Clay-Supported Copper Nitrate (Claycop): A Mild Reagent for the Selective Nitration of Aromatic Olefins

Abstract

A straightforward and highly selective method has been developed for the nitration of a wide variety of aromatic and aliphatic olefins by using a clay-supported copper nitrate (Claycop) and a catalytic amount of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, an inexpensive and mild reagent system. High conversions and exclusive E-selectivity, together with the environmentally benign nature of the Claycop reagent, make this a green method and an attractive alternative to established methods.

Nitro compounds are important synthetic intermediates[1] and are essential starting materials for the synthesis of a variety of useful building blocks, such as amines, ketoximes, nitroalkanes, hydroxylamines, and aldoximes. Unsaturated nitro compounds can act as substrates for C–C bond-forming reactions, such as the Morita–Baylis–Hillman reaction, the Michael reaction, and cycloaddition reactions.[2]

Several methods have been reported for generating nitroolefins directly from olefins.[3] One well-known method for the synthesis of nitroolefins involves the condensation of nitroalkanes with aldehydes or ketones in the presence of a base followed by dehydration.[4] However, many of the known methods have drawbacks, such as the use of hazardous or expensive reagents, extended reaction times, limited scopes, low yields, or the formation of mixtures of E- and Z-isomers.

In this context there is still scope for the development of an environmentally benign method[5] using inexpensive reagents. In recent decades, there has been an upsurge in interest in organic synthesis using solid-supported reagents.[6] [7] [8] In particular, clay-supported reagents[9] have gained widespread use.

Among the clay-supported reagents, Claycop[8] (clay-supported copper nitrate) and Clayfen (clay-supported ferric nitrate) are known to be efficient reagents for ring nitration of a wide variety of phenols, anilines and nitrogen heterocycles.[10] However, there has been no report on the use of a combination of a clay-supported nitrating agent and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) in the selective nitration of olefins. Here, we wish to report the use of Claycop and TEMPO as a suitable reagent system for the synthesis of β-nitro olefin derivatives from the corresponding olefins (Scheme [1]).

Table 1 Screening of Various Nitrating Agents for the Formation of [(E)-2-nitrovinyl]benzene (2a) from Styrene^a

Entry	Nitrating agent	Time (h)	Yield (%)
1	Cu(NO3)2·H2O	12.0	30
2	Clayan	12.0	60
3	Clayfen	12.0	76
4	Claycop	1.0	95

^a Reaction conditions: 1a (1.0 mmol), nitrating agent (1.5 mmol), TEMPO (0.2 mmol), 80 °C, 1,4-dioxane (5 mL).

Initially, we wanted to screen various nitrating agents and to optimize the reaction conditions for the selective conversion of styrene (1a) into [(E)-2-nitrovinyl]benzene (2a) (Table [1]). When copper nitrate was used in the presence of TEMPO, nitroolefin 2a was obtained in low yield (30%; Table [1], entry 1). This provided an incentive to study solid-supported nitrating reagents, such as clay-supported ammonium nitrate (Clayan), Clayfen, and Claycop. When we performed the reaction with Clayan, the reaction took a long time and gave only a moderate yield of the desired product (entry 2). Under similar reaction conditions, Clayfen gave a slightly better yield (entry 3). We then examined the reaction of styrene with Claycop in the presence of a catalytic amount of TEMPO. The reaction proceeded smoothly in 1,4-dioxane at 80 °C for one hour to give nitroolefin 2a exclusively in 95% yield (entry 4). Claycop is therefore the best reagent, as the reaction was complete within one hour and gave an essentially quantitative yield of the product. It is pertinent to mention that Varma et al. reported the use of Clayan for nitrating styrene and p-substituted styrenes; however, their reaction gave only a 14% yield of the desired product, along with unidentified and polymeric compounds as the major products.[9] Claycop is therefore the best nitrating reagent.

To examine the role of the solvent, we performed the reaction in tetrahydrofuran, toluene, 1,2-dichloroethane, N,N-dimethylformamide, and 1,4-dioxane (Table [2]). Of these solvents, 1, 4-dioxane was found to be the best, providing a 95% yield of the product (Table [2], entry 5).

