Homocoupling reactions using telluronium salts

Article abstract of DOI:10.1055/s-2005-872231

The homocoupling reaction of aryldimethyltelluronium iodides in the presence of a catalytic amount of palladium(II) species and two equivalents of silver(I) acetate proceeded to afford the corresponding biaryls. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2005-872231

2
230
LETTER
Homocoupling Reactions Using Telluronium Salts
H
K
omocoupling Re
a
actions Usi
z
u
ium
S
alts nori Hirabayashi, Yuji Takeda, Toshio Shimizu, Nobumasa Kamigata*
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji, Tokyo 192-0397, Japan
E-mail: kamigata-nobumasa@c.metro-u.ac.jp
Received 25 May 2005
acetate (entries 1 and 7). When other palladium catalysts
Abstract: The homocoupling reaction of aryldimethyltelluronium
were used, the homocoupling products were obtained in
low yields after six hours (entries 8–10). These results in-
dicated that phosphine ligands inhibited the reaction. Al-
iodides in the presence of a catalytic amount of palladium(II) spe-
cies and two equivalents of silver(I) acetate proceeded to afford the
corresponding biaryls.
though other group 10 metal halides such as NiCl and
2
Key words: palladium, coupling, organometallic reagents, telluro-
nium salt, silver(I) acetate
PtCl were also examined, the yields of 2a were very low.
2
The reaction was also carried out in the presence of vari-
ous amounts of silver(I) acetate (entries 11–13). The reac-
tion proceeded in excellent yield after six hours when
more than two equivalents of silver(I) acetate was used,
whereas the yield of the homocoupling product was dras-
tically decreased in the presence of 1 equivalent of sil-
ver(I) acetate. From these results, the present reaction
needs at least two equivalents of silver(I) acetate. On the
contrary, when CuCl or Cu(OAc) were used as addi-
Palladium-catalyzed coupling reactions are one of the
useful methods for forming carbon–carbon bonds. In
1
those reactions, the homocoupling reaction occurs to syn-
thesize symmetrical compounds, and the utility of various
2
organometallic reagents has been widely investigated. It
has been reported that the homocoupling reaction of alke-
nyl tellurides occurs in the presence of a catalytic amount
of palladium species; to the best of our knowledge, how-
ever, in the case of aryl tellurides or aryltellurium(IV)
compounds, stoichiometric amounts of palladium species
2
2
tives, the reaction did not proceed catalytically.
cat. [Pd], AgOAc
+
–
Te Me2I
3
are required. Recently, we found that the reaction of aryl-
50 °C
2
telluronium salts with olefins proceeded in the presence of
1a
2a
palladium(II) catalyst and silver(I) acetate to afford aryl-
substituted olefins (Mizoroki–Heck-type reactions). In
Scheme 1
4
that reaction, the aryl groups on tellurium atoms were Table 1 Optimization of the Palladium-Catalyzed Homocoupling
Reaction of 1aa
transferred efficiently to the olefins, and the telluronium
salts were relatively stable for a few months in air. Thus,
Entry Cat. Pd
AgOAc Solvent
equiv)
Time Yield
we examined whether the telluronium salts could be used
as convenient organometallic reagents for other carbon–
carbon bond-forming reactions, and found that the homo-
coupling reaction proceeded in the presence of a catalytic
amount of palladium catalyst. The results are reported
herein.
b
(
(h)
(%)
99
87
99
99
92
28
99
34
8
1
2
3
4
5
6
7
8
9
0
PdCl
4
4
4
4
4
4
4
4
4
4
3
2
1
MeCN
THF
6
2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
12
12
24
24
72
6
DMF
The homocoupling reaction of dimethyl(4-methylphe-
nyl)telluronium iodide (1a) was carried out in acetonitrile
using palladium as the catalyst and silver(I) acetate as the
Hexane
Toluene
DMSO
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
5
additive (Scheme 1). The reaction of 1a proceeded
smoothly to give homocoupling product 2a in 99% yield
after six hours (Table 1, entry 1). In this way, the homo-
coupling reaction of a telluronium salt proceeded in the
presence of a catalytic amount of palladium catalyst. Al-
though the reaction proceeded in both polar solvents, such
as THF or DMF, and less polar solvents, such as hexane
or toluene, a long time was required for its completion
Pd(OAc)2
Pd (dba) ·CHCl
3
6
2
3
[(p-allyl)]PdCl]2
6
1
PdCl (PPh )
6
3
2
2
3 2
(
entries 2–5). In the case of DMSO, the yield was low af- 11
PdCl
6
99
99
35
ter 72 hours (entry 6). The most effective palladium cata-
lysts were palladium(II) chloride and palladium(II)
1
2
3
PdCl2
PdCl2
6
1
10
SYNLETT 2005, No. 14, pp 2230–2232
Advanced online publication: 20.07.2005
DOI: 10.1055/s-2005-872231; Art ID: U16505ST
0
2
.0
9
.2
0
0
5
a
The reaction was carried out using 1a (0.5 mmol) and 10 mol% of
palladium catalyst.
b
The yield was determined by GC analysis.
©
Georg Thieme Verlag Stuttgart · New York

