PEG-SO3H as catalyst for the Beckmann rearrangement and dehydration of oximes

PEG-SO3H as catalyst for the Beckmann rearrangement and dehydration of oximes

Available online at www.sciencedirect.com Chinese Chemical Letters 20 (2009) 651–655 www.elsevier.com/locate/cclet PEG-SO3H as catalyst for the Beck...

159KB Sizes 3 Downloads 245 Views

Available online at www.sciencedirect.com

Chinese Chemical Letters 20 (2009) 651–655 www.elsevier.com/locate/cclet

PEG-SO3H as catalyst for the Beckmann rearrangement and dehydration of oximes Xi Cun Wang *, Lei Li, Zheng Jun Quan, Hai Peng Gong, He Lin Ye, Xiao Feng Cao Gansu Key Laboratory of Polymer Materials, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, PR China Received 23 October 2008

Abstract Under mild conditions, conversion of a variety of ketoximes and aldoximes to their corresponding amides and nitriles proceeded in the presence of PEG-SO3H with high yields. # 2009 Published by Elsevier B.V. on behalf of Chinese Chemical Society. Keywords: Beckmann rearrangement; PEG-SO3H; Dehydration of oximes

The conventional Beckmann rearrangement usually requires relatively high temperature and uses strong Bronsted or Lewis acids, i.e. concentrated sulfuric acid, phosphorus pentachloride in diethyl ether, and hydrogen chloride in acetic anhydride, which lead to large amount of waste and serious corrosion problems [1,2]. On these basis, milder conditions are tried and investigation on clean, simple, and highly efficient processes become the chemists’ interesting undertaking, for example, using chlorosulfonic acid [3], silica sulfate [4], sulfamic acid [5], cyanuric chloride [6,7], chloral [8], anhydrous oxalic acid [9], O-alkyl-N,N-dimethylformamidium salt [10], ethyl chloroformate/boron trifluoride etherate [11], P2O5 [12], and bis(2-oxo-3-oxazolidinyl)phosphinic chloride [13]. The drawbacks in such methods are the use of toxic solvents, expensive reagents, production of considerable amounts of by-products, long reaction time, and low yields. Therefore, the development of a simple, clean, highly efficient and selective Beckmann rearrangement is still in demand. Dehydration of aldoximes to nitriles is also an important transformation in organic synthesis. A number of methods have been introduced, which have their own disadvantages, for example, the use of anhydrous reaction conditions, tedious and cumbersome work-up procedures, the need to prepare the reagent prior to the reaction, and long reaction times [14–19]. Therefore, the search for a more convenient method is on going. In recent years, there has been rapid growth in the development of novel polymer-supported compounds [20], such as supported catalysts, reagents, and scavengers. These species allow rapid and simplified procedures, and their use has become widespread in solution-phase organic synthesis and combinatorial chemistry [21]. Among the soluble

* Corresponding author. E-mail address: [email protected] (X.C. Wang). 1001-8417/$ – see front matter # 2009 Published by Elsevier B.V. on behalf of Chinese Chemical Society. doi:10.1016/j.cclet.2009.02.004

652

X.C. Wang et al. / Chinese Chemical Letters 20 (2009) 651–655

Scheme 1.

Scheme 2.

polymeric matrixes employed, poly(ethylene glycol)s (PEGs) are the most successful. Provided that their Mw is more than 2000, PEGs are soluble in many, mostly polar solvents (including water) and insoluble in a few nonpolar solvents (hexanes, diethyl ether, tert-butyl methyl ether). Because of this solubility profile, PEG-based supports combine the advantageous features of homogeneous solution chemistry (high reactivity, lack of diffusion phenomena, analytical simplicity) and of solid phase methods (ready isolation and purification of products) [22,23].

Table 1 Beckmann rearrangement catalyzed by PEG-SO3H. m.p. [18]

Yieldb (%)

Time (h)

1c

113–115 (113)

87 (1st) 85 (2nd) 86 (3rd)

5

2

162–163 (162)

90

5

3

165–166 (166)

72

5

4

59–60 (59)

80

5

Entry

Substrate

Producta

5

130–132

84

5

6

68–70

85

6

7

40–41 (40)

88

6.5

a b c

All the products are known. Isolated yield. The catalyst was reused for three times without significant loss of activity.

