Ligand-Free Iron/Copper Cocatalyzed Alkynylation Coupling Reactions
COMMUNICATIONS
suitable for the cross-coupling of iodobenzene and Acknowledgements
thiophenol and the desired diphenyl sulfide was iso-
We are grateful to the grants from the Natural Science Foun-
dation of Education Committee of Jiangsu Province
(06KJB150099), the National Natural Science Foundation of
China (No. 20802046) and the Key Laboratory of Organic
Synthesis of Jiangsu Province for financial support.
lated with 97% yield. Under the same conditions, the
reaction did not occur without the iron catalyst. Thus,
it was encouraging to reveal that our catalytic system
could be efficient in other coupling reactions. Further
work is underway in our laboratory.
In summary, we have developed an effective and
promising Fe/Cu catalytic system for the coupling of
aryl halides including aryl iodides and bromides with
various alkynes. A noteworthy finding is that for the
first time the iron-catalyzed alkynylation reactions
could be performed without using any ligand. Thus,
the low-cost, benign character and easy availability of
the catalyst makes this method potentially very
useful, which could be amenable to scale-up. Further
work is in progress in this laboratory with the aim of
reducing the loading of catalysts, mechanistic studies
and extending the application of these readily avail-
able catalytic systems in other coupling transforma-
tions.
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Experimental Section
General Experimental Methods
All reactions were carried out under an argon atmosphere.
Solvents were dried and degassed by the standard methods
and all aryl and heteroaryl halides were purchased from Al-
drich or Alfa. Aryl halides and alkynes are readily available.
Flash column chromatography was performed using silica
gel (300–400 mesh). Analytical thin-layer chromatography
was performed using glass plates pre-coated with 200–400
mesh silica gel impregnated with a fluorescent indicator
(254 nm). NMR spectra were recorded in CDCl3 on a
Varian Inova-400 NMR spectrometer (400 MHz or
300 MHz) with TMS as an internal reference. Products were
1
characterized by comparison of H NMR and HR-MS data
with those in the literature.
Typical Experimental Procedure for the Fe/Cu
Cocatalyzed Alkynylation Coupling Reaction
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A mixture of aryl halide (1.0 equiv.), alkyne (1.2 equiv.), CuI
(20 mol%), Fe
(acac)3 (20 mol%), K3PO4 (2.0 equiv.), and
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DMSO (2 mL) in a Schlenk tube was stirred under an argon
atmosphere at 1408C for the desired time until complete
consumption of starting material as monitored by TLC.
After that the mixture was poured into ether, then washed
with water, extracted with ethyl acetate, dried by anhydrous
MgSO4, then filtered and evaporated under vacuum, the res-
idue was purified by flash column chromatography (petro-
leum ether or petroleum ether/ethyl acetate) to afford the
corresponding coupling products.
1-[2-(4-Methoxyphenyl)ethynyl]benzene: Yellow solid;
1
mp 57–598C; H NMR (400 MHz, CDCl3): d=7.52–7.50 (m,
2H, ArH), 7.47 (d, J=8.8 Hz, 2H, ArH), 7.36–7.32 (m, 3H,
ArH), 6.88 (d, J=8.8 Hz, 2H, ArH), 3.83 (s, 3H, CH3); HR-
MS (ESI+): m/z=208.0896, calcd. for [C15H12O]+: 208.0888.
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Adv. Synth. Catal. 2008, 350, 2477 – 2482
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2481