PHOTOCHEMISTRY OF N-(BENZOYLIMINO)-1,2,4-TRIAZOLIUM AND N-(BENZOYLIMINO)PYRIDINIUM YLIDES - A SOURCE OF BENZOYLNITRENE USEFUL IN PHOTOLABELING AND PHOTO-CROSS-LINKING EXPERIMENTS

The photochemistry of substituted 1-(benzoylimino)pyridinium and 4-(N-benzoylimino)-1,2,4-triazolium ylides was investigated to judge their capacity to give aroylnitrenes and their suitability for use in photolabeling experiments. Evidence presented indicates that the triplet states of the ylides cleave to generate aroylnitrenes. In an attempt to enhance triplet formation, nitro- and acetyl-substituted pyridinium ylides were examined. Their irradiation does not give nitrenes in meaningful yield. However, irradiation of the triazolium ylides gives nitrenes in excellent yield. The mechanism of these reactions was probed, and additional evidence is obtained that supports the proposal that benzoylnitrene is a singlet in its ground state. The triazolium ylides may be suitable reagents for photolabeling applications.