Ru(bpy)2Cl2: A Catalyst Able to Shift the Course of the Photorearrangement in the Boulton-Katritzky Reaction.

Abstract The Boulton–Katritzky reaction represents one of the most popular and efficient strategies used to realize azole-into-azole conversions. For example, under different experimental conditions, it allows the rearrangement of Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazoles (1) into 2-aryl-4-benzoylamino-5-phenyl-2H-1,2,3-triazoles (2) in very high yields. Moreover, we have recently realized this conversion also by UV-photostimulation. Now we have enlarged the scope of the reaction irradiating with visible or UV light an acetonitrile solution of some Z-arylhydrazones (1a–e) in the presence of catalytic amounts of Ru(bpy)2Cl2. We have observed the unexpected formation of the 1-aryl-5-benzoylamino-3-phenyl-1,2,4-triazoles (3a–e) eventually together with the expected 2a–d in high yields.