Stimuli Responsive Switchable Catalysts for Asymmetric Synthesis

Switchable asymmetric catalysts are molecular systems that reversibly switch between divergent catalytic states in response to external stimuli, enabling control over both activity and enantioselectivity within a single chiral catalyst. The catalytic system has a chiral catalytic core, a stimulus-Responsive structural unit, and a mechanistic pathway that translates structural changes into switchable stereochemical control, giving access to the opposite enantiomer from the same starting materials or enabling the “on/off” switching of the catalyst. This review covers advances in switchable asymmetric catalysis since 2017, organized according to the nature of the external stimulus: photo-triggered isomerization of stilbene, azobenzene, hydrazone, and spiropyran scaffolds; pH-driven aggregation-disaggregation processes; thermoresponsive polymer platforms operating via LCST transitions; and gas-triggered catalysts based on reversible carbon dioxide binding. Mechanistic insights into catalyst switching are discussed alongside applications in asymmetric synthesis like Aldol, Henry, Michael, and epoxidation reactions.