Synthesis of α,β-unsaturated aryl esters via Heck reaction of unsymmetrical aryl tellurides

Article abstract of DOI:10.1016/j.tetlet.2009.07.092

A variety of α,β-unsaturated aryl esters were prepared by the direct reaction of unsymmetrical aryltellurides and ethyl acrylate, catalyzed by PdCl₂ via a Heck cross-coupling reaction.

Full text of DOI:10.1016/j.tetlet.2009.07.092

Tetrahedron Letters 50 (2009) 5589–5595
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis of
a,b-unsaturated aryl esters via Heck reaction of unsymmetrical
aryl tellurides
a
a
c
Hélio A. Stefani a,b, , Jesus M. Pena , Kemilla Gueogjian , Nicola Petragnani ,
*
Boniek G. Vaz d, Marcos N. Eberlin d
a Departamento de Farmácia, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, SP, Brazil
b Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, SP, Brazil
c Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil
d Laboratório ThoMSon deEspectrometria de Massas, Instituto de Quimica, Universidade de Campinas, 13084-971 Campinas, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
A variety of
rides and ethyl acrylate, catalyzed by PdCl2 via a Heck cross-coupling reaction.
Ó 2009 Elsevier Ltd. All rights reserved.
a,b-unsaturated aryl esters were prepared by the direct reaction of unsymmetrical aryltellu-
Received 15 June 2009
Revised 14 July 2009
Accepted 16 July 2009
Available online 22 July 2009
1. Introduction
unsymmetrical diaryl tellurides. In recent years, transition-metal-
catalyzed reactions of diaryl dichalcogenides with aryl halides or
boronic acids have become versatile tools for the synthesis of
unsymmetrical diaryl chalcogenides.8 Recently, Taniguchi de-
scribed the preparation of numerous unsymmetrical organotellu-
rides by reaction of organoboronic acids with ditellurides via
copper-catalyzed cleavage of a Te–Te bond.8a
Uemura et al. found that diphenyltellurium(IV) dichloride
reacted with a variety of olefins in the presence of a catalytic amount
of PdCl2 together with NaOAc in HOAc to afford the corresponding
arylated (E)-olefins in variable yields (3–98%).9 A suitable oxidant
such as tert-butyl hydroperoxide or copper(I) or (II) chloride had to
be added for the reaction to proceed catalytically with palladium.
The stereoselectivity was very high, except for with acrylonitrile
(Z/E 26:74). Transmetalation of tellurium with palladium was sug-
gested as the key step in the reaction. Alternatively, diaryltellurides
can be used as arylating agents for a variety of olefins in the presence
of Et3N as base and AgOAc as oxidant.10
The importance of palladium-catalyzed coupling reactions is re-
flected in the numerous reports on their development and applica-
tions, which have revolutionized synthetic efforts toward the
construction of carbon–carbon bonds in complex organic struc-
tures that are pursued today in both academia and industry.1
Along with other known cross-coupling reactions, including
Kumada and Corriu, Negishi, Migita, and Kosugi, Stille, Sonogash-
ira, Suzuki–Miyaura, and others, the Heck reaction is a very conve-
nient protocol for forming carbon–carbon bonds at unsaturated
vinylic positions.2 This reaction allows for the direct coupling of
activated arenes and olefins with an unactivated alkene through
palladium catalysis via a formal C–H activation, creating a
r-bond
between two sp2 carbon centers3 (Scheme 1).
A relevant feature of the Heck reaction is that one can obtain
good results with a broad variety of olefins bearing different func-
tional groups.4 The most important of these olefins are the elec-
tron-deficient substrates.
Kamigata and co-workers used aryldimethyltellurium iodides
for palladium-catalyzed Heck-type reactions with electron-defi-
cient olefins and styrene in the presence of a stoichiometric
amount of silver(I) acetate.11 For the telluronium salt partner, the
best results were obtained when the aryl moiety bore electron-
donating substituents at the para position; those at the ortho
Chalcogenide compounds have become attractive synthetic tar-
gets because of their chemo-, regio-, and stereoselective reactions.5
They are used in the presence of a wide variety of functional groups,
thus avoiding the need for protecting group chemistry and useful
biological activities.6 In this line, many classes of organotellurium
compounds have been prepared and studied to date. Aryl tellurides
are certainly useful and promising compounds in view of their util-
ity in organic synthesis.7 Numerous methodologies have been re-
ported for the preparation of these compounds.5d,7b–d However,
limited synthetic methods have been reported for the synthesis of
PdL2X2
H
R
+
R1
R1
+ HX
RX
solvent, base
X = I, Br, OSO2CF3
Solvent = MeCN, HMPA,
N-Methylpyrrolidine, MeOH
Base = Et3N, R2NH, NaOAc, KOAc, Na2CO3 /H2O
* Corresponding author. Tel.: +55 11 818 3654; fax: +55 11 3 815 4418.
