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Issue 11, 2014
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Ligand mediated iron catalyzed dimerization of terminal aryl alkynes: scope and limitations

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Abstract

Regioselective dimerization of terminal aryl alkynes to produce conjugated enynes has been achieved using FeCl3 and KOtBu in the presence of either DMEDA or dppe. The reaction proceeds smoothly in toluene at 145 °C for 2 h to give the corresponding head-to-head dimers in good to excellent yields (54 to 99%) with high E-selectivity (67 : 33 to 83 : 17 E/Z). Both strongly electron-donating and electron-withdrawing groups are compatible with this procedure. The bidentate phosphine (dppe) ligand exhibits better catalytic activity than the bidentate amine (DMEDA). The aliphatic acetylene fails to react under this catalytic system which suggests that potassium tertiary butoxide activates the conjugated system of aryl acetylene through cation–pi interaction and pi–pi interaction. A radical inhibitor (galvinoxyl or TEMPO) completely suppresses the reaction. Employing FeCl2 as a catalyst instead of FeCl3, only phenyl acetylene afforded the corresponding head to head dimer in good yield. Mechanistic pathways for both FeCl3 catalyzed dimerization of aryl alkynes and FeCl2 catalyzed dimerization of phenyl acetylene have been proposed.

Graphical abstract: Ligand mediated iron catalyzed dimerization of terminal aryl alkynes: scope and limitations

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Publication details

The article was received on 26 Nov 2013, accepted on 17 Dec 2013 and first published on 11 Feb 2014


Article type: Paper
DOI: 10.1039/C3OB42365D
Citation: Org. Biomol. Chem., 2014,12, 1812-1822
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    Ligand mediated iron catalyzed dimerization of terminal aryl alkynes: scope and limitations

    G. C. Midya, B. Parasar, K. Dhara and J. Dash, Org. Biomol. Chem., 2014, 12, 1812
    DOI: 10.1039/C3OB42365D

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