R. Cella et al. / Tetrahedron Letters 47 (2006) 5075–5078
5077
Initially, attention was focused on determination of the
optimal conditions for the Suzuki–Miyaura reaction of
vinylic tellurides (1) and alkenyltrifluoroborates (2).
Toward this end, Z-vinylic telluride 1a and b-styryl
trifluoroborate 2a (Scheme 2) were chosen as model
substrates and a variety of conditions were screened
(Tables 1 and 2). The reactions were monitored by
TLC or GC.
The reaction demonstrated to be effective with a wide
variety of vinylic tellurides. The silyl group attached in
a hydroxyl resisted to the reaction condition and the
product was obtained in 79% yield (Table 3, entry 7).
A vinylic telluride holding the t-butyl group attached
at double bond reacted with 2a in a good yield (Table
3, entry 8).
In summary, a wide variety of 1,3-dienes was obtained
taking advantages the use of ultrasonic energy and
Suzuki–Miyaura reaction. The reaction demonstrated
to be chemoselective and stereodefined. The products
were obtained in moderate to good yields in a mild
and quick method.
First of all, we determined the palladium catalyst, the
Pd(II) and (0) species were used in the coupling reac-
tions and the best result was reached with Pd(PPh3)4
(Table 1, entry 7). It was used Ag2O, K2CO3, and meth-
anol were used as solvents and the reaction was irradi-
ated for 20 min in ultrasound bath. The product was
obtained in 65% isolated yield.
Acknowledgements
The next step was the determination of the best base
and the necessity or not of an additive in the reaction
(Table 2). We tested inorganic bases in the presence of
Ag2O (Table 2, entries 1 and 2). Cesium carbonate
afforded the best result with 67% isolated yield. An
organic base (triethylamine) was also used, but a lower
yield was obtained (Table 2, entry 3). When no base
was used a great decrease on the yield was observed
(Table 2, entry 4).
The authors are grateful to FAPESP (Grant 03/13897-7
and 03/01751-8).
Supplementary data
Supplementary data associated with this article can
In agreement with previous results,7 no reaction
occurred when no additive was used (Table 2, entry 5).
When CuI and AgOAc were tested, the product 3a
was obtained in 15% and 75% isolated yields, respec-
tively (Table 2, entries 6 and 7).
References and notes
1. For a review of metal-catalyzed Suzuki cross-coupling
reactions, see: (a) Miyaura, N.; Suzuki, A. Chem. Rev.
1995, 95, 2457; (b) Suzuki, A. In Metal-Catalyzed Cross-
Coupling Reactions; Diederich, F., Stang, P. J., Eds.;
Wiley-VCH: Weinheim, 1998, Chapter 2; (c) Suzuki, A.
J. Organomet. Chem. 1999, 576, 147; (d) Kotha, S.; Lahiri,
K.; Kashinath, D. Tetrahedron 2002, 58, 9633.
2. (a) Suzuki, A. Pure Appl. Chem. 1985, 57, 1749; (b)
Suzuki, A. Pure Appl. Chem. 1991, 63, 419; (c) Stanforth,
S. P. Tetrahedron 1998, 54, 263; (d) Miyaura, N.. In
Advances in Metal-Organic Chemistry; Libeskind, L. S.,
Ed.; Jai: London, 1998; Vol. 6, pp 187–243.
3. (a) Molander, G. A.; Felix, L. A. J. Org. Chem. 2005, 70,
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J. Org. Chem. 2002, 67, 8416; (c) Molander, G. A.;
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Biolatto, B. J. Org. Chem. 2003, 68, 4302; (e) Molander,
G. A.; Yun, C.; Ribagorda, M.; Biolatto, B. J. Org. Chem.
2003, 68, 5534; (f) Molander, G. A.; Ribagorda, M. J. Am.
Chem. Soc. 2003, 125, 11148.
4. (a) Vedejs, E.; Chapman, R. W.; Fields, S. C.; Lin, S.;
Schrimpf, M. R. J. Org. Chem. 1995, 60, 3020; (b) Vedejs,
E.; Fields, S. C.; Hayashi, R.; Hitchcock, S. R.; Powell, D.
R.; Schrimpf, M. R. J. Am. Chem. Soc. 1999, 121, 2460.
5. For review: (a) Petragnani, N.; Stefani, H. A. Tetrahedron
2005, 61, 1613; (b) Petragnani, N.; Comasseto, J. V.
Synthesis 1991, 793, 897; (c) Comasseto, J. V.; Ling, L. W.;
Petragnani, N.; Stefani, H. A. Synthesis 1997, 373; (d)
Zeni, G.; Braga, A. L.; Stefani, H. A. Acc. Chem. Res.
2003, 36, 731.
The catalyst loadings were analyzed (Table 2, entries
8–10) and the best result was obtained with 20 mol %
of Pd(PPh3)4 (Table 2, entry 10). When this condition
was employed using triethylamine a better result was ob-
tained, 84% isolated yield (Table 2, entry 11). Under con-
ventional conditions (5 h of reflux and magnetic stirring)
a lower yield was observed, 75% (Table 2, entry 12).
Thus, the optimized condition13 was the use of vinylic
telluride 1a, 1.1 equiv of b-styryl trifluoroborate 2a,
10 mol % of Pd(PPh3)4, 2 equiv of AgOAc, 2 equiv of
triethylamine in methanol as solvent and ultrasound
irradiation for 20 min. Once the best conditions were
established, the protocols were extended to other vinylic
tellurides (1). In all the cases studied, the dienes (3) were
obtained from moderate to good yields by using the
optimized conditions described above for the prepara-
tion of 3a (Table 3, entry 1).
The E,E-1,4-diphenyl-1,3-butadiene 3b was obtained
from the cross-coupling between the E-vinylic telluride
1b and 2a in 85% yield. As previously reported by
us,7b,c when vinylic tellurides (1) containing halides
attached to an aromatic ring or attached at the double
bond (Table 3, entries 4 and 9) were used as substrates
in the cross-coupling reaction, they demonstrated high
chemoselectivity, where only the telluride moiety re-
acted and no reaction was observed in the halide moiety
and the respective products were obtained in good
yields.
6. (a) Zeni, G.; Perin, G.; Cella, R.; Jacob, R. G.; Braga, A.
L.; Silveira, C. C.; Stefani, H. A. Synlett 2002, 6, 975; (b)
Braga, A. L.; Ludtke, D. S.; Vargas, F.; Donato, R. K.;
¨
Silveira, C. C.; Stefani, H. A.; Zeni, G. Tetrahedron Lett.
2003, 44, 1779; (c) Braga, A. L.; Vargas, F.; Zeni, G.;