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Updated: Oct 15, 2025

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
Synthesis of Cyclopentenes and Cyclohexenes Via Cobalt(II)-Catalyzed Oxidative Cyclization
Yue Shi1, Xuefeng Xu1, Xinfeng Chen1
1Engineering Technology Research Center of Henan Province for Solar Catalysis, College of Chemistry and Pharmaceutical Engineering, Nanyang Normal University, Nanyang 473061, China.
Abstract:
A unique method for the synthesis of cyclopentenes and cyclohexenes has been achieved by the coupling of diketones and alkenes under cobalt(II) catalysis and dimethyl sulfoxide involvement. Under optimal conditions, the formation of five- and six-membered rings can be readily controlled by the α-position substitution of styrenes. This process is proposed to proceed through a reaction sequence of oxidative coupling (mediated by K2S2O8), regioselective alkene insertion (promoted by cobalt), and intramolecular attack of the resulting allylcobalt species on the carbonyl group or methyl group in the reactive methylene process.
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Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.