Redox-neutral ketyl radical coupling/cyclization of carbonyls with N-aryl acrylamides through consecutive photoinduced electron transfer

While the reductive ketyl couplings of carbonyls have been widely explored, we report in this work on a redox-neutral umpolung carbonyl coupling reaction through ketyl radical formation by consecutive photoinduced electron transfer (ConPET) under metal- and additive-free conditions. The donor-acceptor cyanoarene-based fluorophore, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), was used as an efficient photocatalyst. It undergoes ConPET to form the excited radical anion (4CzIPN(-)*) possessing high reductive potential without an external electron donor. This mild and simple photocatalytic system allows highly efficient coupling/cyclization of N-aryl acrylamides and carbonyls and provides straightforward access to structurally useful hydroxyalkyl oxindoles with formal 100% atom economy.