Photoreductive Alkylative Dearomatization of N‐Alkyl Pyridin‐1‐ium Salts: Site Selective Access to 4‐Alkyl 1,4‐Dihydropyridines

• Published in: European journal of organic chemistry 2024-01, Vol.27 (3), p.n/a
• Main Authors: Xu, Chong‐Hui, Zeng, Liang, Hu, Ming, Qin, Jing‐Hao, Xu, Xin‐Hua, Li, Jin‐Heng
• Format: Article
• Language: English
• Subjects: 4-alkyl 1,4-dihydropyridines; Alkylation; alkylative dearomatization; Harnesses; N-alkyl pyridinium salts; Oxidizing agents; photoredox; Reagents; single electron oxidant (SEO); Single electrons
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202301120

A visible light photoreductive dearomatizative alkylation of N‐alkyl pyridinium salts for producing 4‐alkyl‐1,4‐dihydropyridines is described. The reaction harnesses N‐alkyl pyridinium salts both as the alkyl radical precursors to initiate the reaction and as the 1,4‐dihydropyridin‐4‐yl‐based alkylating reagents to terminate the reaction. In contrast to the reported electroreductive procedure via the key dihydropyridine radical intermediates, mechanistic studies demonstrate that this photoreductive dearomatizative alkylation proceeds via directly alkyl radical addition across the pyridinium ring followed by single electron oxidant (SEO) and dearomatization. A new visible light photoreductive dearomatizative alkylation of N‐alkyl pyridinium salts for producing 4‐alkyl‐1,4‐dihydropyridines by harnessing N‐alkyl pyridinium salts both as the alkyl radical precursors to initiate the reaction and as the 1,4‐dihydropyridin‐4‐yl‐based alkylating reagents to terminate the reaction is developed. Mechanistic studies demonstrate that this reaction proceeds via directly alkyl radical addition across the pyridinium ring followed by single electron oxidant and dearomatization.