Having established the optimal conditions for selective nitration of olefins with Claycop, we next examined the scope and limitations of this reaction with various olefins (Table [3]). It is noteworthy that the E-isomer was obtained exclusively in all cases. Aromatic olefins gave better yields of products than did aliphatic olefins. Note that the nitration of para-substituted styrenes with Claycop gave excellent yields of products (Table [3], entries 2–5 and 17), whereas the same reaction with Clayan or Clayfen gave mainly polymeric compounds, the desired products being obtained in low yields only.

When we attempted to carry out the nitration reaction in the absence of TEMPO, no reaction occurred. The present method is simple, convenient, and selective, as it results in exclusive formation of the (E)-β-nitro olefin derivatives in excellent yield. In addition, the workup is simple, because separation of the product requires only simple filtration to remove the depleted Claycop reagent.

Mechanistically, the reaction is expected to proceed through formation of a nitro radical (O₂N^•).[11] The nitro radical might be generated thermally from Claycop, and the olefin is eventually converted into the β-nitroolefin derivative in the presence of a catalytic amount of TEMPO under aerobic conditions, according to the proposed mechanism (Scheme [2]).[3a] [b] [c]

In conclusion, we have demonstrated an alternative, convenient, and general method for the selective nitration of a variety of alkenes by using Claycop. The use of a clay-supported reagent and an aqueous medium, with minimal waste effluent, make this a very attractive and environmentally benign process.

Table 3 Selective Nitration of Aromatic Olefins^a

Entry	Alkene	Productb	Yieldc (%)
1			95
2			89
3			85
4			84
5			87
6			92
7			90
8			95
9			88
10			60
11			84
12			82
13			84
14			70
15			65
16			80
17			82

^a The reactions were performed on a 1-mmol scale.

^b All the products were characterized by ¹H and ¹³C NMR spectroscopy and by GC/MS.

^c Yield of pure product after column chromatography.

Acknowledgment

E.B. thanks DST New Delhi for an INSPIRE Fellowship (IFA12-CH-29). C.R.S. and U.N.R thank OSDD and UGC, New Delhi, respectively, for research fellowships. The authors thank CSIR, New Delhi for financial support as part of the XII Five-Year Plan under the title ORIGIN (CSC0108).

• References

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• 4b Henry L. Bull. Soc. Chim. Fr. 1895; 13: 999
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• 4c Fioravanti S, Pellacani L, Tardella PA, Vergari MC. Org. Lett. 2008; 10: 1449
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• 5c Yücel AS. Egit. Arast. 2008; 32: 145
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• 6a Preparative Chemistry Using Supported Reagents . Laszlo P. Academic Press; San Diego: 1987. 2nd ed
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• 7b Posner GH. Angew. Chem. Int. Ed. 1978; 17: 487
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• 8 Laszlo P, Pennetreau P. J. Org. Chem. 1987; 52: 2407
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• 9a Varma RS, Naicker KP, Liesen PJ. Tetrahedron Lett. 1998; 39: 3977
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• 9b Pérez C, Pérez-Gutiérrez S, Gómez SA, Fuentes GA, Zavala MA. Org. Prep. Proced. Int. 2005; 37: 387
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• 9c Mohammed S, Padala AK, Dar BA, Singh B, Sreedhar B, Vishwakarma RA, Bharate SB. Tetrahedron 2012; 68: 8156
  CrossrefSearch in Google Scholar
• 9d Mallouk S, Bougrin K, Doua H, Benhida R, Soufiaoui M. Tetrahedron Lett. 2004; 45: 4143
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• 9e Meshram HM, Thakur PB, Madhu Babu B, Bangade VM. Tetrahedron Lett. 2012; 53: 1780
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• 9f Varma RS. Tetrahedron 2002; 58: 1235
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• 10a Cornelis A, Laszlo P, Pennetreau P. J. Org. Chem. 1983; 48: 4772
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• 10b Gigante B, Prazeres AO. Marcelo-Curto M. J. 1995; 60: 3445
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• 11a Taniguchi T, Sugiura Y, Hatta T, Yajima A, Ishibashi H. Chem. Commun. 2013; 49: 2198
  CrossrefSearch in Google Scholar
• 11b Koley D, Colón OC, Savinov SN. Org. Lett. 2009; 11: 4172
  CrossrefSearch in Google Scholar
• 11c Kilpatrick B, Heller M, Arns S. Chem. Commun. 2013; 49: 514
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  Thieme Connect
• 11e Taniguchi T, Yajima A, Ishibashi H. Adv. Synth. Catal. 2011; 353: 2643
  CrossrefSearch in Google Scholar
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• 12 Clay-Supported Copper(II) Nitrate (Claycop) K10 clay (30 g) was added to a stirred mixture of Cu(NO₃)₂·3H₂O (26 g) in acetone (400 mL). Stirring was continued for 5–10 min before the solvent was removed in a rotary evaporator at 50 °C. The dry solid crust that adhered to the walls of the flask was scraped off with a spatula, and rotary drying under vacuum was continued for 50 min at 50 °C to give a free-flowing blue powder that showed no loss of reactivity after several months.
• 13 [(E)-2-Nitrovinyl]benzene (2a); Typical Procedure A mixture of styrene (0.104 g, 1.0 mmol), Claycop [0.605 g, 1.5 mmol containing 1.5 equiv Cu(NO₃)₂], TEMPO (0.0156 g, 20 mol%), and 1,4-dioxane (5 mL) was stirred at 80 °C for 1 h. The mixture was then cooled to r.t., and the Claycop was collected by filtration and washed with 1,4-dioxane (3 × 5 mL). The organic phases were combined and concentrated under vacuum. The crude product was purified by recrystallization or column chromatography (EtOAc–hexanes) to give a crystalline yellow solid; yield: 0.1414 g (95%); mp 56–58 °C (Lit.3c 58 °C); ¹H NMR (200 MHz, CDCl₃): δ = 8.03 (d, J = 13.6 Hz, 1 H), 7.53–7.66 (m, 3 H), 7.41–7.53 (m, 3 H); ¹³C NMR (100 MHz, CDCl₃): δ = 139.1, 137.1, 132.1, 130.0, 129.4, 129.1; GC/MS: m/z = 149.1 [M⁺].

