One-step microwave-assisted asymmetric cyclisation/hydrogenation of citronellal to menthols using supported nanoparticles on mesoporous materials.

The selective conversion of citronellal to menthols, with good diastereoselectivities to (-)-menthol for the case of (+)-citronellal as starting material, can effectively be carried out in a one-step reaction under microwave irradiation catalysed by supported nanoparticles on mesoporous materials. 2% Pt/Ga-MCM-41 was found to be the optimum catalyst for the reaction, with a quantitative conversion of starting material and selectivities above 85% to menthols obtained in short reaction times (typically 15 min). These results constitute the first report of a simple microwave-assisted one-step cyclisation/hydrogenation process for the production of menthols.