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Dodecatungstophosphoric acid (H3PW12O40) as a highly efficient catalyst for the amidation of alcohols and protected alcohols with nitriles in water: A modified Ritter reaction
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Catalysis Communications 9 (2008) 529–531 www.elsevier.com/locate/catcom
Dodecatungstophosphoric acid (H3PW12O40) as a highly efficient catalyst for the amidation of alcohols and protected alcohols with nitriles in water: A modified Ritter reaction Habib Firouzabadi *, Nasser Iranpoor *, Abbas Khoshnood Department of Chemistry, Shiraz University, Shiraz 71454, Iran Received 14 April 2007; received in revised form 30 July 2007; accepted 31 July 2007 Available online 7 August 2007
Abstract Dodecatungstophosphoric acid (H3PW12O40) as a highly efficient catalyst for high yielding amidation of alcohols, and protected alcohols such as silyl, and THP ethers and also t-butyl methyl ether in water is described. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Dodecatungstophosphoric acid; Ritter reaction; Water; Alcohol; Silyl ether; Tetrahydropyranyl ether; Amidation; Nitrile
1. Introduction The use of water instead of toxic organic solvents for organic processes is of interest [1–6]. Furthermore, water has unique physical and chemical properties, and by utilizing these it would be possible to realize reactivity or selectivity that cannot be attained in organic solvents. However, organic solvents are still favourable media for organic reactions for mainly two reasons; first, most organic substrates are not soluble in water and second, many reactive substrates, reagents, and catalysts are sensitive towards water so that they are decomposed or deactivated in aqueous media. Therefore, study upon conditions in which the organic reactions proceed in aqueous media is of attention [7–11]. Dodecatungstophosphoric acid (H3PW12O40) is environmentally benign and commercially available compound. This solid compound is a more active catalyst than conventional inorganic and organic acids which has been used for various organic reactions [12–26]. One of the most useful methods for the synthesis of N-bulky alkyl substituted amides is called Ritter reaction [27–29], in which usually t-BuOH reacts with a nitrile in the
presence of concentrated H2SO4 in organic solvents. As an alternative to H2SO4, Ritter reaction catalyzed by BF3 Æ Et2O [30], Bi(OTf)3 [31], t-butylacetate/H2SO4 [32], trifluromethane sulfonic anhydride [33] and, etc. have been also reported. Very recently, a modified Ritter reaction using camphene and wet nitriles in the presence of dodecatungstophosphoric acid (H3PW12O40) has been also reported [34,35]. 2. Experimental 2.1. General remarks Chemicals were obtained from Fluka and Merck Chemical Companies. Progress of the reactions was monitored by TLC using silica gel SILG/UV 254 plates and Shimadzu GC MS-QP 1000 EX. All products are known compounds and their IR, 1H NMR and 13C NMR were compared with those reported for the authentic samples. All yields refer to the isolated yields. 2.2. General procedure for Ritter reactions in water catalyzed by H3PW12O40
*
Corresponding authors. Tel.: +98 711 2280926; fax: +98 711 2286008. E-mail addresses: fi[email protected] (H. Firouzabadi), [email protected] (N. Iranpoor). 1566-7367/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2007.07.042
To a solution of alcohols, silyl or THP ethers (1 mmol) in water (5 mL) was added H3PW12O40 (0.14 g, 0.05 mmol)
530
H. Firouzabadi et al. / Catalysis Communications 9 (2008) 529–531
and the resulting solution was stirred for 5 min. Then, liquid nitrile (3 mmol) was added to the mixture and the resulting mixture was magnetically stirred vigorously at reflux for the appropriate reaction time (Table 1). For the reaction of solid nitriles, sodium dodecyl sulfate (SDS) (0.028 g, 0.1 mmol ) should be added to the reaction mixture. The progress of the reaction was monitored by TLC and GC. Reaction mixture was cooled and neutralized with 10% aqueous NaOH. Then the resulting mixture extracted by AcOEt (15 mL) using continuous extraction technique in order to minimize the amount of the organic solvent used [36]. The organic phase was separated and
