A novel efficient method for synthesis of propargylamines via three-component coupling of aryl azide, aldehyde, and alkyne promoted by iron-iodine-copper(I) bromide

Article abstract of DOI:10.1016/j.tetlet.2010.08.024

A novel, efficient method has been developed for the synthesis of propargylamines through a three-component coupling of aryl azides, aldehydes, and alkynes in the presence of iron-iodine-copper(I) bromide as catalyst. This method is the first example for directly using aryl azides as an amino component in a three-component coupling reaction. Some of the major advantages of this protocol are: good yields, the involvement of a less-expensive and non-toxic catalyst, mild reaction conditions, and a wide range of substrates.

Full text of DOI:10.1016/j.tetlet.2010.08.024

Tetrahedron Letters 51 (2010) 5463–5465
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Tetrahedron Letters
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A novel efficient method for synthesis of propargylamines via
three-component coupling of aryl azide, aldehyde, and alkyne promoted
by iron–iodine–copper(I) bromide
*
Kui Zhang, You Huang , Ruyu Chen
State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, 94 Wei-Jin Road, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 April 2010
Revised 8 July 2010
Accepted 10 August 2010
Available online 13 August 2010
A novel, efficient method has been developed for the synthesis of propargylamines through a three-com-
ponent coupling of aryl azides, aldehydes, and alkynes in the presence of iron–iodine–copper(I) bromide
as catalyst. This method is the first example for directly using aryl azides as an amino component in a
three-component coupling reaction. Some of the major advantages of this protocol are: good yields,
the involvement of a less-expensive and non-toxic catalyst, mild reaction conditions, and a wide range
of substrates.
Ó 2010 Elsevier Ltd. All rights reserved.
Propargylamines are an attractive class of compounds owing to
their potent biological activities which can act as enzyme inhibi-
tors,1 antitumor antibiotics,2 herbicides,3 and pharmaceutical
agents.4 In addition, they are versatile intermediates for organic syn-
thesisandimportantstructuralelementsofnaturalproductsandpo-
tential drug molecules.5 Thus, the development of new synthetic
methods for propargylamines has attracted the attention of medici-
nal/organic chemists. Recently, various methods have been devel-
oped for the synthesis of propargylamines. There are four common
approaches for the preparation of propargylamines: (1) the direct
nucleophilic attack of lithium acetylides or Grignard reagents to imi-
nes or their derivatives;5d,6 (2) the direct C–C bond formation of ter-
minal alkynes with tertiary amines via C–H activation;7 (3) the
amination of propargylic halides, propargylic phosphates, or propar-
gylic triflates;8 and (4) the three-component coupling of aldehydes,
amines, and alkynes (A3 coupling).9 Among these methods, the di-
rect addition of lithium acetylides or Grignard reagents to imines
is limited by the stoichiometric reagents and highly moisture-sensi-
tive conditions. TheC–Hactivationoftertiary aminesandthe amina-
tion of propargylic halides are limited by its range of substrates. The
last one is a powerful tool for the synthesis of propargylamines in a
single operation. Thus, considerable efforts have been made to de-
velop theA3 couplingreactionscatalyzed by various transitionmetal
catalysts such as copper salts,10 silver salts,11 gold salts,12 and zinc
salts.13 However, these methods were usually limited by the second-
ary amine as an amine component,10b–f,11b,13b,c,14 and few of the ap-
proaches were suitable for the primary amines.10g,15 Thus, there is
still a need to develop a more efficient method for the preparation
of propargylamines from readily available starting materials.
Although azides are versatile intermediates in organic synthe-
sis,16 the use of aromatic azides in organic synthesis has received rel-
atively modest interest until recently, especially since those azides
have been mostly prepared from the anilines via their diazonium
salts.17 Recently, aryl azides as the precursor of many nitrogen-con-
taining compounds have become highly attracting due to the finding
that aryl azides can be prepared in very good yields through copper-
catalyzed coupling reaction of the corresponding aryl halides or aryl
boronic acids with sodium azide under mild conditions.18 To the
best of our knowledge, we reported a novel three-component cou-
pling reaction for the preparation of propargylamines from the read-
ily available starting materials aryl azides for the first time.
An initial study was performed by the treatment of 4-chloro-
phenyl azide 1a (1 mmol), benzaldehyde 2a (1 mmol), and phenyl-
acetylene 3a (1 mmol) in THF (2 mL) in the presence of iron
powder (1 mmol), iodine (0.2 mmol), and CuBr (2 mmol) at room
temperature for 24 h (Table 1), only trace 4a was obtained and this
result encouraged us to continue to study this reaction. After opti-
mizing the reaction temperature, to our delight, when the reaction
was performed at 50 °C, we observed the formation of product 4a
in 74% isolated yield after 24 h.
With this result, other reaction parameters were studied for the
preparation of product 4a at 50 °C and the results are summarized
in Table 1. The copper salts such as CuBr, CuI, CuCl, CuCN, and
CuSO4Á5H2O (commercial) were screened for the A3 coupling.
As a result, CuBr was found to be the most effective catalyst
(Table 2, entry 1). As shown in Table 2, the solvents also played
an important role in this reaction. THF (1 mL) gave the product
in a high yield (84%). Thus, the optimum reaction conditions were
determined as following: THF (1 mL) was used as solvent, the cat-
alyst system was iron/iodine/copper bromide (1:0.2:1), the reac-
tion temperature was 50 °C and the reaction time was 12 h.
* Corresponding author. Tel./fax: +86 02223003610.
E-mail address: yhuang.nk@gmail.com (Y. Huang).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.08.024