E-mail address: hstefani@usp.br (H.A. Stefani).
Scheme 1.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.07.092

5590
H. A. Stefani et al. / Tetrahedron Letters 50 (2009) 5589–5595
Table 1
position retarded the reaction. The yields were good to excellent,
although a threefold excess (with respect to the olefin) of the
expensive silver acetate was needed for the anion exchange and
oxidation steps in the catalytic cycle.
Screening of catalysts for the Heck reaction
EtO
EtO
PdCl2, AgOAc
Et3N, CH3OH
O
O
O
+
Unsymmetrical diaryltellurides can be prepared from alkali
tellurides and non-activated aryl halides, sodium telluride or
potassium tellurocyanate and arenediazonium fluoroborates, tellu-
rium(IV) halides, and arylmagnesium halides, or elemental tellu-
rium and diarylmercury compounds.12
Te
3a
rt ; 8 h
O
O
EtO
4b
4a
Entry
Catalyst
Yields % 4a/4b
Potassium organotrifluoroborate salts have been developed as
a superior class of nucleophilic coupling reagents in terms of their
stability and functional group tolerance as compared to those of
the corresponding boronic acids or boronate esters.13,14 They have
been successfully employed as useful synthetic intermediates in
palladium-catalyzed cross-coupling reactions,15 in rhodium-cata-
lyzed conjugate additions,16 and in the allylation of aldehydes17
and N-toluenesulfonylimines.18 Organotrifluoroborate salts also
have the inherent advantage of being commercially available,
quite air stable, and easily isolated. They show enhanced reactiv-
ity in some cases compared to that of other organoboron
compounds.19
1
2
3
4
5
6
7
8
No catalyst
Pd2(dba)3
Pd(OAc)2
nr
42/28
44/40
49/42
45/42
48/42
nr
Pd(dppf)
Pd PEPPSI
PdCl2(benzonitrile)
Fe(acac)3
PdCl2
44/49
To optimize the reaction conditions, we evaluated the depen-
dence of the arylation of ethyl acrylate with diaryl telluride on
the nature of the base. Inorganic bases such as K2CO3, CS2CO3,
Na2CO3, and NaOAc gave 72%/20%, 65%/20%, 60%/31%, and 51%/
38% yields, respectively, of products 4a and 4b. Of the bases tested,
Et3N gave the best result (47%/47% yield of products I and II).
To get more information on optimal reaction conditions, we car-
ried out investigations to define the best solvent for this transfor-
mation. Apolar solvents such as toluene, dichloromethane, and 1,4-
dioxane all gave poor yields of compounds 4a and 4b (12%/4%, 25%/
13%, and 19%/18%, respectively). DME afforded a moderate yield
(46%/34%) of products 4a and 4b. When protic polar solvents, such
as methanol and ethanol, were used, the yields were high, giving
the desired products 4a and 4b in 47%/47% and 50%/41%,
respectively.
2. Results
The unsymmetrical diaryltellurides starting materials were pre-
pared in good to excellent yields through the reaction of diaryldi-
tellurides20 with potassium aryltrifluoroborate salts bearing
electron-withdrawing, electron-donating, and neutral substitu-
ents, using a catalytic amount of Cu(OAc)2 and bypiridine in
DMSO/H2O at reflux under an air atmosphere.17,21 (Scheme 2).
We started our investigations by testing catalysts to evaluate
their ability to promote the cross-coupling Heck reaction of (4-
methoxyphenyl)(p-tolyl)telluride with ethyl acrylate (Scheme 3).
