Published on Web 05/28/2006
Cobalt-Catalyzed Trimethylsilylmethylmagnesium-Promoted Radical Alkenylation of Alkyl Halides: A Complement to the Heck Reaction Walter Affo,† Hirohisa Ohmiya,† Takuma Fujioka,† Yousuke Ikeda,† Tomoaki Nakamura,† Hideki Yorimitsu,*,† Koichiro Oshima,*,† Yuki Imamura,‡ Tsutomu Mizuta,‡ and Katsuhiko Miyoshi‡ Contribution from the Department of Material Chemistry, Graduate School of Engineering, Kyoto UniVersity, Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510, Japan, and Department of Chemistry, Graduate School of Science, Hiroshima UniVersity, Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan Received March 1, 2006; E-mail:
[email protected];
[email protected] Abstract: A cobalt complex, [CoCl2(dpph)] (DPPH ) [1,6-bis(diphenylphosphino)hexane]), catalyzes an intermolecular styrylation reaction of alkyl halides in the presence of Me3SiCH2MgCl in ether to yield β-alkylstyrenes. A variety of alkyl halides including alkyl chlorides can participate in the styrylation. A radical mechanism is strongly suggested for the styrylation reaction. The sequential isomerization/styrylation reactions of cyclopropylmethyl bromide and 6-bromo-1-hexene provide evidence of the radical mechanism. Crystallographic and spectroscopic investigations on cobalt complexes reveal that the reaction would begin with single electron transfer from an electron-rich (diphosphine)bis(trimethylsilylmethyl)cobalt(II) complex followed by reductive elimination to yield 1,2-bis(trimethylsilyl)ethane and a (diphosphine)cobalt(I) complex. The combination of [CoCl2(dppb)] (DPPB ) [1,4-bis(diphenylphosphino)butane]) catalyst and Me3SiCH2MgCl induces intramolecular Heck-type cyclization reactions of 6-halo-1-hexenes via a radical process. On the other hand, the intramolecular cyclization of the prenyl ether of 2-iodophenol would proceed in a fashion similar to the conventional palladium-catalyzed transformation. The nonradical oxidative addition of carbon(sp2)-halogen bonds to cobalt is separately verified by a cobalt-catalyzed cross-coupling reaction of alkenyl halides with Me3SiCH2MgCl with retention of configuration of the starting vinyl halides. The cobaltcatalyzed intermolecular radical styrylation reaction of alkyl halides is applied to stereoselective variants. Styrylations of 1-alkoxy-2-bromocyclopentane derivatives provide trans-1-alkoxy-2-styrylcyclopentane skeletons, one of which is optically pure.
Introduction
The Heck reaction is among the most powerful carboncarbon bond formation reactions in organic synthesis.1,2 It is applied to various fields of chemical science, ranging from syntheses of chemicals of biological interest to those of highperformance functional organic materials. The scope and limitations have been fully investigated, and considerable efforts † ‡
Kyoto University. Hiroshima University.
