Acylsilane as Energy Transfer Catalyst for Intermolecular [2 + 2] Cyclization of Alkenyl Triflones and Olefins

In response to the bottlenecks of traditional ketone-based photocatalysts, such as narrow visible light absorption range and nonradiative deactivation of excited states, we herein reported readily available acylsilanes as energy transfer catalysts. These catalysts exhibit extended visible light responsiveness, tunable triplet-state energy levels, and suppressed side reactions (e.g., hydrogen atom transfer) through substituent engineering. This work demonstrates that the optimized acylsilane is an effective catalyst for the intermolecular [2 + 2] cyclization of alkenyl triflones and olefins. The reaction works well with mono-, di-, and trisubstituted olefins. Notably, the diastereoisomers of all 2-vinylpyridine derivatives were efficiently separated. Mechanistic studies confirmed that the reaction proceeds through an EnT mechanism. Scaling up the reaction is feasible, and the triflone group can be easily converted into a gem-difluoroalkene.