Asymmetric photocatalysis has emerged as a powerful strategy for constructing chiral molecules under mild conditions, yet the enantioselective activation of aromatic enol systems via visible light remains a significant challenge. In particular, the photochemical dearomatization of salicyclaldehydes through excited-state intramolecular proton transfer (ESIPT) offers unique reactivity but has rarely been harnessed in catalytic asymmetric synthesis. Herein, we report an asymmetric de Mayo reaction catalyzed by a chiral hafnium phosphate complex, enabling visible-light-promoted dearomatization and exo-aromatic C-C bond insertion of salicylaldehyde derivatives with alkenes. By leveraging the unique photophysical properties of ESIPT systems, we demonstrate that coordination of 1-hydroxy-2-naphthaldehyde to a Hf(IV)-chiral phosphate catalyst induces a significant red-shift in absorption, activating the substrate under 480 nm irradiation. This strategy not only enhances photochemical reactivity but also provides excellent stereocontrol, yielding insertion products in up to 95% yield and 98% ee. Mechanistic studies, including transient spectroscopy and DFT calculations, reveal that the reaction proceeds via a triplet-state 2 + 2 cycloaddition pathway facilitated by hafnium-centered ligand-to-metal charge transfer (LMCT). This work establishes a distinctive catalytic strategy for enantioselective transformations of aromatic enol systems under visible light and expands the synthetic utility of ESIPT-driven photochemistry.
Yang et al. (Tue,) studied this question.