• References

• 1a Lu L.-Q, Chen J.-R, Xiao W.-J. Acc. Chem. Res. 2012; 45: 1278
  CrossrefPubMedSearch in Google Scholar
• 1b Reddy MA, Jain N, Yada D, Kishore C, Reddy VJ, Reddy PS, Addlagatta A, Kalivendi SV, Sreedhar B. J. Med. Chem. 2011; 54: 6751
  CrossrefPubMedSearch in Google Scholar
• 1c Uehara H, Imashiro R, Hernández-Torres G, Barbas CF. III. Proc. Natl. Acad. Sci. U. S. A. 2010; 107: 20672
  CrossrefSearch in Google Scholar
• 1d Barrett AG. M, Graboski GG. Chem. Rev. 1986; 86: 751
  CrossrefSearch in Google Scholar
• 1e Kaap S, Quentin I, Tamiru D, Shaheen M, Eger K, Steinfelder HJ. Biochem. Pharmacol. 2003; 65: 603
  CrossrefSearch in Google Scholar
• 1f Meah Y, Massey V. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 10733
  CrossrefSearch in Google Scholar
• 2a Kabalka GW, Varma RS. Org. Prep. Proced. Int. 1987; 19: 283
  CrossrefSearch in Google Scholar
• 2b Ono N In Nitro Compounds: Recent Advances in Synthesis and Chemistry . Feuer H, Nielsen AT. VCH; Weinheim: 1990. Chap. 1, 1-135
  CrossrefSearch in Google Scholar
• 2c Perekalin VV, Lipina ES, Berestovitskaya VM, Efremov DA. Nitroalkenes: Conjugated Nitro Compounds . Wiley; Chichester: 1994. Chap. 2, 53-168
  Search in Google Scholar
• 2d Barrett AG. M. Chem. Soc. Rev. 1991; 20: 95
  CrossrefSearch in Google Scholar
• 2e Basavaiah D, Reddy BS, Badsara SS. Chem. Rev. 2010; 110: 5447
  Search in Google Scholar
• 2f Tripathi CB, Kayal S, Mukherjee S. Org. Lett. 2012; 14: 3296
  CrossrefSearch in Google Scholar
• 2g Ishii T, Fujioka S, Sekiguchi Y, Kotsuki H. J. Am. Chem. Soc. 2004; 126: 9558
  CrossrefPubMedSearch in Google Scholar
• 2h Denmark SE, Thorarensen A. Chem. Rev. 1996; 96: 137
  CrossrefPubMedSearch in Google Scholar
• 2i Evans DA, Mito S, Seidel D. J. Am. Chem. Soc. 2007; 129: 11583
  CrossrefSearch in Google Scholar
• 2j Liu YK, Nappi M, Arceo E, Vera S, Melchiorre P. J. Am. Chem. Soc. 2011; 133: 15212
  CrossrefSearch in Google Scholar
• 3a Naveen T, Maity S, Sharma U, Maiti D. J. Org. Chem. 2013; 78: 5949
  CrossrefPubMedSearch in Google Scholar
• 3b Maity S, Manna S, Rana S, Naveen T, Mallick A, Maiti D. J. Am. Chem. Soc. 2013; 135: 3355
  CrossrefPubMedSearch in Google Scholar
• 3c Maity S, Naveen T, Sharma U, Maiti D. Org. Lett. 2013; 15: 3384
  CrossrefPubMedSearch in Google Scholar
• 3d Manna S, Jana S, Saboo T, Maji A, Maiti D. Chem. Commun. 2013; 49: 5286
  CrossrefPubMedSearch in Google Scholar
• 3e Eiichiro H, Tohru Y, Teruaki M. Bull. Chem. Soc. Jpn. 1995; 68: 3629
  CrossrefSearch in Google Scholar
• 3f Tinsley SW. J. Org. Chem. 1961; 26: 4723
