Photoactivated Reactions without Traditional Photocatalysts: Electron-Donor Complexation of 1,2,3-Triazoles Initiates Denitrogenative Transformations

We present a set of visible-light-promoted denitrogenative transformations of 1,2,3-triazoles that generate high product yields without the use of a traditional, external photocatalyst, with the reaction viable for both benzotriazole and benzotriazinone. Mechanistic studies using UV–vis absorption, 1H NMR spectroscopy, and density functional theory indicate that these reactions are initiated by an electron donor–acceptor (EDA) complex which forms between N,N-diisopropylethylamine (DIPEA) and the 1,2,3-triazole. A comprehensive analysis of how irradiation wavelength impacts reactivity was obtained using an online photochemical reactor coupled mass spectrometer, indicating a lack of correlation between absorptivity and photoreactivity for the reaction between benzotriazinone and methyl acrylate. The reaction was photoinitiated by light-emitting diodes (LEDs) at wavelengths longer than 400 nm, which is unexpected on the basis of solely the absorption spectra of the starting materials.