Selective one-pot carvone oxime hydrogenation over titania supported gold catalyst as a novel approach for dihydrocarvone synthesis

It was shown for the first time that dihydrocarvone can be selectively produced by gold-catalyzed one-pot transformation of carvone oxime. This reaction was carried out at 100 °C under hydrogen pressure of 9 bar over 1.9 wt.% Au/TiO₂ catalyst using methanol as a solvent. Dihydrocarvone synthesis was shown to occur via carvone formation with the subsequent hydrogenation of its conjugated CC double bond. Application of Au/TiO₂ catalyst for both deoximation and selective hydrogenation of olefinic CC functional group is reported for the first time. The combination of these steps provides optimization of the synthetic method for dihydrocarvone production from carvone oxime which is a key intermediate in carvone synthesis from limonene. Despite a lower reaction rate than in the case of carvone, a significant increase in the stereoselectivity towards trans-dihydrocarvone was observed in the case of carvone oxime hydrogenation. The ratio between trans- and cis-dihydrocarvone was close to 4.0 compared to 1.8 achieved in the case of carvone hydrogenation.