8262
led to the isolation of the tetranaphthylbutatriene 3b in acceptable yield (Table 1, entry 5). In
contrast, the 9-anthryl substituted starting materials 1c and 2c gave no coupling products (Table
1, entry 6).
Entries 7–9 result in butatrienes 3 with mixed substituents8 and are of importance for studying
the stereoselectivity of the coupling process: according to NMR and MS data mixture of the cis
and the trans isomers are obtained in all cases. Since the initial carbopalladation step should
proceed in a syn-manner, the cis–trans isomerization presumably takes place at the stage of the
vinyl palladium intermediates 4 and 5; the stereochemical lability of similar palladium species
has been demonstrated previously.1c
Details of the stereoselectivity of this process are to be investigated; however, in the case of
butatriene 3a/d with two mesityl substituents a fraction of a pure stereoisomer was obtained by
crystallization, identified as the trans isomer by an X-ray structure analysis (Fig. 1).7,9 Bond
lengths of the central butatriene unit are virtually identical with those of the tetraphenyl-substi-
tuted derivative 3a.10,11 The two sterically demanding mesityl substituents in structure 3a/d are
of course more twisted with respect to the butatriene unit than the neighboring phenyl groups.
For the two distinct positions in the elemental cell torsion angles of 68 and 70° are found for
the mesityl groups, and 24 and 1° for the phenyl groups, respectively.
Acknowledgements
Financial support of the Fonds der Chemischen Industrie is gratefully acknowledged. We are
indebted to Degussa AG for a generous donation of palladium acetate.
References
1. (a) Wu, G.; Rheingold, A. L.; Geib, S. J.; Heck, R. F. Organometallics 1987, 6, 1941–1946; (b) Dyker, G. J. Org.
Chem. 1993, 58, 234–238; (c) Dyker, G.; Kellner, A. Tetrahedron Lett. 1994, 35, 7633–7636; (d) Larock, R. C.;
Tian, Q. J. Org. Chem. 1998, 63, 2002–2009; (e) Larock, R. C. J. Organomet. Chem. 1999, 576, 111–124; (f)
Dyker, G.; Siemsen, P.; Sostmann, S.; Wiegand, A.; Dix, I.; Jones, P. G. Chem. Ber./Recueil 1997, 130, 261–265.
2. Kusumoto, T.; Hiyama, T. Bull. Chem. Soc. Jpn. 1990, 63, 3103–3110.
3. (a) Canty, A. J. Platinum Met. Rev. 1993, 37, 2–7; (b) Canty, A. J. Acc. Chem. Res. 1992, 25, 83–90.
4. (a) Ozawa, F.; Hidaka, T.; Yamamoto, T.; Yamamoto, A. J. Organomet. Chem. 1987, 330, 253; (b) Ozawa, F.;
Fujimori, M.; Yamamoto, T.; Yamamoto, A. Organometallics 1986, 5, 2144.
5. Dyker, G.; Kellner, A. J. Organomet. Chem. 1998, 555, 141–144.
6. Valette, P. C.R. Acad. Sci. 1951, 12, 537–567.
7. X-ray data of compounds 3a/d and 6a have been deposited at the Cambridge Crystallographic Data Centre
(deposition numbers CCDC-148192 and CCDC-148624, respectively). Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ [Fax. (internat.) +44-1223/336033; e-mail:
deposit@ccdc.cam.ac.uk].
8. (a) Kuhn, R.; Jahn, J. Chem. Ber. 1953, 86, 759-763; (b) Edinger, J. M.; Sisenwine, S. F.; Day, A. R. J. Org.
Chem. 1971, 36, 3614–3619.
9. For X-ray structure analyses of other tetraarylbutatrienes, see: Weber, E.; Seichter, W.; Wang, R.-J.; Mak, T. C.
W. Bull. Chem. Soc. Jpn. 1991, 64, 659–667.
10. Berkovitch-Yellin, Z.; Leiserowitz, L. Acta Crystallogr., Sect. B 1977, 33, 3657.
11. For an early synthesis of 3a, see: Kuhn, R.; Wallenfels, K. Ber. Dtsch. Chem. Ges. 1938, 71, 783–790.
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