Palladium-catalyzed cross-coupling reactions of dimethyl- and diethylzinc with unsaturated organotellurium compounds

Article abstract of DOI:10.1016/S0040-4039(99)02087-0

The cross-coupling reaction of diethyl- or dimethylzinc compounds with disubstituted vinylic tellurides as electrophilic partners is described. These cross-coupling reactions were catalyzed by Pd(PPh₃)₄/CuI and were shown to be gener

Full text of DOI:10.1016/S0040-4039(99)02087-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 433–436
Palladium-catalyzed cross-coupling reactions of dimethyl- and
†
diethylzinc with unsaturated organotellurium compounds
a,∗
b
b,∗,‡
Miguel J. Dabdoub, Vânia B. Dabdoub and Joseph P. Marino
a
Laboratório de Síntese de Compostos Organocalcogênios, Departamento de Química, FFCLRP, Universidade de São Paulo,
Av. Bandeirantes, 3900 Ribeirão, Preto-SP, Brazil
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA
b
Received 30 September 1999; revised 3 November 1999; accepted 4 November 1999
Abstract
The cross-coupling reaction of diethyl- or dimethylzinc compounds with disubstituted vinylic tellurides as
electrophilic partners is described. These cross-coupling reactions were catalyzed by Pd(PPh3)4/CuI and were
3
2
shown to be general, allowing the formation of a new sp –sp carbon–carbon bond. Good yields and high
stereoselectivity were observed in all cases. © 2000 Elsevier Science Ltd. All rights reserved.
It has long been recognized that organotellurium species are an efficient source of aryl, benzyl,1a,b
1
a
1
a,b
1a
1a,c,d
1a,b,2
2b,3
allyl,
alkyl, alkynyl
and vinyllithium
or vinylcopper
intermediates by means of the
Te/metal-exchange. Other Te/metal-exchange reactions are currently attracting the interest of chemists
due to the special regio- and stereoselectivity properties which are unique to tellurium species. Recently,
4
Kambe et al. have described the transmetalation of trisubstituted vinylic tellurides to the corresponding
ethylvinylzinc reagents by reaction with diethylzinc in THF at room temperature. Engman et al.5
observed that the transmetalation of diaryl tellurides and diaryl ditellurides with Et Zn only occurred
2
in the presence of catalytic amounts of Ni(acac) leading to mixed ethyl arylzinc derivatives. Even more
2
6
recently (1998), Uchiyama et al. studied the Te/Zn-exchange reaction in the 2-butyltelluropyridine. They
observed that while this alkyl aryl telluride did not react with lithium trimethyl zincate (rt, 18 h), the
reaction with dilithium tetramethyl zincate (Me ZnLi ) proceeded smoothly at 0°C (2 h) affording the
4
2
mixed dilithium 2-pirydinyltrimethyl zincate intermediate.
As part of our efforts toward the total synthesis of polyene-containing natural products, we required
an efficient cross-coupling methodology for the stereoselective synthesis of diene and polyene systems.
2
a
Due to the easy availability of methods to obtain vinylic tellurides of defined configuration, we directed
4
our efforts at expanding the scope of the Te/Zn transmetalation as described by Kambe et al., pursuing
∗
Corresponding authors. E-mail: migjodab@usp.br (M. J. Dabdoub)
In memory of Professor José Tércio B. Ferreira.
E-mail: jpmarino@umich.edu
†
‡
0
040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(99)02087-0
tetl 16015

