Chinese Chemical Letters  2016, Vol. 27 Issue (7): 1032-1035   PDF    
Intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane induced by N-heterocyclic carbene and thiourea
Cheng Qing-Fanga, Wang Jing-Wenb, Wang Qi-Faa, Liu Zhoub     
a Jiangsu Key Laboratory of Marine Biotechnology, Huaihai Institute of Technology, Lianyungang 222005, China ;
b School of Chemical Engineering, Huaihai Institute of Technology, Lianyungang 222005, China
Abstract: Intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane catalyzed by thiazolium A has been developed. The reaction rate and efficiency are profoundly impacted by the presence of thiourea B. The reaction affords moderate to good yields of the Stetter product. Some factors influencing yield were discussed.
Key words: Intermolecular Stetter reaction     N-heterocyclic carbene     Thiourea     Thiazolium     Nitroalkene     β-Nitro ketone    
1. Introduction

The Stetter reaction, reported by Dr. Hermann Stetter [1] in 1973, is a reaction used in organic chemistry to form carbon- carbon bonds through a 1, 4-addition reaction utilizing a nucleophilic catalyst [2]. Traditional Stetter reactions can only be utilized if N-heterocyclic carbenes (NHCs) are used as organocatalysts. Stetter reactions are quite versatile, working on a wide variety of substrates: aromatic aldehydes, heteroaromatic aldehydes, and benzoins can all be used as acyl anion precursors. In addition, a, bunsaturated esters, ketones, nitriles, nitros, and aldehydes are all appropriate Michael acceptors [3-15]. Besides intramolecular Stetter reactions [4-9], many intermolecular Stetter reactions have been demonstrated [10-17]. Among different acceptors in intermolecular Stetter reactions, nitroalkenes remain limited in their successful application. To the best of our knowledge, only enals, heteroaromatic aldehdyes, and the fluoride promoted carbonyl anion have been successfully used in the intermolecular Stetter reaction with nitroalkenes [15-17]. For the Stetter reaction of aromatic heterocyclic aldehydes and nitroolefins, the β-heteroatom in heterocyclic aldehydes is required for high yield [16]. So far, the direct intermolecular Stetter reaction of aromatic aldehydes with nitroolefins has not been reported. In general, conjugate additions to nitroolefins afford highly useful b-nitro ketone derivatives with diverse functionality for organic synthesis. Thiazolium A was firstly used as a ligand in olefin metathesis [18]. In this communication, we used the thiazolium A and thiourea B (Fig. 1) combination to catalyze the direct intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane to synthesize highly useful b-nitro ketone derivatives.

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Figure 1. The structures of thiazolium A and thiourea B.

2. Experimental

General procedure for the intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane: In an oven dried vial, an aromatic aldehyde (0.5 mmol), (E)-(2-nitrovinyl) cyclohexane (0.6 mmol), thiourea (0.1 mmol), thiazolium A (0.05 mmol), Cs2CO3 (0.1 mmol), and toluene (2 mL) were added under N2. The resulting solution was stirred at 5 ℃ until the reaction was complete, as indicated by TLC. The mixture was filtered over a short pad of silica gel, then evaporated in vacuo. The residue was purified by a column silica gel chromatography (petroleum ether/acetate, v/v = 19: 1) to afford b-nitro ketones 3a-3k.

1-(4-Chlorophenyl)-2-cyclohexyl-3-nitropropan-1-one 3a was obtained in 75.4% yield. IR (KBr, cm-1): 2939, 1719, 1542, 1369. 1H NMR (CDCl3): δ 7.87 (d, 2H, J = 8.6 Hz, ArH), 7.48 (d, 2H, J = 8.6 Hz, ArH), 5.06 (dd, 1H, J = 14.7, 10.4 Hz, CHNO2), 4.50 (dd, 1H, J = 14.7, 3.4 Hz, CHNO2), 4.17-4.07 (m, 1H, CHCO), 1.81-1.53 (m, 6H, cyclohexyl-H), 1.25-1.04 (m, 4H, cyclohexyl-H), 0.97-0.88 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 198.97, 140.14, 134.99, 130.06, 129.21, 73.67, 48.91, 39.28, 31.78, 29.83, 26.64, 26.19, 25.77. Anal. Calcd. for C15H18ClNO3: C, 60.91; H, 6.13; N, 4.74. Found: C, 60.98; H, 6.07; N, 4.71.

