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Communications
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Hence, when employing 1-chloro-2-iodobenzene, the reaction
occurred with a lower yield than with less hindered substrates
(Table 3, entry 2 vs. entries 5 and 8), and when 2-iodoanisole
was used, the cross-coupling did not even occur (Table 3,
entry 3).
In summary, we have demonstrated that the cheap and
environmentally friendly catalyst system composed of FeCl3
and diketone ligand TMHD is highly effective for the
synthesis of diaryl ethers. This novel process constitutes a
powerful and practical O-arylation protocol that appears
promising for large-scale applications. Its scope is currently
under investigation in our research group.
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Experimental Section
General procedure for O-arylation of phenols: A sealable tube
equipped with a magnetic stir bar was charged with phenol (1, 100 mg,
1.1 mmol), Cs2CO3 (700 mg, 2.2 mmol), and anhydrous FeCl3 (17 mg,
0.11 mmol). The aperture of the tube was then covered with a rubber
septum, and an argon atmosphere was established. Phenyl iodide (2,
0.18 mL, 1.65 mmol), 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD,
L3, 0.22 mmol, 46 mL), and DMF (1.7 mL) were added by syringe.
The septum was then replaced by a teflon-coated screw cap, and the
reaction vessel was placed in an oil bath at 1358C. After being stirred
at this temperature for 20 h, the heterogeneous mixture was cooled to
room temperature and diluted with dichloromethane. The resulting
suspension was directly filtered through a pad of celite and the filtrate
was concentrated to yield the product, which was purified by silica gel
chromatography (pentane) to yield diphenyl ether 3a as a colorless oil
(154 mg, 85% yield). The identity and purity of the product was
confirmed by 1H and 13C NMR spectroscopic analysis. See the
Supporting Information for full details.
Received: August 31, 2007
Published online: December 3, 2007
Keywords: arylation · catalysis · cross-coupling · iron · phenol
.
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(1108C), diphenyl ether (3a) was obtained in much lower yields.
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the corresponding O-arylated product was obtained in 59%
yield after 20 h.
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