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Green Chemistry
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And the secondary aromatic amine, such as N-methylaniline,
was also investigated and efficiently converted to 2e with a
comparable lower yield of 78%. Different substitution positions
of methyl group on the benzene ring did not possess significant
effect on the reaction with the similar isolated yields (2f-2h) of
73%, 74% and 70%, respectively. The electronic properties on
the benzene ring were tested in this reaction. It is found that
aniline with electron-donating groups such as OMe and OH
afforded the corresponding formylated products 2i and 2j in 79%
and 89% respectively. Halogenated substitutions (-F, -Cl, -Br) on
aniline furnished the desired products 2k, 2l and 2m in
moderate yields. Aniline with strong electron-withdrawing
group NO2 could also be formylated, providing 2p with an
acceptable yield of 50%. Reductive-sensitive group alkynyl can
be tolerated under this condition to deliver 2q in good yield
(86%). Additionally, benzamide was investigated for the
substrate scope. To our delight, N-formylbenzamide (2r) was
obtained in an acceptable yield of 40%. And the 2, 6-
dimethylaniline afforded a trace of product 2s possibly due to
the high steric effect.
DOI: 10.1039/C9GC01137D
as well as benzamide in good to excellent yields. Control
experiments were also studied and a plausible mechanism was
proposed.
-
O
H
OAc
O
OAc
O
B
-CH3COONa
OAc
H
OAc
H
H
O
C O
AcO
B
N
Na
H
N
H
B
A
Scheme 4. Proposed mechanism of N-formylation with
NaBH(OAc)3 and CO2
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This project was supported from the National Key R&D Program
of China (No. 2017YFE0102200), National Natural Science
Foundation of China (No. 81673291), and Arthritis & Chronic
Pain Research Institute, USA to Y. Yu.
For a better understanding about this reaction, multiple
control experiments have also been performed. As showed in
Scheme 3, in the absence of NaBH(OAc)3, the reaction failed to
give the desired formamide. This indicated the important role
of NaBH(OAc)3. However, when the reaction performed without
CO2, only a trace amount of N-acetylated product could be
detected after two-hour reaction. When CO2 firstly reacted with
NaBH(OAc)3 for one hour, then the replacement of CO2 with N2
for another 60 minutes following the addition of one equivalent
of aniline, the formylation reaction proceeded well with an
isolated yield of 82%. Such results indicated CO2 could be
captured by NaBH(OAc)3 forming an active intermediate that
would further react with aniline to give the desirable product .
Notes and references
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Chem. 2017, 3, 22-27.
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ChemCatChem, 2015, 7, 3895-3902.
5. P. Ju, J. Chen, A. Chen, L. Chen, Y. Yu, ACS Sustainable Chem.
Eng., 2017, 5, 2516-2528.
6. P. K. Hota, S. C. Sau, S. K. Mandal, ACS Catal., 2018, 8, 11999-
12003.
NH2
H
CH3CN, 50 o
2 hrs
C
N
H
CO2
1)
+
O
Not detected
7. X. Liu, X. Li, C. Qiao, H. Fu, L. He, Angew. Chem. Int. Ed., 2017,
56, 7425-7429.
8. J. Song, B. Zhou, H. Liu, C. Xie, Q. Meng, Z. Zhang, B. Han,
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Liu, ACS Catal., 2015, 5, 4989-4993.
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2015, 5, 3983-3987.
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12116–12120.
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14. I. Dovqaliuk, D. A. Safin, N. A. Tumanov, F. Morelle, A.
Moulai, R. Černý, Z. Łodziana, M. Devillers, Y. Filinchuk,
ChemSusChem, 2017, 10, 4725-4734.
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O
O
O
NH2
H
CH3CN, 50 o
2 hrs
C
N
O
2)
3)
O
O
BH
O
+
Na
O
trace amount
H
O
O
O
CO2 replaced by N2
N
H
1 hr
O
BH
O
CH3CN, 50 o
C
Aniline added,
CH3CN, 50 oC, 1 hr
O
CO2
+
Na
yield 82%
Scheme 3. Control experiments
According to the results above, a plausible mechanism of this
reaction is proposed. (Scheme 4) First, CO2 reacted with
NaBH(OAc)3 generating a boron-formate intermediate (A). Then
amine nucleophilic attacked the intermediate (A) to afford the
corresponding formamide product (B).
16. V. B. Saptal, G. Juneja, B. M. Bhanage, New. J. Chem. 2018,
42, 15847-15851.
17. L. Hao, H. Zhang, X. Luo, C. Wu, Y. Zhao, X. Liu, X. Gao, Y.
Chen, Z. Liu, J. CO₂ UTIL. 2017, 28, 208-211.
18. A. F. Abdel-Magid, S. J. Mehrman, Org. Process Res. Dev.
2006, 10, 971-1031.
In conclusion, we have developed an N-formylation method
under an atmospheric pressure of CO2 at mild conditions (in
CH3CN, 50 C, 5 hours). Using NaBH(OAc)3 as reductant, this
o
transformation was proceeded well with a good tolerance of
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