Zhang Zhiqin, Wang Jianwei, Yu Chenfeng, Tan Jiajing, Du Hongguang, Chen Ning
Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China.
Org Lett. 2024 Jun 7;26(22):4727-4732. doi: 10.1021/acs.orglett.4c01508. Epub 2024 May 29.
A visible-light-induced photocatalyst-free acylative pyridylation of styrenes with 4-acyl-1,4-dihydropyridines (DHPs) and 4-cyanopyridines has been described, featuring mild reaction conditions, a broad substrate scope, and good functional group tolerance. The reaction could also be performed under sunlight irradiation albeit with a slightly lower conversion. 4-Acyl-1,4-DHPs serve a dual role, acting as both a photoreductant to reduce the cyanopyridine to its radical anion intermediate and a radical precursor to produce the acyl radical. The mechanism was especially elucidated through the Hammett analysis, with the quadratic linear regression analysis by using radical dual parameters, σ and σ. The findings from Hammett analysis further demonstrate that the rate-limiting step of the process is the single electron transfer between 4-acyl-1,4-DHPs and 4-cyanopyridines.
已报道了一种可见光诱导的、无光催化剂的苯乙烯与4-酰基-1,4-二氢吡啶（DHPs）和4-氰基吡啶的酰基化吡啶化反应，其具有温和的反应条件、广泛的底物范围和良好的官能团耐受性。该反应也可在阳光照射下进行，尽管转化率略低。4-酰基-1,4-DHPs起着双重作用，既是将氰基吡啶还原为其自由基阴离子中间体的光还原剂，又是产生酰基自由基的自由基前体。通过哈米特分析，特别是使用自由基双参数σ和σ进行二次线性回归分析，阐明了该反应机理。哈米特分析的结果进一步证明，该过程的限速步骤是4-酰基-1,4-DHPs与4-氰基吡啶之间的单电子转移。
