Synthesis of Cage‐Shaped Borates Bearing Pyrenylmethyl Groups: Efficient Lewis Acid Catalyst for Photoactivated Glycosylations Driven by Intramolecular Excimer Formation

We describe the synthesis and characterization of a photoactivated boron‐based Lewis acid catalyst based on a cage‐shaped triphenolic ligand with three pyrenylmethyl moieties. The obtained cage‐shaped borate functioned as a photoactivated Lewis acid catalyst thanks to the flexible three pyrenylmethyl moieties. The deformation of the cage‐shaped scaffold driven by intramolecular excimer formations of the pyrenes is a critical factor in realizing the photoactivation. Mannich‐type reactions and glycosylations significantly were accelerated under 370 nm light irradiations. It is noteworthy that various glycosyl fluorides, which are not easily activated in photocatalytic systems due to their high C−F bond stability, are activated by the photoimproved catalytic activity of the catalyst. A cage‐shaped borate 3aB having pyrenylmethyl groups was synthesized. The obtained 3aB functioned as a photoactivated Lewis acid catalyst. The photoactivation originates from the deformation of the cage‐shaped scaffold driven by intramolecular excimer formations of the pyrenes, allowing the catalytic O‐glycosylation using glycosyl fluorides to proceed with a high efficiency.