The yield of both products was high when the reaction was per-
formed with Pd2(dba)3 (42%/48%, Table 1, entry 2). Similar results
were obtained with Pd(OAc)2 and Pd PEPPSI (44%/40% and 45%/
42%, respectively, Table 1, entries 3 and 5). Better yields were ob-
tained when the reaction was performed using Pd(dppf),
PdCl2(benzonitrile), and PdCl2 (49%/40%, 48%/42%, and 44%/49%,
respectively, Table 1, entries 4, 6, and 8). Since the yields were
high, we chose to work with PdCl2 because of its availability in
our laboratory and its efficiency in the reaction. Unfortunately,
no reaction was observed in the absence of catalyst or in presence
of a Fe(acac)3 catalyst.
After identifying the most efficient catalyst, solvent, and base
for the cross-coupling Heck reaction of aryl tellurides and ethyl
acrylate, we decided to explore the scope of this process22 with a
variety of different aryl tellurides (Table 2). As can be seen in the
following table, a large array of ortho-, para-, or meta-substituted
(e.g., –OMe, –Me, –Cl, –F, and –CF3) aryl tellurides underwent the
coupling reaction, giving the desired
in good to excellent yields.
a,b-unsaturated aryl esters
The reactions of the substrates with electron-donating substit-
uents such as methyl and methoxy groups on the aryl group affor-
ded the products 4R and 4R1 in 50%/44%, 47%/40%, 55%/44%, and
61%/31% yields (Table 2, entries 4, 5, and 8, respectively). In the
case of electron-withdrawing substituents such as F or Cl, very
good yields were also achieved, with 44%/37%, 43%/56%, 71%/25%
yields for compounds 4R and 4R1, respectively (Table 2, entries
3, 6 and 9). In general, reaction yields were not severely affected
by the electronic influence of the groups connected to the aromatic
ring. In no example was isomerization of the carbon–carbon dou-
ble bond observed.
Cu(OAc)2 (1%)
bpy (1%)
Ar Te Ar1
3
66-94%
+ Ar1BF3K
Ar TeTe Ar
DMSO/H2O
reflux, 12 h
air
1
2
Ar, Ar1 = Aryl and Heteroaryl
To further investigate the scope and limitations of this method-
ology, we carried out the cross-coupling of unsymmetrical aryltel-
Scheme 2.
lurides with two different
summarized in Table 3.
a,b-unsaturated carbonyl compounds, as
Both compounds (5R and 5R1) were obtained in low to good
yields.
PdCl2, AgOAc
Et3N, CH3OH
EtO
EtO
O
+
O
Te
OMe
rt, 8 h
O
3. ESI-MS(/MS) mechanistic investigation
3a
MeO
4a
47%
4b
47%
EtO
Electrospray ionization mass spectrometry (ESI-MS and its tan-
dem version ESI-MS/MS) has recently been incorporated as a suit-
able technique for mechanistic studies of organic and inorganic
Scheme 3.

H. A. Stefani et al. / Tetrahedron Letters 50 (2009) 5589–5595
5591
Table 2
Heck reaction of unsymmetrical aryl tellurides with ethyl acrylate
EtO
EtO
PdCl2, AgOAc
Et3N, CH3OH
R
R1
O
O
+
Te
rt ; 8 h
O
3a-i
R1
R
EtO
4R1
4R
Entry
Aryl telluride
Product 4R (%)
Product 4R1 (%)
O
O
O
O
1
Te
O
O
44 (4a1)
3a
49 (4a)
O
O
O
O
O
2
3
Te
O
O
3b
44 (4b1)
50 (4b)
Cl
Cl
O
Te
O
O
3c
37 (4c1)
44 (4c)
O
O
O
O
O
4
5
Te
O
O
40 (4d1)
3d
47 (4d)
F3C
CF3
O
Te
O
O
3e
55* (4e)
44* (4e1)
O
O
56* (4f1)
O
Te
6
7
8
F
F
O
43* (4f)
3f
S
S
O
O
Te
O
O
3g
13
72
O
O
O
O
O
O
Te
O
3h
31 (4h1)
25 (4i1)
61 (4h)
Cl
F
F
Cl
O
O
9
Te
O
3i
71 (4i)
*Not separable mixture.

