LETTER
Synthesis of a Linear Oligomeric Styrylpyrrole
339
N
Boc
5
+
2 x
N
Boc
I
10
Pd(OAc)2 (5 mol-%),
KOAc, nPr4NBr, DMF,
80 °C, 3 h
45 %
N
Boc
1
Boc
Boc
N
N
Scheme 4
ppm and δ = 7.56 ppm (2’-H and 1’-H) as well as at
δ = 6.89 ppm and δ = 7.79 ppm (1’’’’’-H and 2’’’’’-H)
with J = 16.5 Hz in all cases. The hydrogens of the two
stilbene subunits resonate as a singlet at δ = 7.10 ppm.
The signals of the aromatic hydrogens are found as a mul-
tiplet at δ = 7.39-7.55 ppm and those of the carbamate
moieties as two singlets at δ = 1.64 ppm and δ = 1.68
ppm. The E-configuration of the double bonds at the pyr-
roles can clearly be supposed from the large coupling con-
stants of J = 16.5 Hz. The E-configuration of the stilbene
Müllen, K.; Wegner, G., Ed.; Wiley-VCH: Weinheim 1997, p.
105. Roncali, J. Chem. Rev. 1996, 97, 173.
(3) Handbook of Conducting Polymers; Skotheim, T.;
Elsenbaumer, R. L.; Reynolds, J. R.; Marcel Dekker: New
York, 1998. Handbook of Organic Conductive Molecules and
Polymers; H. S. Nalwa, Ed.; J. Wiley & Sons: Chichester,
1997.
(4) Groenendaal, L.; Meijer, E.-W.; Vekemans, J. A. J. M. In
Electronic Materials: The Oligomer Approach; Müllen, K.;
Wegner, G.; Wiley-VCH: Weinheim 1997, p. 235.
(5) Tietze, L. F.; Schirok, H.; Wöhrmann, M. Chem. Eur. J. 2000,
6, 510. Tietze, L. F.; Schirok, H.; Wöhrmann, M.; Schrader,
K. Eur. J. Org. Chem. 2000, 2433. Tietze, L. F.; Petersen, S.
Eur. J. Org. Chem. 2000, 1827. Tietze, L. F.; Schirok, H. J.
Am. Chem. Soc. 1999, 121, 10264. Tietze, L. F.; Nöbel, T.;
Spescha, M. J. Am. Chem. Soc. 1998, 35, 8971. Tietze, L. F.;
Schirok, H. Angew. Chem. 1997, 109, 1159; Angew. Chem.,
Int. Ed. Engl. 1997, 36, 1124.
1
subunits can not be deduced directly from the H NMR
spectrum; however the Z-compound should be much less
stable und should isomerize to the E-compound, and on
the other hand, the signals of the aromatic hydrogens
should be more diversified due to shielding effects.
In conclusion, we have shown that defined oligomers of
type 1 can be obtained in a straightforward modular ap-
proach by combination of several multiple Heck and
Wittig reactions.
(6) Kim, I. T; Elsenbaumer, R. L. Macromolecules 2000, 33,
6407.
(7) Beller, M.; Riermeier, T. H.; Stark, G. In Transition Metals for
Organic Synthesis; Beller, M.; Bolm, C., Ed.; Wiley-VCH:
Weinheim 1998, p 208. Bräse, S.; de Meijere, A. In Metal-
catalyzed Cross-coupling Reactions; Diederich, F.; Stang, P.
J., Ed.; Wiley-VCH: Weinheim, 1998, p 99.
Acknowledgement
(8) Tietze, L. F.; Kettschau, G.; Heuschert, U.; Nordmann, G.
Chem. Eur. J., in press.
Support of this work by the Fonds der Chemischen Industrie is
gratefully acknowledged. We also thank the BASF AG, Bayer AG,
Degussa AG and the Wacker AG for their generous donations of
chemicals.
(9) Pioneer work in the synthesis of tert-butoxycarbonyl
protected pyrrole oligomers and polymers is described in:
Martina, S.; Enkelmann, V.; Wegner, G.; Schlueter, A. D.
Synth. Met. 1992, 51, 299. Martina, S.; Schlueter, A. D.
Macromolecules 1992, 25, 3607. Martina, S.; Enkelmann, V.;
Schlueter, A. D.; Wegner, G. Synth. Met. 1991, 41, 403.
(10) Gossauer, A. Die Chemie der Pyrrole; Springer Verlag:
Heidelberg 1974.
(11) Andersson, C.-M.; Hallberg, A.; Daves, G. D., Jr. J. Org.
Chem. 1987, 52, 3529. see also Cabri, W.; Candiani, I. Acc.
Chem. Res. 1995, 28, 2.
References and Notes
(1) Electronic Materials: The Oligomer Approach; Müllen, K.;
Wegner G., Ed.; Wiley-VCH: Weinheim, 1997.
(2) Reviews: Diederich, F.; Martin, R. E. ; Angew. Chem., Int. Ed.
1999, 111, 1350. Tour, J. M. Chem. Rev. 1996, 96, 537.
Bäuerle, P. In Electronic Materials: The Oligomer Approach;
Synlett 2001, No. 3, 337–340 ISSN 0936-5214 © Thieme Stuttgart · New York