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Cite this: DOI: 10.1039/c4cc09820j Received 9th December 2014, Accepted 2nd January 2015

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Chiral N,N 0 -dioxide–In(OTf)3-catalyzed asymmetric vinylogous Mukaiyama aldol reactions† Kai Fu,a Jianfeng Zheng,a Lili Lin,*a Xiaohua Liua and Xiaoming Feng*ab

DOI: 10.1039/c4cc09820j www.rsc.org/chemcomm

Chiral N,N 0 -dioxide–In(OTf)3 complexes were developed as efficient catalysts to catalyze the vinylogous Mukaiyama aldol reaction of the silyl dienol ester with aldehydes. The corresponding d-hydroxy-a,bunsaturated esters were obtained in up to 99% yield and 98% ee. Moreover, the obtained (R)-3v can be easily transformed to natural bioactive products.

The vinylogous Mukaiyama aldol reaction (VMAR),1 especially the g-selective aldol process (Fig. 1), belongs to one of the elemental transformations in organic chemistry. It provides an efficient assembly of d-hydroxy-a,b-unsaturated carbonyl compounds and related polyketide networks, which are attractive targets for biologydriven research.2 There have been considerable efforts towards the catalytic asymmetric VMAR of dioxanone-derived dienol ethers3 and simple ester-derived dienol ethers. For the more difficult enantioselective VMAR of simple ester-derived dienol ethers,4 chiral oxazaborolidinone,5 bis-phosphoramide6 and disulfonimide7 have been developed as nonmetallic catalysts to promote the g-adduct transformation. What’s more, Carreira,8 Campagne,9 Scetti,10 Paterson,11 Evans12 and others13 have also developed the chiral Cu and Ti complexes for the highly enantioselective g-addition of simple ester-derived dienol ethers to carbonyl compounds, and some have also demonstrated their application in bioactive natural product synthesis.8,9a,c,11,12,14

Fig. 1

Regioselectivity in the VMAR.

a

Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, P. R. China. E-mail: [email protected]; Fax: +86 28 85418249; Tel: +86 28 85418249 b Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, P. R. China † Electronic supplementary information (ESI) available: Additional experimental and spectroscopic data. See DOI: 10.1039/c4cc09820j

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Despite the enormous success, developing new catalysts for the VMAR of simple ester-derived dienol ethers is still desirable. In terms of the powerful metal complex catalysis, only copper and titanium complexes have been developed. So, developing other metal-based chiral catalysts is greatly meaningful. Indium, which is three times as abundant as silver, has been proved to be particularly effective at activating carbonyl groups.15 On the other hand, chiral N,N0 -dioxides, developed by our group, have been proved to be efficient in various asymmetric transformations by acting as ligands or organocatalysts.16,17 Herein, we describe a highly efficient asymmetric VMAR of the methyl crotonate-derived silyl dienol ester with aldehydes catalyzed by chiral N,N0 -dioxide–indium complexes to afford optically active g-products in high yield and ee. What’s the most important is that this method provides an efficient way to synthesize (R)-d-decalactone, (3R,5R)-valerolactone and (4R,6R,10R,12R)-verbalactone. Initial investigations with methyl crotonate-derived silyl dienol ester 1 and cinnamic aldehyde 2a revealed that the addition proceeded mainly in the g-position of the ketene acetal, providing d-hydroxy-a,bunsaturated ester 3a in the presence of the N,N0 -dioxide–metal complex in THF at 35 1C. When a series of metal salts complexed with L-pipecolic acid-derived N,N0 -dioxide L-PiPr2 were detected, compared to lanthanoids Sc(OTf)3 and Yb(OTf)3, In(OTf)3 gave higher yield (38%) and ee (72%) (Table 1, entries 1–3). The following investigation of the ligand structure revealed that both the framework and the steric hindrance of ortho-substituents on the aniline ring of the N,N 0 -dioxide affected the activity and enantioselectivity of the reaction. L-Ramipril-derived L-RiPr2 offered a similar yield (33%) and ee (69%) with L-PiPr2 (Table 1, entry 4). However, when L-proline-derived L-PrPr2 was applied, only a trace amount of the product was obtained and the ee of 3a was decreased to 55% (Table 1, entry 5), which might be caused by less flexibility and less steric hindrance of the five-membered ring of L-PrPr2. On the other hand, with a decrease in the steric hindrance of ortho-substituents on the aniline ring of the N,N 0 -dioxide from 2,6-diisopropyl to 2,6-diethyl and 2,6-dimethyl, the ee was decreased from 72% to 63% and 50%, respectively (Table 1, entries 3, 6 and 7). In order to further improve the reactivity and selectivity

