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

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 CF3SO2Na (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 CF3-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(5H)-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.

Automated summary

This study presents a complementary oxidative photocatalytic strategy for the cyclizative aryltrifluoromethylations of alkenes and CF3SO2Na. The protocol is general and functional-group tolerant, offering a variety of CF3-containing heterocycles. Extensive mechanistic investigations revealed the role of p-nitroanisole in enhancing proton photoreduction via proton-coupled electron transfer.