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Iron-Promoted Oxidative Alkylation/Cyclization of Ynones with 4-Alkyl-1,4-dihydropyridines: Access to 2-Alkylated Indenones

Fang-Ting Xiong, Bin-Hong He, Yu Liu*, Quan Zhou and Jian-Hong Fan*

*Department of Chemistry and Chemical Engineering, Hunan Institute of Science and Technology, Yueyang 414006, China, Email: lyxtmj_613163.com, 13548535911163.com

F.-T. Xiong, B.-H. He, Y. Liu, Q. Zhou, J.-H. Fan, J. Org. Chem., 2022, 87, 8599-8610.

DOI: 10.1021/acs.joc.2c00766


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Abstract

An iron-promoted oxidative tandem alkylation/cyclization of ynones with 4-alkyl-substituted 1,4-dihydropyridines provides 2-alkylated indenones with excellent selectivity under mild conditions. The process occurs via oxidative homolysis of a C-C σ-bond in 1,4-dihydropyridines to generate an alkyl radical followed by its addition to the C-C triple bond and an intramolecular cyclization.


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Details

The article discusses an iron-promoted oxidative tandem alkylation/cyclization of ynones with 4-alkyl-1,4-dihydropyridines (DHPs) to synthesize 2-alkylated indenones. This method involves the oxidative homolysis of a C−C σ-bond in DHPs to generate an alkyl radical, which then adds to the C−C triple bonds in ynones, followed by intramolecular cyclization. The process is efficient, selective, and occurs under mild conditions, making it environmentally friendly. The study explores various iron catalysts and oxidants, with FeCl3 and K2S2O8 proving optimal. The reaction tolerates a wide range of functional groups, producing various 2-alkylated indenones in good yields. Control experiments confirmed the involvement of an alkyl radical pathway. The method offers a cost-effective alternative to noble metal-catalyzed processes and has potential applications in synthesizing bioactive molecules and drugs. The research was supported by several Chinese scientific foundations and conducted by a team from the Hunan Institute of Science and Technology.


Key Words

indenones, potassium peroxydisulfate


ID: J42-Y2022