxide to phenylacetaldehyde over supported phosphotungstic heteropoly acid

“…[8]. Previously, we have reported HPAs to be versatile catalysts for isomerization of various compounds, e.g., ␣-pinene oxide [9,10].…”

Selective Isomerization of Epoxides to Allylic Alcohols Catalyzed by TiO2‐Supported Gold Nanoparticles

“…Apart from 1, terpenoid epoxides 2-4, which are prone to undergo acidcatalyzed cyclization, [9] exclusively provide their isomeric allylic alcohols 2 a-4 a in high yields. a-Pinene oxide (7), a highly sensitive substrate towards acids, [14] reacts to primarily give trans-pinocarveol (7 a) and a mixture of campholenic Scheme 1. Schematic representation of the isomerization of an epoxide into an allylic alcohol using a bifunctional acid/base catalyst.…”

Catalytic isomerisation of α-pinene oxide in the presence of ETS-10 supported ferrocenium ions

“…Encouraging results were obtained for the indenyl allyl dicarbonyl derivative (h 5 -Ind)Mo(h 3 -C 3 H 5 )(CO) 2 [32], the dimeric complex [{(h 5 -Ind)Mo(CO) 2 (m-Cl)} 2 ] [33] and methyltrioxorhenium(VII) [34]. CPA is useful as an aroma chemical and as a synthetic intermediate for other aroma chemicals and also for some pharmaceuticals [35,36]. In particular, CPA is used in the manufacture of commercial sandalwood-like fragrances, e.g.…”