5516
S. B. Park, H. Alper / Tetrahedron Letters 45 (2004) 5515–5517
a
6
Table 1. Homocoupling of iodoarenes in [bmim][PF ]
b
Entry
1
ArI
PhI
Base (equiv)
Et N (2)
NH (2)
Cycle no. (yield, %)
2 (63)
3
1 (71)
(6)
3 (52)
i
Pr
CO
2
K
2
3
(1.5)
(Trace)
2
3
4
4-MeOC
6
H
4
I
Et
3
3
3
N (2)
N (2)
N (2)
1 (82)
(70)
2 (10)
1-Iodothiophene
4-AcC
Et
Et
6
H
4
I
(Trace)
Piperidine (3)
Et N (2)
––
––
5
4-NO
2
C
6
H
4
I
3
a
All reactions were carried out using 1 mmol of iodobenzene, 2 mol % of 1, 2 mL of the ionic liquid, 120 °C, 24 h.
Yields are GC yields (%).
b
a
Table 2. Homocoupling of 4-iodoanisole in [bmim][PF
6
]
reactions of ortho-substituted iodoarenes progressed
slowly and afforded products in low yields (entries 3 and
b
Entry
Cat.
Yield (%)
5
).
1
2
3
4
5
6
7
PdCl
PdCl
PdCl
2
2
2
98
95
96
96
98
89
95
7
(cod)
In a typical reaction procedure (entry 1, Table 2), iodo-
benzene (204 mg, 1 mmol) and phenylacetylene (128 mg,
1.2 mmol) were added to the Pd(II) catalyst (1, 6.4 mg,
(MeCN)
2
Pd(OAc)
2
PdCl
PdCl
2
(dppf)
(PPh
2
3
)
2
6
0.02 mmol) and 2 mL of [bmim]PF . The reaction mix-
3 4
Pd(PPh )
tures were stirred at 120 °C until the reaction was com-
pleted (indicated by the disappearance of starting
material on TLC). After extraction with ethyl ether to
separate the products from the catalyst, the resulting
ionic liquid layer was washed with water to remove the
amine salt. The recovered ionic liquid layer was reused
without any pretreatment.
c
8
d
PdCl
PdCl
2
9
2
0
a
All reactions were carried out using 1 mmol of iodobenzene, 5 mol %
of cat., 2 equiv of TDAE, 2 mL of the ionic liquid at 120 °C for 2 h.
Yields are GC yields (%).
b
c
2
4
equiv of TEA was used.
-Bromoanisole was employed.
d
In conclusion, we have developed an efficientand recy-
clable TDAE/Pd-promoted homocoupling reaction
using an ionic liquid.
was recovered in the case of the less active 4-bromo-
anisole (entry 9). To examine the recyclability of the
catalyst and the versatility of this method, the homo-
coupling reaction was carried out with various iodo-
2
arenes using the TDAE/PdCl system (Table 3). The
Acknowledgements
coupling reaction of electron-rich iodoarenes worked
well and the catalyst could be recycled (entries 1, 2, 8).
Substrates bearing substituents at the meta- or para-
positions reacted particularly well and gave the corres-
ponding biaryls in fine yield (entries 1, 2, 5–7), but
This research was supported by the Natural Sciences
and Engineering Research Council of Canada
(NSERC).
a
6
Table 3. Homocoupling of iodoarenes in [bmim][PF ]
b
References and notes
. For reviews, see: (a) Green Industrial Applications of Ionic
Liquids; Sethi, A. R., Smith, P., Srinivasa, N., Welton, T.,
Rogers, R. D., Seddon, K. R., Volkov, S., Eds.; NATO
Science; Kluwer: Boston, 2002; Vol. 92; (b) Dupont, J.; de
Souza, R. F.; Suarez, P. A. Z. Chem. Rev. 2002, 102, 3367;
Entry
1
ArI
Cycle no. (time, h)
4-MeOC
6
6
6
H
H
H
4
4
4
I
I
I
1 (2)
2 (4)
85
3 (4)
67
4 (4)
59
1
98
1 (2)
2
3
4
5
6
7
8
3-MeOC
2-MeOC
PhI
2 (4)
72
3 (4)
58
9
8
(2)
9
1 (2)
(
c) Sheldon, R. Chem. Commun. 2001, 2399; (d) Wassersc-
2 (4)
30
heid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3772.
. Park, S.-B.; Alper, H. Org. Lett. 2003, 5, 3209.
. Fanta, P. E. Synthesis 1974, 9; Meyers, A. I. J. Heterocycl.
Chem. 1998, 35, 991.
. Tieco, M.; Testaferri, L.; Tingoli, M.; Chianelli, D.;
Montanucci, M. Synthesis 1974, 736.
. Penalva, V.; Hassan, J.; Lavenot, L.; Gozzi, C.; Lemaire,
M. Tetrahedron Lett. 1998, 39, 2559; Hassan, J.; Penalva,
V.; Lavenot, L.; Gozzi, C.; Lemaire, M. Tetrahedron 1998,
8
3
7
7
8
2
3
2-MeC
4-ClC
4-CF
2-Iodothiophene
6
H
4
I
(2)
4
6
H
4
I
(2)
4
5
8
3
C
6
H
4
I
(2)
7
1 (2)
9
2 (4)
90
3 (4)
90
4 (4)
57
8
5
4, 13793; Hennings, D. D.; Iwama, T.; Rawal, V. H. Org.
a
All reactions were carried out using 1 mmol of iodoarene, 5 mol% of
PdCl
, 2 equiv of TDAE, 2 mL of the ionic liquid, 120 °C.
Yields given for each cycle are GC yields (%).
Lett. 1999, 1, 1205; Silveira, P. B.; Lando, V. R.; Dupont,
J.; Monterio, A. L. Tetrahedron Lett. 2002, 43, 2327; Lei,
A.; Zhang, X. Tetrahedron Lett. 2002, 43, 2525.
2
b