(1) (a) Mizoroki, T.; Mori, K.; Ozaki, A. Bull. Chem. Soc. Jpn. 1971, 44, 581. (b) Heck, R. F.; Nolley, J. P., Jr. J. Org. Chem. 1972, 37, 2320-2322. (2) For review, see: (a) Bra¨se, S.; de Meijere, A. In Metal-catalyzed Crosscoupling Reactions; Diederich, F., Stang, P. J., Eds; Wiley-VCH: Weinheim, 1998; Chapter 3. (b) Link, J. T.; Overman, L. E. In Metal-catalyzed Cross-coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, 1998; Chapter 6. (c) Bra¨se, S.; de Meijere, A. In Metal-catalyzed Cross-coupling Reactions, 2nd ed.; de Meijere, A., Diederich, F., Eds; Wiley-VCH: Weinheim, 2004; Chapter 5. (d) Heck, R. F. Org. React. 1982, 27, 345-390. (e) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009-3066. (f) Crips, G. T. Chem. Soc. ReV. 1998, 27, 427-436. (g) de Meijere, A.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994, 33, 23792411. (h) Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2-7. (i) Beller, M.; Riermeier, T. H.; Stark, G. In Transition Metals for Organic Synthesis; Beller, M., Bolm, C., Ed.; Wiley-VCH: Weinheim, 1998; Volume 1, Chapter 2.13. (j) Handbook of Organopalladium Chemistry for Organic Synthesis; Negishi, E., Ed.; Wiley: New York, 2002; Vol. 1, Chapter IV.2. 8068
9
J. AM. CHEM. SOC. 2006, 128, 8068-8077
have been made to increase the utility. Despite such devotions to the reaction during the last three decades, the major limitation unsolved so far is that one cannot use alkyl halides having hydrogen at the β position to the halide atom as substrates. The alkylpalladiums formed from such halides normally undergo β-hydride elimination more rapidly than insertion of alkenes (Scheme 1a). Although there are some reports on the palladiumcatalyzed Heck reaction of alkyl halides, the reactions employ iodomethane, R-haloacetate,3 benzyl halide,4 and 1-bromoadamantane,5 which have no detachable β-hydrogens. An additional difficulty stems from the much slower oxidative addition of alkyl halides due to the lack of proximal π-systems.6 To overcome these difficulties, Heck-type reactions of alkyl halides with alkenes mediated by transition metals other than (3) Glorius, F. Tetrahedron Lett. 2003, 44, 5751-5754. (4) (a) Wu, G. Z.; Lamaty, F.; Negishi, E. J. Org. Chem. 1989, 54, 25072508. (b) Pan, Y.; Jiang, X.; Hu, H. Tetrahedron Lett. 2000, 41, 725-727. (5) (a) Hori, K.; Ando, M.; Takaishi, N.; Inamoto, Y. Tetrahedron Lett. 1987, 28, 5883-5886. (b) Bra¨se, S.; Waegell, B.; de Meijere, A. Synthesis 1998, 148-152. (c) Narahashi, H.; Yamamoto, A.; Shimizu, I. Chem. Lett. 2004, 33, 348-349 and references cited therein. (6) Negishi, E. In Handbook of Organopalladium Chemistry for Organic Synthesis; Negishi, E., Ed.; Wiley: New York, 2002; Vol. 1, Chapter II.3.1. 10.1021/ja061417t CCC: $33.50 © 2006 American Chemical Society
Cobalt-Catalyzed Alkenylation of Alkyl Halides Scheme 1
ARTICLES Table 1. Cobalt-Catalyzed Styrylation of Alkyl Halidesa
entry
1 2 3 4 5 6 7 8 9 10 11 12
R−X 1
time/h
temp/°C
3
yield/%
6H13CH(CH3)Br nC H Br 12 25 nC H Br 12 25 Ad-Brb tC H Br 4 9 tC H Br 4 9 nC H I 12 25 nC H Cl 12 25 Ad-Clb cC H Cl 6 11 CH3I CH2dCH(CH2)3Br
8 8 3 8 8 3 3 3 3 3 3 3
20 20 35 20 20 35 35 35 35 35 35 35
3b 3c 3c 3d 3e 3e 3c 3c 3d 3a 3f 3g
73 76 71 87 11 67 57 74 90 84 55c 53
nC
a Conditions: R-X (1, 1.5 mmol), styrene (2a, 1.0 mmol), the Grignard reagent (2.5 mmol), CoCl2 (0.05 mmol), and DPPH (0.06 mmol). b Ad ) 1-adamantyl. c p-Chlorostyrene was used instead of styrene.
