Ruthenium-Catalyzed Cyclopropanation of Alkenes Using Propargylic Carboxylates as Precursors of Vinylcarbenoids Koji Miki, Kouichi Ohe,* and Sakae Uemura* Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
[email protected];
[email protected] Received June 17, 2003
Intermolecular cyclopropanation reactions of various alkenes with propargylic carboxylates 1 are catalyzed by [RuCl2(CO)3]2 to give vinylcyclopropanes 2 in good yields. The key intermediate of the reaction is a vinylcarbene complex generated in situ by nucleophilic attack of a carbonyl oxygen of the carboxylates to an internal carbon of the alkyne activated by the ruthenium complex. A variety of transition-metal compounds other than the Ru compound can also be employed in this system. Similar cyclopropanation proceeds with conjugated dienes as well to give trans-vic-divinylcyclopropane derivatives and cycloheptadiene derivatives 5, the latter being thermally derived from the initially formed cis-vic-isomers via Cope-type rearrangement. The present reaction is chemically equivalent to the transition metal-catalyzed cyclopropanation reaction using R-diazoketones as carbenoid precursors. Introduction The in situ generation of carbenoid species involving transition metals is well-known, and the species has been applied mostly to cyclopropanation and insertion reactions. One of the most versatile methods to generate carbenoids is a decomposition reaction of diazoalkanes by transition metal complexes.1 This method is quite useful but formidable because of its explosive hazard and a number of unfavorable side reactions such as diazo dimerization and azine formation. To aviod such problems, safe alternatives for diazoalkane handling or special techniques involving slow addition of them are usually required. Recently, much attention has been paid to the activation of alkynes with transition metal complexes as another method to generate carbenoid species. For example, cyclopropylcarbenoids by skeletal reorganization of R,ω-enynes,2,3 dialkylidene ruthenium species from ω-diynes,4 transition metal-containing carbonyl ylides from o-ethynylphenylcarbonyl compounds,5,6 and copper(isoindazolyl)carbene intermediates from (2-ethy(1) (a) Hegedus, L. S. Transition Metals in the Synthesis of Complex Organic Molecules, 2nd ed.; University Science Books: Mill Valley, CA, 1999; p 143. (b) Doyle, M. P.; Forbes, D. C. Chem. Rev. 1998, 98, 911. (c) Padwa, A.; Weingarten, M. D. Chem. Rev. 1996, 96, 223. (d) Ye, T.; McKervey, M. A. Chem. Rev. 1994, 94, 1091. (2) Transition metal-catalyzed reorganization reaction of enynes. For example, [Pd] cat.: (a) Trost, B. M.; Tanoury, G. J. J. Am. Chem. Soc. 1988, 110, 1636. (b) Trost, B. M.; Trost, M. K. Tetrahedron Lett. 1991, 32, 3647. (c) Trost, B. M.; Trost, M. K. J. Am. Chem. Soc. 1991, 113, 1850. [Ru] cat.: (d) Chatani, N.; Morimoto, T.; Muto, T.; Murai, S. J. Am. Chem. Soc. 1994, 116, 6049. [Ru] or [Pt] cat.: (e) Chatani, N.; Kataoka, K.; Murai, S.; Furukawa, N.; Seki, Y. J. Am. Chem. Soc. 1998, 120, 9140. (f) Chatani, N.; Inoue, H.; Ikeda, T.; Murai, S. J. Org. Chem. 2000, 65, 4913. [Pt] cat.: (g) Chatani, N.; Furukawa, N.; Sakurai, H.; Murai, S. Organometallics 1996, 15, 901. (h) Oi, S.; Tsukamoto, I.; Miyano, S.; Inoue, Y. Organometallics 2001, 20, 3704. [Ir] cat.: (i) Chatani, N.; Inoue, H.; Morimoto, T.; Muto, T.; Murai, S. J. Org. Chem. 2001, 66, 4433.
