Catalytic Asymmetric [2,3]-Sigmatropic Rearrangement of Sulfur Ylides Generated from Copper(I) Carbenoids and Allyl Sulfides Xiaomei Zhang,† Zhaohui Qu,† Zhihua Ma,† Weifeng Shi,† Xianglin Jin,† and Jianbo Wang*,†,‡ Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Department of Chemical Biology, College of Chemistry, Peking University, Beijing 100871, P. R. China, and State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, P. R. China
[email protected] Received March 6, 2002
Catalytic asymmetric sulfur ylide [2,3]-sigmatropic rearrangement of carbenoids generated from aryldiazoacetates has been investigated with a number of chiral Rh(II) and Cu(I) catalysts, and moderately high enantioselectivity (52-78% ee) can be achieved with Cu(MeCN)4PF6/2,2′isopropylidenebis[(4S)-4-tert-butyl-2-oxazoline]. Introduction Rh(II)-carbene and Cu(I)-carbene can efficiently react with allylic sulfides to generate sulfur ylides, which can subsequently undergo [2,3]-sigmatropic rearrangement.1 [2,3]-Sigmatropic rearrangement is a synthetically useful reaction. It can generate tertiary sulfides, which are not easily available. Recently a catalytic asymmetric system was developed that could introduce chirality into the newly formed tertiary carbon center. Although the [2,3]sigmatropic rearrangement reaction of the ylide generated by transition metal catalyzed diazo decomposition in the presence of sulfide is generally believed to occur from free ylide rather than metal-associated ylide,2 recent developments of asymmetric induction in similar oxygen and iodine ylide reactions strongly suggest that the metal complex may still be attached to the ylide intermediate during the subsequent reaction.3 If a chiral metal complex is associated with the ylide, it will be likely that it transfers chirality to the final product. Inter- and intramolecular [2,3]-sigmatropic rearrangement through oxonium ylide has been studied with chiral Rh(II) and Cu(I) catalysts,3,4 but the corresponding reaction through †
Peking University. Nankai University. (1) For reviews, see: (a) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic Methods for Organic Synthesis with Diazo Compounds; Wiley-Interscience: New York, 1998. (b) Li, A.-H.; Dai, L.-X.; Aggarwal, V. K. Chem. Rev. 1997, 97, 2341. (c) Doyle, M. P.; Forbes, D. C. Chem. Rev. 1998, 98, 911. (d) Hodgson, O. M.; Pierard, F. Y. T. M.; Stupple, P. A. Chem. Soc. Rev. 2001, 30, 50. (2) (a) Trost, B. M.; Hammen, R. F. J. Am. Chem. Soc. 1973, 95, 962. (b) Doyle, M. P.; Tamblyn, W. H.; Bagheri, V. J. Org. Chem. 1981, 46, 5094. (3) (a) Doyle, M. P.; Forbes, D. C.; Vasbinder, M. M.; Peterson, C. S. J. Am. Chem. Soc. 1998, 120, 7653. (b) Clark, J. S.; Fretwell, M.; Whitlock, G. A.; Burns, C. J.; Fox, D. N. A. Tetrahedron Lett. 1998, 39, 97. (c) Kitagawa, S.; Anada, M.; Kataoka, O.; Matsuno, K.; Umeda, C.; Watanabe, N.; Hashimoto, S.-i. J. Am. Chem. Soc. 1999, 121, 1417. (d) Hodgson, D. M.; Petroliagi, M. Tetrahedron: Asymmetry 2001, 12, 877. (e) Pierson, N.; Fernanadez-Garcia, C.; McKervey, M. A. Tetrahedron Lett. 1997, 38, 4705. (f) Hodgson, D. M.; Stupple, P. A.; Johnstone, C. Tetrahedron Lett. 1997, 38, 6471. (g) Kitagaki, S.; Yanamoto, Y.; Tsutsui, H.; Anada, M.; Nakajima, M.; Hashimoto, S. Tetrahedron Lett. 2001, 42, 6361. ‡
SCHEME 1
sulfur ylide has not been fully investigated. Uemura et al. in 1995 published first work on sulfur ylide [2,3]sigmatropic rearrangement in chiral Cu(OTf)/bis(oxazoline)-catalyzed reaction of trans-cinnamyl phenyl sulfide with ethyl diazoacetate, although the enantioselectivity was low (highest 22% ee).4 Later Katsuki et al. improved the enantioselectivity in similar reaction with chiral cobalt(III)-salen (up to 64% ee).5 McMillen et al. reported a detailed investigation on the effect of the sulfide structure on the enantioselectivity in Cu(OTf)/bis(oxazoline)-catalyzed reaction.6 More recently, Hashimoto et al. investigated the similar system with chiral Rh(II) complexes.7 In these previous investigations, ethyl diazoacetate or its derivatives were employed as carbenoids source. On the other hand, Davies and co-workers have recently published a series of papers on the exceptionally high enantioselectivity in C-H insertion and cyclopropanation of carbenoids derived from aryldiazoacetate.8 Herein we report our study on asymmetric [2,3]-sigmatropic rearrangement with aryldiazoacetates (Scheme 1). Results and Discussion First, the phenyldiazoacetate was employed as the substrate to optimize the reaction conditions. We have (4) Nishibayashi, Y.; Ohe, K.; Uemura, S. J. Chem. Soc., Chem. Commun. 1995, 1245. (5) Fukuda, T.; Irie, R.; Katsuki, T. Tetrahedron 1999, 55, 649. (6) McMillen, D. W.; Varga, N.; Reed, B. A.; King, C. J. Org. Chem. 2000, 65, 2532. (7) Kitagaki, S.; Yanamoto, Y.; Okubo, H.; Nakajima, M.; Hashimoto, S. Heterocycles 2001, 54, 623. (8) For a review, see: Davies, H. M. L.; Antoulinakis, E. G. J. Organomet. Chem. 2001, 617-618, 47.