5464
K. Zhang et al. / Tetrahedron Letters 51 (2010) 5463–5465
Table 1
Table 3
Fe–I2–CuBr-promoted three-component coupling reactiona
The three-component coupling of aromatic azides, aldehydes, and alkynes promoted
by Fe–I2–CuBra,b
Cl
N3
R1
CHO
N3
Fe-I2-CuBr
THF(2 mL)
NH
Fe-I2-CuBr
THF (1mL)
+
+
CHO
R2
NH
+
+
R3
R2
R1
Cl
1a
R3
2a
3a
4a
3
1
2
4
Entry
Fe/I2/CuBr
Temp (°C)
Yieldb,c (%)
Entry
R1
R2
R3
Yieldc (%)
1
2
3
4
5
1:0.2:2
1:0.2:2
1:0.2:2
1:0.2:1.5
1:0.2:1
25
50
Reflux
50
50
Trace
74
56
44
39
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
p-Cl (1a)
p-Cl (1a)
p-Cl (1a)
p-Cl (1a)
H (1b)
H (1b)
H (1b)
H (1b)
H (1b)
C6H5– (2a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
C6H5– (3a)
81 (4a)
91 (4b)
84 (4c)
74 (4d)
72 (4e)
72 (4f)
84 (4g)
82 (4h)
92 (4i)
95 (4j)
89 (4k)
81 (4l)
82 (4m)
78 (4n)
64 (4o)
74 (4p)
84 (4q)
87 (4r)
47 (4s)
67 (4t)
74 (4u)
76 (4v)
p-Cl–C6H5– (2b)
p-F–C6H5– (2c)
o-Cl–C6H5– (2d)
C6H5– (2a)
p-Me–C6H5– (2e)
p-Cl–C6H5– (2b)
o-Cl–C6H5– (2d)
m-Cl–C6H5– (2f)
p-F–C6H5– (2g)
p-Cl–C6H5– (2b)
C6H5– (2a)
o-Cl–C6H5– (2d)
m-Cl–C6H5– (2f)
p-OMe–C6H5– (2h)
C6H5– (2a)
m-Cl–C6H5– (2f)
o-Cl–C6H5– (2d)
Cyclohexane– (2i)
Cyclohex-3-ene– (2j)
C6H5– (2a)
a
Reaction conditions: 4-chlorophenyl azide/benzaldehyde/phenylacetylene
(1:1:1).
b
Reaction time was 24 h.
Isolated yield was based on 4-chlorophenyl azide.
c
H (1b)
p-Me (1c)
p-Me (1c)
p-Me (1c)
p-Me (1c)
p-Me (1c)
o-OMe (1d)
o-OMe (1d)
o-OMe (1d)
p-Cl (1a)
Table 2
Optimization of the reaction conditionsa,b
Cl
N3
CHO
Fe-I2-cat
THF 50 ºC 24h
NH
+
+
p-Cl (1a)
H (1b)
p-Cl (1a)
n-Butyl- (3b)
n-Butyl- (3b)
C6H5– (2a)
Cl
1a
2a
3a
4a
a
b
c
Reaction conditions: aryl azide/aldehyde/phenylacetylene (1:1:1).
Reaction time was 12 h.
Isolated yield was based on aryl azide.
Entry
Catalyst
Solvent
Yieldd (%)
1
2
CuBr
CuI
THF (2 mL)
THF (2 mL)
74
3
3
4
5
6
7
8
9
10
11
12
13c
CuCl
CuCN
THF (2 mL)
THF (2 mL)
THF (2 mL)
24
6
3
28
8
25
5
84
55
19
83
and alkynes for the first time. This method not only provides an
excellent complement to propargylamine synthesis, but also opens
a new way to convert azides directly to useful amino compounds
by new three-component coupling reactions.
CuSO4Á5H2O
CuBr
Toluene (2 mL)
Dioxane (2 mL)
Acetonitrile (2 mL)
Water (2 mL)
THF (1 mL)
THF (5 mL)
THF (10 mL)
THF (1 mL)
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
Acknowledgments
We thank the National Nature Science Foundation of China
(20772061) and the Natural Science Foundation of Tianjin
(05YFJMJC00600) for financial support.
a
Reaction conditions: 4-chlorophenyl azide/benzaldehyde/phenylacetylene
(1:1:1).
b
Reaction time was 24 h.
Reaction time was 12 h.
Isolated yield was based on 4-chlorophenyl azide.
Supplementary data
c
d
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2010.08.024.
To demonstrate the generality of this method, we investigated
References and notes
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alkyne 3a and b to produce a range of propargylamines 4a–v,
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K. Zhang et al. / Tetrahedron Letters 51 (2010) 5463–5465
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