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Nickel-catalyzed coupling reaction of alkyl halides with aryl Grignard reagents in the presence of 1,3-butadiene: Mechanistic studies of four-component coupling and competing cross-coupling reactions

Abstract

We describe the mechanism, substituent effects, and origins of the selectivity of nickel-catalyzed four-component coupling reaction of alkyl fluorides, aryl Grignard reagents, and two molecules of 1,3-butadiene that affords a 1,6-octadiene carbon framework bearing alkyl and aryl groups at 3- and 8-positions, respectively, and the competing cross-coupling reaction. Both the four-component coupling reaction and the cross-coupling reaction are triggered by the formation of anionic nickel complexes, which are generated by the oxidative dimerization of two molecules of 1,3-butadiene on Ni(0) and the subsequent complexation with aryl Grignard reagents. The C–C bond formation of alkyl fluorides with the γ-carbon of anionic nickel complexes leads to the four-component coupling product, whereas the cross-coupling product is yielded via nucleophilic attack of the Ni center toward alkyl fluorides. These steps are found to be the rate-determining and selectivity-determining steps of the whole catalytic cycle, in which the C–F bond of alkyl fluorides is activated by Mg cation rather than Li or Zn cation. ortho-Substituent(s) of aryl Grignard reagents suppressed the cross-coupling reaction leading to the selective formation of the four-component products. Such steric effects of the ortho-substituent(s) were clearly demonstrated by crystal structure characterizations of ate complexes and DFT calculations. Electronic effects of para-substituent of aryl Grignard reagents on both the selectivity and reaction rates are thoroughly discussed. The present mechanistic study offers new insight into anionic complexes, which are proposed as the key intermediates in catalytic transformations though detailed mechanisms are not established in many cases, and demonstrates their synthetic utility as promising intermediates for C–C bond forming reactions, providing useful information for developing efficient and straightforward multicomponent reactions.

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Publication details

The article was received on 29 Oct 2017, accepted on 04 Jan 2018 and first published on 05 Jan 2018


Article type: Edge Article
DOI: 10.1039/C7SC04675H
Citation: Chem. Sci., 2018, Accepted Manuscript
  • Open access: Creative Commons BY license
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    Nickel-catalyzed coupling reaction of alkyl halides with aryl Grignard reagents in the presence of 1,3-butadiene: Mechanistic studies of four-component coupling and competing cross-coupling reactions

    T. Iwasaki, A. Fukuoka, W. Yokoyama, X. Min, I. Hisaki, T. Yang, M. Ehara, H. Kuniyasu and N. Kambe, Chem. Sci., 2018, Accepted Manuscript , DOI: 10.1039/C7SC04675H

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