Photoinduced Site-Selective C-H Functionalization by Pyridine N-oxide Based HAT Catalysts

Abstract

Readily available and facilely tunable pyridine N-oxides have been developed as effective photoinduced hydrogen-atom-transfer (HAT) catalyst for site-selective C-H functionalizations of a broad range of C-H substrates, including unactivated al-kanes. Pyridine N-oxide radicals, catalytically generated from N-oxides by photoredox catalyzed single-electron oxidation, are the key intermediate that enable effective HAT process for carbon radical generation to achieve alkylation, amination, azidation, and allylation. Additionally, the fine tuning of reactivity and selectivity of pyridine N-oxides through operationally simple structural modification was investigated and shown promising capability for selective functionalization of unactivat-ed secondary and primary C(sp3)–H bonds.

Aliphatic C–H Functionalization Using Pyridine N-Oxides as H-Atom Abstraction Agents

“…17 Our continuous interest in developing photoredox catalyzed C−H functionalization reactions that are operationally simple, sustainable, highly efficient and selective, and allow structural fine-tuning of the catalysts led to the discovery of pyridine Noxides as organic precursors for oxygen-centered radicals that allow HAT processes (Figure 1b). 18 Although these compounds had previously been utilized as substrates in a limited number of visible light-mediated transformations, 19 their catalytic application under photoredox catalysis remained unprecedented to the best of our knowledge. Wu and coworkers first described the generation of pyridine N-oxy radicals by single electron oxidation with an acridinium photoredox catalyst.…”