4‐Nitroanisole Facilitates Proton Reduction: Visible Light‐Induced Oxidative Aryltrifluoromethylation of Alkenes with Hydrogen Evolution

Abstract A complementary oxidative photocatalytic strategy is presented. In the presence of 4‐nitroanisole, hexafluoroisopropanol (HFIP) as a proton source is activated and the proton photoreduction is enhanced, enabling a range of cyclizative aryltrifluoromethylations of alkenes and CF 3 SO 2 Na (Langlois’ reagent) with hydrogen evolution. Such a protocol is general, for both activated and unactivated olefins could be used as the substrates, affording a variety of CF 3 ‐containing heterocycles such as indolines, indolin‐2‐ones, 3,4‐dihydroisoquinolin‐1‐ones, 5,6‐dihydrobenzoimidazo[2,1‐ a ]isoquinolines, benzoimidazo[2,1‐ a ]isoquinolin‐6(5 H )‐ones and 1,2,3,4‐tetrahydroisoquinolines, under mild and metal‐ and oxidant‐free conditions with a good functional‐group tolerance. Extensive mechanistic investigations revealed that p ‐nitroanisole ( p ‐NA) does not react with the photocatalyst directly as an oxidant, but rather activates HFIP via proton‐coupled electron transfer (PCET) and scavenges some of the reduced protons to improve proton photoreduction.