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H. A. Stefani et al. / Tetrahedron Letters 50 (2009) 5589–5595
Table 3
a
,b-Unsaturated carbonyl compounds
PdCl2, AgOAc
Et3N, CH3OH
O
O
O
+
Te
rt; 3 h
O
3a
O
5R1
5R
Entry
a,b-Unsaturated carbonyl
Product 5R (%)
Product 5R1 (%)
O
O
O
1
O
11 (5a1)
30 (5a)
O
O
O
2
O
32 (5b1)
51 (5b)
reactions. Its usefulness arises mainly from its outstanding ability
to ‘fish’, with high sensitivity and gentleness, ionic or ionized inter-
mediates directly from the reaction solutions and into the gas
phase,23 providing therefore continuous snapshots of the composi-
tion of reaction solutions.24
To scrutinize the catalytic cycle for the reaction investigated
herein, we monitored via ESI-MS(/MS) the cross-coupling of aryl
tellurides with olefins promoted by Pd(OAc)2. We first studied
the reaction of 1 with ethyl acrylate in the presence of Pd(OAc)2.
In the ESI-MS (Fig. 1), a series of cationic species were detected
and some ions were identified as key reaction species, that is, those
of m/z 313, 344, and 450.
The ion of m/z 344 is the ionized reactant 1+Å, whereas species of
m/z 313 and m/z 450 are key reaction intermediates. The ion m/z
450 results from Pd insertion into the Te–Ar bond and its oxidative
addition to the olefin forms the key intermediate of m/z 313. Struc-
tures were corroborated via characteristic Pd/Te multi-isotopic
patterns and via ESI-MS/MS. For instance, the collision-induced
dissociation (CID) of the ion of m/z 313 involves substantial molec-
ular rearrangement, which enables the loss of the final product 4a
O
435
100
Pd
O
O
Te
EtO
Pd
O
O
O
Na+
O
229
Te
641
O
EtO
%
450
313
344
0
m/z
50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950
Figure 1. ESI(+)-MS of the reaction solution of aryl telluride with ethyl acrylate after 1 h.

H. A. Stefani et al. / Tetrahedron Letters 50 (2009) 5589–5595
5593
O
313
Pd
313
100
Ar
O
EtO
O
O
EtO
%
PdH
107
0
m/z
100
120
140
160
180
200
220
240
260
280
300
320
Figure 2. ESI-MS/MS for the key intermediates of m/z 313.
Pd(OAc)2
R
R1
Pd(0)
Te
R = OMe
1 = Cl
(R1)R
PdH
R
(R1)R
O
EtO
Te
Pd
R1(R)
OEt
R
NCCH3
NCCH3
O
Pd
O
EtO
m/z 395, R1 m/z 401
R
Scheme 4. Proposed mechanism for the palladium-catalyzed Heck reaction of aryl telluride with ethyl acrylate, with key intermediates intercepted by ESI-MS and
characterized by ESI-MS/MS.
as a neutral molecule thus yielding the fragment ion PhH+ of m/z
107.
and detected by ESI-MS as its molecular ion. This intermediate
then undergoes carbopalladation of the olefin double bond (1) to
yield a Pd cationic intermediate (m/z 313 or m/z 395 and 401).
These species then undergo b-elimination of PdH to yield the final
cross-coupling products, and a similar process occurs under CID
(Fig. 2). PdH is reduced to Pd(0) in the presence of base (carbonate).
The fade of TeAr species is still unclear since no late Te-intermedi-
ates could be detected.
In summary, we have shown that tellurium can be a good elec-
trophilic alternative to the halides that are traditional in the cross-
coupling Heck reaction. Further studies associated with other spe-
cies containing tellurides as electrophilic partners in the Heck reac-
tion are currently in progress.
When the reaction of the unsymmetrical 2 was monitored, two
key cationic palladium species of m/z 395 and 400 (Fig. 3), analo-
gous to that of m/z 313, were detected by ESI-MS now as the MeCN
adducts. They dissociated extensively upon CID via ESI-MS/MS to
form ions of m/z 354 and 359 by MeCN loss, and subsequently to
form an ion of m/z 189 after loss of the final Heck products (see
supporting information).
