Photo-Lewis Acid Generator Based on Radical-Free 6π Photo-Cyclization Reaction

We present here a new photo-active molecule which acts
as a photo-Lewis
acid generator (PLAG) based on photo-chemical 6π-percyclization.
Photo-illumination of the PLAG molecule produces a condensed aromatic
carbocation with a triflate counteranion, which exhibits Lewis acid
chemical catalytic reactivity such as initiation of the polymerization
of epoxy monomers and catalysis of Mukaiyama-aldol reactions. The
terminal-end structure in the epoxy polymerization was modified with
the Lewis acid fragment. The carbocation induced the Mukaiyama-aldol
reaction as a new photo-gated system with remarkably high catalytic
reactivity and turnover numbers higher than 60. The photo-chemical
quantum yield of the carbocation generation is 50%, which is considerably
higher than obtained with most Brønsted photo-acid generators.