dried over anhydrous Na2SO4 which after filtration and evaporation of the solvent gave the crude desired product. Purification of the crude product was performed by column chromatography on silica gel eluted with petroleum ether (40–60 °C)/AcOEt to afford the pure product (Table 1). 3. Results and discussion In this communication we have reported an efficient and a high yielding Ritter reaction of alcohols and protected alcohols such as; silyl and THP ethers and also t-butyl methyl ether with different nitriles in the absence of any
Table 1 Reaction of different nitriles with alcohols, silyl ethers, THP ethers and t-butyl methyl ether in water catalyzed by H3PW12O40 Entry
Nitrilesa
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 29 30 31 32 33 34 35 36 37 38 39 40 41 42 a b
CN
CN
MeO
Cl
CN
CN
Cl
CN
F3C
MeCN
ROH,ROSiMe3,ROTHP,R1OR2
Time (h)
Isolated yield (%)
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP p-MeO-PhCH2OH p-MeOPhCH2OSiMe3 p-MeO-PhCH2OTHP t-Butyl methyl ether
10 10 10 10 10 10 10 10 10 10
99 97 97 99 97 97 89 80 85 99
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP p-MeOPhCH2OH p-MeOPhCH2OSiMe3 p-MeOPhCH2OTHP t-Butyl methyl ether
15 15 15 15 15 15 15 15 15 15
96 97 97 99 97 97 90 90 90 99
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP t-Butyl methyl ether
20 20 20 20 20 20 20
90 86 89 93 88 86 90
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP t-Butyl methyl ether
15 15 15 15 15 15 15
98 97 97 98 95 95 98
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP t-Butyl methyl ether
30 30 30 30 30 30 30
50b 54b 57b 88b 80b 82b 61b
t-BuOH t-BuOSiMe3 t-BuOTHP
10 10 10
98 90 90
0.1 mmol SDS was used for 4-methoxybenzonitrile, 3-chlorobenzonitrile, 4-chlorobenzonitrile and 4-trifloromethylbenzonitrile. (0.2 mmol, 0.56 g ) of H3PW12O40 was used.
H. Firouzabadi et al. / Catalysis Communications 9 (2008) 529–531
References
O
R1CN
R2 X
H3PW12O40 H2O, reflux
R2 R1
531
N H
R1=4-ClC6H5-, 3-ClC6H5-, 4-CF3C6H5-, 4-OMeC6H5-, Ph-, CH3 X=OH, OSiMe3, OTHP, OMe
Scheme 1.
organic co-solvent in water using dodecatungstophosphoric acid (H3PW12O40) as a catalyst (Scheme 1). As it is shown in Table 1, for solid nitriles tiny amounts of sodium dodecyl sulfate (SDS) should be added to the reaction mixture as a phase-transfer catalyst. In order to optimize the reaction conditions, we have studied the reaction of 4-methoxybenzonitrile as a solid nitrile with tBuOH in the presence H3PW12O40 and SDS in water at reflux conditions. We have found that the optimized condition with respect to the molar ratio of nitrile/alcohol/cat./ SDS/water was 3 mmol/1 mmol/0.1 mmol/0.1 mmol/5 mL. Then we applied this molar ratio for the reaction of other nitriles with alcohols, and also silyl, THP ethers and t-butyl methyl ether. All the reactions proceeded well in high yields as summarized in Table 1. For the reaction of liquid nitriles, addition of SDS as a phase-transfer catalyst was not necessary. In order to show the merit of the catalyst for Ritter reactions in water, we have also studied the reaction of several nitriles with t-BuOH in aqueous solutions of H2SO4, H2SO4/SDS, and water with SDS. However, the results were not satisfactory and after elongated reaction time (24 h) only 2–20% conversion was detected. Extraction of polar organic compounds from aqueous solution with organic solvents is not usually an easy task which requires a large amount of the solvent that would be also a time consuming process. In order to surmount this problem we have applied a simple continuous extraction technique [36] by which a minimum amount of the organic solvent was required to isolate the product. 4. Conclusion In conclusion, in this study we have reported a modified Ritter reaction in water in the absence of any organic cosolvent. This reaction has been catalyzed by dodecatungstophosphoric acid (H3PW12O40) as the catalyst which is an environmentally benign and a cheap commercially available compound. The application of this protocol for the high yielding amidation reaction of alcohols, silyl and THP ethers and also t-butyl methyl ether with structurally diverse nitriles shows the broad application of the method in organic synthesis. Acknowledgements We are thankful to TWAS Chapter of Iran based at ISMO and the Shiraz University Research Council for the support of this work.