10.1021/jo025687f CCC: $22.00 © 2002 American Chemical Society
Published on Web 07/03/2002
J. Org. Chem. 2002, 67, 5621-5625
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Zhang et al. CHART 1
examined two Rh(II) catalysts, Rh2(5S-MEPY)4, 4,9 and Rh2(S-BNP)4, 5,10 and five Cu(I) catalysts, 6,11 7a,12 7b,12 8,13 and 914 (Chart 1). These chiral catalysts have been demonstrated to be highly effective in asymmetric cyclopropanations or C-H insertions of carbenoids.1c,15 From the results summarized in Table 1, it is obvious that Rh(II) catalysts are less effective in the sulfur ylide [2,3]sigmatropic rearrangement compared with Cu(I) catalyst. Cu(MeCN)4PF6/bis(oxazoline) 7a,b or 9 gave the highest enantioselectivity, although the reaction was generally slower compared to the reaction with catalyst 6. The structure of the allylic aryl sulfide also has influence over the enantioselectivity. The best result was obtained with allylic 2-methylphenyl sulfide. The C2symmetrical 2,6-dimethylphenyl sulfide, which shown highest enantioselectivity (52% ee) in McMillen’s investigation,6 was not effective in our case (entries 9 and 13). The reaction with this sulfide is slow, and enantioselectivity was not significantly improved. The combination of allylic 2-methylphenyl sulfide, ethyl diazoacetate, and 7a in McMillen’s work gave an ee value 14%.6 On the other hand, solvent and temperature also influence the reaction. It was observed that benzene and toluene are better solvents for the enantioselectivity. Low temperature can slightly improve the ee values in general, but the reaction is markedly slowed at low temperature. From the above optimization experiments, we concluded that higher enantioselectivity could be obtained with chiral Cu(I) catalysts 7a or 9 in benzene or toluene, using allylic 2-methylphenyl sulfide. Thus, a number of aryldiazoacetates were examined with this condition, and the results are summarized in Table 2. From the data (9) Doyle, M. P.; Winchester, W. R.; Hoorn, J. A. A.; Lynch, V.; Simonsen, S. H.; Ghosh, R. J. Am. Chem. Soc. 1993, 115, 9968. (10) Pirrung, M. C.; Zhang, J. Tetrahedron Lett. 1992, 33, 5987. (11) Li, Z.; Conser, K. R.; Jacobsen, E. N. J. Am. Soc. Chem. 1993, 115, 5326. (12) Evans, D. A.; Woerpel, K. A.; Hinman, M. M.; Faul, M. M. J. Am. Chem. Soc. 1991, 113, 726. (13) Nishiyama, H.; Kondo, M.; Nakamura, T.; Itoh, K. Organometallics 1991, 10, 500. (14) Davies, I. W.; Senanayake, C. H.; Larsen, R. D.; Verhoeven, T. R.; Reider, P. J. Tetrahedron Lett. 1996, 37, 1725. (15) For recent reviews, see: (a) Ghosh, A. K.; Mathivanan, P.; Cappiello, J. Tetrahedron: Asymmetry 1998, 9, 1. (b) Doyle, M. P.; Protopopova, M. N. Tetrahedron 1998, 54, 7919.
