Visible-light-induced dehydrogenation of Indolines

The indole structure, commonly found in natural products and pharmaceuticals, draws attention for its potential in liquid organic hydrogen carriers, leading to interest in the transformation between indolines and indoles. Here, a protocol utilizing visible light for the dehydrogenation of indolines is developed, employing thioxanthone (TX) as photocatalyst and di-tert-butyl peroxide (DTBP) as oxidant. In this method, DTBP is excited through the energy transfer (EnT) process with TX*, resulting in the homolysis and the formation of crucial tert-butoxy radicals. These radicals then facilitate a two-step hydrogen atom transfer (HAT) process with the substrate to yield indoles. The entire dehydrogenation has latent practicability due to its broad substrate compatibility and mild reaction conditions, which further expands the application of TX in the organophotocatalytic field.