Synthesis of a 13C,15N labeled imidazole and characterization of the 2,5-endoperoxide and its decomposition

A synthesis of 13C, 15N labeled imidazoles was developed which allows the direct detection of a transient 2,5-endoperoxide at −100°C. The endoperoxide was thoroughly characterized by 1H, 13C, and 15N NMR. Upon warming, the endoperoxide decomposes via a series of transient intermediates to 13CO2 and 1,2-diphenyl-ethanediimine.