One-pot monoterpene alcohol amination over Au/ZrO2 catalyst: Effect of the substrate structure

One-pot amination of natural monoterpene alcohols was studied over Au/ZrO2 catalyst, focusing on the structure effect of substrates selected based on their pharmaceutical relevance. Bicyclic (myrtenol and nopol, bearing an unconjugated –OH group) and monocyclic (perillyl) alcohols were chosen for aniline amination under comparable conditions. Utilization of nopol resulted in a tenfold decrease in the reaction rate from that for myrtenol, increasing selectivity to the amine. The influence of secondary transformation was more noticeable for monocyclic perillyl alcohol with a conjugated –OH group. Myrtenol amination was explored with a range of aliphatic and aromatic amines, showing that the primary amine structure affected both the initial dehydrogenation rate and the selectivity to the desired amine. A good correlation was found between substrate structure and reactivity using the Hammett equation. The myrtenol consumption rate was tentatively proposed to be affected by the Auδ+ availability required for alcohol dehydrogenation. Propanol-2, introduced as a hydrogen donor, improved the yield of the target amine.