X.C. Wang et al. / Chinese Chemical Letters 20 (2009) 651–655

653

Table 2 Dehydration of aldoximes to nitriles in the presence of PEG-SO3H. Entry

Substrate

Producta

m.p. [18]

Yieldb (%)

Time (h)

1

94–95 (94)

90

5

2

60–62

94

5

3

90–91 (92)

87

5

4

148–150 (149)

90

5

5

65–66 (65)

88

5

6

180–182 (181)

89

5

a b

All the products are known. Isolated yield.

In continuation of our work [24] on the application of PEG-bound sulfonic acid (PEG-SO3H) for the development of useful synthetic methodologies, we now show a protocol that uses PEG-bound sulfonic acid as a novel and efficient catalyst for the Beckmann rearrangement and dehydration reaction (Schemes 1 and 2). 1. Experimental PEG-SO3H was prepared according to our laboratory method reported earlier [24]. A mixture of oxime (2 mmol) and acetonitrile (5 mL) was added into a 50 mL two mouth round-bottom flask equipped with a magnetic stirrer and condenser. Then the reactor was heated to 65 8C and PEG-SO3H (0.6 mmol, 3.66 g) was added drop-wise to the mixture from the other mouth of the round-bottomed flask. After 5.0 h, the solvent was evaporated from the reaction mixture and appropriate ether was added to the residue, the precipitate of PEG-SO3H was separated out and filtered, then the filtrate was concentrated under vacuum to afford the crude product. The product was recrystallized from ethanol (Tables 1 and 2). All reactions were monitored with TLC, and all products were characterized by comparison of their melting points, IR, 1H NMR and 13C NMR spectra with those of authentic samples. The analytical data for representative products are given below: Acetylaniline (Table 1, entry 1): white solid, m.p. 113–115 8C. IR (KBr, nmax): 3294, 3063, 2927, 1662 cm 1. 1H NMR (400 MHz, CDCl3, d ppm): 2.16 (s, 3H), 7.09 (t, 1H, J = 8.0 Hz), 7.29 (q, 2H, J = 8.8 Hz), 7.50 (d, 2H, J = 8.0 Hz), 7.56 (brs, 1H, NH). 13C NMR (100 MHz, CDCl3, d ppm): 168.5, 137.9, 128.9, 124.3, 119.9, 24.5. Caprolactam (Table 1, entry 6): white solid, m.p. 68–70 8C. IR (KBr, nmax): 3211, 2885, 1660 cm 1. 1H NMR (400 MHz, CDCl3, d ppm): 1.51–1.80 (m, 6H), 2.45 (t, 2H, J = 8.0 Hz), 3.21 (q, 2H, J = 8.0 Hz), 7.21 (brs, 1H, NH). 13C NMR (100 MHz, CDCl3, d ppm): 179.4, 42.5, 36.5, 30.4, 29.6, 23.1. 4-Methoxybenzonitrile (Table 2, entry 2): White solid, m.p. 57–60 8C. IR (KBr, nmax): 3079, 2914, 2216 cm 1. 1H NMR (400 MHz, CDCl3, d ppm): 3.84 (s, 3H), 6.94 (d, 2H, J = 8.8 Hz), 7.58 (d, 2H, J = 8.8 Hz). 13C NMR (100 MHz, CDCl3, d ppm): 162.8, 133.9, 119.1, 114.7, 103.8, 55.4.