  CrossrefSearch in Google Scholar
• 3g Grebenyuk AD, Ismailova RA, Tokbolatov RB, Ovadova T. Zh. Org. Khim. 1990; 26: 680
  Search in Google Scholar
• 3h Corey EJ, Estreicher H. J. Am. Chem. Soc. 1978; 100: 6294
  CrossrefSearch in Google Scholar
• 3i Kancharla PK, Reddy YS, Dharuman S, Vankar YD. J. Org. Chem. 2011; 76: 5832
  CrossrefPubMedSearch in Google Scholar
• 3j Mukaiyama T, Hata E, Yamada T. Chem. Lett. 1995; 505
• 3k Suzuki H, Mori T. J. Org. Chem. 1997; 62: 6498
  CrossrefSearch in Google Scholar
• 3l Campos PJ, Garcıa B, Rodrıguez MA. Tetrahedron Lett. 2000; 41: 979
  CrossrefSearch in Google Scholar
• 3m Sy WW, By AW. Tetrahedron Lett. 1985; 26: 1193
  CrossrefSearch in Google Scholar
• 3n Jovel I, Prateeptongkum S, Jackstell R, Vogl N, Weckbecker C, Beller M. Adv. Synth. Catal. 2008; 350: 2493
  CrossrefSearch in Google Scholar
• 3o Yan G, Borah AJ, Wang L. Org. Biomol. Chem. 2014; DOI: 10.1039/C4OB00573B
• 4a Henry L. C. R. Seances Acad. Sci., Ser. C 1895; 120: 1265
  Search in Google Scholar
• 4b Henry L. Bull. Soc. Chim. Fr. 1895; 13: 999
  Search in Google Scholar
• 4c Fioravanti S, Pellacani L, Tardella PA, Vergari MC. Org. Lett. 2008; 10: 1449
  CrossrefSearch in Google Scholar
• 4d Ballini R, Bosica G. J. Org. Chem. 1997; 62: 425
  CrossrefPubMedSearch in Google Scholar
• 4e Shulgin AT. J. Med. Chem. 1966; 9: 445
  CrossrefSearch in Google Scholar
• 5a Horváth IT, Anastas PT. Chem. Rev. 2007; 107: 2169
  CrossrefSearch in Google Scholar
• 5b Horváth IT. Chem. Rev. 1995; 95: 1
  CrossrefSearch in Google Scholar
• 5c Yücel AS. Egit. Arast. 2008; 32: 145
  Search in Google Scholar
• 6a Preparative Chemistry Using Supported Reagents . Laszlo P. Academic Press; San Diego: 1987. 2nd ed
  CrossrefSearch in Google Scholar
• 6b McKillop A, Young DW. Synthesis 1979; 401
  Thieme Connect
• 6c McKillop A, Young DW. Synthesis 1979; 481
  Thieme Connect
• 7a Varma RS. Tetrahedron 2002; 58: 1235
  CrossrefSearch in Google Scholar
• 7b Posner GH. Angew. Chem. Int. Ed. 1978; 17: 487
  CrossrefSearch in Google Scholar
• 7c Clark HP, Kybett AP, Macquarie DJ. Supported Reagents: Preparation, Analysis and Applications . VCH; New York: 1992
  Search in Google Scholar
• 8 Laszlo P, Pennetreau P. J. Org. Chem. 1987; 52: 2407
  CrossrefSearch in Google Scholar
• 9a Varma RS, Naicker KP, Liesen PJ. Tetrahedron Lett. 1998; 39: 3977
  CrossrefSearch in Google Scholar
• 9b Pérez C, Pérez-Gutiérrez S, Gómez SA, Fuentes GA, Zavala MA. Org. Prep. Proced. Int. 2005; 37: 387
  CrossrefSearch in Google Scholar
• 9c Mohammed S, Padala AK, Dar BA, Singh B, Sreedhar B, Vishwakarma RA, Bharate SB. Tetrahedron 2012; 68: 8156