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Table 1

ChemComm Table 2

Optimization of the reaction conditions

Substrate scope of the VMAR of silyl dienol ester 1 with aldehydes 2

Entrya

R

Product

Yieldb (%)

eec (%)

1 2 3 4

PhCHQCH2 2-MeOC6H4CHQCH2 4-ClC6H4CHQCH2 2-furylCHQCH2

3a 3b 3c 3d

91 85 64 70

92(S) 93 90 92

3e

99

92

3f 3g 3h 3i 3j 3k 3l 3m 3n 3o 3p

90 86 96 93 97 90 99 99 94 96 94

95(S) 86 94 92 95 95 96 87 94 95 96

3q

99

98

3r 3s 3t 3u 3v 3w 3x 3v 3v

92 99 96 88 60 65 45 64 65

93 94 92(S) 83 82(R) 89(S) 98(S) 80(S) 93(R)

5 a

Entry

Ligand

Metal

1 2 3 4 5 6 7 8 9 10d 11d 12d 13d,e

L-PiPr2

Sc(OTf)3 35 Yb(OTf)3 35 In(OTf)3 35 In(OTf)3 35 In(OTf)3 35 In(OTf)3 35 In(OTf)3 35 In(OTf)3 35 In(OTf)3 35 In(OTf)3 35 In(OTf)3 0 In(OTf)3 20 In(OTf)3 20

L-PiPr2 L-PiPr2 L-RiPr2 L-PrPr2 L-PiEt2 L-PiMe2 L-PiPr2 L-PiPr2 L-PiPr2 L-PiPr2 L-PiPr2 L-PiPr2

T (1C) Solvent THF THF THF THF THF THF THF EtOAc Ethyl caproate Ethyl caproate Ethyl caproate Ethyl caproate Ethyl caproate

b

c

Yield (%) ee (%) 19 27 38 33 Trace 38 16 48 58 76 84 89 91

37 59 72 69 55 63 50 75 76 76 81 89 92

a

Unless specified, all reactions were performed with the L-metal (10 mol%, 2 : 1), 1 (0.15 mmol), 2a (0.10 mmol) in THF (0.5 mL) at 35 1C for 24 h. b Isolated yields. c Determined by HPLC analysis. d The reaction time was 48 h. e 20 mol% of 5-methylsalicylic acid was added.

of the reaction, other reaction conditions were examined. It was found that the reaction proceeded better in ester solvents. In EtOAc, higher 48% yield and 75% ee were obtained (Table 1, entry 8). And in ethyl caproate, 58% yield and 76% ee were obtained (Table 1, entry 9). The yield could be increased to 76% when the reaction time was prolonged from 24 h to 48 h (Table 1, entry 10). What’s more, when the reaction temperature was lowered to 0 1C, the yield was increased to 84% and the ee was improved to 81% (Table 1, entry 11). By further lowering the temperature to 20 1C, the yield and ee of 3a were both improved to 89% (Table 1, entry 12). Finally, the yield and ee of 3a were further improved to 91% and 92%, respectively, by adding 20 mol% of 5-methylsalicylic acid to the system (Table 1, entry 13). With the optimized reaction conditions in hand (Table 1, entry 13), the vinylogous Mukaiyama aldol reaction of 1 with various aldehydes 2 was explored (Table 2). For substituted cinnamaldehydes, the electron-donating or electronwithdrawing substituted phenyl group and the heterocyclic furyl group on the b-position didn’t affect the enantioselectivity (90–93% ee) (Table 2, entries 1–4). Notably, a-bromo substituted cinnamic aldehyde 2e also reacted well, giving 3e in quantitative yield with 92% ee (Table 2, entry 5). Aromatic aldehydes with electron-withdrawing or electron-donating substituents at different positions on the phenyl ring caused the reaction to proceed well, providing the corresponding products in 86–99% yields with 86–98% ee (Table 2, entries 6–18). Generally, ortho-substituted aldehydes gave a little lower yields and ee values than meta- and para-substituted ones (Table 2, entry 7 vs. entry 8; entry 9 vs. entries 10 and 11; entry 13 vs. entries 14

