C O M M U N I C A T I O N S
Table 2. Palladium(0)-Catalyzed Cross-Coupling of Alkenylcopper
Species with Aryl and Alkenyl Iodides
yields. The stereochemistry of 6l and 6m was determined to be Z
by NOE experiment. The other products were also expected to have
Z configuration.
The Brook-type rearrangement-based preparations of enol silyl
ethers from acylsilanes have been investigated.9 Their typical
strategy involves 1,2-addition of carbon nucleophiles bearing a
leaving group, 1,2-Csp3-to-O silyl migration, and â-elimination.10
In contrast, the present reaction provides the reactive 1-siloxy-1-
alkenylcopper species by the 1,2-silyl migration from the carbonyl
carbon to the carbonyl oxygen. The alkenylcopper species are
applicable to the subsequent carbon-carbon bond formation to
produce the synthetically useful enole silyl ethers stereoselectively.
Acknowledgment. This work was carried out under the 21st
Century COE program of “Future Nanomaterial” in Tokyo Uni-
versity of Agriculture & Technology.
Supporting Information Available: Typical experimental proce-
dures and characterization of all products in the paper. This material is
References
(1) (a) Brook, A. G. Pure Appl. Chem. 1966, 13, 215. (b) Brook, A. G. Acc.
Chem. Res. 1974, 7, 77. (c) Moser, W. H. Tetrahedron 2001, 57, 2065.
(d) Kira, M.; Iwamoto, T. In The Chemistry of Organosilicon Compounds;
Rappoport, Z.; Apeloig, Y. Eds.; Wiley: Chichester, U.K., 2001; Vol. 3,
p 853.
(2) For 1,4-Csp2-to-O silyl migration, see (a) Spinazze´, P. G.; Keay, B. A.;
Tetrahedron Lett. 1989, 30, 1765. (b) Kim, K. D.; Magriotis, P. A.
Tetrahedron Lett. 1990, 31, 6137. (c) Lautens, M.; Delanghe, P. H. M.;
Goh, J. B.; Zhang, C. H. J. Org. Chem. 1995, 60, 4213. (d) Bures, E.;
Spinazze´, P. G.; Beese, G.; Hunt, I. R.; Rogers, C.; Keay, B. A. J. Org.
Chem. 1997, 62, 8741. (e) Moser, W. H.; Endsley, K. E.; Colyer, J. T.
Org. Lett. 2000, 2, 717. (f) Moser, W. H.; Zhang, J.; Lecher, C. S.; Frazier,
T. L.; Pink, M. Org. Lett. 2002, 4, 1981. For 1,3-Csp2-to-O silyl migration,
see (g) Wilson, S. R.; Georgiadis, G. M. J. Org. Chem. 1983, 48, 4143.
(h) Sato, F.; Tanaka, Y.; Sato, M. J. Chem. Soc., Chem. Commun. 1983,
165. (i) Urabe, H.; Sato, F. J. Am. Chem. Soc. 1999, 121, 1245. (j)
Radinov, R.; Schnurman, E. S. Tetrahedron Lett. 1990, 40, 243.
(3) Tsubouchi, A.; Itoh, M.; Onishi, K.; Takeda, T. Synthesis 2004, 1504.
(4) (a) Taguchi, H.; Ghoroku, K.; Tadaki, M.; Tsubouchi, A.; Takeda, T. Org.
Lett. 2001, 3, 3811. (b) Taguchi, H.; Ghoroku, K.; Tadaki, M.; Tsubouchi,
A.; Takeda, T. J. Org. Chem. 2002, 67, 8450. (c) Taguchi, H.; Miyashita,
H.; Tsubouchi, A.; Takeda, T. Chem. Commun. 2002, 2218. (d) Taguchi,
H.; Tsubouchi, A.; Takeda, T. Tetrahedron Lett. 2003, 44, 5205. (e)
Taguchi, H.; Takami, K.; Tsubouchi, A.; Takeda, T. Tetrahedron Lett.
2004, 45, 429.
(5) Tsuda, T.; Hashimoto, T.; Saegusa, T. J. Am. Chem. Soc. 1972, 94, 658.
(6) When the trimethylsilyl analogue of 1a was employed for the reaction,
the C-allylation product of its enolate 2a was obtained in 47% yield as a
major product without the formation of the TMS analogue of 6a.
