Controlling selectivity in the reaction network of aldoxime hydrogenation to primary amines

During the hydrogenation of oximes, the temporary protection of the nitrogen moiety by a hydroxyl group promises to provide access to a highly selective synthetic route to primary amines. We will show that the reaction, however, proceeds via the more general network of imine and Schiff base chemistry. By choosing the right catalyst and conditions, specific pathways can be selected enabling us to steer the route from a pool of intermediate compounds to either primary or secondary amines. Thus, nickel catalysts provide high selectivity towards primary amines albeit at a moderate activity, while noble metal catalysts show good selectivity towards secondary amines, as well as high activity. Detailed analysis of the reaction sequence over Ni/SiO2 provides insight into the pathways and provides understanding for the tools to obtain outstanding selectivities in the hydrogenation of oximes and other amine precursors.