1-(4-Nitrophenyl)-2-cyclohexyl-3-nitropropan-1-one 3b was obtained in 57.4% yield. IR (KBr, cm-1): 2947, 1755, 1713, 1632, 1561, 1522, 1372. 1H NMR (CDCl3): δ 8.48 (d, 2H, J = 8.7 Hz, ArH), 8.07 (d, 2H, J = 8.7 Hz, ArH), 5.15-5.04 (m, 1H, CHNO2), 4.55 (dd, 1H, J = 14.7, 3.4 Hz, CHNO2), 4.21-4.11 (m, 1H, CHCO), 1.75-1.61 (m, 6H, cyclohexyl-H), 1.22-1.05 (m, 4H, cyclohexyl-H), 0.98-0.77 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 198.78, 151.15, 140.05, 130.49, 124.33, 73.66, 48.89, 39.27, 31.98, 29.74, 26.26, 26.18, 25.71. Anal. Calcd. for C15H18N2O5: C, 58.81; H, 5.92; N, 9.15. Found: C, 58.76; H, 5.98; N, 9.11.

1-(4-Trifluoromethylphenyl)-2-cyclohexyl-3-nitropropan-1- one3cwasobtained in 78.6%yield. IR (KBr, cm-1):2927, 1733, 1529, 1354. 1H NMR (CDCl3): δ 8.11 (d, 2H, J = 8.1 Hz, ArH), 7.76 (d, 2H, J = 8.1 Hz, ArH), 5.08 (dd, 1H, J = 14.8, 10.6 Hz, CHNO2), 4.54 (dd, 1H, J = 14.8, 3.3 Hz, CHNO2), 4.21 (ddd, 1H, J = 10.5, 5.4, 3.3 Hz, CHCO), 1.74-1.55 (m, 6H, cyclohexyl-H), 1.23-1.09 (m, 4H, cyclohexyl-H), 0.97-0.82 (m, 1H, cyclohexyl-H). 13CNMR(CDCl3): δ 198.93, 139.41, 134.81, 128.78, 128.68, 125.87, 73.61, 49.30, 39.18, 31.61, 29.76, 26.29, 26.15, 25.78. Anal. Calcd. for C16H18NO3F3: C, 58.35; H, 5.51; N, 4.25. Found: C, 58.41; H, 5.44; N, 4.31.

1-(4-Me(1a)e 3d was obtained in 59.1% yield. IR (KBr, cm-1): 3031, 2911, 1746, 1536, 1331. 1H NMR (CDCl3): δ 7.73 (d, 2H, J = 8.1 Hz, ArH), 7.27 (d, 2H, J = 7.8 Hz, ArH), 5.05 (dd, 1H, J = 14.8, 10.6 Hz, CHNO2), 4.51 (dd, 1H, J = 14.9, 3.4 Hz, CHNO2), 4.14-4.06 (m, 1H, CHCO), 2.23 (s, 3H, CH3), 1.74-1.56 (m, 6H, cyclohexyl-H), 1.21-1.04 (m, 4H, cyclohexyl-H), 0.95-0.78 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 198.88, 145.89, 134.79, 130.02, 129.74, 73.61, 49.05, 39.14, 31.76, 30.01, 26.68, 26.36, 26.09, 21.95. Anal. Calcd. for C16H21NO3: C, 69.79; H, 7.69; N, 5.09. Found: C, 69.71; H, 7.63; N, 5.04.

1-(4-Methyoxyphenyl)-2-cyclohexyl-3-nitropropan-1-one 3e was obtained in 56.4% yield. IR (KBr, cm-1): 3043, 2936, 1755, 1576, 1531, 1347, 1238. 1H NMR (CDCl3): δ 8.15-8.05 (m, 2H, ArH), 7.27 (d, 2H, J = 8.7 Hz, ArH), 5.13-5.03 (m, 1H, CHNO2), 4.53 (dd, 1H, J = 14.7, 3.4 Hz, CHNO2), 4.23-4.11 (m, 1H, CHCO), 3.94 (s, 3H, CH3), 1.74-1.58 (m, 6H, cyclohexyl-H), 1.23-1.05 (m, 4H, cyclohexyl-H), 0.99-0.83 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): d 199.88, 165.40, 133.75, 130.83, 114.30, 73.84, 55.16, 49.11, 39.27, 32.49, 30.03, 26.72, 26.25, 25.89. Anal. Calcd. for C16H21NO4: C, 65.96; H, 7.26; N, 4.81. Found: C, 66.01; H, 7.29; N, 4.87.

