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Enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinones to nitroalkenes catalyzed by binaphthyl-derived organocatalysts
 
 
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Enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinones to nitroalkenes catalyzed by binaphthyl-derived organocatalysts

Saet Byeol Woo and Dae Young Kim
Department of Chemistry, Soonchunhyang University, Asan, Chungnam, 336-745, Korea
Email of corresponding author Corresponding author email     
This article is part of the Thematic Series "Organocatalysis".
Guest Editor: B. List
Beilstein J. Org. Chem. 2012, 8, 699–704.
doi:10.3762/bjoc.8.78

Part of Thematic Series

Organocatalysis
 
 
 
 

Abstract

The highly enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinones to nitroalkenes, promoted by binaphthyl-modified chiral bifunctional organocatalysts is described. This reaction afforded the chiral functionalized naphthoquinones in high yields (81–95%) and excellent enantioselectivities (91–98% ee) under low catalyst loading (1 mol %).

Keywords: asymmetric catalysis; Michael addition; 1,4-naphthoquinones; nitroalkenes; organocatalysis

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Introduction

Quinone and naphthoquinone structures exist in a large number of natural products and biologically active molecules [1-4]. Many of these naturally occurring naphthoquinones and their synthetic analogues are important precursors for the synthesis of natural products and pharmaceuticals [5-9]. The stereoselective formation of C–C bonds is of great importance for the synthesis of enantiomerically pure, biologically active organic compounds [10,11]. It is widely recognized that the Michael addition is one of the most versatile and general methods for C–C bond formation in organic synthesis [12], and intensive research efforts have been directed toward the development of enantioselective catalytic protocols for this reaction [13-15]. The organocatalyst-mediated enantioselective conjugate addition reactions, which are both powerful and environmentally friendly, have been subjected to rigorous investigation in recent years [16-22]. The asymmetric Michael addition of various nucleophiles to nitroalkenes is of great interest, because the products obtained are versatile intermediates in organic synthesis [23-26]. Extensive studies have been devoted to the development of asymmetric conjugate additions of 1,3-dicarbonyl compounds to various Michael acceptors [27-33]. Recently, the groups of Du and Zhou reported a highly enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinones to nitroalkenes catalyzed by chiral, bifunctional tertiary-amine thioureas, thiophosphorodiamides, and squaramide-based organocatalysts [34-36].

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Findings

In the framework of our research program for the development of synthetic methods for the enantioselective construction of stereogenic carbon centers [37-42], we recently reported the enantioselective Michael addition of active methines to nitroalkenes [43,44]. Herein, we describe the direct enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinone with nitroalkenes, catalyzed by bifunctional organocatalysts (Figure 1) that bear both central and axial chiral elements [45-47].

[1860-5397-8-78-1]
Figure 1: Structures of chiral organocatalysts.

We initially investigated the reaction system with 2-hydroxy-1,4-naphthoquinone (1) and nitrostyrene 2a in the presence of 10 mol % of Takemoto's catalyst I in acetonitrile at room temperature, to determine the optimum reaction conditions for the catalytic, enantioselective Michael addition. This reaction exhibited good yield and high enantioselectivity (89% ee, Table 1, entry 1). In order to enhance the enantioselectivity, other bifunctional organocatalysts IIVIII were evaluated in the model reaction (Table 1, entries 2–8). The quinine-derived thiourea catalyst II was less effective (Table 1, entries 1 and 2), whereas the binaphthyl-modified, chiral, bifunctional organocatalysts IIIVIII, bearing both central and axial chiral elements, effectively promoted the addition reaction in high yield, with high enantioselectivity (78–97% ee, Table 1, entries 3–8). Catalyst III gave the desired product 3a with high enantioselectivity (97%, Table 1, entry 3), whereas the diastereomeric catalyst VII afforded product 3a in lower enantioselectivity (78% ee, Table 1, entry 7). These results demonstrate that the central and axial chiral elements in the chiral amine-thiourea catalyst III are matched, thus enhancing the stereochemical control, whereas in the diastereomeric catalyst VII this is not the case.

Table 1: Optimization of the reaction conditions.
[Graphic 1]
entry cat. solvent time (h) yield (%)a ee (%)b
1 I CH3CN 2 84 89
2 II CH3CN 2 87 77
3 III CH3CN 2 96 97
4 IV CH3CN 2 95 87
5 V CH3CN 2 93 81
6 VI CH3CN 2 90 93
7 VII CH3CN 2 85 78
8 VIII CH3CN 2 88 93
9 III toluene 4 75 95
10 III DCM 4 93 89
11 III THF 2 92 99
12 III Et2O 3 81 91
13 III H2O 17 89 19
14 III brine 17 86 37
15c III THF 2 90 98
16d III THF 2 90 99
17e III THF 2 89 99

Different solvents were then tested in the presence of 10 mol % of catalyst III together with 2-hydroxy-1,4-naphthoquinone (1) and nitrostyrene 2a in order to further improve the selectivity of the reaction. Aprotic solvents, such as acetonitrile, toluene, dichloromethane, THF, diethyl ether, were well tolerated in this conjugate addition without a significant decrease of enantioselectivities (89–99% ee, Table 1, entries 3 and 9–12). Remarkably, water and brine also afforded products in good yields; however, the selectivity dropped significantly (Table 1, entries 13 and 14). Among the solvents probed, the best results (92% yield and 99% ee) were achieved when the reaction was conducted in THF (Table 1, entry 11). The present catalytic system tolerates catalyst loading down to 5, 2.5, and 1 mol % without compromising the yield or enantioselectivity (Table 1, entries 11 and 15–17).