palladium have been attracting increasing attention. However, most of the variants are not satisfactory with regard to yield and/or reaction conditions. Nickel-catalyzed reaction of alkyl bromides with styrene afforded the desired products in moderate yields.7 Cobaloxime-catalyzed zinc-mediated similar transformations required photolysis and resulted in unsatisfactory yields.8 Very recently, it was found that titanocene-catalyzed butylmagnesium bromide-promoted styrylation of alkyl bromides and some chlorides is very effective in attaining satisfactory yields.9 We independently found that a cobalt salt catalyzes intermolecular styrylation of alkyl halides in the presence of trimethylsilylmethylmagnesium chloride.10 Here we report the full details and application of the cobalt-catalyzed Heck-type reactions.11 Our approach to an alkyl version of the Heck reaction is outlined in Scheme 1b. We have been interested in the synthetic use of single electron transfer from electron-rich cobalt complexes to alkyl halides.12 Compared with the conventional oxidative addition of alkyl halides to palladium, the cobaltmediated single electron transfer process is reasonably rapid to (7) Lebedev. S. A.; Lopatina, V. S.; Petrov, E. S.; Beletskaya, I. P. J. Organomet. Chem. 1988, 344, 253-259. (8) (a) Branchaud, B. P.; Detlefsen, W. D. Tetrahedron Lett. 1991, 32, 62736276. Transformation with a stoichiometric amount of cobaloximes: (b) Tada, M.; Okabe, M. Chem. Lett. 1980, 201-204. (c) Branchaud, B. P.; Yu, G.-X. Organometallics 1993, 12, 4262-4264. (d) Ali, A.; Gill, G. B.; Pattenden, G.; Roan, G. A.; Kam, T.-S. J. Chem. Soc., Perkin Trans. 1 1996, 1081-1093 and references therein. (e) Iqbal, J.; Bhatia, B.; Nayyar, N. K. Chem. ReV. 1994, 94, 519-564. (9) (a) Terao, J.; Watabe, H.; Miyamoto, M.; Kambe, N. Bull. Chem. Soc. Jpn. 2003, 76, 2209-2214. (b) Terao, J.; Kambe, N. Yuki Gosei Kagaku Kyokaishi 2001, 59, 1044-1051. (10) Ikeda, Y.; Nakamura, T.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2002, 124, 6514-6515. (11) Cobalt-catalyzed Heck reactions of aryl halides with alkenes were reported: (a) Gomes, P.; Gosmini, C.; Ne´de´lec, J.-Y.; Pe´richon, J. Tetrahedron Lett. 2002, 43, 5901-5903. (b) Gomes, P.; Gosmini, C.; Pe´richon, J. Tetrahedron 2003, 59, 2999-3002. (c) Amatore, M.; Gosmini, C.; Pe´richon, J. Eur. J. Org. Chem. 2005, 989-992. (12) (a) Wakabayashi, K.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2001, 123, 5374-5375. (b) Tsuji, T.; Yorimitsu, H.; Oshima, K. Angew. Chem., Int. Ed. 2002, 41, 4137-4139. (c) Mizutani, K.; Shinokubo, H.; Oshima, K. Org. Lett. 2003, 5, 3959-3961. (d) Ohmiya, H.; Yorimitsu, H.; Oshima, K. Chem. Lett. 2004, 33, 1240-1241. (e) Mizutani, K.; Yorimitsu, H.; Oshima, K. Chem. Lett. 2004, 33, 832-833. (f) Ohmiya, H.; Tsuji, T.; Yorimitsu, H.; Oshima, K. Chem.sEur. J. 2004, 10, 5640-5648. (g) Ikeda, Y.; Yorimitsu, H. Shinokubo, H.; Oshima, K. AdV. Synth. Catal. 2004, 346, 1631-1634. (h) Ohmiya, H.; Wakabayashi, K.; Yorimitsu, H.; Oshima, K. Tetrahedron 2006, 62, 2207-2213. (i) Ohmiya, H.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2006, 128, 1886-1889. (j) Shinokubo, H.; Oshima, K. Eur. J. Org. Chem. 2004, 2081-2091. (k) Yorimitsu, H.; Oshima, K. Pure Appl. Chem. 2006, 78, 441-449.
generate the corresponding alkyl radical and halide anion. The radical generated does not suffer from β-hydride elimination and adds to an activated alkene, styrene, for instance, to yield a new stabilized radical. The new radical is trapped by a cobalt complex, and subsequent β-hydride elimination provides the desired Heck-type product. Results and Discussion
Styrylation of Alkyl Halides. A mixture of bromocyclohexane (1a, 1.5 mmol) and styrene (2a, 1.0 mmol) was treated with trimethylsilylmethylmagnesium chloride (1.0 M ethereal solution, 2.5 mmol) in ether in the presence of [CoCl2(dpph)] (DPPH ) 1,6-bis(diphenylphosphino)hexane). The reaction mixture was stirred for 8 h at 20 °C to afford β-cyclohexylstyrene (3a) in 86% yield (eq 1). Heating the reaction mixture
at reflux improved the yield of 3a up to 91% and the reaction time to 3 h. A trace amount of dimerized product 3a′ was the only detectable byproduct, which was readily separable from 3a upon purification on silica gel. The reaction proceeded similarly in the absence of light, which eliminates the possibility of a photoinduced reaction. Cobalt(II) bromide, instead of cobalt chloride, served as well. The amount of the Grignard reagent also affected the yield of 3a. Use of 1.5 or 3.5 equiv of the Grignard reagent led to a decreased yield of 3a. PhMe2SiCH2MgCl also effected the alkylation reaction (78% yield of 3a at 35 °C). Trialkylsilylmethyl Grignard reagents were essential to obtain the desired product. The reaction with phenyl, methyl, ethyl, and neopentyl Grignard reagents provided traces of 3a. Cyclohexene was detected mainly. The effect of the ligand deserves discussion (vide infra). A variety of alkyl halides were examined (Table 1). Primary and tertiary alkyl bromides as well as secondary ones underwent J. AM. CHEM. SOC.