nylphenyl)triazenes7 are recognized as new alternatives of carbenoid species in the catalytic process.8 Most recently, we have reported the synthesis of (2-furyl)carbene complexes from ene-yne-ketones with group 6 transition metal complexes and their application to catalytic cyclopropanation of alkenes (Scheme 1a).9 A wide range of transition metal compounds such as Cr(3) For the reactions of R,ω-enynes with dienes via cyclopropylcarbene complexes have been reported: (a) Trost, B. M.; Hashmi, A. S. K. Angew. Chem., Int. Ed. Engl. 1993, 32, 1085. (b) Trost, B. M.; Hashmi, A. S. K. J. Am. Chem. Soc. 1994, 116, 2183. The reactions of R, ω-enynes with alcohols via cyclopropylcarbene complexes, see: (c) Me´ndez, M.; Mun˜oz, M. P.; Echavarren, A. M. J. Am. Chem. Soc. 2000, 122, 11549. (d) Me´ndez, M.; Mun˜oz, M. P.; Nevado, C.; Ca´rdenas, D. J.; Echavarren, A. M. J. Am. Chem. Soc. 2001, 123, 10511. (e) Ferna´ndez-Rivas, C.; Me´ndez, M.; Nieto-Oberhuber, C.; Echavarren, A. M. J. Org. Chem. 2002, 67, 5197. (f) Martı´n-Matute, B.; Nevado, C.; Ca´rdenas, D. J.; Echavarren, A. M. J. Am. Chem. Soc. 2003, 125, 5757. (4) Yamamoto, Y.; Kitahara, H.; Ogawa, R.; Kawaguchi, H.; Tatsumi, K.; Itoh, K. J. Am. Chem. Soc. 2000, 122, 4310. (5) (a) Iwasawa, N.; Shido, M.; Kusama, H. J. Am. Chem. Soc. 2001, 123, 5814. For an example of an azomethine ylide, see: (b) Kusama, H.; Takaya, J.; Iwasawa, N. J. Am. Chem. Soc. 2002, 124, 11592. (6) Asao, N.; Takahashi, K.; Lee, S.; Kasahara, T.; Yamamoto, Y. J. Am. Chem. Soc. 2002, 124, 12650. (7) (a) Kimball, D. B.; Herges, R.; Haley, M. M. J. Am. Chem. Soc. 2002, 124, 1572. (b) Kimball, D. B.; Weakley, T. J. R.; Herges, R.; Haley, M. M. J. Org. Chem. 2002, 67, 6395. (c) Kimball, D. B.; Weakley, T. J. R.; Herges, R.; Haley, M. M. J. Am. Chem. Soc. 2002, 124, 13463. (d) Kimball, D. B.; Haley, M. M. Angew. Chem., Int. Ed. 2002, 41, 3339. (8) There are many reports on generation of carbene complexes such as the Do¨tz reaction via metathesis between alkynes and carbene complexes. For reviews on enyne metathesis, see: (a) Poulsen, C. S.; Madsen, R. Synthesis 2003, 1 and references therein. (b) Mori, M. Top. Organomet. Chem. 1998, 1, 133. (9) (a) Miki, K.; Nishino, F.; Ohe, K.; Uemura, S. J. Am. Chem. Soc. 2002, 124, 5260. For the synthesis of (2-furyl)carbene complexes, see: (b) Miki, K.; Yokoi, T.; Nishino, F.; Ohe, K.; Uemura, S. J. Organomet. Chem. 2002, 645, 228. Stoichiometric furan formations via the metathesis approach from similar compounds have been reported. See: (c) Jiang, D.; Herndon, J. W. Org. Lett. 2000, 2, 1267. (d) Ghorai, B. K.; Herndon, J. W.; Lam, Y.-F. Org. Lett. 2001, 3, 3535. (e) Ghorai, B. K.; Herndon, J. W. Organometallics 2003, ASAP.
10.1021/jo034841a CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/09/2003
J. Org. Chem. 2003, 68, 8505-8513
8505
Miki et al. SCHEME 1
SCHEME 2
(CO)5(THF), [Rh(OAc)2]2, [(p-cymene)RuCl2]2, [RhCl(cod)]2, [RuCl2(CO)3]2, PdCl2, and PtCl2 were found to be effective catalysts for the cyclopropanation. The key of the reaction is 5-exo-dig cyclization via nucleophilic attack of a carbonyl oxygen to an internal carbon of alkynes activated by transition metal compounds leading to a stable furan structure as a resonance form. This success stimulated us to develop a new method for the preparation of vinylcarbenoid intermediates A from propargylic carboxylates, in which nucleophilic attack of a carbonyl oxygen followed by bond cleavage at the propargylic position has been envisioned (Scheme 1b). Although this concept was invalid in most cases due to facile isomerization of propargylic carboxylates into allenyl carboxylates catalyzed by transtion metal compounds,10 Rautenstrauch first demonstrated the validity of the protocol for a vinylcarbenoid intermediate in palladium-catalyzed inter- and intramolecular carbene transfer reactions using propargylic acetate.11 Most recently, it was shown that intermediary vinylcarboids were effectively trapped by an alkenyl moiety in the molecule to give carbocyclic compounds in PtCl2-catalyzed cyclization of dienynes.12 Our continuous investigation for