With the ESI-MS(/MS) data in hand, we rationalize a mechanism
for the palladium-catalyzed Heck reaction with tellurides (Scheme
4). The first step is an oxidative insertion of Pd(0) into the telluride,
forming an arylpalladium telluride species which was intercepted

5594
H. A. Stefani et al. / Tetrahedron Letters 50 (2009) 5589–5595
O
NCMe
NCMe
Cl
Pd
NCMe
Pd
O
NCMe
EtO
O
EtO
100
395
401
399
397
398
394
403
OMe
400
393
Cl
405
Pd
Te
Pd
Te
%
395
401
O
793
0
m/z
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
Figure 3. ESI(+)-MS for the reaction solution of aryl telluride with ethyl acrylate acquired after 1 h.
15. (a) Molander, G. A.; Felix, L. A. J. Org. Chem. 2005, 70, 3950; (b) Molander, G. A.;
Figueroa, R. Org. Lett. 2006, 8, 75; (c) Cella, R.; Cunha, R. L. O. R.; Reis, A. E. S.;
Pimenta, D. C.; Klitzke, C. F.; Stefani, H. A. J. Org. Chem. 2006, 71, 244; (d)
Stefani, H. A.; Cella, R.; Dorr, F. A.; Pereira, C. M. P.; Zeni, G., Jr. Tetrahedron Lett.
2005, 46, 563; (e) Stefani, H. A.; Cella, R. Tetrahedron 2006, 62, 5656; (f) Cella,
R.; Orfão, A. T. G.; Stefani, H. A. Tetrahedron Lett. 2006, 47, 5075; (g) Molander,
G. A.; Sommers, E. M.; Baker, S. R. J. Org. Chem. 2006, 71, 1563; (h) Molander, G.
A.; Yokoyama, Y. J. Org. Chem. 2006, 71, 2493.
16. (a) Batey, R. A.; Thadani, A. N. Org. Lett. 1999, 1, 1683; (b) Pucheault, M.; Darses,
S.; Genêt, J.-P. Tetrahedron Lett. 2002, 43, 6155; (c) Pucheault, M.; Darses, S.;
Genêt, J.-P. Eur. J. Org. Chem. 2002, 3552; (d) Navarre, L.; Pucheault, M.; Darses,
S.; Genêt, J.-P. Tetrahedron Lett. 2005, 46, 4247.
Acknowledgments
The authors are grateful to FAPESP (Grant 07/59404-2 and 03/
09931-5) and CNPq (300.613/2007-5 and 302.674/2005-5) for
their generous support.
References and notes
1. Corbet, J.-P.; Mignani, G. Chem. Rev. 2006, 106, 2651.
2. (a) de Meijere, A.; Diederich, F. Metal-Catalyzed Cross-Coupling Reactions, 2nd
ed.; Wiley-VCH: Weinheim, 2004; (b) Tsuji, J.. Palladium Reagents and Catalysts.
In New Perspectives For the 21st Century; Wiley: West Sussex, 2004;
(c)Handbook of Organopalladium Chemistry for Organic Synthesis; Negishi, E.,
Ed.; Wiley-Interscience: New York, 2002.
17. (a) Batey, R. A.; Thadani, A. N.; Smil, D. V. Tetrahedron Lett. 1999, 40, 4289; (b)
Batey, R. A.; Thadani, A. N.; Smil, D. V. Synthesis 2000, 990; (c) Thadani, A. N.;
Batey, R. A. Org. Lett. 2002, 4, 3827; (d) Thadani, A. N.; Batey, R. A. Tetrahedron
Lett. 2003, 44, 8051.
18. Li, S.-W.; Batey, R. A. Chem. Commun. 2004, 1382.
3. For some recent reviews on the Heck reaction, see: (a) Heck, R. F. Synlett 2006,
2855; (b) Phan, N. T. S.; Van Der Sluys, M.; Jones, C. W. Adv. Synth. Catal. 2006,
348, 609; (c) Alonso, F.; Beletskaya, I. P.; Yus, M. Tetrahedron 2005, 61, 11771.
4. Heck, R. F. Org. React. 1982, 27, 345–389.
5. (a)Organoselenium Chemistry; Wirth, T., Ed.Topics in Current Chemistry;
Springer: Heidelberg, 2000; Vol. 208, (b) Krief, A.. In Comprehensive
Organometallic Chemistry II; Abel, E. V., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon Press: New York, 1995; Vol. 11,. Chapter 13 (c) Paulmier, C. In
Selenium Reagents and Intermediates in Organic Synthesis; Baldwin, J. E., Ed.;
Organic Chemistry Series 4; Pergamon Press: Oxford, 1986; (d)Tellurium in
Organic Synthesis; Petragnani, N., Stefani, H. A., Eds., 2nd ed.; Academic Press:
London, 2007.
