A facile reduction of azides to the corresponding amines with Sm/NiCl2·6H2O system

Article abstract of DOI:10.1081/SCC-120002001

Azides can be easily reduced to the corresponding amines with Sm/NiCl₂·6H₂O in excellent yields under mild and neutral conditions.

Full text of DOI:10.1081/SCC-120002001

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A FACILE REDUCTION OF AZIDES TO THE
CORRESPONDING AMINES WITH Sm/NiCl ·6H O
2
2
SYSTEM
a
b
Huayue Wu , Rener Chen & Yongmin Zhang
a
Department of Chemistry , Zhejiang University at Xixi Campus, Hangzhou, 310028, P. R.
China
b
Department of Chemistry , Zhejiang University at Xixi Campus, Hangzhou, 310028, P. R.
China
Published online: 16 Aug 2006.
To cite this article: Huayue Wu , Rener Chen & Yongmin Zhang (2002) A FACILE REDUCTION OF AZIDES TO THE
CORRESPONDING AMINES WITH Sm/NiCl ·6H O SYSTEM, Synthetic Communications: An International Journal for Rapid
2
2
Communication of Synthetic Organic Chemistry, 32:2, 189-193, DOI: 10.1081/SCC-120002001
To link to this article: http://dx.doi.org/10.1081/SCC-120002001
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SYNTHETIC COMMUNICATIONS, 32(2), 189–193 (2002)
A FACILE REDUCTION OF AZIDES TO
THE CORRESPONDING AMINES WITH
Sm/NiCl ꢀ6H O SYSTEM
2
2
y
Huayue Wu,* Rener Chen, and Yongmin Zhang
Department of Chemistry, Zhejiang University at
Xixi Campus, Hangzhou, 310028, P. R. China
ABSTRACT
Azides can be easily reduced to the corresponding amines with
Sm/NiCl ꢀ6H O in excellent yields under mild and neutral
2
2
conditions.
The reduction of azides to corresponding amines is an important reac-
1
tion in organic synthesis. A wide variety of reagents have been used for
–2
3
this conversion, for example, zinc borohydride, lithium aluminium
4
hydride, triethyl phosphate, sodium borohydride, lithium aminoborohy-
5
6
7
dride, benzyltriethylammonium tetrathiomolybdate, etc. We also reported
8
9
the reduction of azides to amines with Sm/cat. I , SmI and Cp TiCl -Sm
2
2
2
2
1
0
system.
But some of these reagents have one or more limitations with regard to
general applicability, selectivity, ready availability, operational convenience,
and toxicity. For instance, LiAlH is not tolerable to many functionalities
4
*
Visiting scholar from Wenzhou Normal College.
Corresponding author.
y
1
89
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

ORDER
REPRINTS
1
90
WU, CHEN, AND ZHANG
such as CO R, NO etc. and on the other hand, catalytic hydrogenation and
2
2
diborane reduction have limitations for being applied to unsaturated com-
pounds containing a double or a triple bond. As a result, there is always
considerable interest in finding more selective methods.
Here we wish to report a novel reduction of azides to the corres-
ponding amines with samarium-nickel chloride hexahydrate in high yield
in tetrahydrofuran under mild and neutral condition.
Scheme 1.
Table 1 summarizes our results on the reduction of a number of alkyl,
aryl, aroyl and arylsulfonyl azides. In all the reactions, the cleavage takes
place between the N–N bond, rather than the C–N or S–N bond. At the
same time, aryl, aroyl and arylsulfonyl azides containing halides, carbonyl,
or sulfonyl groups are reduced to the corresponding amines or amides.
The amides are not reduced further to the amines. Chloro, bromo, iodo,
carbonyl and sulfonyl groups cannot be reduced under the reaction
conditions and do not influence the rate of reduction. Furthermore, a,b-
unsaturated acyl azides are selectively reduced with the double bond
Table 1. Reduction of Azides to Amines with Sm/NiCl ꢀ6H O
2
2
Entry
Azides
Reduction Time (h)
Yield* (%)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
p-ClC
p-BrC H N
3
6
H
4
N
3
2.5
2.5
2.5
2.5
2.5
3
85
83
87
88
90
70
8
6
4
p-IC H N
6
4
3
p-CH
3
C
6
H N
4 3
6 5 3
C H N
C H N
3
7
15
o-NO
2
C
H
6 4
N
3
3
3
2
3
2,4-Cl
2
C
6
H
3
N
3
8
C H CON
3
2.5
2.5
2.5
2.5
3
85
83
85
87
76
75
6
5
1
1
1
1
1
m-CH
3
C
6
4
H CON
3
C
6
H SO N
5 2 3
p-CH C H SO N
2
3
6
4
3
N
3 2 3
CH COOCH
C
6
5
H CH¼CHCON
3
3
*
Isolated yield.

