SCHEME 1. Products from Catalytic Dimerization of
Terminal Alkynes
Selective Dimerization of Arylalkynes to
(E)-1,4-Diaryl Enynes Catalyzed by the
[Ru(p-cymene)Cl2]2/Acetic Acid System under
Phosphine-Free Conditions
Mauro Bassetti,* Chiara Pasquini, Antonino Raneri, and
Deborah Rosato
CNR, Istituto di Metodologie Chimiche, Dipartimento di
Progettazione Molecolare, and Dipartimento di Chimica,
UniVersita` La Sapienza, 00185 Roma, Italy
the selectivity of the dimerization process. Catalytic systems
easily accessible and tolerant toward substituents and reaction
conditions are also highly desirable for extending the application
profile of this atom economical reaction in organic synthesis.
Active catalytic systems for this reaction are found in main
group elements,4 rare-earth,5 or transition metal complexes.6
Among these, palladium complexes afford predominantly 2,4-
disubstituted enynes,6a while appropriate additives can shift the
selectivity toward 1,4-disubstitution.7 Rhodium complexes
catalyze the dimerization of alkylalkynes,8 but the reactions of
arylalkynes require the presence of excess phosphine,9a of MeI,9b
or of bulky diarylamino based PNP ligands.9c Ruthenium
complexes are excellent catalysts, with preference for head to
head coupling and Z-selectivity.1a,b,10 Important breakthroughs
are the Z-selective dimerization in aqueous media,11 or the
ReceiVed February 13, 2007
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(9) (a) Wendt, J.; Klinger, U.; Singer, H. Inorg. Chim. Acta 1991, 183,
133-143. (b) Lee, C.-C.; Lin, Y.-C.; Liu, Y.-H.; Wang, Y. Organometallics
2005, 24, 136-143. (c) Weng, W.; Guo, C.; C¸ elenligil-C¸ etin, R.; Foxman,
B. M.; Ozerov, O. V. Chem. Commun. 2006, 197-199.
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Organomet. Chem. 1991, 407, 115-124. (b) Bianchini, C.; Peruzzini, M.;
Zanobini, F.; Frediani, P.; Albinati, A. J. Am. Chem. Soc. 1991, 113, 5453-
5454. (c) Echavarren, A. M.; Lo´pez, J.; Santos, A.; Montoya, J. J.
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metallics 1996, 15, 3968-3971. (e) Slugovc, C.; Mereiter, K.; Zobetz, E.;
Schmid, R.; Kirchner, K. Organometallics 1996, 15, 5275-5277. (f) Fryzuk,
M. D.; Jonker, M. J.; Rettig, S. J. Chem. Commun. 1997, 377-378. (g) Yi,
C. S.; Liu, N.; Rheingold, A. L.; Liable-Sands, L. M. Organometallics 1997,
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F. Macromolecules 2004, 37, 13-17.
The commercially available di-µ-chlorobis[(p-cymene)chlo-
roruthenium(II)] complex catalyzes the dimerization of
aromatic alkynes in acetic acid at room temperature to form
the corresponding (E)-1,4-diarylbut-1-ene-3-yne derivatives,
with high stereoselectivity. The procedure does not require
the use of additives and can be carried out in the presence
of water or aprotic cosolvents, under homogeneous condi-
tions.
The catalytic dimerization of terminal alkynes represents an
attractive route for the preparation of 1,4-disubstituted enynes,
which are versatile building blocks in organic synthesis.1 These
C-4 unsaturated moieties are key units in naturally occurring
compounds,2 and in organic materials,3 especially when derived
from aromatic alkynes. Due to competition among head to head
coupling to give 1,4-disubstituted E and Z enynes (a or b,
Scheme 1) or butatrienes, head to tail coupling yielding 2,4-
disubstituted enynes (c), cyclotrimerization, or polymerization,
there is an increasing demand for improving the efficiency and
(1) (a) Handbook of C-H Transformations; Dyker, G., Ed.; Wiley-
VCH: Weinheim, 2005; Vol. 1, Chapter II, p 62. (b) Wakatsuki, Y. J.
Organomet. Chem. 2004, 689, 4092-4109. (c) Trost, B. M.; Toste, F. D.;
Pinkerton, A. B. Chem. ReV. 2001, 101, 2067-2096. (d) Bruneau, C.;
Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311-323.
(2) Nicolau, K. C.; Dai, W. M.; Tsay, S. C.; Estevez, V. A.; Wrasidlo,
W. Science 1992, 256, 1172-1178.
(3) (a) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem. Int.
Ed. 2000, 39, 2632-2657 and references therein. (b) Pahadi, N. K.;
Camacho, D. H.; Nakamura, I.; Yamamoto, Y. J. Org. Chem. 2006, 71,
1152-1155. (c) Liu, Y.; Nishiura, M.; Wang, Y.; Hou, Z. J. Am. Chem.
Soc. 2006, 128, 5592-5593.
10.1021/jo0702692 CCC: $37.00 © 2007 American Chemical Society
Published on Web 05/12/2007
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J. Org. Chem. 2007, 72, 4558-4561