M. Shenglof et al. / Tetrahedron Letters 44 (2003) 8593–8595
8595
The exact function of the lanthanide salt in the cross-
coupling process is not quite clear. As AlCl3 and BF3
etherate have no effect whatsoever on either the cross-
coupling of Et3Al with 1-bromonaphthalene, or on the
hydrodehalogenation of the latter compound, and
freshly fused ZnCl2 even reduces the rate and the
selectivity, it is unlikely that the lanthanides function in
our case (as they do in many other processes5) as Lewis
acids. Although complexes of trialkylaluminum and
some lanthanides are known7 we were unable to prove
Stang, P. J., Eds.; VCH: Weinheim, Germany, 1998; (b)
Suzuki, A. J. Organomet. Chem. 1999, 576, 147; (c) Lie,
J. J.; Gribble, G. W. Palladium in Heterocyclic Chem-
istry; Pergamon: New York, NY, 2000; (d) Negishi, E.-I.
Handbook of Organopalladium Chemistry for Organic
Synthesis; Wiley: Hoboken, N.J., 2002; Vol. 1, pp. 229–
247; (e) The special issue of J. Organomet. Chem. 2002,
653 devoted to the Symposium of 30 Years of the
Cross-Coupling Reaction; (f) Littke, A. F.; Fu, G. C.
Angew. Chem., Int. Ed. 2002, 41, 4176 and references
cited therein.
1
unequivocally by H, 13C and 27Al NMR studies that
Et3Al and the diamagnetic LaCl3 forms a discrete alkyl
lanthanium compound. Yet we assume on the basis of
the observation that alkyl lanthanide derivatives can act
as active reagents in alkylation and cross-coupling pro-
cesses,8 that transmetallation may also occur in our
reactions.
2. See for e.g. Eisch, J. J. In Comprehensive Organometallic
Chemistry II; Abel, E. W.; Stone, F. G. A.; Wilkinson,
G.; Housecroft, C. E., Eds.; Pergamon: Oxford, UK,
1995; Vol. 1, p. 464.
3. Gelman, D.; Dechert, S.; Schumann, H.; Blum, J. Inorg.
Chim. Acta 2002, 334, 149.
4. Shenglof, M.; Gelman, D.; Heymer, B.; Schumann, H.;
Molander, G. A.; Blum, J. Synthesis 2003, 302.
5. Molander, G. A. Chem. Rev. 1992, 92, 29 and references
cited therein.
6. Schumann, H.; Meese-Marktscheffel, J. A.; Esser, L.
Chem. Rev. 1995, 95, 865 and references therein.
7. For a recent example see: Fischbach, A.; Herdtweck, E.;
Anwander, R.; Eickerling, G.; Scherer, W. Organometal-
lics 2003, 22, 499.
8. (a) Sigalov, A. B.; Rybakova, L. F.; Beletskaya, I. P.
Izv. Akad. Nauk SSSR, Ser. Khim. 1983, 1692; (b)
Yokoo, K.; Fukagawa, T.; Yamanaka, Y.; Taniguchi,
H.; Fujiwara, Y. J. Org. Chem. 1984, 49, 3237; (c)
Collin, J.; Namy, J. L.; Bied, C.; Kagan, H. B. Inorg.
Chim. Acta 1987, 140, 29; (d) Rybakova, L. F.;
Syutkina, O. P.; Garbar, A. V.; Petrov, E. S. Zh.
Obshch. Khim. 1988, 58, 1053; (e) Syutkina, O. P.
Rybakova, L. F.; Petrov, E. S. Metallorg. Khim. 1989, 2,
Finally, we also examined the effect of a lanthanide salt
[Eu(OTf) 3] on the cross-coupling of an aryl chloride. We
found that indeed the NiCl2(PPh3)2-catalyzed reaction of
1-chloronaphthalene9 with Me3Al is enhanced by the
added europium salt. While in the absence of the
lanthanide compound 25% of 1-methylnaphthalene and
2% of naphthalene were formed after 6 h, the respective
percentages of these products were 56 and 0.2 in its
presence.
In summary, CeCl3 and some other Ln+3 salts are useful
additives for effective cross-coupling of bromoarenes
with triethylaluminum. They both increase the reaction
rate and diminish the disproportionation of the alu-
minum reagent which leads to undesired hydrogenolysis
of the starting halide.
1146; (f) Inamoto, T.; Hatajiama, T.; Nishimura, S.;
;
Acknowledgements
Togo, H.; Yokoyama, M. Kidorui 1990, 16, 3081 [Chem.
Abstr. 1991, 114, 61235z]; (g) Fujiwara, Y.; Makioka, Y.
Kikan Kagaku Sosetsu 1998, 37, 18 [Chem. Abstr. 1999,
129, 315727d]; (h) Fujiwara, Y.; Tanikguchi, Y. Kikan
Kagaku Sosetsu 1998, 37, 63 [Chem. Abstr. 1999, 129,
330287d]; (i) Zheleznova, T. A.; Bochkarev, L. N.;
Safronova, A. V.; Zhil’tsov, S. F. Russ. J. Gen. Chem.
1999, 69, 784.
We thank the United States–Israel Binational Science
Foundation (BSF) for financial support of this study
through grant No. 2000013.
References
9. cf.: Gelman, D.; Schumann, H.; Blum, J. Tetrahedron
Lett. 2000, 41, 7555.
1. For some recent reviews and leading summaries see: (a)
Metal-Catalyzed Cross-Coupling Reactions. Diederich, F.;