ORDER
REPRINTS
AZIDE REDUCTION TO CORRESPONDING AMINES
191
remained (Entry 14), and the corresponding nitro aniline was selectively
obtained without any further reduction of nitro group (Entry 7), but
1
1
nitroarenes can be reduced to the corresponding amines with SmI ,
2
1
Sm/cat. I2, and Cp TiCl /Sm.
2
13
2
2
In conclusion, it has been found that the Sm/NiCl ꢀ6H O system can
2
2
be used for the reduction of azides to amines. The advantages of this
reaction are excellent yields, unique selectivity, simple operation, mild and
neutral reaction condition.
EXPERIMENTAL
1
H NMR spectra were recorded on a Brucker AC 80 instrument. All
NMR samples were measured in CDCl using TMS as internal standard, IR
3
spectra were determined on a Perkin-Elmer 683 spectrometer.
Metallic samarium and other chemicals were purchased from
commercial sources and used without purification. All azides were prepared
1
4
according to known method.
General Procedure: Under a nitrogen atmosphere, metallic samarium
powder (4.0 mmol) and nickel chloride hexahydrate (4.0 mmol) were placed
in a three-necked reaction flask and THF (10 ml) was added in one portion.
ꢁ
Azides was then added to the mixture and stirred at 40 C for a given
time (Table 1). A satd. aq. Na S O was added to quench the reaction
2
2
3
and the mixture was extracted with ether (20 ml ꢂ 3). The organic layer
was washed with brine (20 ml ꢂ 3) and dried over anhydrous Na SO . The
2
4
solvent was removed in vacuo. The residue was then purified by preparative
TLC on silica gel (dichloromethane-cyclohexane as eluent) to give pure
product.
1
2
ꢃ1
5
ꢁ
ꢁ
p-ClC H NH : mp 70 C (Lit. 71–73 C); d 3.40 (s, 2H), 6.30–7.00
6
4
H
(
m, 4H); nmax/cm 3470, 3400, 1600, 1500, 1290, 830, 640.
15
2
ꢁ
ꢁ
p-BrC H NH : mp 61 C (Lit. 62–64 C); d 3.40 (s, 2H), 6.25–7.15
6
4
H
ꢃ1
5
(
m, 4H); nmax/cm 3480, 3370, 1610, 1500, 1280, 810, 620.
1
2
ꢁ
ꢁ
p-IC H NH : mp 62 C (Lit. 62–63 C); d 3.60 (s, 2H), 6.30–7.30 (m,
6
4
ꢃ1
H
4
8
H); nmax/cm 3390, 3350, 3200, 3050, 1620, 1600, 1480, 1280, 1180, 940,
10, 590.
p-CH C H NH : mp 43 C (Lit. 44 C); d 2.10 (s, 3H), 3.15 (s, 2H),
.25–6.80 (m, 4H); nmax/cm 3460, 3400, 3010, 2960, 1610, 1490, 1310,
260, 860, 770.
1
5
ꢁ
ꢁ
3
5
4
2
H
ꢃ1
6
1
1
0
ꢃ1
C H NH : Oil; d 3.25 (s, 2H), 6.30–7.10 (m, 5H); nmax/cm 3410,
6
4
2
H
3
350, 3020, 1640, 1600, 1500, 1280, 1200, 750, 690.
10
C H NH : Oil; d 0.90 (t, 3H), 1.25 (m, 10H), 2.27 (s, 2H), 2.65
7
15
2
ꢃ1
H
(
t, 2H); nmax/cm 3400, 3380, 2960, 2880, 2760, 1600, 1450, 1050, 800, 720.