  CrossrefSearch in Google Scholar
• 9d Mallouk S, Bougrin K, Doua H, Benhida R, Soufiaoui M. Tetrahedron Lett. 2004; 45: 4143
  CrossrefSearch in Google Scholar
• 9e Meshram HM, Thakur PB, Madhu Babu B, Bangade VM. Tetrahedron Lett. 2012; 53: 1780
  CrossrefSearch in Google Scholar
• 9f Varma RS. Tetrahedron 2002; 58: 1235
  CrossrefSearch in Google Scholar
• 10a Cornelis A, Laszlo P, Pennetreau P. J. Org. Chem. 1983; 48: 4772
  CrossrefSearch in Google Scholar
• 10b Gigante B, Prazeres AO. Marcelo-Curto M. J. 1995; 60: 3445
  Search in Google Scholar
• 11a Taniguchi T, Sugiura Y, Hatta T, Yajima A, Ishibashi H. Chem. Commun. 2013; 49: 2198
  CrossrefSearch in Google Scholar
• 11b Koley D, Colón OC, Savinov SN. Org. Lett. 2009; 11: 4172
  CrossrefSearch in Google Scholar
• 11c Kilpatrick B, Heller M, Arns S. Chem. Commun. 2013; 49: 514
  CrossrefPubMedSearch in Google Scholar
• 11d Liu Y. Synlett 2011; 1184
  Thieme Connect
• 11e Taniguchi T, Yajima A, Ishibashi H. Adv. Synth. Catal. 2011; 353: 2643
  CrossrefSearch in Google Scholar
• 11f Wu X.-F, Schranck J, Neumann H, Beller M. Chem. Commun. 2011; 47: 12462
  CrossrefPubMedSearch in Google Scholar
• 11g Galliker B, Kissner R, Nauser T, Koppenol WH. Chem. Eur. J. 2009; 15: 6161
  CrossrefSearch in Google Scholar
• 12 Clay-Supported Copper(II) Nitrate (Claycop) K10 clay (30 g) was added to a stirred mixture of Cu(NO₃)₂·3H₂O (26 g) in acetone (400 mL). Stirring was continued for 5–10 min before the solvent was removed in a rotary evaporator at 50 °C. The dry solid crust that adhered to the walls of the flask was scraped off with a spatula, and rotary drying under vacuum was continued for 50 min at 50 °C to give a free-flowing blue powder that showed no loss of reactivity after several months.
• 13 [(E)-2-Nitrovinyl]benzene (2a); Typical Procedure A mixture of styrene (0.104 g, 1.0 mmol), Claycop [0.605 g, 1.5 mmol containing 1.5 equiv Cu(NO₃)₂], TEMPO (0.0156 g, 20 mol%), and 1,4-dioxane (5 mL) was stirred at 80 °C for 1 h. The mixture was then cooled to r.t., and the Claycop was collected by filtration and washed with 1,4-dioxane (3 × 5 mL). The organic phases were combined and concentrated under vacuum. The crude product was purified by recrystallization or column chromatography (EtOAc–hexanes) to give a crystalline yellow solid; yield: 0.1414 g (95%); mp 56–58 °C (Lit.3c 58 °C); ¹H NMR (200 MHz, CDCl₃): δ = 8.03 (d, J = 13.6 Hz, 1 H), 7.53–7.66 (m, 3 H), 7.41–7.53 (m, 3 H); ¹³C NMR (100 MHz, CDCl₃): δ = 139.1, 137.1, 132.1, 130.0, 129.4, 129.1; GC/MS: m/z = 149.1 [M⁺].