[1] P.A. Grieco (Ed.), Organic Synthesis in Water, Blacky Academic, Professional, London, 1998. [2] C.-J. Li, Chem. Soc. Rev 35 (2006) 68. [3] U.-M. Lindstro¨m, Chem. Rev. 102 (2002) 2751. [4] C.-J. Li, Chem. Rev. 105 (2005) 3095. [5] K. Manabe, S. Kobayashi, Chem. Eur. J. 8 (2002) 4094. [6] D. Sinou, Adv. Synth. Catal. 344 (2002) 237. [7] H. Firouzabadi, N. Iranpoor, A.A. Jafari, Adv. Synth. Catal. 347 (2005) 655. [8] H. Firouzabadi, N. Iranpoor, A. Garzan, Adv. Synth. Catal. 347 (2005) 1925. [9] N. Iranpoor, H. Firouzabadi, M. Shekarrize, Org. Biomol. Chem. 1 (2003) 724. [10] H. Firouzabadi, N. Iranpoor, A.A. Jafari, E. Riazymontazer, Adv. Synth. Catal. 348 (2006) 434. [11] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, Chem. Commun. 6 (2005) 789. [12] V. Kozhevnikov, in: E. Derouane (Ed.), Catalyst for Fine Chemical Synthesis, Catalyst by Polyoxometalates, vol. 2, Wiley, New York, 2002. [13] S. Nakato, M. Kimura, T. Okuhara, Chem. Lett. (1997) 389. [14] H. Firouzabadi, A.A. Jafari, J. Iran. Chem. Soc. 2 (2005) 85. [15] H. Firouzabadi, N. Iranpoor, A.A. Jafari, Synlett (2005) 299. [16] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, Tetrahedron 60 (2004) 10843. [17] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, Tetrahedron Lett. 44 (2003) 5343. [18] H. Firouzabadi, N. Iranpoor, A.A. Jafari, J. Organomet. Chem. 690 (2005) 1556. [19] H. Firouzabadi, N. Iranpoor, A.A. Jafari, J. Mol. Cat. A: Chem. 227 (2005) 97. [20] H. Firouzabadi, N. Iranpoor, A.A. Jafari, Tetrahedron Lett. 46 (2005) 2683. [21] H. Firouzabadi, N. Iranpoor, K. Amani, Synthesis (2002) 59. [22] H. Firouzabadi, N. Iranpoor, K. Amani, F. Nowrouzi, J. Chem. Soc. Perkin Trans. 1 (2002) 2601. [23] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, K. Amani, Chem. Commun. (2003) 764. [24] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, K. Amani, Tetrahedron Lett. 44 (2003) 3951. [25] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, K. Amani, Green Chem. 3 (2001) 131. [26] H. Firouzabadi, N. Iranpoor, K. Amani, Synth. Commun. 34 (2004) 3587. [27] F.R. Benson, J.J. Ritter, J. Am. Chem. Soc. 71 (1949) 4128. [28] J.J. Ritter, P.P. Minieri, J. Am. Chem. Soc. 70 (1948) 4045. [29] L.I. Krimen, D. Cota, J.J. Ritter, Org. React. 17 (1969) 213. [30] H. Firouzabadi, A.R. Sardarian, H. Badparva, Synth. Commun. 24 (1994) 601. [31] E. Callens, A.J. Burton, A.G.M. Barrett, Tetrahedron Lett. 47 (2006) 8699. [32] K.L. Reddy, Tetrahedron Lett. 44 (2003) 1453. [33] A.G. Martinez, R.M. Alvarez, E.T. Vilar, A.G. Fraile, M. Hanack, L.R. Subramanian, Tetrahedron Lett. 30 (1989) 581. [34] V.R. Kartashov, K.V. Malkova, A.V. Arkhipova, T.N. Sokolova, Russ. J. Org. Chem. 42 (2006) 966. [35] V.R. Kartashov, A.V. Arkhipova, K.V. Malkova, T.N. Sokolova, Russ. Chem. Bull. Int. Ed. 55 (2006) 387. [36] Vogel’s Textbook of Practical Organic Chemistry, fourth ed., Longman, London, 1986.