ORDER
REPRINTS
1
92
WU, CHEN, AND ZHANG
1
2
5a
ꢁ
ꢁ
o-NO C H NH : mp 71 C (Lit. 71–72 C); d 6.25 (s, 2H), 6.67–
2
6
4
H
ꢃ1
8
1
.08 (m, 4H); nmax/cm 3470, 3320, 1630, 1570, 1500, 1430, 1350, 1250,
100, 750.
1
2
5
ꢁ
ꢁ
2
,4-Cl C H NH : mp 62 C (Lit. 63 C); d 3.87 (s, 2H), 6.42–7.10 (m,
2
6
ꢃ1
3
H
3
H); nmax/cm 3430, 3300, 3200, 1620, 1580, 1470, 1400, 850, 810, 700, 640.
C H CONH : mp 128 C (Lit. 130 C); d 5.69 (s, 2H), 7.20–7.90 (m,
H); nmax/cm 3380, 3210, 1670, 1610, 1580, 1400, 650.
m-CH C H CONH : mp 93–94 C (Lit. 94–95 C); d 2.30 (s, 3H),
.50 (s, 2H), 7.28–7.64 (m, 4H); nmax/cm 3400, 3210, 1650, 1620, 1590,
400, 750, 690, 630.
C H SO NH : mp 151 C (Lit. 152–154 C); d 3.30 (s, 2H), 7.30–7.95
m, 5H); nmax/cm 3310, 3240, 1550, 1450, 1320, 1300, 1160, 1100, 990, 890,
1
5
ꢁ
ꢁ
6
5
2
H
ꢃ1
5
1
2
5
ꢁ
ꢁ
3
6
4
H
ꢃ1
6
1
1
5
ꢁ
ꢁ
6
5
2
2
H
ꢃ1
(
7
60, 680.
1
5
ꢁ
ꢁ
p-CH C H SO NH : mp 156 C (Lit. 157 C); d 2.33 (s, 3H), 3.20 (s,
H), 7.20–7.80 (m, 4H); nmax/cm 3320, 3240, 3020, 2920, 1600, 1480, 1400,
310, 1170, 1090, 910, 800, 680.
3
6
4
2
2
H
ꢃ1
2
1
9
3
NH CH COOCH : Oil; d 2.25 (s, 2H), 3.35 (s, 2H) 3.86 (s, 3H);
2
2
H
ꢃ1
nmax/cm 3450, 3380, 2970, 2870, 1750, 1370, 1350, 1300, 1200, 1090, 1020.
1
6b
ꢁ
ꢁ
C H CH¼CHCONH : mp 147 C (Lit. 148–150 C); d 6.39 (d, 1H),
6
5
2
H
ꢃ1
7
.10–7.50 (m, 5H), 8.00 (d, 1H); nmax/cm 3360, 3180, 1670, 1600, 1490,
1400, 1250, 1120, 970, 870, 700.
ACKNOWLEDGMENTS
We are grateful to the National Natural Science Foundation of China
Project No. 29872010), the NSF of Zhejiang Province, China, and the
(
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences for financial support.
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1
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AZIDE REDUCTION TO CORRESPONDING AMINES
193
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Received in the Netherlands February 15, 2000

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