Site‐Selective Pyridylic C−H Functionalization by Photocatalytic Radical Cascades

• Published in: Angewandte Chemie 2022-07, Vol.134 (29), p.n/a
• Main Authors: Kim, Myojeong, You, Euna, Kim, Jieun, Hong, Sungwoo
• Format: Article
• Language: English
• Subjects: Alkylidene; Cascade chemical reactions; Chemistry; C−H Functionalization; Dihydropyridine; Heterocycles; Intermediates; Organic compounds; Photocatalysis; Pyridines; Quinolines; Radicals; Reaction Mechanisms; Retirement; Salts; Substrates; Sulfur dioxide
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202204217

An efficient pyridylic C(sp3)−H functionalization has been developed through photocatalytic radical‐mediated fluoroalkylation or cascade reactions. This method is enabled by the reversible formation of alkylidene dihydropyridine intermediates via the facile enolate formation of C4‐alkyl N‐amidopyridinium salts in the absence of an external base, thereby establishing the conditions necessary for subsequent intermolecular radical trapping. Rapid structural diversification of the pyridylic site can be achieved through photocatalytic multicomponent cascade reactions involving alkene trifluoromethylation, SO2‐reincorporation, and sulfonyl radical addition. This operationally simple method features a broad substrate scope and high chemoselectivity and offers a unique approach for the rational modification of the heterobenzylic C−H bonds of pyridines and quinolines with uniform site‐selective control. Furthermore, experimental and theoretical studies were performed to elucidate the reaction mechanism. An efficient method for pyridylic C(sp3)−H functionalization has been achieved through photocatalytic radical‐mediated fluoroalkylation or cascade reactions. This operationally simple method offers a unique approach for the highly selective modification of the heterobenzylic C−H bonds of pyridines and quinolines under mild, metal‐free conditions.