Functional monolithic resins for the development of enantioselective versatile catalytic minireactors with long-term stability: TADDOL supported systems

Abstract

Polymeric monoliths containing TADDOL subunits have been prepared by polymerization of the corresponding functional monomers. Treatment with TiX₄ species affords Ti-TADDOLates, which can be used sequentially for two different reactions, namely the Diels–Alder reaction and the ZnEt₂ addition to benzaldehyde. These monolithic materials allow working either in batch or under flow conditions. The Diels–Alder reaction is carried out more efficiently in batch that under flow conditions, but the opposite is found for the ZnEt₂ addition. Enantioselectivities obtained compare well with those for other related supported systems. In some cases ee values found for the polymer-bound system are higher than those for the homogeneous analogue. The supported Ti-catalysts show an extraordinary long-term stability, being active for at least one year.