4
34
the use of the generated vinylzinc reagents in the palladium-catalyzed cross-coupling reaction with vinyl
7
halides in a modified Negishi’s cross-coupling process. However, all the attempts to carry out the Te/Zn-
exchange reaction of disubstituted vinylic tellurides with diethylzinc in THF at room temperature failed
to work in our chosen vinylic tellurides. We now describe our results concerning this reaction and the
palladium-catalyzed cross-coupling reaction of dialkylzinc reagents with vinylic tellurides. Our studies
provide a modification of the experimental conditions in an attempt to perform the Te/Zn-exchange
reaction in an efficient manner (Scheme 1).
Scheme 1.
Despite extensive investigation of various substrates (compounds 1–5, 14–16), different amounts of
8
Et Zn or Me Zn (up to 6.0 equiv.) and reaction times (up to 24 h), no synthetically useful yields (<20%)
2
2
4
were obtained using the described approach. It was considered that the steric bulkiness of the R group in
a cis orientation to the butyltellurium group could be responsible for the slow Te/Zn-exchange reaction.
Consequently, the reactions of compounds 14 and 15 were carried out under literature conditions to
4
4
compare the reactivity when the butyltellurium group is in a trans- or in a cis-relation to the group
attached to the adjacent carbon. However, these reactions with 1.0, 2.0, 5.0 and 6.0 equiv. of Et Zn (5 h
2
up to 24 h) did not occur even with the trans-isomer 15. In these cases, the starting materials were almost
completely recovered.
Trisubstituted vinylic tellurides 5 and 16 were also allowed to react with Et Zn in THF. Compound 16
2
was detellurated in 10% yield (Et Zn in toluene, 2.0 equiv., 5 h) and in 15% yield (E tZn in toluene,
2
2
6.0 equiv., 5 h) only. In the case of compound 5, which contained a phenyl group attached to the
carbon bearing the butyltellurium moiety, the reaction occurred to a considerably larger extent (55%)
1
9
as confirmed by H NMR analysis of the crude mixture (2.0 equiv. of Et Zn in hexane, 5 h rt) although
2
it was not complete even when 6.0 equiv. of Et Zn in toluene was used (rt, 5 h). We assume that these
2
4
facts indicate that the Te/Zn-exchange reaction occurred with the examples described by Kambe et al.
because all the vinylic tellurides employed by these authors had a group (phenyl, ester or trimethylsilyl)
that could stabilize the vinylzinc formed in the α-position.
During our experimental work, we decided to investigate different experimental conditions. The
addition of Pd(PPh ) and the use of DMF as co-solvent resulted in the formation of the corresponding
3
4
methylated or ethylated products. However, the transformation of the starting material was still incom-
plete. The addition of CuI (1.0 equiv.) proved to be beneficial in bringing the cross-coupling reaction to
10
completion (4 h, rt). In our reaction no use of LiCl was necessary, as is the case for the Stille reaction.
Our cross-coupling reaction required the use of an excess of dialkylzinc reagent (4–6 equiv.) and was
1
1
carried out with a series of vinylic tellurides (Table 1, Scheme 1).
To confirm the necessity of the Pd(PPh ) as a catalyst and the accelerating effect we decided to carry
3
4

4
35
Table 1
Cross-coupling products obtained using dialkylzinc compounds and vinylic tellurides
out the reaction in the absence of this compound, but still in the presence of CuI. In this case, removal of
the butyltellurium group becomes the preferred reaction. The role of CuI was critical and hypothetically
the reaction pathway was based on the formation of a copper intermediate by transmetalation of the
dialkylzinc reagent.
In summary, we have shown that the Te/Zn-exchange reaction using Et Zn is not a general method to
2
obtain vinylzinc reagents; however, a new carbon–carbon bond is formed when the reaction is carried
out employing the CuI/Pd(PPh ) /DMF system. It is evident from the results presented here, and in
3
4
the accompanying communication, that our palladium-catalyzed cross-coupling could be potentially
useful for other kinds of carbon–carbon bond formation. In this context, we are currently investigating
a different Te/Zn transmetalation protocol to obtain vinylzinc intermediates and the cross-coupling
reactions involving the latter species will be reported in due course.

