The scope of the present methodologies was also explored
with organolithium species and results are summarized in
Table S4 (in ESI). Aryl lithium species underwent cross-
coupling reaction with cyclic ether THF and gave desired
products in good to excellent yields.
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The exact mechanism of this remarkable C–C bond forma-
tion is ambiguous, but previous reports proposed a radical
process for iron mediated C–C cross-coupling reactions.14 We
speculate that there is involvement of radical intermediates
and a plausible mechanism can be visualized via the addition
of organometallic species on iron oxide, leading to generation
of organoiron species followed by abstraction of proton from
the 2-position of tetrahydrofuran to produce 2-tetrahydro-
furanyl radical. This radical and organometallic species could
then be coupled directly to generate 2-phenyltetrahydrofuran
2a. The formation of phenol 4 and bis-phenol 5 byproducts
may suggest intervention of unstable radicals or organoiron
intermediates. However, the reaction of allyl substrate was
sluggish (entry e in Table S3 of ESI) and the desired product
was obtained in very low yield along with a mixture of
unidentified products, suggesting a radical mechanism. The
results of the present methodology suggest that Fe2O3 based
intermediates help in generation of carbon radicals and
provide d-block organometallic surfaces for cross-coupling.
In summary, we have discovered a new method for cross-
coupling of organometallic species with cyclic ether THF via
activation of the C(sp3)–H bond using Fe2O3. No toxic or/and
expensive ligand is required for this metallic catalysis. Further
studies on the mechanism of this new method and its extension
to related alkyl ether substrates are in progress and will be
reported in due course.
Notes and references
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c
5854 Chem. Commun., 2011, 47, 5852–5854
This journal is The Royal Society of Chemistry 2011