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6 7 8 9 10 11 12 13 14 15 16

Ph 2-MeC6H4 3-MeC6H4 2-MeOC6H4 3-MeOC6H4 4-MeOC6H4 3-PhOC6H4 2-FC6H4 3-FC6H4 4-FC6H4 3-BrC6H4

17 18 19 20 21 22 23 24 25d 26e

3,4-Cl2C6H3 1-Naphthyl 2-Furyl n-Propyl n-Pentyl i-Propyl t-Butyl n-Pentyl n-Pentyl

a Unless specified, all reactions were carried out with 10 mol% L-PiPr2/ In(OTf)3 (2 : 1), 1 (0.15 mmol), 2 (0.10 mmol) and 20 mol% of 5-methylsalicylic acid in ethyl caproate (0.5 mL) at 20 1C for 48 h. b Isolated yields. c Determined by HPLC analysis. d D-pipecolic acid-derived L-PiPr2 was used as the ligand. e L-RiPr2 was used as the ligand.

and 15), which might be caused by the steric hindrance of the orthosubstituents with the catalyst. Ring-condensed 1-naphthaldehyde and heteroaromatic 2-furaldehyde were also suitable, affording the corresponding product 3s in 99% yield with 94% ee and 3t in 96% yield with 92% ee (Table 2, entries 19 and 20). It is worth pointing out that aliphatic aldehydes were also tolerant (Table 2, entries 21– 24). Linear n-butanal and n-hexanal gave the corresponding 3u in 88% yield with 83% ee and (R)-3v in 60% yield with 82% ee (Table 2, entries 21 and 22). As expected, a-branched aliphatic aldehydes were beneficial for the enantioselectivity. Isobutyraldehyde could give 3w with 89% ee and pivaldehyde gave product 3x with 98% ee, albeit with 45% yield (Table 2, entries 23 and 24). What’s more, (S)-3v could be obtained in 64% yield with 80% ee value when D-pipecolic acidderived L-PiPr2 was used as the ligand (Table 2, entry 25 vs. entry 22), which indicated that the configuration of the product was determined by the framework of the ligand. Besides, when L-ramipril-derived L-RiPr2 was used as the ligand, the ee of 3v could be further improved to 93% (Table 2, entry 26). The absolute configuration of products 3a, 3f, 3t, 3w and 3x were determined to be (S)5a and that of product 3v was determined to be (R)18d by comparison of the optical rotation with that reported in the literature.

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4 5 6

Scheme 1

Gram-scale synthesis and synthetic utility.

7 8

To show the prospect of the methodology in synthesis, a gram-scale synthesis of (R)-3v was carried out. By treatment of 5 mmol of 2v and 7.5 mmol of 1 in the presence of the L-RiPr2– In(OTf)3 complex for 48 h, 0.79 g (79% yield) of the isolated (R)-3v with 94% ee was obtained (Scheme 1). What’s more, the highly enantiomerically enriched (R)-3v can be easily converted into (R)-d-decalactone, which has a specific odour and is an important constituent of cheese and butter, by simple reduction of the carbon–carbon double bond with 5% Pd/C in CH3OH and the following cyclization with p-TSA in CH2Cl2. Besides, (R)-3v is also a good intermediate to synthesize (3R,5R)-valerolactone 7v, which is present in mevinolin and compactin and is responsible for inhibition of cholesterol-induced accumulation of fat, as well as (4R,6R,10R,12R)-verbalactone 8v, which shows a strong antibacterial activity against three strains of Gram-positive and five strains of Gram-negative bacteria (Scheme 1).18 In summary, we have developed efficient chiral N,N0 -dioxide– In(III) complexes for the highly enantioselective vinylogous Mukaiyama aldol reaction of the methyl crotonate-derived silyl dienol ester with aldehydes. The substrate scope was remarkably wide, affording the corresponding products in up to 99% yield and with up to 98% ee. The utility of the methodology is highlighted by the gram-scale synthesis and the useful conversions. Further studies of carbonyl compounds with other dienes by the chiral N,N0 -dioxide–metal complex system are ongoing. We appreciate the National Basic Research Program of China (973 Program: No. 2011CB808600) and the National Natural Science Foundation of China (No. 21372162 and 21432006) for financial support.

