Abstract:
Over the past decade, visible-light-mediated photocatalysis has demonstrated its unique role in enabling new reactivity and selectivity in organic synthesis. Single electron transfer (SET) and energy transfer (EnT) catalysis are two different mechanistic pathways of photocatalysis. In recent years, merging nickel catalysis and photocatalysis has opened new reaction pathways and enabled novel synthetic disconnections. First, with a combination of nickel catalysis and photoredox-catalyzed 1,5-hydrogen atom transfer (HAT), we developed a regioselective remote arylation of unfunctionalized C(sp3)-H bonds. By changing the ligand environment around nickel, we achieved selective γ- or δ-arylation of amides, respectively. Second, we reported a mild and general protocol for E to Z photoisomerization of oximes via triplet-triplet energy transfer (EnT) catalysis. The synthetic utility of Z-oximes was demonstrated with regioselective Nonclassical Beckmann Rearrangement and chemodivergent N- or O- cyclizations of alkenyl oximes. Last, utilizing photoinduced ligand dissociation of nickel complex, we developed selective N-demethylation of trialkylamines, where C(sp2) radicals generated from aryl bromides were employed as HAT reagents. The site selectivity of N-demethylation was further improved by steric control of the C(sp2) radicals.