6. (a) Nogueira, C. W.; Zeni, G.; Rocha, J. B. T. Chem. Rev. 2004, 104, 6255; (b)
Mugesh, G.; du Mont, W.-W.; Sies, H. Chem. Rev. 2001, 101, 2125; (c) Parnham,
M. J.; Graf, E. Prog. Drug Res. 1991, 36, 9.
7. (a) Zeni, G.; Braga, A. L.; Stefani, H. A. Acc. Chem. Res. 2003, 36, 731; (b) Zeni, G.;
Ludtke, D. S.; Panatieri, R. B.; Braga, A. L. Chem. Rev. 2006, 106, 1032; (c)
Petragnani, N.; Stefani, H. A. Tetrahedron 2005, 61, 1613; (d) Comasseto, J. V.;
Ling, L. W.; Petragnani, N.; Stefani, H. A. Synthesis 1997, 373.
8. (a) Taniguchi, N. J. Org. Chem. 2007, 72, 1241; (b) Taniguchi, N. Synlett 2006,
1351; (c) Taniguchi, N.; Onami, T. J. Org. Chem. 2004, 69, 915; (d) Wang, L.;
Wang, M.; Huang, F. Synlett 2005, 2007; (e) Fukuzawa, S.; Tanihara, D.; Kikuchi,
S. Synlett 2006, 2145; (f) Kumar, S.; Engman, L. J. Org. Chem. 2006, 71, 5400.
9. Uemura, S.; Wakasugi, M.; Okano, M. J. Organomet. Chem. 1980, 194, 277.
10. Nishibayashi, Y.; Cho, S. C.; Uemura, S. J. Organomet. Chem. 1996, 507, 197.
11. Hirabayashi, K.; Nara, Y.; Shimizu, T.; Kamigata, N. Chem. Lett. 2004, 33, 1280.
12. Petragnani, N.; Stefani, H. A. Tellurium in Organic Chemistry-Second, Updated
and Enlarged ed.; Academic Press/Elsevier, 2007.
19. (a) Batey, R. A.; Thadani, A. N.; Smil, D. V. Org. Lett. 1999, 1, 1683; (b) Darses, S.;
Genêt, J.-P. Eur. J. Org. Chem. 2003, 4313; (c) Paixão, M. W.; Weber, M.; Braga, A.
L.; de Azeredo, J. B.; Deobalde, A. M.; Stefani, H. A. Tetrahedron Lett. 2008, 49,
8051.
20. Alves, D.; Pena, J. M.; Vieira, A. S.; Botteselle, G. V.; Guadagnin, R. C.; Stefani, H.
A. J. Braz. Chem. Soc. 2009, 20, 988–992.
21. General procedure for the cross-coupling reaction of diaryl ditellurides with
potassium aryltrifluoroborates: To a round-bottomed flask containing diaryl
ditelluride (0.25 mmol), potassium aryltrifluoroborate salt (0.5 mmol),
Cu(OAc)2 (1 mol %), and bpy (1 mol %) were added DMSO (1 mL) and H2O
(0.5 mL). The reaction mixture was allowed to stir at reflux for 12 h. After this
time, the solution was cooled to room temperature, diluted with
dichloromethane (20 mL), and washed with saturated aqueous NH4Cl
(3 Â 20 mL). The organic phase was separated, dried over MgSO4, and
concentrated under vacuum. The residue was purified by flash
chromatography on silica gel using ethyl acetate/hexane as the eluent.
Selected spectral and analytical data for p-methoxyphenyl-p-tolyl-telluride 3a:
Yield: 0.146 g (90%). 1H NMR (CDCl3, 300 MHz): d 7.69 (d, J = 8.5 Hz, 2H), 7.53
(d, J = 7.8 Hz, 2H), 7.02 (d, J = 7.8 Hz, 2H), 6.79 (d, J = 8.5 Hz, 2H), 3.80 (s, 3H),
2.32 (s, 3H). 13C NMR (CDCl3, 75 MHz): d 159.64, 140.36, 137.25, 137.02,
130.10, 115.26, 111.21, 103.48, 54.96, 20.96. MS (relative intensity) m/z: 328
(28), 198 (100), 183 (74), 155 (25), 91 (23), 65 (17). HRMS calcd for C14H14OTe:
