A new approach to the synthesis of oligomers. Application to the synthesis of p-phenylene thioether wires

Article abstract of DOI:10.1016/j.tetlet.2005.06.143

Oligothioethers 4-RC₆H₄(SC₆H ₄-4)_nX (n = 1-3; X = Br, I; R = NO₂; X = Br; R = MeO. n = 1 and 2; X = I; R = MeO. n = 4; X = Br; R = NO₂) have been prepared through a process invol

Full text of DOI:10.1016/j.tetlet.2005.06.143

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 5839–5840
A new approach to the synthesis of oligomers. Application to
the synthesis of p-phenylene thioether wires
*
´
´
´
´
Jose Vicente, Jose A. Abad and Rosa M. Lopez-Nicolas
Grupo de Quı´mica Organometa´lica, Departamento de Quı´mica Inorga´nica, Facultad de Quı´mica, Universidad de Murcia,
Apdo. 4021, 30071 Murcia, Spain
Received 6 May 2005; revised 22 June 2005; accepted 27 June 2005
Available online 14 July 2005
Abstract—Oligothioethers 4-RC6H4(SC6H4-4)nX (n = 1–3; X = Br, I; R = NO2; X = Br; R = MeO. n = 1 and 2; X = I; R = MeO.
n = 4; X = Br; R = NO2) have been prepared through a process involving (i) palladium-catalyzed C–S coupling between
4-RC6H4(SC6H4-4)nꢀ1I and 4-BrC6H4SH to give 4-RC6H4(SC6H4-4)nBr and (ii) copper-catalyzed replacement of Br by I.
Ó 2005 Elsevier Ltd. All rights reserved.
R
The design and tailoring of linear or branched oligo-
meric molecules (molecular wires or dendrimers, respec-
tively) are receiving considerable attention because they
may play an important role in different key research
areas. To build such oligomers, a variety of repeating
step-by-step coupling methods have been used.1–11 We
report here a new approach to prepare thioether wires
involving (i) C–S coupling between R–I and HS–R0–Br
to give R–S–R0–Br and (ii) replacement of bromo by
iodo to give R–S–R0–I.
I
SH
Br
[Pd]
S
R
R
Br
1bM, 1bN
[Cu]
S
R
MeO
NO2
M
N
The reaction of equimolecular amounts of 4-BrC6H4SH
with KOtBu and 4–RC6H4I, catalyzed by 1% molar
amounts of a mixture of Pd(dba)2 (dba = dibenzylide-
nacetone) and diphenylphosphinoferrocene (dppf)
(Scheme 1), gave the corresponding thioethers 4-
BrC6H4SC6H4R-4 (R = MeO (1bM, 71%), NO2 (1bN,
75%)).12–14 These bromides were transformed into the
iodides 4-IC6H4SC6H4R-4 (R = MeO (1iM, 75%),
NO2 (1iN, 78%))15 following a slight modification of
the copper/diamine-catalyzed method of Klapars and
Buchwald.16 The amounts of the palladium and copper
catalysts must be increased (up to 10% and 40%, respec-
tively) as the length of the chain grows. The oligomers
2bM (84%), 2bN (80%), 2iM (77%), 2iN (89%), 3bM
(80%), 3bN (76%), 3iN (71%), and 4bN (69%), were
obtained similarly (Scheme 2).
I
1iM, 1iN
Scheme 1. Reagents and conditions: [Pd] = 1 mol% (Pd(dba)2 +
days; [Cu] = 8 mol% (CuI + 2
dppf) + KOtBu, toluene, 50 °C,
3
racemic trans-N,N0-dimethyl-1,2-cyclohexanediamine) + 2 equiv NaI,
dioxane, 140 °C, 48 h.
Similar oligomers have been reported by Gingras and
co-workers through a three step process: (i) p-bromina-
tion of a thiomethyl arene to give Br–Ar–SMe, (ii) Pd-
or Cu-catalyzed coupling of the bromoarenes with a thio-
phenol R–Ar0–SH to give R–Ar0–S–Ar–SMe and (iii)
dealkylation of the SMe group to give R–Ar0–S–Ar–
SH.17,18 With respect to our method, the reported yields
are similar or lower, the reaction conditions are harsher
(100–160 °C for the C–S coupling and 160–200 °C for
the deprotection of thiols from the thiomethyl com-
pounds) and the end group R is limited to H or a group
with +M effect (OiPr) while our method is compatible
with both +M (OMe) and ꢀM groups (NO2). We
unsuccessfully attempted to apply the above-mentioned
Keywords: Oligomer; Thioether; C–S Coupling; Palladium catalyst;
Molecular wires.
*
Corresponding author. Tel./fax: +34 968364143; e-mail: jvs1@um.es
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.06.143

