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Green Chemistry
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Journal Name
COMMUNICATION
Based on this mechanism, it can be inferred that 0.1 equiv of for support with the NMR instruments VieawnAdrticlemOnalisnes
spectrometers.
DOI: 10.1039/C9GC04126E
Fe(dipm)3 exhibit the same catalytic activity as 0.07 equiv of
Fe(dipm)3 combined with 0.03 equiv of FeCl3. The reaction of
0.07 equiv of Fe(dipm)3 with a substrate will release 0.07 equiv
of Hdipm. The released Hdipm will react with FeCl3 (0.03 equiv)
Notes and references
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to form Fe(dipm)3 until FeCl3 is completely consumed. To
further verify this inference, we explored the catalytic effect
on benzylation of mannoside 9 under condition that Fe(dipm)3
(0.07 equiv), Fe(dipm)3 (0.1 equiv), or Fe(dipm)3 (0.07 equiv)
and FeCl3 (0.03equiv) was used as the catalyst respectively.
1
The H NMR yields of 9a and recovered 9 were recorded after
45 mins’ reaction (Figure 4). As expected, the yields of 9a and
9 were 76% and 10% respectively with the combination of 0.07
equiv of Fe(dipm)3 and 0.03 equiv of FeCl3 as the catalyst,
which is almost similar to the result with 0.1 equiv of Fe(dipm)3
as the catalyst where the yields of 9a and 9 were 79% and 9%
respectively. In contrast, the yields of 9a and 9 were 63% and
27% respectively with 0.07 equiv of Fe(dipm)3 as the catalyst.
In conclusion, we have demonstrated that FeCl3 could be used
as the catalyst in the regioselective alkylation with the
assistance of Hdipm. The optimized ratio of FeCl3 to Hdipm is
1/2. High selectivities and isolated yields for alkylation were
obtained, with wide scopes of substrates and alkylation
reagents. Mechanism studies have confirmed that FeCl3 react
with Hdipm in acetonitrile in the presence of a base to form
[Fe(dipm)3]. [Fe(dipm)3] then further reacts with a substrate in
the presence of the base to form a five or six-membered ring
intermediate between iron and two hydroxyl groups, while
releasing one molecule of Hdipm. The cyclic intermediate
subsequently reacts with a alkylation reagent, leading to
regio/site-selective alkylation of the substrate. The released
Hdipm reacts with an excess of FeCl3 to form [Fe(dipm)3] again
until FeCl3 is completely consumed in this cycle. All key
intermediates have been observed by HRMS detection,
therefore confirming the mechanism for the first time.
Compared to the reaction using FeL3 (L = acylacetone ligands)
as the catalyst, similar selectivities and isolated yields were
obtained in the benzylation in most cases. These FeL3 catalysts
are not commercially available and have to be synthesized
prior to use. However, either FeCl3 or Hdipm is very common
and inexpensive nontoxic reagent in the lab, thereby making
the process much greener.
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Conflicts of interest
The authors declare no competing financial interest.
Acknowledgements
6
(a) B. Ren, J. Lv, Y. Zhang, J. Tian and H. Dong,
ChemCatChem, 2017, 9, 950; (b) B. Ren, N. Yan and L. Gan,
RSC Adv. 2017, 7, 46257. (c) B. Ren, O. Ramström, Q. Zhang, J.-
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This study was supported by the National Nature Science
Foundation of China (Nos. 21772049). The authors are also
grateful to the staffs in the Analytical and Test Center of HUST
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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