One-pot photocatalytic transformation of indolines into 3-thiocyanate indoles with new Ir(iii) photosensitizers bearing β-carbolines

Abstract

Current societies demand sustainable synthetic procedures and accordingly the combination of two photocatalytic reactions in a one-pot process is a very appealing chemical tool. In the present work, we report on the development of new Ir(III) bis-cyclometallated photosensitizers with β-carboline ligands and disclose a simple and unprecedented photocatalytic one-pot two-step protocol for the chemoselective and C-3 regioselective oxidative thiocyanation of indolines to produce the corresponding 3-thiocyanato-indoles. The procedure is performed in THF at room temperature, in the presence of NH₄SCN, O₂ and the Ir(III) photocatalysts under blue light exposure. Moreover, this methodology combines important advantages such as an outstanding efficiency, based on good yields for low catalyst loadings, along with an excellent sustainability founded on the use of O₂ as a green oxidant and light as the energy source. In addition, DFT studies have allowed a clear interpretation of the photophysical and electrochemical properties of the Ir(III) complexes and transient absorption experiments, along with other experimental proof, have demonstrated that the two photocatalytic processes are mediated by ¹O₂. Our results pave the way for future developments in the field of photocatalysis using Ir(III) biscyclometallated complexes as photosensitizers.