M. Tamura, M. Shibakami, A. Sekiya
FULL PAPER
Table 2. Deaminative fluorination of aromatic amines[a]
In conclusion, we have demonstrated that the diazoti-
zation of aniline derivatives proceeds with SiF and t-butyl
nitrite, and the corresponding fluoroarenes are obtained by
following decomposition of the diazonium salts. This is a
4
Entry Aromatic amine
Yield[b] of
fluoroben-
zene [%]
Yield by the other method
[c] [d]
A
[%]
B
[%]
first report of the deaminative fluorination using SiF as a
sole fluorine source.
4
1
2
3
4
5
6
7
8
9
0
1
2
3
C
6
H
5
-NH
o-CH -C
m-CH -C
p-CH -C
o-Cl-C
m-Cl-C
p-Cl-C
2
60 (69)[e]
69
60
64
40
50
60
61
51Ϫ90
45Ϫ65
69Ϫ87
70
6Ϫ65
83
99
99
98
98
72
98
92
Ϫ
3
6
H
4
-NH
-NH
-NH
-NH
-NH
-NH
OCO-C
O-C
2
3
6
H
4
2
Scheme 2. Possible reaction route
3
6
H
H
4
4
2
6
2
6
H
4
2
6
H
4
2
63
Ϫ
p-CH
p-CH
p-NC-C
p-NO -C
1-C10
2-C
3
6
H
4
-NH
2
3
6
H
-NH
4
-NH
2
49
56
43
35
47Ϫ73
Ϫ
35Ϫ58
55Ϫ61
34
71
14
92
Ϫ
1
1
1
1
6
H
4
2
2
H
6
H
-NH
4
-NH
2
7
2
5
H
4
N-NH
2
0
94
[
a]
Aromatic amine (1 mmol), t-butyl nitrite (1.2 mmol) and SiF
1.0Ϫ1.5 mmol) were agitated in CH Cl (3 ml) at room temp. for
h. After the solvent was evaporated, the reaction mixture was
4
(
2
2
1
[b]
heated at 130Ϫ140°C (entry 11, 150Ϫ160°C) for 1 h. Ϫ Isolated
[
c]
yield. Ϫ
The yields obtained by the Schiemann reaction (via
[
7][8]
[d]
ArN
2
BF
4
)
. Ϫ The yields obtained by the reaction with pyri-
[
8][12][13]
[e]
dine Ϫ HF
. Ϫ Yield determined by gas chromatography.
Experimental Section
General: All of the reagents are commercially available. All of
cause the reaction condition is much less-acidic. Although
the deaminative fluorination using pyridineϪHF (method
B in Table2) affords high yields of fluoroarenes from almost
the organic reagents and solvents were purified prior to use. SiF
was used without purification. Ϫ IR: Japan Spectroscopic FT-IR
4
1
8
900. Ϫ NMR: JEOL JNM-EX270 (270 MHz). For H NMR,
all substrates, in the case of p-cyanoaniline, p-fluorobenzo-
as solvent, TMS as internal standard; for 19F NMR, CDCl
CDCl
3
3
nitrile was obtained only in 14% yield[
12][13]
. On the other as solvent, CFCl as internal standard.
3
hand, 56% yield of p-fluorobenzonitrile was obtained by
Typical Experimental Procedure for Deaminative Fluorination:
Aniline derivative (1.0 mmol) dissolved in 3 ml of dichloromethane
was placed in a stainless-steel reactor equipped with a stop valve.
the method using SiF (entry 10 in Table 2).