LETTER
Homocoupling Reactions Using Telluronium Salts
2231
Thus, the homocoupling reaction of various aryldimethyl- cies 5 occurred to afford homocoupling product 2 and pal-
telluronium iodides was carried out in the presence of a ladium(0) species. In the case of organic tellurides, the
catalytic amount of palladium(II) chloride and two reaction did not proceed catalytically, because the organic
equivalents of silver(I) acetate at 50 °C in acetonitrile, and tellurides might coordinate with palladium species to in-
5
the results are shown in Table 2. Dimethylphenyltelluro- hibit the catalytic reaction. The coordination of telluroni-
nium iodide (1b) also reacted to give 2b in good yield um salts was weaker than that of organic tellurides. Thus,
(
entry 2). The reactions of telluronium salts that possessed the present reactions might proceed catalytically.
electron-donating or electron-withdrawing groups pro-
ceeded smoothly to give the corresponding products in
high yields (entries 3–5). By contrast, in the case of tellu-
ronium salts possessing a substituent at the 2-position,
such as 1f and 1g, the yields of the homocoupling
products were low (entries 6 and 7). Telluronium salts 1h
and 1i also gave the coupling products in good yields
(
entries 8 and 9). From these results, the homocoupling
reactions were found to be affected by not the electronic
factor but the steric factor. Noteworthy was that the homo-
coupling products were obtained easily by filtration
through silica gel to remove solids (palladium or silver
residue) in the reaction mixture.
Scheme 2
Table 2 Homocoupling Reaction of Telluronium Salts 1a
In summary, the palladium-catalyzed homocoupling
reaction of telluronium salts was achieved. The present
reaction proceeded catalytically when silver acetate was
used as the additive.
Entry Telluronium salt
Time Product Yield
b
(
h)
(%)
82
88
84
99
91
46
37
79
93
+
–
1
2
3
4
5
6
7
8
4-MeC H Te Me I
(1a)
(1b)
(1c)
(1d)
(1e)
(1f)
(1g)
(1h)
(1i)
6
2a
2b
2c
2d
2e
2f
6
4
2
+
–
PhTe Me I
6
2
Acknowledgment
+
–
4-MeOC H Te Me I
6
6
4
2
This work was supported in part by a Grant-in-Aid for Young
Scientists (B), The Ministry of Education, Culture, Sports, Science
and Technology, Japan.
+
–
4-CF C H Te Me I
6
3
6
4
2
+
–
4-ClC H Te Me I
6
6
4
2
+
–
2-MeC H Te Me I
24
12
6
6
4
2
References
+
–
2-MeOC H Te Me I
2g
2h
2i
6
4
2
(
1) (a) Metal-Catalysed Cross-Coupling Reactions; Diederich,
F.; Stang, P., Eds.; Wiley-VCH: Weinheim, 1998. (b)Tsuji,
J. Palladium Reagents and Catalysts. Innovations in
Organic Synthesis; Wiley-VCH: New York, 1995.
+
–
1-C H Te Me I
1
0
7
2
+
–
9
2-C H Te Me I
6
1
0
7
2
(
c) Tsuji, J. Transition Metal Reagents and Catalysts.
Innovations in Organic Synthesis; Wiley-VCH: New York,
000.
a
The reaction was carried out using 1 (0.5 mmol), 10 mol% of PdCl2,
and AgOAc (1 mmol).
2
b
Isolated yields.
(
2) For recent reports about palladium-catalyzed homocoupling
reaction using organometallic reagents, see: (a) Yoshida,
H.; Yamaryo, Y.; Ohshita, J.; Kunai, A. Tetrahedron Lett.
One plausible mechanism for this reaction is shown in
Scheme 2, which refers to the Mizoroki–Heck-type reac-
tion of telluronium salts. Silver(I) acetate plays an impor-
tant role in the exchange of the counter ion from iodide to
acetate in the initial step and in reproducing palladium(II)
species in the final step. Thus, silver(I) acetate was con-
verted into AgI and Ag(0). It was also confirmed that AgI
2
003, 44, 1541. (b) Yoshida, H.; Yamaryo, Y.; Ohshita, J.;
Kunai, A. Chem. Commun. 2003, 1510. (c) Li, J. H.; Xie, Y.
X.; Yin, D. L. J. Org. Chem. 2003, 68, 9867; and references
cited therein.
4
(3) (a) Uemura, S.; Wakasugi, M.; Okano, M. J. Organomet.
Chem. 1980, 194, 277. (b) Uemura, S.; Ohe, K.; Kim, J.-R.;
Kudo, K.; Sugita, N. J. Chem. Soc., Chem. Commun. 1985,
2
71. (c) Ohe, K.; Takahashi, H.; Uemura, S.; Sugita, N. J.
6
and Ag(0) were produced in the present reaction. The
Organomet. Chem. 1987, 326, 35. (d) Ohe, K.; Takahashi,
H.; Uemura, S.; Sugita, N. J. Org. Chem. 1987, 52, 4859.
(e) Nishibayashi, Y.; Cho, C. S.; Ohe, K.; Uemura, S. J.
Organomet. Chem. 1996, 526, 335. (f) Barton, D. H. R.;
Ozbalik, N.; Ramesh, M. Tetrahedron Lett. 1988, 29, 3533.
See also: (g) Bergman, J. Tetrahedron 1972, 28, 3323.
aryl group of telluronium salt 3, which was produced from
telluronium salt 1, was transferred from the tellurium
atom to the palladium species to afford arylpalladium
species 4. There might be two possibilities for producing7
diarylpalladium species 5; one is the disproportionation
of arylpalladium species 4, and the other is the transmet-
allation from telluronium salt to arylpalladium species 4.
Then, the reductive elimination of diarylpalladium spe-
(
h) Bergman, J.; Carlsson, R.; Sjöberg, B. Org. Synth. Coll.
Vol. VI 1988, 468.
(
4) Hirabayashi, K.; Nara, Y.; Shimizu, T.; Kamigata, N. Chem.
Lett. 2004, 33, 1280.
Synlett 2005, No. 14, 2230–2232 © Thieme Stuttgart · New York