1-(3-Chlorophenyl)-2-cyclohexyl-3-nitropropan-1-one 3f was obtained in 63.7% yield. IR (KBr, cm-1): 2931, 1735, 1561, 1372. 1H NMR (CDCl3): δ 8.11 (t, 1H, J = 1.8 Hz, ArH), 7.82 (dt, 1H, J = 7.8, 1.4 Hz, ArH), 7.71 (ddd, 1H, J = 8.0, 2.1, 1.0 Hz, ArH), 7.35 (t, 1H, J = 7.9 Hz, ArH), 5.07 (dd, 1H, J = 14.7, 10.5 Hz, CHNO2), 4.53 (dd, 1H, J = 14.8, 3.4 Hz, CHNO2), 4.10-4.05 (m, 1H, CHCO), 1.75-1.54 (m, 6H, cyclohexyl-H), 1.16-1.03 (m, 4H, cyclohexyl-H), 0.93-0.79 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 198.26, 139.64, 136.42, 131.45, 130.32, 126.95, 123.27, 73.81, 49.12, 39.30, 31.72, 29.63, 26.32, 26.18, 25.91. Anal. Calcd. for C15H18ClNO3: C, 60.91; H, 6.13; N, 4.74. Found: C, 60.87; H, 6.05; N, 4.69.

1-(3-Methyoxyphenyl)-2-cyclohexyl-3-nitropropan-1-one 3g was obtained in 67.4% yield. IR (KBr, cm-1): 3036, 2947, 1749, 1589, 1547, 1336, 1243. 1H NMR (CDCl3): δ 7.58 (dt, 1H, J = 7.6, 1.2 Hz, ArH), 7.40 (t, 1H, J = 7.9 Hz, ArH), 7.34 (dd, 2H, J = 2.6, 1.5 Hz, ArH), 7.14 (ddd, 1H, J = 8.2, 2.6, 1.0 Hz, ArH), 5.07 (dd, 1H, J = 14.6, 10.3 Hz, CHNO2), 4.53 (dd, 1H, J = 14.6, 3.5 Hz, CHNO2), 4.23-4.11(m, 1H, CHCO), 3.85 (s, 3H, OCH3), 1.77-1.53 (m, 6H, cyclohexyl-H), 1.24-1.05 (m, 4H, cyclohexyl-H), 0.97 (dt, J = 12.4, 3.4 Hz, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 199.41, 159.99, 137.94, 129.81, 121.64, 119.93, 113.45, 73.87, 55.65, 49.09, 38.91, 31.69, 29.78, 26.43, 26.22, 25.89. Anal. Calcd. for C16H21NO4: C, 65.96; H, 7.26; N, 4.81. Found: C, 66.05; H, 7.23; N, 4.76.

1-(2-Chlorophenyl)-2-cyclohexyl-3-nitropropan-1-one 3h was obtained in 51.8% yield. IR (KBr, cm-1): 2963, 1764, 1577, 1362. 1H NMR (CDCl3): δ 7.70 (dd, 1H, J = 7.7, 2.0 Hz, ArH), 7.31 (td, 1H, J = 7.7, 1.9 Hz, ArH), 7.24-7.20 (m, 1H, ArH), 7.18 (t, 1H, J = 7.6 Hz, ArH), 5.09 (dd, 1H, J = 14.7, 10.4 Hz, CHNO2), 4.53 (dd, 1H, J = 14.7, 3.4 Hz, CHNO2), 4.21-4.07 (m, 1H, CHCO), 1.78-1.45 (m, 6H, cyclohexyl-H), 1.25-1.03 (m, 4H, cyclohexyl-H), 0.93-0.81 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 198.75, 138.91, 135.83, 134.52, 131.59, 129.77, 127.33, 73.74, 49.17, 39.86, 31.32, 29.96, 26.44, 26.20, 25.79. Anal. Calcd. for C15H18ClNO3: C, 60.91; H, 6.13; N, 4.74. Found: C, 60.87; H, 6.09; N, 4.69.