Catalysis Communications 9 (2008) 529–531 www.elsevier.com/locate/catcom
Dodecatungstophosphoric acid (H3PW12O40) as a highly efficient catalyst for the amidation of alcohols and protected alcohols with nitriles in water: A modified Ritter reaction Habib Firouzabadi *, Nasser Iranpoor *, Abbas Khoshnood Department of Chemistry, Shiraz University, Shiraz 71454, Iran Received 14 April 2007; received in revised form 30 July 2007; accepted 31 July 2007 Available online 7 August 2007
Abstract Dodecatungstophosphoric acid (H3PW12O40) as a highly efficient catalyst for high yielding amidation of alcohols, and protected alcohols such as silyl, and THP ethers and also t-butyl methyl ether in water is described. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Dodecatungstophosphoric acid; Ritter reaction; Water; Alcohol; Silyl ether; Tetrahydropyranyl ether; Amidation; Nitrile
1. Introduction The use of water instead of toxic organic solvents for organic processes is of interest [1–6]. Furthermore, water has unique physical and chemical properties, and by utilizing these it would be possible to realize reactivity or selectivity that cannot be attained in organic solvents. However, organic solvents are still favourable media for organic reactions for mainly two reasons; first, most organic substrates are not soluble in water and second, many reactive substrates, reagents, and catalysts are sensitive towards water so that they are decomposed or deactivated in aqueous media. Therefore, study upon conditions in which the organic reactions proceed in aqueous media is of attention [7–11]. Dodecatungstophosphoric acid (H3PW12O40) is environmentally benign and commercially available compound. This solid compound is a more active catalyst than conventional inorganic and organic acids which has been used for various organic reactions [12–26]. One of the most useful methods for the synthesis of N-bulky alkyl substituted amides is called Ritter reaction [27–29], in which usually t-BuOH reacts with a nitrile in the
presence of concentrated H2SO4 in organic solvents. As an alternative to H2SO4, Ritter reaction catalyzed by BF3 Æ Et2O [30], Bi(OTf)3 [31], t-butylacetate/H2SO4 [32], trifluromethane sulfonic anhydride [33] and, etc. have been also reported. Very recently, a modified Ritter reaction using camphene and wet nitriles in the presence of dodecatungstophosphoric acid (H3PW12O40) has been also reported [34,35]. 2. Experimental 2.1. General remarks Chemicals were obtained from Fluka and Merck Chemical Companies. Progress of the reactions was monitored by TLC using silica gel SILG/UV 254 plates and Shimadzu GC MS-QP 1000 EX. All products are known compounds and their IR, 1H NMR and 13C NMR were compared with those reported for the authentic samples. All yields refer to the isolated yields. 2.2. General procedure for Ritter reactions in water catalyzed by H3PW12O40
*
Corresponding authors. Tel.: +98 711 2280926; fax: +98 711 2286008. E-mail addresses: fi[email protected] (H. Firouzabadi), [email protected] (N. Iranpoor). 1566-7367/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2007.07.042
To a solution of alcohols, silyl or THP ethers (1 mmol) in water (5 mL) was added H3PW12O40 (0.14 g, 0.05 mmol)
530
H. Firouzabadi et al. / Catalysis Communications 9 (2008) 529–531
and the resulting solution was stirred for 5 min. Then, liquid nitrile (3 mmol) was added to the mixture and the resulting mixture was magnetically stirred vigorously at reflux for the appropriate reaction time (Table 1). For the reaction of solid nitriles, sodium dodecyl sulfate (SDS) (0.028 g, 0.1 mmol ) should be added to the reaction mixture. The progress of the reaction was monitored by TLC and GC. Reaction mixture was cooled and neutralized with 10% aqueous NaOH. Then the resulting mixture extracted by AcOEt (15 mL) using continuous extraction technique in order to minimize the amount of the organic solvent used [36]. The organic phase was separated and