With the optimized reaction conditions in hand, the scope of the methodology was investigated in reactions with 2-hydroxy-1,4-naphthoquinone (1) and various nitroalkenes 2al in the presence of 1 mol % of catalyst III in THF at room temperature (Table 2). A range of electron-donating and electron-withdrawing substitutions on the β-aryl ring of the nitrostyrenes 2bh provided reaction products in high yields and excellent enantioselectivities. Heteroaryl- and naphthyl-substituted nitroalkenes 2i and 2j provided products with high selectivity (93–99% ee, Table 2, entries 9 and 10). The β-alkyl-substituted nitroalkene, 4-methyl-1-nitropent-1-ene (2k), was also an acceptable starting material and provided the corresponding Michael adducts in high yield and excellent enantioeselectivity (97% ee, Table 2, entry 11).

Table 2: Catalytic asymmetric Michael addition of 2-hydroxy-1,4-naphthoquinone 1 to nitroalkenes 2.
[Graphic 2]
entry 2, R time (h) yield (%)a ee (%)b
1 2a, Ph 2 3a, 89 99
2 2b, p-MeC6H4 2 3b, 93 95
3 2c, p-MeOC6H4 4 3c, 81 99
4 2d, p-FC6H4 3 3d, 95 95
5 2e, p-ClC6H4 3 3e, 90 91
6 2f, p-BrC6H4 3 3f, 95 95
7 2g, o-FC6H4 4 3g, 95 95
8 2h, o-BrC6H4 4 3h, 95 95
9 2i, 2-thienyl 5 3i, 93 93
10 2j, 2-naphthyl 5 3j, 93 99
11 2k, isobutyl 5 3k, 90 97

In conclusion, we have developed a highly efficient catalytic, enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinone to nitroalkenes using a binaphthyl-derived tertiary amine-thiourea organocatalyst. The various types of nitroalkylated naphthoquinone derivatives were obtained in good to high yields with excellent enantioselectivities (91–99% ee) for all the substrates examined in this work. We believe that this method should provide a practical entry for the preparation of chiral nitroalkylated naphthoquinone derivatives. Further details and application of this asymmetric Michael addition of 2-hydroxy-1,4-naphthoquinone nucleophiles will be presented in due course.

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Experimental

General procedure for the Michael addition of 2-hydroxy-1,4-naphthoquinone (1) with nitroalkenes 2: A mixture of 2-hydroxy-1,4-naphthoquinones (1, 34.8 mg, 0.2 mmol) and catalyst III (1.3 mg, 0.002 mmol) in THF (0.4 mL) was stirred at room temperature for 5 min. A solution of nitroalkene 2 (0.2 mmol) was added. The reaction mixture was stirred for 2–5 h at room temperature. After completion of the reaction, the resulting solution was concentrated in vacuo and the obtained residue was purified by flash chromatography (EtOAc–hexane) to afford the corresponding Michael adducts 3. Products 3 are known compounds, and their data were identical to those reported in the literature [34-36].

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Supporting Information

Supporting Information File 1: Characterization data of products 3.
Format: PDF   Size: 206.2 KB   Download

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Acknowledgements

This work was supported in part by the Soonchunhyang University Research Fund.

