C O M M U N I C A T I O N S
Table 2. Iron-Catalyzed Arylation of 2-Arylpyridine Derivatives with
mono- and diphenylated products in comparable yields (entry 15).
The reaction was very slow for 4-phenylpyrimidine (entry 16). The
reaction of 1-phenyl-1H-pyrazole was also slow but gave the
desired product in a moderate yield (entry 17). The reaction of
1-phenyl-1H-1,2,3-triazole or 1-phenyl-1H-1,2,4-triazole gave only
a trace amount of the desired product (data not shown). We consider
it likely that the extra remote nitrogen groups cause a nonproductive
coordination of the metal atom and, hence, interfere with the
progress of the desired C-H activation reaction.
Arylzinc Reagentsa
In summary, we have developed a new class of homogeneous
iron catalysis: an iron-catalyzed C-C bond formation reaction that
features C-H bond activation. The overall synthetic transformation
formally represents the nucleophilic displacement of the ortho-
hydrogen atom by an arylzinc nucleophile.9 We consider it
remarkable that the reaction took place at 0 °C since C-H bond
activation reactions often require a reaction temperature above 80
°C.6,9,10 This study shows that the combination of iron, zinc,
magnesium, 1,10-phenanthroline, TMEDA, and 1,2-dichloro-2-
methylpropane is important for the success of the reaction. We
speculate that the phenanthroline coordinates to the iron and
TMEDA to the zinc, and that the reaction involves a redox cycle
of iron with the dichloride acting as an electron acceptor,8 but so
far, we have obtained no solid evidence that proactively supports
such a conjecture. The mechanism and the synthetic scope of the
reaction will be the next stage of our investigation.
Acknowledgment. We thank MEXT, Japan for financial
support (Grant-in-Aid for scientific research, No. 18105004) and
the Global COE Program for Chemistry Innovation) and T.
Ichiki for initial experiments.
Supporting Information Available: Experimental procedures
and characterization of new compounds. This material is available
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a Unless otherwise noted, the reaction was carried out on a 0.4 mmol
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0 °C using 10 mol % of Fe(acac)3/phen, 3 equiv of
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(7) Cross-coupling of 1,2-dichloroethane and the phenylzinc reagent also took place
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electronic effect of the substitutent on the aryl group (entries
6-10), while it was very sensitive to any steric effects, as
suggested by the extremely slow reaction of the 2-tolylzinc
reagent (entry 11). Neither of zinc reagents prepared from
MeMgBr or BuMgBr gave corresponding alkylated products.
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only one ortho C-H bond on the phenyl ring. The R-benzo-
quinoline example shown in entry 12 has already been discussed
in eq 1. The 2-(biphenyl-2-yl)pyridine (3) in entry 13 is the
monophenylated product obtained from 2 (entry 1). We found
that the reaction was slower than that of 2 but still took place
to give 4 in a yield of 60% after a period of 48 h (entry 13).
The reaction of 2-o-tolylpyridine was very slow and gave the
arylation product in a yield of only 15% (entry 14). We surmise
that the restricted conformational possibility of these compounds
is responsible for the low reactivity.
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Nitrogen-containing heterocycles other than pyridine also un-
dergo the present reaction. 2-Phenylpyrimidine reacted more slowly
than the pyridine counterpart 2 did but still gave the corresponding
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