4
Tetrahedron
and mild alternative method for the synthesis of primary amides
from acyl azides.
2
6
2
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the results showed that this method was not compatible with
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A proposed mechanism for the reduction is illustrated in
Scheme 1. The key active catalyst, a copper boryl species
IPr)CuBpin is formed via a σ-bond metathesis reaction.[7] The
reaction between this copper boryl complex and the azide would
generate a copper (II) amide. In the last step, this copper amide
2 2
reacts with B pin to form the diborylamine compound A and
(
2
7
2
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regenerate the active catalyst. The compound A is hydrolyzed to
give the amine product. All attempts to isolate the diborylamine
intermediate A have so far failed, possibly due to its high air and
moisture sensitivities [9].
3.
Kawazoe, Y.; Shimogawa, H.; Sato, A.; Uesugi, M. Angew. Chem.,
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4
.
(a) Neeve. E.; Geier. S.; Mkhalid, I.; Westcott. S.; Marder. T.
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In conclusion, we have reported the first NHC-copper
catalyzed reduction of azides to amines/amides by reaction with
diborons. The most efficient CuCl/IAmd·HCl catalytic system by
5
.
2
018, 140, 6221−6225; (b) Yang. K.; Zhou, F.; Kuang. Z.; Gao.
2 2
employing B pin as the reducing agent is developed. This
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method can perform the reductions of aromatic, aliphatic and
acyl azides to the corresponding amines/amides with good
chemoselectivity and high functional group tolerance under very
mild conditions. The reaction employs a cheap copper salt as the
5
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2
2 2
catalyst, a simple NHC as the ligand, a safe diboron B pin as the
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reducing agent, is chemoselective and convenient for work-up
and purification. Further investigations on the synthetic
applications of this method are in progress in our laboratory.
6
7
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Acknowledgments
1
7196–17197. (b) Han. J.; Yun. J. Org. Lett. 2018, 20, 2104−2107;
We gratefully acknowledge grants from the Sichuan Science
and Technology Program (2019YJ0284), the Antibiotics
Research and Re-evaluation Key Laboratory of Sichuan Province
(
(
c) Gao. S.; Wang. M.; Chen. M. Org. Lett. 2018, 20, 7921−7925;
d) Mazzacano. T.; Mankad. N. ACS Catal. 2017, 7, 146−149; (e)
Kuehn. L.; Huang. M.; Radius. U.; Marder. T. Org. Biomol. Chem.
019, 17, 6601–6606; (f) Jordan. A.; Thompson. P.; Sadighi. J.
(
ARRLKF18-04), the Educational Commission of Sichuan
Province of China (18ZB0134) and Chengdu University
2081916036).
2
Org. Lett. 2018, 20, 5242–5246; (g) Kleeberg. C.; Borner. C.;
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(
Supplementary data
8
9
.
.
Supplementary data to this article can be found online at
References and notes
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(
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1
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619.
•
Mild reaction conditions, good
functional group tolerance, high
chemoselectivity.
Highlights
•
Applicable to sterically hindered azides
•
A general and practical copper
catalyzed reduction of azides with
B pin .
Declaration of interests
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2