dried over anhydrous Na2SO4 which after filtration and evaporation of the solvent gave the crude desired product. Purification of the crude product was performed by column chromatography on silica gel eluted with petroleum ether (40–60 °C)/AcOEt to afford the pure product (Table 1). 3. Results and discussion In this communication we have reported an efficient and a high yielding Ritter reaction of alcohols and protected alcohols such as; silyl and THP ethers and also t-butyl methyl ether with different nitriles in the absence of any
Table 1 Reaction of different nitriles with alcohols, silyl ethers, THP ethers and t-butyl methyl ether in water catalyzed by H3PW12O40 Entry
Nitrilesa
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 29 30 31 32 33 34 35 36 37 38 39 40 41 42 a b
CN
CN
MeO
Cl
CN
CN
Cl
CN
F3C
MeCN
ROH,ROSiMe3,ROTHP,R1OR2
Time (h)
Isolated yield (%)
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP p-MeO-PhCH2OH p-MeOPhCH2OSiMe3 p-MeO-PhCH2OTHP t-Butyl methyl ether
10 10 10 10 10 10 10 10 10 10
99 97 97 99 97 97 89 80 85 99
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP p-MeOPhCH2OH p-MeOPhCH2OSiMe3 p-MeOPhCH2OTHP t-Butyl methyl ether
15 15 15 15 15 15 15 15 15 15
96 97 97 99 97 97 90 90 90 99
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP t-Butyl methyl ether
20 20 20 20 20 20 20
90 86 89 93 88 86 90
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP t-Butyl methyl ether
15 15 15 15 15 15 15
98 97 97 98 95 95 98
t-BuOH t-BuOSiMe3 t-BuOTHP 1-Adamantol 1-Adamantol-OSiMe3 1-Adamantol-OTHP t-Butyl methyl ether
30 30 30 30 30 30 30
50b 54b 57b 88b 80b 82b 61b
t-BuOH t-BuOSiMe3 t-BuOTHP
10 10 10
98 90 90
0.1 mmol SDS was used for 4-methoxybenzonitrile, 3-chlorobenzonitrile, 4-chlorobenzonitrile and 4-trifloromethylbenzonitrile. (0.2 mmol, 0.56 g ) of H3PW12O40 was used.
H. Firouzabadi et al. / Catalysis Communications 9 (2008) 529–531
References
O
R1CN
R2 X
H3PW12O40 H2O, reflux
R2 R1
531
N H
R1=4-ClC6H5-, 3-ClC6H5-, 4-CF3C6H5-, 4-OMeC6H5-, Ph-, CH3 X=OH, OSiMe3, OTHP, OMe
Scheme 1.
organic co-solvent in water using dodecatungstophosphoric acid (H3PW12O40) as a catalyst (Scheme 1). As it is shown in Table 1, for solid nitriles tiny amounts of sodium dodecyl sulfate (SDS) should be added to the reaction mixture as a phase-transfer catalyst. In order to optimize the reaction conditions, we have studied the reaction of 4-methoxybenzonitrile as a solid nitrile with tBuOH in the presence H3PW12O40 and SDS in water at reflux conditions. We have found that the optimized condition with respect to the molar ratio of nitrile/alcohol/cat./ SDS/water was 3 mmol/1 mmol/0.1 mmol/0.1 mmol/5 mL. Then we applied this molar ratio for the reaction of other nitriles with alcohols, and also silyl, THP ethers and t-butyl methyl ether. All the reactions proceeded well in high yields as summarized in Table 1. For the reaction of liquid nitriles, addition of SDS as a phase-transfer catalyst was not necessary. In order to show the merit of the catalyst for Ritter reactions in water, we have also studied the reaction of several nitriles with t-BuOH in aqueous solutions of H2SO4, H2SO4/SDS, and water with SDS. However, the results were not satisfactory and after elongated reaction time (24 h) only 2–20% conversion was detected. Extraction of polar organic compounds from aqueous solution with organic solvents is not usually an easy task which requires a large amount of the solvent that would be also a time consuming process. In order to surmount this problem we have applied a simple continuous extraction technique [36] by which a minimum amount of the organic solvent was required to isolate the product. 4. Conclusion In conclusion, in this study we have reported a modified Ritter reaction in water in the absence of any organic cosolvent. This reaction has been catalyzed by dodecatungstophosphoric acid (H3PW12O40) as the catalyst which is an environmentally benign and a cheap commercially available compound. The application of this protocol for the high yielding amidation reaction of alcohols, silyl and THP ethers and also t-butyl methyl ether with structurally diverse nitriles shows the broad application of the method in organic synthesis. Acknowledgements We are thankful to TWAS Chapter of Iran based at ISMO and the Shiraz University Research Council for the support of this work.