2
232
K. Hirabayashi et al.
LETTER
(6) XRD Pattern of the Residue: 2q (rel. intensity): 22.430
(
5) General Procedure.
Palladium(II) chloride (0.05 mmol), silver(I) acetate (1.0
mmol), telluronium salt (0.5 mmol) and MeCN (3 mL) were
placed in a dry screw-capped glass-tube. After stirring at
(746), 23.770 (696), 25.400 (342), 31.760 (159), 38.180
(1402), 39.280 (670), 42.730 (326), 44.380 (408), 46.400
(300), 59.380 (108), 64.500 (368), 77.460 (331).
Ag(0): 38.100 (98), 44.369 (60), 64.177 (43), 77.547 (100).
AgI: 22.337 (98), 23.675 (60), 25.321 (68), 32.775 (42),
39.204 (97), 42.624 (100), 45.584 (14), 46.312 (58), 59.303
(28).
50 °C for 6–72 h, the resulting mixture was diluted with
Et O and passed through silica gel pad. The eluate was
2
washed with 1 M HCl aq, NaHCO aq, and brine. The
3
organic layer was dried over anhyd MgSO , filtered, and
4
concentrated under reduced pressure. The product was
obtained in adequate purity. Further purification was
performed with flash column chromatography on silica gel.
(7) (a) Ozawa, F.; Fujimori, M.; Yamamoto, T.; Yamamoto, A.
Organometallics 1986, 5, 2144. (b) Ozawa, F.; Hidaka, T.;
Yamamoto, T.; Yamamoto, A. J. Organomet. Chem. 1987,
330, 253. (c) See also: Scott, J. D.; Puddephatt, R. J.
Organometallics 1983, 2, 1643.
Synlett 2005, No. 14, 2230–2232 © Thieme Stuttgart · New York