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References

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Top
Figure 1: Structures of chiral organocatalysts. Move  Close
Table 1: Optimization of the reaction conditions. Move  Close
[Graphic 1]
entry cat. solvent time (h) yield (%)a ee (%)b
1 I CH3CN 2 84 89
2 II CH3CN 2 87 77
3 III CH3CN 2 96 97
4 IV CH3CN 2 95 87
5 V CH3CN 2 93 81
6 VI CH3CN 2 90 93
7 VII CH3CN 2 85 78
8 VIII CH3CN 2 88 93
9 III toluene 4 75 95
10 III DCM 4 93 89
11 III THF 2 92 99
12 III Et2O 3 81 91
13 III H2O 17 89 19
14 III brine 17 86 37
15c III THF 2 90 98
16d III THF 2 90 99
17e III THF 2 89 99
Table 2: Catalytic asymmetric Michael addition of 2-hydroxy-1,4-naphthoquinone 1 to nitroalkenes 2. Move  Close
[Graphic 2]
entry 2, R time (h) yield (%)a ee (%)b
1 2a, Ph 2 3a, 89 99
2 2b, p-MeC6H4 2 3b, 93 95
3 2c, p-MeOC6H4 4 3c, 81 99
4 2d, p-FC6H4 3 3d, 95 95
5 2e, p-ClC6H4 3 3e, 90 91
6 2f, p-BrC6H4 3 3f, 95 95
7 2g, o-FC6H4 4 3g, 95 95
8 2h, o-BrC6H4 4 3h, 95 95
9 2i, 2-thienyl 5 3i, 93 93
10 2j, 2-naphthyl 5 3j, 93 99
11 2k, isobutyl 5 3k, 90 97
27. Hamashima, Y.; Hotta, D.; Sodeoka, M. J. Am. Chem. Soc. 2002, 124, 11240–11241. doi:10.1021/ja027075i
28. Wu, F.; Li, H.; Hong, R.; Deng, L. Angew. Chem., Int. Ed. 2006, 45, 947–950. doi:10.1002/anie.200502658
29. Kang, Y. K.; Kim, D. Y. Tetrahedron Lett. 2006, 47, 4565–4568. doi:10.1016/j.tetlet.2006.05.003
30. Bartoli, G.; Bosco, M.; Carlone, A.; Cavalli, A.; Locatelli, M.; Mazzanti, A.; Ricci, P.; Sambri, L.; Melchiorre, P. Angew. Chem., Int. Ed. 2006, 45, 4966–4970. doi:10.1002/anie.200600370
31. Rigby, C. L.; Dixon, D. J. Chem. Commun. 2008, 3798–3800. doi:10.1039/B805233F
32. Jung, S. H.; Kim, D. Y. Tetrahedron Lett. 2008, 49, 5527–5530. doi:10.1016/j.tetlet.2008.07.041
33. Capuzzi, M.; Perdicchia, D.; Jørgensen, K. A. Chem.–Eur. J. 2008, 14, 128–135. doi:10.1002/chem.200701317
Go to references 27-33
34. Zhou, W.-M.; Liu, H.; Du, D.-M. Org. Lett. 2008, 10, 2817–2820. doi:10.1021/ol800945e
35. Wu, R.; Chang, X.; Lu, A.; Wang, Y.; Wu, G.; Song, H.; Zhou, Z.; Tang, C. Chem. Commun. 2011, 47, 5034–5036. doi:10.1039/c1cc10797f
36. Yang, W.; Du, D.-M. Adv. Synth. Catal. 2011, 353, 1241–1246. doi:10.1002/adsc.201000981
Go to references 34-36
16. Connon, S. J. Angew. Chem., Int. Ed. 2006, 45, 3909–3912. doi:10.1002/anie.200600529
17. Tylor, M. S.; Jacobson, E. N. Angew. Chem., Int. Ed. 2006, 45, 1520–1543. doi:10.1002/anie.200503132
18. Doyle, A. G.; Jacobsen, E. N. Chem. Rev. 2007, 107, 5713–5743. doi:10.1021/cr068373r
19. Yu, X.; Wang, W. Chem.–Asian J. 2008, 3, 516–532. doi:10.1002/asia.200700415
20. Connon, S. J. Synlett 2009, 354–376. doi:10.1055/s-0028-1087557
21. Tsogoeva, S. B. Eur. J. Org. Chem. 2007, 1701–1716. doi:10.1002/ejoc.200600653
22. Almaşi, D.; Alonso, D. A.; Nájera, D. Tetrahedron: Asymmetry 2007, 18, 299–365. doi:10.1016/j.tetasy.2007.01.023
Go to references 16-22
23. Ono, N. The Nitro Group in Organic Synthesis; Wiley-VCH: New York, 2001.
24. Calderari, G.; Seebach, D. Helv. Chim. Acta 1985, 68, 1592–1604. doi:10.1002/hlca.19850680611
25. Ballini, R.; Petrini, M. Tetrahedron 2004, 60, 1017–1047. doi:10.1016/j.tet.2003.11.016
26. Czekelius, C.; Carreira, E. M. Angew. Chem., Int. Ed. 2005, 44, 612–615. doi:10.1002/anie.200461879
Go to references 23-26
12. Leonard, J. Contemp. Org. Synth. 1994, 1, 387–415. doi:10.1039/CO9940100387
Go to reference 12
13. Krause, N.; Hoffmann-Röder, A. Synthesis 2001, 171–196. doi:10.1055/s-2001-10803
14. Berner, O. M.; Tedeschi, L.; Enders, D. Eur. J. Org. Chem. 2002, 1877–1894. doi:10.1002/1099-0690(200206)2002:12<1877::AID-EJOC1877>3.0.CO;2-U
15. Christoffers, J.; Baro, A. Angew. Chem., Int. Ed. 2003, 42, 1688–1690. doi:10.1002/anie.200201614
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