1-(2-Methyoxyphenyl)-2-cyclohexyl-3-nitropropan-1-one 3i was obtained in 43.2% yield. IR (KBr, cm-1): 2976, 1758, 1583, 1372. 1H NMR (CDCl3): δ 7.79 (dd, 1H, J = 7.9, 2.2 Hz, ArH), 7.58 (td, 1H, J = 7.9, 2.1 Hz, ArH), 7.17-6.92 (m, 2H, ArH), 5.10 (dd, 1H, J = 14.8, 10.6 Hz, CHNO2), 4.53 (dd, 1H, J = 14.8, 3.4 Hz, CHNO2), 4.19-4.07 (m, 1H, CHCO), 3.83 (s, 3H, OCH3), 1.77-1.53 (m, 6H, cyclohexyl-H), 1.24-1.06 (m, 4H, cyclohexyl-H), 0.98-0.82 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 199.85, 158.43, 138.69, 129.84, 121.65, 120.11, 114.63, 73.89, 55.89, 48.91, 39.13, 31.65, 29.87, 26.18, 26.04, 25.75. Anal. Calcd. for C16H21NO4: C, 65.96; H, 7.26; N, 4.81. Found: C, 65.91; H, 7.21; N, 4.77.

1-(3, 4-Dichlorophenyl)-2-cyclohexyl-3-nitropropan-1-one 3j was obtained in 86.5% yield. IR (KBr, cm-1): 2976, 1758, 1583, 1372. 1H NMR (CDCl3): δ 8.05 (d, 1H, J = 2.1 Hz, ArH), 7.80 (dd, 1H, J = 2.1, 2.3 Hz, ArH), 7.58 (d, 1H, J = 8.3 1 Hz, ArH), 5.06 (dd, 1H, J = 14.8, 10.6 Hz, CHNO2), 4.52 (dd, 1H, J = 14.9, 3.4 Hz, CHNO2), 4.11-3.96 (m, 1H, CHCO), 1.76-1.53 (m, 6H, cyclohexyl-H), 1.27- 1.05 (m, 4H, cyclohexyl-H), 0.98-0.79 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 197.96, 138.29, 136.39, 133.67, 130.99, 130.40, 127.53, 73.76, 49.04, 39.25, 31.47, 29.82, 26.78, 26.16, 25.76. Anal. Calcd. for C15H17Cl2NO3: C, 54.55; H, 5.19; N, 4.24. Found: C, 54.62; H, 5.23; N, 4.18.

1-(2-Bromo-5-fluorophenyl)-2-cyclohexyl-3-nitropropan-1- one 3k was obtained in 35.6% yield. IR (KBr, cm-1): 2976, 1758, 1583, 1372. 1H NMR (CDCl3): δ 7.67-7.51 (m, 2H, ArH), 7.18 (ddd, 1H, J = 8.7, 7.4, 3.2 Hz, ArH), 5.07 (dd, 1H, J = 14.9, 10.5 Hz, CHNO2), 4.51 (dd, 1H, J = 14.9, 3.5 Hz, CHNO2), 4.15-4.04 (m, 1H, CHCO), 1.75-1.58 (m, 6H, cyclohexyl-H), 1.19-0.99 (m, 4H, cyclohexyl-H), 0.87-0.76 (m, 1H, cyclohexyl-H). 13C NMR (CDCl3): δ 199.23, 135.81, 135.32, 124.71, 123.27, 116.47, 116.24, 73.83, 48.89, 38.88, 31.84, 29.93, 26.71, 26.19, 25.83. Anal. Calcd. for C15H17FBrNO3: C, 50.29; H, 4.78; N, 3.91. Found: C, 50.26; H, 4.72; N, 3.96.

3. Results and discussion

The direct intermolecular Stetter reaction of 4-chlorobenzaldehyde (1a) with (E)-(2-nitrovinyl)cyclohexane (2) catalyzed by thiazolium A was selected as a model reaction and performed under different conditions (Scheme 1).

