Heterogeneous Catalysis for Tandem Mukaiyama–Michael and Hydrogenation Reactions: One-Pot vs Sequential Processes

Abstract

Mukaiyama–Michael and hydrogenation reactions can be combined by the use of two heterogeneous catalysts: a copper-exchanged laponite and Pd/Al2O3. Although in principle, this combination would be suitable for a one-pot tandem process, it is useful in only two reaction cycles because of irreversible deactivation of the copper catalyst. However, much better results are obtained in a sequential tandem process when the copper catalyst is filtered and the reaction crude is directly used in the hydrogenation reaction without further purification. Under such conditions, it is possible to fully optimize the reuse of each catalyst, up to 10 times the copper catalyst by washing it every two cycles with THF in a Soxhlet extractor, and four times the palladium catalyst that must be renewed every four cycles, whereas the purification steps of the synthetic route are minimized.