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-2 H -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) 2 Cl 2 . 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.