vinylcarbene transfer reactions led us to find an efficient ruthenium-catalyzed intermolecular cyclopropanation of alkenes using propargylic carboxylates (Scheme 2).13 In this paper, we describe the scope and limitations of the cyclopropanation reaction involving vinylcarbenoids generated in situ from propargylic carboxylates and [RuCl2(CO)3]2. The reaction has also been applied to conjugated dienes to construct cycloheptadiene structures, representing a formal [3 + 4] cyclization using the carboxylates as three-carbon components. (10) Transition metal-catalyzed isomerization of propargylic acetates has been established as a standard method to prepare allenyl acetates. See: (a) Schlossarczyk, H.; Sieber, W.; Hesse, M.; Hansen, H.-J.; Schmid, H. Helv. Chim. Acta 1973, 56, 875. (b) Oelberg, D. G.; Schiavelli, M. D. J. Org. Chem. 1977, 42, 1804. (c) Cookson, R. C.; Cramp, M. C.; Parsons, P. J. J. Chem. Soc., Chem. Commun. 1980, 197 and references therein. (11) (a) Rautenstrauch, V. Tetrahedron Lett. 1984, 25, 3845. (b) Rautenstrauch, V. J. Org. Chem. 1984, 49, 950. Oxidative rearrangement of propargyl esters by palladium catalyst has been reported. See: (c) Kataoka, H.; Watanabe, K.; Goto, K. Tetrahedron Lett. 1990, 31, 4181. (12) Mainett, E.; Mourie`s, V.; Fensterbank, L.; Malacria, M.; MarcoContelles, J. Angew. Chem., Int. Ed. 2002, 41, 2132. (13) For preliminary communication, see: Miki, K.; Ohe, K.; Uemura, S. Tetrahedron Lett. 2003, 44, 2019.
8506 J. Org. Chem., Vol. 68, No. 22, 2003
TABLE 1. Transition Metal-Catalyzed Cyclopropanation of Styrene with 1aa
entry
[M]
time
1 2 3 4 5 6 7 8
[RuCl2(CO)3]2 [RuCl2(CO)3]2c [Rh(OCOCF3)2]2 IrCl3 [IrCl(cod)]2 AuCl3d PtCl2 GaCl3c,e
18 h 15 h 30 min 24 h 18 h 10 min 1h 28 h
2a (%)b
cis/transb
86 90 trace 45 37 63 93 26
84:16 86:14 72:28 70:30 79:21 78:22 65:35
3 (%)b 5 0 99 53 7 26 7 0
a Reaction conditions: 1a (0.2 mmol), styrene (1.0 mmol), catalyst (0.005 mmol), toluene (1.0 mL), 60 °C. b Determined by GLC. c 0.01 mmol. d AuCl3 (0.002 mmol) was used at room temperature. e 1 M solution in methylcyclohexane.
Results and Discussion Effect of Catalyst. At first, the cyclopropanation of styrene with 2-methyl-3-butyn-2-yl acetate (1a) in the presence of a transition metal catalyst (2.5-5 mol %), which had been effective for catalytic cyclopropanation via (2-furyl)carbene complexes, was examined.9a Results of the catalyst screening are given in Table 1. The reaction of 1a with styrene in the presence of a catalytic amount of [RuCl2(CO)3]2 (2.5 mol %) in toluene at 60 °C for 18 h afforded the cyclopropanated product 2a in 86% yield (cis/trans ) 84:16), along with 5% of allenyl acetate 3, the isomerization product of 1a (entry 1). The use of 5 mol % Ru catalyst completely suppressed the formation of 3 (entry 2), and the desired cyclopropane 2a was produced in 90% yield (cis/trans ) 86:14). In contrast, [Rh(OCOCF3)2]2, which is known as a good catalyst for carbene transfer reaction, could not catalyze the present cyclopropanation, but it gave only 3 quantitatively (entry 3). IrCl3, [IrCl(cod)]2, and AuCl3 were also found to catalyze the cyclopropanation to give 2a in 45%, 37%, and 63% yields with 72:28, 70:30, and 79:21 dr, respectively, along with 3 as a byproduct (entries 4, 5, and 6). Particularly, AuCl3 showed a highest activity for both cyclopropanation and allene formation, but it was difficult to control the product selectivity (entry 6). PtCl2, which can act as a good catalyst for intramolecular cyclopropanation (vide supra),12 catalyzed the present reaction effectively, along with allene formation to some extent (entry 7). GaCl3 was marginally effective in the cyclo-
Rhenium-Catalyzed Cyclopropanation of Alkenes TABLE 2. Effect of Solventa
TABLE 4. Ru-Catalyzed Cyclopropanation of Styrene with 1a
entry
solvent
conv of 1a (%)
yieldb (%) (cis/trans)c
1 2 3d 4 5 6
toluene DCE cyclohexane THF MeCN MeOH
100 100 97 24 5 18
86 (84:16) 95 (79:21) 64 (75:25) 9 (67:33) 2 1
a Reaction conditions: 1a (0.2 mmol), styrene (1.0 mmol), [RuCl2(CO)3]2 (0.005 mmol), solvent (1 mL), 60 °C, 18 h. b GLC yield. c Determined by GLC. d 42 h.
