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T. Daßskapan / Tetrahedron Letters 47 (2006) 2879–2881
Table 2. Scope of the copper-catalyzed amination reaction of arylzinc
chlorides with 1 in the presence of DMPU
has been used as a co-solvent to promote the reactions of
organozinc reagents. In this connection, we decided to
investigate the effect of DMPU in the electrophilic amina-
tion of arylzinc chlorides with 1.
1. THF, 10 mol% CuCN,
2 equiv. DMPU, r.t., 3 h
ArZnCla + 1
ArNH2
2. Conc. HCl, r.t.
In the first part of this work, we aimed to determine the
optimal reaction conditions using the amination reac-
tion of phenylzinc chloride with 1 as a model reaction.
Phenylzinc chloride was prepared by transmetallation
of phenylmagnesium bromide with ZnCl2 in THF. The
final product, aniline, was removed from the reaction
mixture as its benzanilide derivative. The results are
given in Table 1.
b
Entry
Ar
Yield of ArNH2 (%)
1
2
3
4
5
C6H5
78
72
75
70
79
4-CH3C6H4
4-CH3OC6H4
3-BrC6H4
1-C10H7
a Organozinc reagents were prepared by transmetallation of the cor-
responding arylmagnesium bromides with ZnCl2 in THF.
b Yield of amines isolated as the N-benzoyl derivatives and these
known compounds were identified from their melting point27 and
FT-IR analysis.
As show in Table 1, this yield of aniline after one hour
using 3.35 equiv of DMPU (entry 1) was 40% and when
the reaction time was extended to 3 h the yield increased
to 65% (entry 3). The highest yield of aniline (78%) was
obtained at room temperature in 3 h when 10 mol %
CuCN and 2 equiv of DMPU were used (Table 1, entry
7). It was observed that, when less than 2 equiv of
PhZnCl or DMPU was used, or when the amount of
CuCN was below 10 mol %, the yield decreased.
In conclusion, we have described an easy and good
yielding preparation for primary arylamines by electro-
philic amination of arylzinc chlorides with acetone O-
(2,4,6-trimethylphenylsulfonyl)oxime in the presence of
DMPU. Our investigations are continuing on this sub-
ject and the results will be published when our studies
are complete.
In the second part of this study, to broaden the scope of
this procedure, we investigated the amination of naph-
thylzinc chloride and some functionalized arylzinc chlo-
rides with 1 under the optimal reaction conditions28
(Table 2). As seen, functionalized arylamines were pre-
pared in good yields in the presence of 2 equiv of
DMPU. Previously,26 p-toluidine and p-anisidine were
obtained in 49% and 54% yields, respectively, without
the use of DMPU. Using the improved method the
yields of these amines were 72% and 75%, respectively
(entries 2 and 3).
Acknowledgement
I thank the Ankara University Research Fund for finan-
cial support.
References and notes
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Table 1. Amination of phenylzinc chloride with 1 in the presence of
DMPU
1. THF, CuCN, DMPU, r.t., 1-3 h
PhZnCla
ArNH2
+ 1
2. Conc. HCl, r.t.
Entry
1 (equiv)
CuCN
(%)
DMPU:PhZnCl
Yield of
ArNH2 (%)
b
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1c
2d
3
4
5
6
7
8
9
10
11
12
13
2
2
2
2
2
2
2
2
2
2
1
1.25
1.5
20
20
20
10
5
20
10
5
3.35
3.35
3.35
3.35
3.35
2
2
2
1
1.7
2
40
43
65
58
40
42
78
67
57
60
30
35
65
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_
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5
10
10
10
10
2
2
a Phenylzinc chloride was prepared by Mg-to-Zn transmetallation.
b Aniline was isolated as its benzanilide and this known compound was
identified from its melting point27 and FT-IR analysis.
c Reaction time was 1 h.
d Reaction time was 2 h.