4
36
Acknowledgements
Professor Miguel J. Dabdoub thanks CNPq for financial support.
References
1
. (a) Hiiro, T.; Kambe, N.; Ogawa, A.; Miyoshi, N.; Sonoda, N. Angew. Chem., Int. Ed. Engl. 1987, 26, 1187. (b) Kanda, T.;
Kato, S.; Sugino, T.; Kambe, N.; Sonoda, N. J. Organometal. Chem. 1994, 473, 71. (c) Dabdoub, M. J.; Comasseto, J. V.
Organometallics 1988, 7, 84. (d) Engman, L.; Stern, D. Organometallics 1993, 12, 1445.
2
. (a) Dabdoub, M. J.; Begnini, M. L.; Cassol, T. M.; Guerrero Jr., P. G.; Silveira, C. C. Tetrahedron Lett. 1995, 36, 7623, and
references cited therein. (b) Ogawa, A.; Tsuboi, Y.; Obayashi, R.; Yokoyama, K.; Ryu, I.; Sonoda, N. J. Org. Chem. 1994,
5
9, 1600. (c) Barros, S. M.; Dabdoub, M. J.; Dabdoub, V. B.; Comasseto, J. V. Organometallics 1989, 8, 1661. (d) Barros,
S. M.; Comasseto, J. V.; Berriel, J. N. Tetrahedron Lett. 1989, 30, 7353. (e) Dabdoub, M. J.; Dabdoub, V. B.; Pereira, M. A.;
Zukerman-Schpector, J. J. Org. Chem. 1996, 61, 9503. (f) Dabdoub, M. J.; Dabdoub, V. B.; Guerrero Jr., P. G.; Silveira, C.
C. Tetrahedron 1997, 53, 4199. (g) Mo, X.-S.; Huang, Y.-Z. Tetrahedron Lett. 1995, 36, 3539. (h) Huang, Y.-Z.; Mo, X.-S.
Tetrahedron Lett. 1998, 39, 1945.
3
. (a) Comasseto, J. V.; Berriel, J. N. Synth. Commun. 1990, 20, 1681. (b) Tucci, F. C.; Chieffi, A.; Comasseto, J. V. Tetrahedron
Lett. 1992, 33, 5721. (c) Marino, J. P.; Tucci, F. C.; Comasseto, J. V. Synlett 1993, 761. (d) Chieffi, A.; Comasseto, J. V.
Tetrahedron Lett. 1994, 35, 1993. (e) Araujo, M.; Comasseto, J. V. Synlett 1995, 1145.
4
5
6
. Terao, J.; Kambe, N.; Sonoda, N. Tetrahedron Lett. 1996, 37, 4741.
. Stüdemann, T.; Gupta, V.; Engman, L.; Knochel, P. Tetrahedron Lett. 1997, 38, 1005.
. Uchiyama, M.; Kameda, M.; Mishima, O.; Yokoyama, N.; Koike, M.; Kondo, Y.; Sakamoto, T. J. Am. Chem. Soc. 1998,
1
20, 4934.
7
8
9
. (a) Negishi, E.; Takahashi, T.; Baba, S.; Van Horn, D. E.; Okukado, N. J. Am. Chem. Soc. 1987, 109, 2393. (b) Negishi, E.;
Ay, M.; Gulevich, Y. V.; Noda, Y. Tetrahedron Lett. 1993, 34, 1437.
. Different presentations of Et
1.1 M) or neat. Similar results were obtained using Me
. Different results were obtained using neat Et Zn or a solution (1.0 M) of this reagent in toluene.
2
Zn used in this work were purchased from Aldrich as solutions in hexane (1.0 M), in toluene
(
2
Zn (2.0 M in toluene).
2
1
0. (a) Han, X.; Stoltz, B. M.; Corey, E. J. J. Am. Chem. Soc. 1999, 1212, 7600. (b) Takeda, T.; Matsunaga, K.; Kabasawa, Y.;
Fujiwara, T. Chem. Lett. 1995, 771.
1
1. Typical procedure: To a solution of compound 2 (1.0 mmol) in THF (5 mL), Pd(PPh
g, 1.0 mmol) and DMF (5 mL) were added at room temperature under N . Then a commercial dimethylzinc solution
3.0 mL) (2.0 M, in toluene) was transferred dropwise via syringe. The dark brown resulting mixture was stirred for 3
3 4
) (0.055 g; 0.05 mmol), CuI (0.19
2
(
h (followed by TLC) and was carefully treated with water and extracted with diethyl ether. The product was purified by
column chromatography using hexane as eluent.