9

10

11 12

13

14

15

16 17

Notes and references 1 (a) G. Casiraghi, F. Zanardi, G. Appendino and G. Rassu, Chem. Rev., 2000, 100, 1929; (b) S. E. Denmark, J. R. Heemstra, Jr. and G. L. Beutner, Angew. Chem., Int. Ed., 2005, 44, 4682; (c) M. Kalesse, Top. Curr. Chem., 2005, 244, 43; (d) S. V. Pansare and E. K. Paul, Chem. – Eur. J., 2011, 17, 8770; (e) G. Casiraghi, L. Battistini, C. Curti, G. Rassu and F. Zanardi, Chem. Rev., 2011, 111, 3076; ( f ) S. B. J. Kan, K. K.-H. Ng and I. Paterson, Angew.

This journal is © The Royal Society of Chemistry 2015

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Chem., Int. Ed., 2013, 52, 9097; (g) M. Kalesse, M. Cordes, G. Symkenberg and H.-H. Lu, Nat. Prod. Rep., 2014, 31, 563; (h) Enantioselective vinylogous Reformatsky-aldol reaction, see: A. Hassan, J. R. Zbieg and M. J. Krische, Angew. Chem., Int. Ed., 2011, 50, 3493. (a) J. Staunton and K. J. Weissman, Nat. Prod. Rep., 2001, 18, 380; (b) B. Schetter and R. Mahrwald, Angew. Chem., Int. Ed., 2006, 45, 7506. (a) Y. Shimada, Y. Matsuoka, R. Irie and T. Katsuki, Synlett, 2004, 57; (b) J. C.-D. Le and B. L. Pagenkopf, Org. Lett., 2004, 6, 4097; (c) V. B. Gondi, M. Gravel and V. H. Rawal, Org. Lett., 2005, 7, 5657. S. E. Denmark and G. L. Beutner, J. Am. Chem. Soc., 2003, 125, 7800. (a) S. Simsek, M. Horzella and M. Kalesse, Org. Lett., 2007, 9, 5637; (b) S. Simsek and M. Kalesse, Tetrahedron Lett., 2009, 50, 3485; (c) M. T. Gieseler and M. Kalesse, Org. Lett., 2014, 16, 548. (a) S. E. Denmark, G. L. Beutner, T. Wynn and M. D. Eastgate, J. Am. Chem. Soc., 2005, 127, 3774; (b) S. E. Denmark and S. Fujimori, J. Am. Chem. Soc., 2005, 127, 8971; (c) S. E. Denmark and J. R. Heemstra, Jr., J. Am. Chem. Soc., 2006, 128, 1038; (d) L. J. Fang, H. R. Xue and J. Yang, Org. Lett., 2008, 10, 4645; (e) G. Rassu, V. Zambrano, R. Tanca, A. Sartori, L. Battistini, F. Zanardi, C. Curti and G. Casiraghi, Eur. J. Org. Chem., 2012, 466. L. Ratjen, P. Garcı´a-Garcı´a, F. Lay, M. E. Beck and B. List, Angew. Chem., Int. Ed., 2011, 50, 754. (a) Y. Kim, R. A. Singer and E. M. Carreira, Angew. Chem., Int. Ed., 1998, 37, 1261; (b) A. Fettes and E. M. Carreira, J. Org. Chem., 2003, 68, 9274. (a) C. J. Brennan and J.-M. Campagne, Tetrahedron Lett., 2001, 42, 5195; (b) G. Bluet and J.-M. Campagne, J. Org. Chem., 2001, ´n-Tejeda and J.-M. Campagne, Org. 66, 4293; (c) G. Bluet, B. Baza ´n-Tejeda and J.