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.

本文报道了一种新型光活性分子，其基于光化学6π周环化反应（6π-percyclization），可作为光路易斯酸发生器（photo-Lewis acid generator, PLAG）。对该PLAG分子进行光辐照后，可生成带有三氟甲磺酸根反离子的稠环芳香碳正离子，该物种展现出路易斯酸催化活性，例如引发环氧单体的聚合反应以及催化Mukaiyama羟醛反应（Mukaiyama-aldol reaction）。该路易斯酸片段可对环氧聚合反应的端基结构进行修饰。该碳正离子作为一种新型光控催化体系，可诱导Mukaiyama羟醛反应，其催化活性优异，转化数超过60。该碳正离子生成过程的光化学量子产率可达50%，远高于多数布朗斯特光酸发生器（Brønsted photo-acid generator）的量子产率。