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Scheme. 1. The model intermolecular Stetter reaction

As shown in Table 1, when the model reaction was only conducted by thiazolium A, a trace amount of Stetter product was obtained from the model reaction (Table 1, entry 1) . Thioureas, bearing hydrogen bonding donors, have previously been used in a diverse range of reactions, with high yields attributed to their strong activation of carbonyl or nitro groups through efficient hydro-bonding interactions [19-21], which led us to investigate them as potential additives in the model reaction. Among those surveyed, thiourea B was the most effective at increasing catalyst turnover (Table 1, entries 5, 8-10) . The effect of mole ratio of thiourea B was also investigated, and an addition of 5% equivalent of thiourea B to the reaction mixture afforded obvious improvement (Table 1, entry 2) , addition of 20% equivalent of thiourea B shows a remarkable increase in isolated yield.

Table 1
The influence of thiourea additives on the model reactiona

In the presence of thiourea B, the thiazolium A is highly effective. As shown in Table 2, the model reaction could be carried out with 2 mol% catalyst loading, affording 37.6% yield of Stetter product (Table 2, entry 1) , and with 10 mol% catalyst loading afforded 75.4% yield of Stetter product (Table 2, entry 4) . The influence of reaction temperature was also investigated, a lower yield of 39.6% can be obtained at -10 ℃ as shown in Table 2, however, a lower yield of 43.4% was also obtained upon increasing the temperature to 15 ℃ for the model reaction (Table 2, entries 6, 10) , this may be due to the low catalytic activity of thiazolium A at lower temperature and the instability of carbene intermediates at higher temperature. According to these data, the preferable amount of thiazolium A and temperature for this model are 10 mol% and 5 ℃.

Table 2
The influence of the amount of thiazolium A and the temperature on the model reaction.a

We then extended our investigation to some intermolecular Stetter reactions of aromatic aldehydes with (E)-(2-nitrovinyl) cyclohexane. The intermolecular Stetter reaction of various aromotic aldehydes and (E)-(2-nitrovinyl)cyclohexane was carried out using 10 mol% of thiazolium A, 20 mol% of thiourea B and 20 mol% of Cs2CO3 at 5 ℃ with toluene as the solvent. The results are summarized in Table 3.

Table 3
The intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)- cyclohexane induced by A and B in toluene at 5 ℃.

It was found that, a wide range of β-nitro ketone derivatives were produced in moderate to good yields by this intermolecular Stetter reaction. Aromatic aldehydes with electron-withdrawing groups on the 4-position in the aromatic ring reacted faster than aromatic aldehydes bearing electron-donating groups and good yields were obtained (Table 3, entries 1, 3-5) . For 4-nitrobenzaldehyde, the Stetter reaction was finished in 3 h with only 57.4% yield, and some by-product was obtained (Table 3, entry 2) . For aromatic aldehydes with electron-withdrawing or electrondonating groups on the 3-position in the aromatic ring, moderate yields were obtained (Table 3, entries 6, 7) . Aromatic aldehydes with electron-withdrawing groups on 3, 4-position in the aromatic ring reacted in very short time and excellent yield was obtained (Table 3, entry 10) , but aromatic aldehydes with electronwithdrawing or electron-donating groups on ortho-position appeared to be disadvantageous for the yield (Table 3, entries 8-9, 11) .

Our initial investigations also indicate that the model Stetter reaction can be rendered stereoselective. The incorporation of achiral thiourea B produced b-nitro ketone 3a in 75.4% yield and 8.9% ee. These unoptimized results provide a strong impetus to explore the potential of chiral thiourea catalysis on the title reaction.

4. Conclusion

In conclusion, the direct intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane has been developed. In the presence of thiazolium A and thiourea B in combination, this intermolecular Stetter reaction affords moderate to good yields of the Stetter product, and a wide range of b-nitro ketone derivatives were produced. Further attempts of application of some chiral thiourea instead of thiourea B for this asymmetric intermolecular Stetter reaction are under investigation.

Acknowledgment

This work is supported by the Prospective Research Funds of Jiangsu Provincial Department of Science and Technology (No. BY2015049-02) , the Open-end Funds of Jiangsu Key Laboratory of Marine Biotechnology, Huaihai Institute of Technology, (No. 2014HS005) and the Funds of Technology Research of Lianyungang (No. CG1301) .

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