654

X.C. Wang et al. / Chinese Chemical Letters 20 (2009) 651–655

2. Results and discussion Initially, acetophenone oxime was used as a substrate to examine the feasibility of Beckmann rearrangement using PEG-SO3H as catalyst. It was found that acetophenone oxime (2 mmol) mixed with PEG-SO3H (0.6 mmol, 3.66 g) was the optimized ratio. The amount of PEG-SO3H is enough to be used three times consecutively. The solvent effect on the Beckmann rearrangement catalyzed by PEG-SO3H was also investigated. Several solvents were tested by acetophenone oxime such as CCl4, CH3COCH3, MeCN, CH2Cl2, toluene and THF, their corresponding yields are 70%, 10%, 87%, 10%, 90% and 55%. In MeCN and toluene, the conversion of the substrate was proved to be good. In addition, the reaction hardly proceeded in CH3COCH3 and CH2Cl2. The probable reason is that the Beckmann rearrangement need higher temperature and toluene was more toxic and hazardous than MeCN, so MeCN was proved to be the best solvent. In contrast, aldoximes could be also catalyzed by PEG-SO3H using the similar reaction conditions to ketoximes, but the dehydration products, nitriles, were obtained in high yields (Table 2). Aromatic aldoximes with different substituents on the ring, such as hydroxyl, methoxy and nitro, could tolerate dehydration reactions (entries 1–6). The catalyst was easily separated from the reaction system, and reused for three consecutive runs, and no obvious diminishing activity was observed (the yield was 87% for 1st run; 85% for 2nd run; 86% for 3rd run; 70% for 4th run; 50% for 5th run). Each run the amount of acetophenone oxime is constant, and the recycle rate of PEG-SO3H is 80% each run, so the corresponding yields of 4th run and 5th run are declined to 70% and 50%. To explore the generality and scope of the Beckmann rearrangement and dehydration of oximes catalyzed by PEGSO3H, representative ketoximes and aldoximes as substrates were examined in MeCN. Not only aromatic but also aliphatic oximes were smoothly rearranged under given condition. In particular, the rearrangement of most substrates was completed within 5 h. In the case of unsymmetrical oximes the reaction of the Beckmann rearrangement was selective and only one amide was produced. 3. Conclusion A simple and efficient technique for direct conversion of ketoximes and aldoximes via Beckmann rearrangement and dehydration to the corresponding amides and nitriles has been presented, respectively. This method has advantages of high conversion, high selectivity and simple work-up procedure. Acknowledgments We are thankful for the financial support from the Natural Science Foundation of Gansu Province (No. 3ZS061A25-019), the Scientific Research fund of Gansu Provincial Education Department (No. 0601-25). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

M.B. Smith, J. March, Advanced Organic Chemistry, 5th ed., John Wiley & Sons, New York, 2001, p. 1415. K. Maruoka, H. Yamamoto, Comprehensive Organic Synthesis, vol. 6, Pergamon Press, Oxford, 1991, pp. 763–765. D. Li, F. Shi, S. Guo, Y. Deng, Tetrahedron Lett. 46 (2005) 671. Z. Li, J. Mol. Catal. A: Chem. 250 (2006) 100. B. Wang, Y. Gu, C. Luo, T. Yang, L. Yang, J. Suo, Tetrahedron Lett. 45 (2004) 3369. L.L. De, G. Giacomelli, A.J. Porcheddu, J. Org. Chem. 67 (2002) 6272. Y. Furuya, K. Ishihara, H.J. Yamamoto, J. Am. Chem. Soc. 127 (2005) 11240. S. Chandrasekhar, K. Gopalaiah, Tetrahedron Lett. 44 (2003) 755. S. Chandrasekhar, K. Gopalaiah, Tetrahedron Lett. 43 (2002) 2455. Y. Izumi, Chem. Lett. 19 (1990) 2171. S. Antikumar, S. Chandrasekhar, Tetrahedron Lett. 41 (2000) 5427. R.X. Ren, L.D. Zueva, W. Ou, Tetrahedron Lett. 42 (2001) 8441. M. Zhu, C. Cha, W. Deng, X. Shi, Tetrahedron Lett. 47 (2006) 4861. G. Sosnovsky, J.A. Krogh, Synthesis (1978) 703. A. Sacdnya, Synthesis (1983) 748. P. Molina, M. Alajarian, M.J. Vilaploma, Synthesis (1982) 1016. J.P. Dulcere, Tetrahedron Lett. 22 (1981) 1599. A.R. Katritzky, G.F. Zhang, W.G. Fan, Org. Prep. Proced. Int. 25 (1993) 315.

X.C. Wang et al. / Chinese Chemical Letters 20 (2009) 651–655 [19] [20] [21] [22] [23] [24]

G.A. Olah, S.C. Narang, A. Garcia-Luna, Synthesis (1980) 659. J. Eames, M. Watkinson, J. Org. Chem. 66 (2001) 1213. C.C. Tzschucke, C. Markert, W. Bannwarth, S. Roller, A. Hebel, R. Haag, Angew. Chem. 114 (2002) 4136. L.A. Thompson, J.A. Ellman, Chem. Rev. 96 (1996) 555. D.W. Sun, H.G. Zhai, Catal. Commun. 8 (2007) 1027. X.C. Wang, Z.J. Quan, F. Wang, M.G. Wang, Z. Zhang, Z. Li, Synth. Commun. 36 (2006) 451.

655