TABLE 3. Effect of Temperaturea
entry
solvent
temp (°C)
yield (%)b (cis/trans)c
1 2 3d 4e 5 6 7d
toluene toluene toluene DCE DCE DCE DCE
50 60 80 30 50 60 80
75 (87:13) 86 (84:16) 83 (76:24) 83 (93:7) 99 (87:13) 95 (79:21) 83 (77:23)
a Reaction conditions: 1a (0.2 mmol), styrene (1.0 mmol), [RuCl2(CO)3]2 (0.005 mmol), solvent (1 mL), 18 h. b GLC yield. c Determined by GLC. d 5 h. e 17% of 1a remained unreacted.
propanation to give 2a in 26% yield with other unidentified products (entry 8). Among other catalysts examined, Cr(CO)5(THF), RuCl3, RuCl3‚3H2O, [(p-cymene)RuCl2]2, PdCl2, and PdCl2(CH3CN)211,14 were not effective for the present cyclopropanation. Optimization of Reaction Conditions. Since the cyclopropanation of styrene using propargylic acetate as a vinylcarbenoid precursor was revealed to be efficiently carried out with [RuCl2(CO)3]2 as a catalyst, the effects of other parameters such as solvent and reaction temperature on this catalytic reaction were investigated. Ruthenium-catalyzed cyclopropanation in 1,2-dichloroethane (DCE) occurred more efficiently than that in toluene, producing 2a in 95% yield with 79:21 dr (Table 2, entry 1 vs entry 2).15 The desired cyclopropanation occurred in cyclohexane as well to give 2a in 64% yield, but the prolonged time (42 h) was required (entry 3). On the other hand, the reactions conducted in THF, MeCN, and MeOH at 60 °C were very slow, giving only a trace amount of the desired cyclopropanated product in each reaction (entries 4-6). Next, the cyclopropanation using toluene or DCE as effective solvent was carried out by varying the reaction temperature (Table 3). As a consequence, it was found that the cyclopropanation took place (14) Recently, Yamamoto et al. have reported indenol ether formation from arylalkynes via Pd-carbene intermediates. Nakamura, I.; Bajracharya, G. B.; Mizushima, Y.; Yamamoto, Y. Angew. Chem., Int. Ed. 2002, 41, 4328. (15) In the PtCl2-catalyzed case, cyclopropanation in DCE resulted in lower yield of 2a (74%) together with the formation of a substantial amount of allenyl acetate (23%).
a Reaction conditions: 1 (0.2 mmol), styrene (1.0 mmol), [RuCl2(CO)3]2 (0.005 mmol), DCE, 60 °C. b The values in the parentheses were obtained from reactions in toluene at 60 °C. c Diastereomeric ratios were determined by 1H NMR or GLC.
with excellent chemical yield and high diastereoselectivity by heating a solution of 1a and styrene in toluene at 60 °C or in DCE at 50 °C (entries 2 and 5). As optimized reaction conditions for the ruthenium-catalyzed cyclopropanation with a propargylic acetate were finely tuned by employing either DCE or toluene as solvent, the generality of this new reaction was next examined. Cyclopropanation Using Various Propargylic Carboxylates and Alkenes. The reactions of styrene with other propargylic carboxylates in the presence of [RuCl2(CO)3]2 (2.5 mol %) in DCE at 50 °C or in toluene at 60 °C were examined. Typical results are shown in Table 4.16 The reaction of propargylic benzoate 1b with styrene also gave the cyclopropanated product 2b in 90% yield (cis/trans ) 88:12) (entry 1). Cyclic acetates 1c-e reacted with styrene to give the corresponding products 2c-e in 91%, 97%, and 93% yields, respectively (entries 2-4). In the case of tertiary propargylic carboxylates, the reactions conducted in toluene gave the corresponding products with slightly lower yields compared with those in DCE. (16) Almost all of the cyclopropanes could not be easily separated by column chromatography. Each pure isomer was separated by gel permeation chromatography on CHCl3. Purification details are shown in the Experimental Section.
J. Org. Chem, Vol. 68, No. 22, 2003 8507
Miki et al. SCHEME 3
The reaction with secondary propargylic acetate 1f proceeded smoothly to give 2f in 77% yield with a 75:25 dr, although the treatment in toluene at 60 °C was essential (entry 5).17,18 For the secondary propargylic acetate 1g, having an alkyl group at the propargylic position was less reactive than 1f, affording a desired product in
