Azo-crown ether-based photoswitching chiral phase transfer catalysts have been developed to control the catalytic activity by photoirradiation. Azobenzene binaphthyl crown ether (ABCE) can switch its reactivity and selectivity through structural transformation of the crown ether moiety induced by E/Z photoisomerization of azobenzene. (Z)-ABCE promoted enantioselective alkylation of the glycine Schiff base to afford chiral amino acid derivatives in good yields with high enantiomer ratios. In contrast, (E)-ABCE hindered the reaction progress under the same conditions.
An azopyridine-based oxazoline was developed for utilizing azo group coordination and isomerization as a photoswitchable ligand. The ligand coordinated to rare-earth metal (RE) catalyst underwent efficient E/Z photoisomerization, suggesting tri-...
Planar chiral [2.2]paracyclophane-based phosphine-phenol catalysts, which have a benzene ring spacer inserted between the pseudo-ortho-substituted [2.2]paracyclophanol skeleton and the diarylphosphino group, are highly suitable for enantioselective [3 + 2] annulations of allenoates and N-tosylimines. These catalysts can be tuned by changing the substituent on the benzene rings of the diarylphosphino group. The observed enantioselectivity of 92% is the highest reported to date for phosphine-catalyzed annulations of unsubstituted allenic esters and N-tosylaldimines.
This study presents recent advances in photoswitchable chiral organocatalysts and their applications in the photomodulation of enantioselective reactions. Under irradiation with an appropriate wavelength of light, the E/Z‐photoisomerization of the photoresponsive units on the catalysts leads to the control of the catalytic activity and/or selectivity of the enantioselective reactions. Additionally, this study elucidates the design, synthesis, and catalytic application of the fabricated azobenzene BINOL‐based photoswitchable chiral phase‐transfer catalysts. This account will provide insights into the appropriate design of a photoswitchable chiral organocatalyst that can achieve both good enantioselectivity and photocontrol.
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