328.0107. Found: 328.0111.
22. General procedure for the Heck cross-coupling reaction of unsymmetrical diaryl
telluride 3a with ethyl acrylate: Into a two-necked 25-mL round-bottomed flask
containing PdCl2 (0.05 mmol), AgOAc (2.00 mmol), and unsymmetrical diaryl
telluride 3a (0.50 mmol) were added dry methanol (10 mL), Et3N (2.00 mmol),
and ethyl acrylate (1.00 mmol). After the heterogeneous reaction mixture had
been stirred at 25 °C for 8 h, the solid part was filtered. The filtrate was poured
into brine (60 mL) and extracted with ethyl acetate (3 Â 20 mL). The organic
phase was separated, dried over MgSO4, and concentrated under vacuum. The
13. (a) Stefani, H. A.; Cella, R.; Vieira, A. S. Tetrahedron 2007, 63, 3623; (b)
Molander, G. A.; Ellis, N. Acc. Chem. Res. 2007, 40, 275; (c) Molander, G. A.;
Figueroa, R. Aldrichim. Acta 2005, 38, 49.
14. Brown, H. C.; Gupta, S. K. J. Am. Chem. Soc. 1972, 94, 4370.

H. A. Stefani et al. / Tetrahedron Letters 50 (2009) 5589–5595
5595
residue was purified by flash chromatography on silica gel using ethyl acetate/
hexane as the eluent. Selected spectral and analytical data for (E)-Ethyl 3-(4-
methoxyphenyl)acrylate (4a): 1H NMR (300 MHz, CDCl3): 1,34 (t, J = 6,12 Hz,
3H); 2,35 (s, 1H); 4,23 (q, J = 6, 54 Hz); 6,37 (d, J = 15,99 Hz, 1H); 7,17 (d,
J = 7,92 Hz, 1H); 7,40 (d, J = 7,89 Hz, 1H); 7,64 (d, J = 15,96 Hz, 1H). 13C NMR
(125.8 MHz, CDCl3): 14,10; 19,56; 60,26; 119,09; 126,12; 129,71; 130,54;
133,21; 137,40; 142,06; 166,85. CG/MS: m/z (%) 190 (25); 175 (3,6); 162 (12);
145 (100); 131 (8,8); 115 (46,5); 102 (5); 91 (21,8); 65 (12,4); 51 (5,7). (E)-
Ethyl 3-p-tolylacrylate (4b): 1H NMR (300 MHz, CDCl3): 1,32 (t, J = 7,0 Hz, 3H);
3,8 (s, 3H); 4,24 (q, J = 7,14 Hz, 2H); 6,30 (d, 15,96 Hz, 1H); 6,88 (d, 2H); 7,47 (d,
2H); 7,63 (d, 15,96 Hz, 2H). 13C NMR (125.8 MHz, CDCl3):14,12; 55,13; 60,09;
114,07; 115,53; 126,98; 129,44; 161,09; 167,11. CG/MS: m/z (%) 206 (64,4);
191 (2,1); 178 (10,9); 161 (100); 147 (5,4); 134 (49,9); 118 (11,8); 103 (5,8); 89
(14,7); 77 (13,8); 63 (10).
23. (a) Santos, L. S. Eur. J. Org. Chem. 2008, 235; (b) Eberlin, M. N. Eur. J. Mass
Spectrom. 2007, 13, 18.
24. (a) Amarante, G. W.; Milagre, H. M. S.; Vaz, B. G.; Ferreira, B. R. V.; Eberlin, M.
N.; Coelho, F. J. Org. Chem. 2009, 74, 3031; (b) Orth, E. S.; Brandão, T. A. S.;
Milagre, H. M. S.; Eberlin, M. N.; Nome, F. J. Am. Chem Soc. 2008, 130, 2436; (c)
Sabino, A. A.; Machado, A. H. L.; Correia, C. R. D.; Eberlin, M. N. Angew. Chem.,
Int. Ed. 2004, 43, 2514; (d) Santos, L. S.; Rosso, G. B.; Pilli, R. A.; Eberlin, M. N. J.
Org. Chem. 2007, 72, 5809.