ORGANIC
LETTERS
2001
Vol. 3, No. 13
2097-2100
Zr-Catalyzed Electrophilic
Carbomagnesation of Aryl Olefins.
Mechanism-Based Control of Zr−Mg
Ligand Exchange
Judith de Armas and Amir H. Hoveyda*
Department of Chemistry, Merkert Chemistry Center, Boston College,
Chestnut Hill, Massachusetts 02467
Received May 2, 2001
ABSTRACT
The first examples of efficient electrophilic Zr-catalyzed carbomagnesations are disclosed, where in contrast to previous catalytic
carbomagnesations the alkyl moiety of the electrophile is transferred (vs that of the Grignard reagent). The identity of the Grignard reagent
is manipulated so that Zr−Mg exchange is facilitated, leading to the formation of alkylmagnesium halide products.
Design and study of efficient and selective catalytic alky-
lation of unactivated olefins is an important objective in
organic synthesis.1 Past research in these laboratories has
led to the development of Zr-catalyzed carbomagnesation
of terminal and cyclic disubstituted allylic alcohols and
ethers.2 Despite the demonstrated utility of catalytic carbo-
magnesation in stereoselective synthesis,1e a number of
limitations still remain.3 A notable shortcoming is that alkyl
Grignard reagents other than ethylmagnesium halides are less
efficient or fail to participate in catalytic carbomagnesation.4
To address this problem, we recently initiated an investiga-
tion regarding Zr-catalyzed olefin alkylations, where various
electrophiles (e.g., alkyl tosylates and bromides) are used in
the presence of a Grignard reagent and 5-10 mol % of Cp2-
ZrCl2 (see i f ix, Scheme 1).5
There are two significant factors that distinguish the two
alkylation pathways: (i) In catalytic ethylmagnesation (i f
W, Scheme 1), the Et group of the Grignard reagent is
transferred,6 whereas in the more recent variant (i f ix),
the alkyl moiety of the electrophile is incorporated within
the product structure. (ii) Whereas the earlier transformations
(1) For representative examples, see: (a) Dzhemilev, U. M.; Vostrikova,
O. S. J. Organomet. Chem. 1985, 285, 43-51. (b) Yanagisawa, A.; Habaue,
S.; Yamamoto, H. J. Am. Chem. Soc. 1989, 111, 366-368. (c) Tsukada,
N.; Sato, T.; Inoue, Y. Chem. Commun. 2001, 237-238. (d) Liepins, V.;
Backvall, J. E. Chem. Commun. 2001, 265-266. For reviews on metal-
catalyzed enantioselective alkylation of olefins and applications to total
synthesis, see: (e) Hoveyda, A. H.; Heron, N. M. In ComprehensiVe
Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.;
Springer-Verlag: Berlin, 1999; pp 431-454. (f) Marek, I. J. Chem. Soc.,
Perkin Trans 1 1999, 535-544.
(2) Zr-catalyzed diastereoselective alkylations: (a) Hoveyda, A. H.; Xu,
Z. J. Am. Chem. Soc. 1991, 113, 5079-5080. (b) Morken, J. P.; Hoveyda,
A. H. J. Org. Chem. 1993, 58, 4237-4244. (c) Hoveyda, A. H.; Morken,
J. P.; Houri, A. F.; Xu, Z. J. Am. Chem. Soc. 1992, 114, 6692-6697. (d)
Houri, A. F.; Didiuk, M. T.; Xu, Z.; Horan, N. R.; Hoveyda, A. H. J. Am.
Chem. Soc. 1993, 115, 6614-6624.
(3) For previous studies from these laboratories that address this issue,
see: (a) Didiuk, M. T.; Morken, J. P.; Hoveyda, A. H. J. Am. Chem. Soc.
1995, 117, 7273-7274. (b) Heron, N. M.; Adams, J. A.; Hoveyda, A. H.
J. Am. Chem. Soc. 1997, 119, 6205-6206. (c) Gomez-Bengoa, E.; Heron,
N. M.; Didiuk, M. T.; Luchaco, C. A.; Hoveyda, A. H. J. Am. Chem. Soc.
1998, 120, 7649-7650. (d) Adams, J. A.; Heron, N. M.; Koss, A. M.;
Hoveyda, A. H. J. Org. Chem. 1999, 64, 854-860.
(4) Didiuk, M. T.; Johannes, C. W.; Morken, J. P.; Hoveyda, A. H. J.
Am. Chem. Soc. 1995, 117, 7097-7104.
(5) (a) de Armas, J.; Kolis, S. P.; Hoveyda, A. H. J. Am. Chem. Soc.
2000, 122, 5977-5983. For related studies, see: (b) Terao, J.; Watanabe,
T.; Saito, K.; Kambe, N.; Sonoda, N. Tetrahedron Lett. 1998, 39, 9201-
9204.
10.1021/ol0160607 CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/06/2001