9
VOL. 128, NO. 24, 2006 8069
Affo et al.
ARTICLES Table 2. Reaction with Styrene Derivativesa
Table 3. Optimization of Liganda
entry
2
Ar
4
yield/%
1 2 3 4 5 6 7 8
2b 2c 2d 2e 2f 2g 2h 2i
C6H4-p-Me C6H4-p-Cl C6H4-m-Cl C6H4-o-Cl C6H4-p-OMe C6H4-p-CON(CH2Ph)2 C6H4-m-CON(CH2Ph)2 C6H4-m-COOtC4H9
4b 4c 4d 4e 4f 4g 4h 4i
87 85 82 85 82 29 95 66
a Conditions: 1a (1.5 mmol), 2 (1.0 mmol), the Grignard reagent (2.5 mmol), CoCl2 (0.05 mmol), and DPPH (0.06 mmol).
the styrylation reaction (entries 1-6). The reaction of tert-butyl bromide required a higher temperature to attain an acceptable result (entries 5 and 6). Compared to the use of lauryl bromide, the use of lauryl iodide resulted in a low yield of 3c (entry 7). It is worth noting that alkyl chlorides, which are often unreactive in transition metal-catalyzed reactions, proved to be excellent alkyl sources in this reaction (entries 8-10). For instance, treatment of a mixture of lauryl chloride and styrene with Me3SiCH2MgCl in ether at reflux furnished 3c in 74% yield under the [CoCl2(dpph)] catalysis. The reaction with iodomethane afforded the corresponding product 3f in moderate yield (entry 11). Because the Grignard reagent was used, functional groups such as ester, phthalimide, and hydroxy groups were not compatible. A terminal alkenyl moiety survived under the reaction conditions (entry 12). The reaction tolerates seemingly labile functionalities (Table 2). Methoxy- and chlorostyrenes were alkylated efficiently in refluxing ether (entries 2-5). Unfortunately, the para substitution with a carbamoyl group decreased the yield of the product since the phenylogous acrylamide 2g is so reactive that uncatalyzed side reactions took place (entry 6). The meta substituted 2h underwent alkylation efficiently (entry 7). A tert-butoxycarbonyl group also was left untouched under the reaction conditions (entry 8). Unfortunately, the reactions with 1-octene and butyl vinyl ether resulted in failure. An attempted alkylation of methyl acrylate resulted in the formation of a complex mixture. The reaction with cyclopropylmethyl bromide yielded a ringopening product, β-(3-butenyl)styrene (5), in 50% yield (eq 2). In addition, a tetrahydrofuran derivative 7 was obtained when iodo acetal 6 was employed (eq 3). Ring opening of a
cyclopropylmethyl radical and ring closure of a 5-hexenyl radical are well-known processes.13 These observations strongly 8070 J. AM. CHEM. SOC.
9
VOL. 128, NO. 24, 2006
entry
ligand
yield of 3a/%
1 2 3 4 5 6 7 8 9 10
Ph2PCH2PPh2 (DPPM) Ph2P(CH2)2PPh2 (DPPE) Ph2P(CH2)3PPh2 (DPPP) Ph2P(CH2)4PPh2 (DPPB) Ph2P(CH2)5PPh2 (DPPPEN) Ph2P(CH2)6PPh2 (DPPH) Ph2P(CH2)8PPh2 (DPPO) Ph3P (2 equiv to Co) EtPh2P (2 equiv to Co) Ph2PCH2C6H4CH2PPh2 (DPPX)