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collected in the table, it is seen that there is no obvious dependence of the enantioselectivity on the electronic properties of the substituent in the diazo substrate phenyl ring,16 although the reaction of the diazo substrate bearing an electron-donating group (Ar ) p-MeOC6H4-) is much faster.17 Catalysts 7a and 9 gave comparable level of enantioselectivity, and moderate to good ee values can be obtained in general. The 78% ee for methyl 1-nathyldiazoacetate is the highest selectivity reported so far for this type of reaction (entry 13). The absolute configuration of the major product reaction with Cu(MeCN)4PF6/bis(oxazoline) 7a as the catalyst was determined to be R by comparing the product 3 (Ar ) Ar′ ) C6H5, 41 ee %, Table 1, entry 16) with a sample prepared by diastereoselective [2,3]-sigmatropic rearrangement (Scheme 2). The [2,3]-sigmatropic rearrangement of phenyldiazoacetamide 1018 with Cu(MeCN)4PF6 and allylic phenyl sulfide gave a mixture of diastereomers in a ratio of 75:25. Recrystallization of the mixture gave a pure major diastereomer 11. The stereochemistry of the newly formed chiral center was determined to be R by X-ray structure. The camphorsultam auxiliary was removed under basic condition, and subsequent treatment with diazomethane gave methyl ester 13, which was compared with 3 (Ar ) Ar′ ) C6H5) by chiral HPLC. A key issue in the catalytic asymmetric induction in [2,3]-sigmatropic rearrangement of sulfur ylide is whether the catalyst remains bound to the ylide during the subsequent reaction, or stereochemical outcome of the reaction is simply dictated by the stereochemistry of the initially formed ylide. Although there is evidence to show that in the reactions of oxonium3c,g and iodonium ylides3a the catalyst remains bound to the ylide during subsequent reactions, for sulfur ylide reaction the latter possibility cannot be ruled out in view of the fact that sulfonium ylides are expected to be considerably more stable, both in terms of their overall reactivity and their configurational stability. Katsuki and Hashimoto have demonstrated that the [2,3]-sigmatropic rearrangement of the sulfur ylide generated from allylic sulfides and diazoacetates in the presence of chiral Co(III) or Rh(II) catalysts gives the products in which the diastereoselectivities are independent of the nature of the catalyst. They thus conclude that the reaction proceeds through nonracemic free sulfur ylides detached from the chiral catalyst.5,7 However, Aggarwal reported the opposite observation in the reaction of allylic sulfur ylides derived from (trimethylsilyl)diazomethane, in which the diastereoselectivity was markedly influenced by the metal catalyst used, thus suggesting that a metal-associated ylide was involved in product-forming step.19 To gain some insights into the detailed mechanism of the reaction in this investigation, several experiments were carried out. First, a symmetrical diallyl sulfide 14 was employed in the reaction instead of allylic aryl sulfide. In this case, the initially formed ylide is achiral, as in the case of iodonium ylides;3a thus, any asymmetric (16) Dakin, L. A.; Schaus, S. E.; Jacobsen, E. N.; Panek, J. S. Tetrahedron Lett. 1998, 39, 8947. (17) Qu, Z.; Shi, W.; Wang, J. J. Org. Chem. 2001, 66, 8139. (18) Aller, E.; Brown, D. S.; Cox, G. G.; Miller, D. J.; Moody, C. J. J. Org. Chem. 1995, 60, 4449. (19) Aggarwal, V. K.; Ferrara, M.; Hainz, R.; Spey, S. E. Tetrahedron Lett. 1999, 40, 8923.
[2,3]-Sigmatropic Rearrangement of Sulfur Ylides TABLE 1. Effects of the Catalyst, Structure of Allyl Sulfide, Solvent, and Temperature on the Enantioselectivity entry
catala
sulfide: Ar′ b
solvent
temp (°C)
reacn time (h)
ee (%)c
yield (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
4 5 6 6 6 6 6 6 6 6 6 7a 7a 7a 7a 7a 7b 8 9
C6H5 C6H5 C6H5 2-CH3C6H4 2-CH3C6H4 2-CH3C6H4 C6H5 2-ClC6H4 2,6-(CH3)2C6H3 2-CH3C6H4 C6H5 2-ClC6H4 2,6-(CH3)2C6H3 2-CH3C6H4 2-CH3C6H4 C6H5 2-CH3C6H4 2-CH3C6H4 2-CH3C6H4
C6H6 C6H6 C6H6 C6H6 CH2Cl2 THF PhCH3 C6H6 C6H6 PhCH3 PhCH3 C6H6 C6H6 C6H6 PhCH3 C6H6 C6H6 C6H6 C6H6
25 25 25 25 25 25 25 25 25 0 0 25 25 25 -41 25 25 25 25
38 36 24 24 16 36 24 24 47 120 120 24 48 36 72 24 24 36 17
7 7 24 41 12 27 21 26 30 30 25 34 37 62 67 41 48 8 56
79 64 79 80 56 70 62 67 50