(7) Brook, A. G.; Schwartz, N. V. J. Org. Chem. 1962, 27, 2311.
(8) Brook, A. G.; Vandersar, T. J. D.; Limburg, W. Can. J. Chem. 1978, 56,
2758.
(9) For example, see (a) Brook, A. G.; Limburg, W. W.; MacRae, D. M.;
Fieldhouse, S. A. J. Am. Chem. Soc. 1967, 89, 704. (b) Brook, A. G.;
Fieldhouse, S. A. J. Organomet. Chem. 1967, 10, 235. (c) Kato, M.; Mori,
A.; Oshino, H.; Enda, J.; Kobayashi, K.; Kuwajima, I. J. Am. Chem. Soc.
1984, 106, 1773. (d) Enda, J.; Kuwajima, I. J. Am. Chem. Soc. 1985,
107, 5495. (e) Reich, H. J.; Holtan, R. C.; Bolm, C. J. Am. Chem. Soc.
1990, 112, 5609. (f) Jin, F.; Jiang, B.; Xu, Y. Tetrahedron Lett. 1992, 33,
1221. (g) Jin, F.; Xu, Y.; Huang, W. J. Chem. Soc., Perkin Trans. 1 1993,
795. (h) Nakajima, T.; Segi, M.; Sugimoto, F.; Hioki, R.; Yokota, S.;
Miyashita, K. Tetrahedron 1993, 49, 8343. (i) Takeda, K.; Nakajima, A.;
Takeda, M.; Okamoto, Y.; Sato, T.; Yoshii, E.; Koizumi, T.; Shiro, M. J.
Am. Chem. Soc. 1998, 120, 4947. (j) Berber, H.; Brigaud, T.; Lefebvre,
O.; Plantier-Royon, R.; Portella, C. Chem.sEur. J. 2001, 7. (k) Ngo, S.
C.; Chung, W. J.; Lim, D. S.; Higashiya, S.; Welch, J. T. J. Fluorine
Chem. 2002, 117, 207.
a Isolated yield.
potassium tert-butoxide was used instead of 3 for the reaction of
1a, 1,3-diphenyl-1-propanol was formed in 48% yield via formation
of a pentacoordinate silicate by nucleophilic attack of the alkoxide
on silicon atom, followed by phenyl migration from the silicate to
a carbonyl carbon. A similar reaction of acetyltriphenylsilane with
sodium alkoxide has been reported by Brook et al.7 Nuleophilic
addition of potassium tert-butoxide to the carbonyl group of a
certain acetylsilane followed by the 1,2-silyl migration has also
appeared.8
The reactions of several acylsilanes 1b-e with allylic halides 5
were performed under the similar reaction conditions and the (Z)-
R-allylated enol silyl ethers 6b, 6c, and 6g-j were obtained
stereoselectively. The reaction of 1a with prenyl chloride 5d
produced a mixture of the formal SN2 and SN2′ products 6c in which
the former predominated (entry 4). The alkenylcopper species 4
also reacted with methyl iodide 5e and benzyl bromide 5f to produce
the corresponding (Z)-enol silyl ethers 6d and 6e in good yields
(entries 5 and 6). Chlorotributylstannane 5g is also reactive toward
the alkenylcopper species 4, and the alkenylstannane 6f was
obtained in 70% yield (entry 7).
The above process has been extended to palladium catalyzed
cross coupling with aryl and alkenyl iodides 7. The acylsilanes 1
were treated with 3 (2 equiv) in the presence of a catalytic amount
(3 mol %) of Pd(PPh3)4 in DMF for 30 min at 25 °C and then with
aryl and alkenyl iodides 7 (Table 2). In all cases, the cross-coupling
proceeded to form the enol silyl ethers 6 as single isomers in good
(10) Alternative strategies have also appeared, for example the reaction of the
acylsilanes having an R-leaving group with the carbon nucleophiles (see
ref 9e); 1,2-addition of 1-alkenyl Grignard reagents to acylsilane; 1,2-
silyl migration of the resulting R-silylallylic alkoxides; and reaction of
nucleophiles at γ-position of R-siloxyallylic anions (see ref 9c and 9d).
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