Scope studies for Brønsted acid-catalyzed triplet sensitization of [2 + 2] cycloaddition reactions^a.

^aReactions conducted using 1 equiv. 2-acyl imidazole, 10 equiv. alkene coupling partner, 2.5 mol% Ru(bpy)₃Cl₂, and 20 mol% p-TsOH in MeCN, irradiating with a blue LED for 24 h. Isolated yields reported. Diastereomer ratios determined by ¹H NMR. NMI = 2-(N-methylimidazolyl).