4
Concerning the reaction intermediate, the product ob-
tained by the reaction of aniline with t-butyl nitrite and
4
SiF (1.0Ϫ1.5 mmol) and t-butyl nitrite (1.2 mmol) were introduced
Ϫ1
SiF showed IR absorption at 2290 cm , which is assigned into the reactor at Ϫ196°C from a vacuum line. The reactor
4
[14]
19
to NϪN stretching of benzenediazonium ion . From F- warmed up to ambient temp. and shaken vigorously for 1 h. After
1
9
NMR spectrum of the product, broad F signal was ob- the solvent was evaporated, the reactor was heated to 130Ϫ140°C
(
150Ϫ160°C for p-nitroaniline) for 1 h. The crude product was
served at Ϫ134.5 ppm ([D ]DMSO as solvent, CFCl as
6
3
transferred from the reactor using a vacuum line system and puri-
internal standard). These result suggests that the intermedi-
ate of this reaction is benzenediazonium hexafluorosilicate
fied by bulb-to-bulb or trap-to-trap distillation[ to give the prod-
19]
1
uct. The products were identified by comparison of their IR, H-
ϩ
2Ϫ
[
(PhN2 )2SiF
], which was identified by comparison of
6
19
NMR, and F-NMR spectra with those of authentic samples.
the spectral data with those of the authentic sample pre-
pared by a literature method[
15]
Attempt for Identification of the Intermediate: A solution of 290
mg of aniline (3.1 mmol) dissolved in 6 ml of dichloromethane was
.
It is well-known that alkyl nitrite is a mild reagent for
diazotization in organic solvent, and the mechanism of di-
azotization is considered that nucleophilic attack of amine
placed in a stainless-steel reactor equipped with a stop valve. SiF
3.8 mmol) and t-butyl nitrite (4.7 mmol) were introduced into the
4
(
reactor at Ϫ196°C from a vacuum line. The reactor warmed up to
on the nitroso nitrogen atom affords N-nitrosoamine, which
ambient temperature and shaken vigorously for 1 h. The solvent
isomerizes to diazohydroxide[
16][17][18]
(Scheme 2, equation
1
was evaporated to obtain the crude product, and its IR, H-NMR,
1
9
1
). If the Brønsted acid exists, the diazohydroxide is pro- and F-NMR spectra was measured. Ϫ IR (n-dodecane disp.): ν˜ ϭ
Ϫ1
1
tonated and forms diazonium ion. But in this reaction, it is 2290 cm (NN str.). Ϫ H NMR ([D ]DMSO): δ ϭ 7.95Ϫ8.00
6
assumed that the arenediazohydroxide reacts with SiF4, (m, 2 H, aromatic H), 8.23Ϫ8.29 (m, 2 H, aromatic H), 8.66Ϫ8.69
(
m, 2 H, aromatic H), small signals, which would be due to by-
which is a week Lewis acid, to form the intermediate
1
9
ϩ
2Ϫ
products, were observed from 6.7 to 7.8 ppm. Ϫ F NMR
[D ]DMSO): δ ϭ Ϫ134.5 (br).
[
(PhN2 )2SiF6 ] (Scheme 2, equation 2). The product
(
6
fluoroarene would be obtained by the decomposition of
ϩ
2Ϫ
[15]
(
PhN2 )2SiF6 as usual Schiemann reaction (Scheme 2,
equation 3). From the stoicheiometry of this hypothesis,
.75 mol of SiF is necessary for 1 mol of the substrate. The
[
[
1]
2]
Gmelin Handbook, Si Suppl., B7, p. 117.
Gmelin Handbook, Si Suppl., B7, pp. 244-248.
M. Shimizu, H. Yoshioka, Tetrahedron Lett. 1988, 29,
4101Ϫ4104.
0
[3]
4
result that 1 mol of SiF to 1 mol of the substrate was neces-
4
[
4]
M. Shimizu, H. Yoshioka, J. Chem. Soc., Chem. Commun.
sary to obtain a maximum yield (Table 1, entry 10) is
reasonable in consideration of the effectiveness of the reac-
tion.
1
989, 1881Ϫ1882.
[5]
M. Tamura, M. Shibakami, S. Kurosawa, T. Arimura, A. Se-
kiya, J. Chem. Soc., Chem. Commun. 1995, 1891Ϫ1892.
726
Eur. J. Org. Chem. 1998, 725Ϫ727