Integration of heterogeneous catalysts into complex synthetic routes: sequential vs. one-pot reactions in a (Knoevenagel + Mukaiyama–Michael + hydrogenation + transesterification) sequence

Abstract

Heterogeneous catalysts of different nature can be combined in one-pot tandem reactions, but the compatibility issues of catalysts with reagents, products, and by-products make more convenient the application of a sequential procedure, in which the catalyst is filtered after each reaction and the crude is used in the following reaction without purification. In this way the recovery and reuse of each catalyst can be optimized to obtain the maximum productivity. The nature of the reactions, and the catalysts involved in them, conditions the maximum number of successive steps in the sequence. In the case of the (Knoevenagel + Mukaiyama–Michael + hydrogenation + transesterification) process tested in this work, the optimal results are obtained when the sequential method is applied to only three reactions, whereas the four reactions sequence shows limitations in the yield of the last transesterification step.