[1] P.A. Grieco (Ed.), Organic Synthesis in Water, Blacky Academic, Professional, London, 1998. [2] C.-J. Li, Chem. Soc. Rev 35 (2006) 68. [3] U.-M. Lindstro¨m, Chem. Rev. 102 (2002) 2751. [4] C.-J. Li, Chem. Rev. 105 (2005) 3095. [5] K. Manabe, S. Kobayashi, Chem. Eur. J. 8 (2002) 4094. [6] D. Sinou, Adv. Synth. Catal. 344 (2002) 237. [7] H. Firouzabadi, N. Iranpoor, A.A. Jafari, Adv. Synth. Catal. 347 (2005) 655. [8] H. Firouzabadi, N. Iranpoor, A. Garzan, Adv. Synth. Catal. 347 (2005) 1925. [9] N. Iranpoor, H. Firouzabadi, M. Shekarrize, Org. Biomol. Chem. 1 (2003) 724. [10] H. Firouzabadi, N. Iranpoor, A.A. Jafari, E. Riazymontazer, Adv. Synth. Catal. 348 (2006) 434. [11] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, Chem. Commun. 6 (2005) 789. [12] V. Kozhevnikov, in: E. Derouane (Ed.), Catalyst for Fine Chemical Synthesis, Catalyst by Polyoxometalates, vol. 2, Wiley, New York, 2002. [13] S. Nakato, M. Kimura, T. Okuhara, Chem. Lett. (1997) 389. [14] H. Firouzabadi, A.A. Jafari, J. Iran. Chem. Soc. 2 (2005) 85. [15] H. Firouzabadi, N. Iranpoor, A.A. Jafari, Synlett (2005) 299. [16] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, Tetrahedron 60 (2004) 10843. [17] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, Tetrahedron Lett. 44 (2003) 5343. [18] H. Firouzabadi, N. Iranpoor, A.A. Jafari, J. Organomet. Chem. 690 (2005) 1556. [19] H. Firouzabadi, N. Iranpoor, A.A. Jafari, J. Mol. Cat. A: Chem. 227 (2005) 97. [20] H. Firouzabadi, N. Iranpoor, A.A. Jafari, Tetrahedron Lett. 46 (2005) 2683. [21] H. Firouzabadi, N. Iranpoor, K. Amani, Synthesis (2002) 59. [22] H. Firouzabadi, N. Iranpoor, K. Amani, F. Nowrouzi, J. Chem. Soc. Perkin Trans. 1 (2002) 2601. [23] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, K. Amani, Chem. Commun. (2003) 764. [24] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, K. Amani, Tetrahedron Lett. 44 (2003) 3951. [25] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, K. Amani, Green Chem. 3 (2001) 131. [26] H. Firouzabadi, N. Iranpoor, K. Amani, Synth. Commun. 34 (2004) 3587. [27] F.R. Benson, J.J. Ritter, J. Am. Chem. Soc. 71 (1949) 4128. [28] J.J. Ritter, P.P. Minieri, J. Am. Chem. Soc. 70 (1948) 4045. [29] L.I. Krimen, D. Cota, J.J. Ritter, Org. React. 17 (1969) 213. [30] H. Firouzabadi, A.R. Sardarian, H. Badparva, Synth. Commun. 24 (1994) 601. [31] E. Callens, A.J. Burton, A.G.M. Barrett, Tetrahedron Lett. 47 (2006) 8699. [32] K.L. Reddy, Tetrahedron Lett. 44 (2003) 1453. [33] A.G. Martinez, R.M. Alvarez, E.T. Vilar, A.G. Fraile, M. Hanack, L.R. Subramanian, Tetrahedron Lett. 30 (1989) 581. [34] V.R. Kartashov, K.V. Malkova, A.V. Arkhipova, T.N. Sokolova, Russ. J. Org. Chem. 42 (2006) 966. [35] V.R. Kartashov, A.V. Arkhipova, K.V. Malkova, T.N. Sokolova, Russ. Chem. Bull. Int. Ed. 55 (2006) 387. [36] Vogel’s Textbook of Practical Organic Chemistry, fourth ed., Longman, London, 1986.