290
J. Org. Chem. 1996,60, 290-291
Stereo- and Regioselective Generation of Alkenylzinc Reagents via Titanium-CatalyzedHydrozincation of Internal Acetylenes Yuan Gao, Kousuke Harada, Takeshi Hata, Hirokazu Urabe, and Fumie Sato* Department of Biomolecular Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho,Midori-ku, Yokohama, Kanagawa 226, Japan
drozincation of (mono)olefinswith ZnHz under zirconium catalysis had been reported almost 10 years ago5 and, more recently, hydrozincation of l,&dienes with a 1:2 mixture of ZnIz and LiH in the presence of 10 mol % of CpzTiClz has been described,6there is no precedent for hydrozincation of acetylenes. We have examined the CpzTiClz-catalyzed hydrozincation of 6-dodecyne with zinc hydride reagents generated in situ from ZnXz (X= C1, Br, I) and MH (M = Li, Na, K)(eq 2).6p7 Like the forementioned hydrozincation
Received October 17, 1994
Hydrometalation of acetylenes illustrated in eq 1is a superior method for preparing stereodefined alkenylmetal species, which are particularly useful for the construction of olefinic linkages with predictable stereochemistry. Hydrometalation reactions1including hydro-
9‘
11
(2)
El+_
+
“M-H
(3)
A2
boration,la -alumination,lb -magnesation,lc -silylation,ld -stannation,le and -zirconation,lfetc., have been routinely utilized in the synthesis of complex natural products. Herein we report a new entry to this series of reactions, namely the first hydrozincation of acetylenes, and demonstrate its application to further synthetic transformations. Recently, organozinc compounds of the type RZnX (R = alkyl; X = halogen, R, etc.) have been widely recognized as versatile carbon nucleophiles in organic synthesis owing to their selective reactivities.2 Alkenylzinc compounds are usually prepared via transmetalation of appropriate organometallic reagents, typically organolithium, -magnesium, or -boron compounds, with zinc salts or diethylzin~.~~-~,3 Direct reductive metalation of alkenyl halides with zinc metal can also be effected, but the stereochemicalintegrity of the starting alkenyl halide is not always retained in the zinc reagent.4 If hydrozincation of acetylenes (eq 1, “M-H = “ZnHX”) could be executed in a stereoselective manner, this reaction could become a straightforward method t o prepare stereochemically defined alkenylzinc reagents. While hy(1)Review: (a) Smith, K.; Pelter, A.; Brown, H. C. Borane Reagents; Academic Press: London, 1988. Smith, 11;Pelter, A. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, 1991; Vol. 8,p 703. (b) Sato, F.Janssen Chim. Acta 1990,8,3. Eisch, J.J. In comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, 1991;Vol. 8,p 733. (c) Sato, F.J. Organomet. Chem. 1985,285,53.(d) Weber, W. P. Silicon Reagents for Organic Synthesis; Springer-Verlag: Berlin, 1983. Hiyama, T.; Kusumoto, T. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, 1991;Vol. 8, p 763. (e) Pereyre, M.; Quintard, J.-P.;Rahm, A. Tin in Organic Synthesis; Buttenvorths: London, 1987. (0 Labinger, J. A. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, 1991;Vol. 8,p 667. (2)Review: (a)Knochel, P.; Singer, R. D. Chem. Rev. 1993,93,2117. (b) Erdik, E. Tetrahedron 1992,48,9577. (c) Knochel, P. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, 1991;Vol. 1, p 211. (d) Soai, K.;Niwa, S. Chem. Rev. 1992,92,833. (e) Noyori, R.; Kitamura, M. Angew. Chem., Int. Ed. Engl. 1991,30, 49. (3)Review: Boersma, J. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982;Vol. 2,p 823. Erdick, E. Tetrahedron 1987,43, 2203. (4)Majid, T. N.; Knochel, P. Tetrahedron Lett. 1990, 31, 4413. However, (E)-styrylzinc bromide could be prepared from (E)-styryl bromide with highly activated zinc: Zhu, L.; Wehmeyer, R. M.; Rieke, R. D. J. Org. Chem. 1991,56,1445.
0022-326319511960-0290$09.0010
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