-M. Lett., 2001, 3, 3807; (d) X. Moreau, B. Baza Campagne, J. Am. Chem. Soc., 2005, 127, 7288. (a) M. D. Rosa, A. Soriente and A. Scettri, Tetrahedron: Asymmetry, 2000, 11, 3187; (b) A. Soriente, M. D. Rosa, M. Stanzione, R. Villano and A. Scettri, Tetrahedron: Asymmetry, 2001, 12, 959; (c) M. D. Rosa, M. R. Acocella, M. F. Rega and A. Scettri, Tetrahedron: Asymmetry, 2004, 15, 3029. (a) I. Paterson, G. J. Florence, A. C. Heimann and A. C. Mackay, Angew. Chem., Int. Ed., 2005, 44, 1130; (b) I. Paterson, A. D. Findlay and G. J. Florence, Org. Lett., 2006, 8, 2131. (a) D. A. Evans, E. Hu, J. D. Burch and G. Jaeschke, J. Am. Chem. Soc., 2002, 124, 5654; (b) D. A. Evans, P. Nagorny, D. J. Reynolds and K. J. McRae, Angew. Chem., Int. Ed., 2007, 46, 541; (c) D. A. Evans, J. D. Burch, E. Hu and G. Jaeschke, Tetrahedron, 2008, 64, 4671. ´my, M. Langner and C. Bolm, Org. Lett., 2006, 8, 1209; (a) P. Re (b) L. V. Heumann and G. E. Keck, Org. Lett., 2007, 9, 4275; (c) G. W. Wang, B. M. Wang, S. Qi, J. F. Zhao, Y. H. Zhou and J. P. Qu, Org. Lett., 2012, 14, 2734. (a) D. L. Aubele, S. Wan and P. E. Floreancig, Angew. Chem., Int. Ed., 2005, 44, 3485; (b) D. W. Custar, T. P. Zabawa and K. A. Scheidt, J. Am. Chem. Soc., 2008, 130, 804; (c) K. Fujita, R. Matsui, T. Suzuki and S. Kobayashi, Angew. Chem., Int. Ed., 2012, 51, 7271; (d) G. J. Florence and J. Wlochal, Chem. – Eur. J., 2012, 18, 14250; (e) H. Fuwa, T. Muto, K. Sekine and M. Sasaki, Chem. – Eur. J., 2014, 20, 1848. Selected examples, see: (a) J. Lu, M.-L. Hong, S.-J. Ji, Y.-C. Teo and T.-P. Loh, Chem. Commun., 2005, 4217; (b) T. Fujimoto, K. Endo, H. Tsuji, M. Nakamura and E. Nakamura, J. Am. Chem. Soc., 2008, 130, 4492; (c) U. Schneider, M. Ueno and S. Kobayashi, J. Am. Chem. Soc., 2008, 130, 13824; (d) Z. P. Yu, X. H. Liu, Z. H. Dong, M. S. Xie and X. M. Feng, Angew. Chem., Int. Ed., 2008, 47, 1308; (e) L. L. Lin, Y. L. Kuang, X. H. Liu and X. M. Feng, Org. Lett., 2011, 13, 3868. X. H. Liu, L. L. Lin and X. M. Feng, Acc. Chem. Res., 2011, 44, 574. For recent examples of N,N0 -dioxide–metal complexes, see: (a) K. Shen, X. H. Liu, L. L. Lin and X. M. Feng, Chem. Sci., 2012, 3, 327; (b) K. Zheng, L. L. Lin and X. M. Feng, Acta Chim. Sin., 2012, 70, 1785; (c) Z. Wang, Z. L. Chen, S. Bai, W. Li, X. H. Liu, L. L. Lin and X. M. Feng, Angew. Chem., Int. Ed., 2012, 51, 2776; (d) L. Zhou, X. H. Liu, J. Ji, Y. H. Zhang, X. L. Hu, L. L. Lin and X. M. Feng, J. Am. Chem. Soc., 2012, 134, 17023; (e) J. Guo, S. X. Dong, Y. L. Zhang, Y. L. Kuang, X. H. Liu, L. L. Lin and X. M. Feng, Angew. Chem., Int. Ed., 2013, 52, 10245; ( f ) X. H. Liu, L. L. Lin and X. M. Feng, Org. Chem. Front., 2014, 1, 298. (a) S. Gogoi, N. C. Barua and B. Kalita, Tetrahedron Lett., 2004, 45, 5577; (b) A. Garg and V. K. Singh, Tetrahedron, 2009, 65, 8677; (c) A. Venkatesham, R. S. Rao and K. Nagaiah, Tetrahedron: Asymmetry, 2012, 23, 381; (d) I. V. Mineeva, Russ. J. Org. Chem., 2013, 49, 979.

Chem. Commun.

Chiral N,N'-dioxide-In(OTf)3-catalyzed asymmetric vinylogous Mukaiyama aldol reactions.

Chiral N,N'-dioxide-In(OTf)3 complexes were developed as efficient catalysts to catalyze the vinylogous Mukaiyama aldol reaction of the silyl dienol e...
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