Energy Transfer Photolysis of N-Enoxybenzotriazoles into Benzotriazolyl and α-Carbonyl Radicals

Irradiation of N-enoxybenzotriazoles with blue LEDs in the presence of photosensitizers productively rendered two reactive radical intermediates, that is, benzotriazolyl- and α-carbonyl radicals. The formation of these radicals as discrete species was suggested in the cross-over experiment, and this N–O fragmentation initiated synthetically useful transformations, such as an atom-economical [1,3]-shift and group transfer radical addition, leading to biologically interesting benzotriazolyl derivatives. The facility of these transformations (<5 min) was rationalized by the triplet state energy transfer and the presence of a very long-lived radical chain (Φ = 210 and 131, respectively, for [1,3]-shift and carboamination), which was initiated by the addition of electrophilic benzotriazolyl radicals to the olefin moieties. The N–O homolysis was further characterized by electrochemical and photophysical studies, as well as density functional theory computation.