5840
J. Vicente et al. / Tetrahedron Letters 46 (2005) 5839–5840
R
R
(CTQ2004-05396); R.M.L.-N. thanks to MEC for a
grant.
SH
Br
[Pd]
S
S
Supplementary data
n-1
n
I
Br
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tet-
let.2005.06.143. Detailed descriptions of experimental
(n-1)iM, (n-1)iN
nbM, nbN
[Cu]
1
procedures and H and 13C NMR spectra of the new
R
R
S
I
MeO
NO2
M
N
compounds.
References and notes
niM, niN
n
1. De Nicola, A.; Goeb, S.; Ziessel, R. Tetrahedron Lett.
2004, 44, 7963.
Scheme 2. Reagents and conditions: [Pd] = 1–10 mol% (Pd(dba)2 +
dppf) + KOtBu, toluene, 50 °C, 1–3 days; [Cu] = 8–40 mol% (CuI + 2
racemic trans-N,N0-dimethyl-1,2-cyclohexanediamine) + 2 equiv NaI,
dioxane, 140 °C, 48 h.
2. Rozalska, I.; Kulyk, P.; Kulszewicz-Bajer, I. New J. Chem.
2004, 28, 1235.
3. Dahan, A.; Weissberg, A.; Portnoy, M. Chem. Commun.
2003, 1206.
´
4. Rodrıguez, J. G.; Tejedor, J. L.; Esquivias, J.; Diaz, C.
deprotection method18 to prepare Br(C6H4-1,4)S(C6H4-
1,4)SH, which would allow growing the chains using less
steps.19 Our method is only limited by the very low solu-
bility of the longest chains. Thus the poor solubility of
4iN rules out its purification and the preparation of pure
5bN. The synthesis of a few linear or cyclic oligo(p-phen-
ylene)thioethers 4-XC6H4(SC6H4-4)nX (n = 2, X = H;
n = 4, X = Br, I)20 or (SC6H4-4)n (n = 4, 5 and 621)22
has also been reported.
Tetrahedron Lett. 2003, 44, 6375.
5. Hurst, S. K.; Cifuentes, M. P.; Humphrey, M. G.
Organometallics 2002, 21, 2353.
6. Yamamoto, K.; Higuchi, M.; Shiki, S.; Tsuruta, M.;
Chiba, H. Nature 2002, 415, 509.
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M.; Reek, J. N. H. Chem. Rev. 2002, 102, 3717, and
references therein.
This new approach for preparing oligomers is also open
to: (1) growing chains in two or more directions using S
or other links, for example, by reacting C6HnI6ꢀn with
HX–R0–Br (X = C„C, NH, O, etc.), or HX–R0–XH
with IC6H4 Br; (2) growing long chains by transforming
R–(X–R0)n–Br into R–(X–R0)n–XH and then reacting it
with R–(X–R0)m–I; (3) if R is a protecting group, to pre-
pare chains H–(X–R0)n–Br that could be used to grow
longer chains in less steps; (4) preparing chains with
the same or different X links (X = C„C, NH, O, S,
etc.; R or/and R0 5 aryl group); (5) building molecular
wires through the catalytic Heck, Stille or Suzuki reac-
tions. Of course, it is necessary, to find the experimental
conditions allowing the coupling step to occur selec-
tively with the carbon atom bonded to I but not to Br.
In conclusion, the great flexibility of this approach
opens the way to preparing wires or dendrimers fulfilling
some desired properties.
10. Valasek, M.; Pecka, J.; Jindrich, J.; Calleja, G.; Craig, P.
R.; Michl, J. J. Org. Chem. 2005, 70, 405.
11. Dong, T.-Y.; Lin, M.-C.; Chiang, M. Y.-N.; Wu, J.-Y.
Organometallics 2004, 23, 3921.
12. Schopfer, U.; Schlapbach, A. Tetrahedron 2001, 57, 3069.
13. Hartwig, J. F. Acc. Chem. Res. 1998, 31, 852.
14. Kondo, T.; Mitsudo, T. Chem. Rev. 2000, 100, 3205.
15. The name of the compounds indicates the number of
C6H4S groups, n, followed by b or i when the compound is
a bromo or iodo derivative, and M or N when R = MeO
or NO2, respectively.
16. Klapars, A.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124,
14844.
17. Pinchart, A.; Dallaire, C.; Gingras, M. Tetrahedron Lett.
1998, 39, 543.
18. Pinchart, A.; Dallaire, C.; Van Bierbeek, A.; Gingras, M.
Tetrahedron Lett. 1999, 40, 5479.
19. Compound Br(C6H4-1,4)S(C6H4-1,4)SMe was obtained
by reacting I(C6H4)SMe-4 with BrC6H4SH-4 under the
same conditions used for 1bM.
20. Tsuchida, E.; Yamamoto, K.; Oyaizu, K.; Suzuki, F.;
Hay, A. S.; Wang, Z. Y. Macromolecules 1995, 28, 409.
21. Franke, J.; Vo¨gtle, F. Tetrahedron Lett. 1984, 25, 3445.
22. Kaplan, M. L.; Reents, W. D., Jr. Tetrahedron Lett. 1982,
23, 373.
Acknowledgements
We thank the financial support of Ministerio de Edu-
´
cacion
y
Ciencia (MEC), Spain and FEDER