Recent advances in amine catalyzed aldol condensations

During the past two decades, new insights have driven the development and optimization of aminated materials as aldol condensation catalysts. Amines, either primary or secondary, facilitate the reaction via an enamine mechanism. If the spatial placement with respect to the amine allows it, weak acid sites such as silanols or hydroxyls, can cooperate as hydrogen bond donors and aid in proton transfer steps. Furthermore, the reaction environment, i.e., support and solvent and their mutual interactions, is also a key determining factor. In particular, co-feeding small amounts of water suppresses the formation of inhibiting and site-blocking species. However, silica-based materials are susceptible to hydrolysis. This led to the development of water tolerant (bio)polymer supported amine catalysts which also exhibit selective component enrichment properties, opening up opportunities for further catalyst development.