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Regioselective iodination of aromatic compounds with potassium iodide in the presence of benzyltriphenylphosphonium perchlorate
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Chinese Chemical Letters 23 (2012) 261–264 www.elsevier.com/locate/cclet
Regioselective iodination of aromatic compounds with potassium iodide in the presence of benzyltriphenylphosphonium perchlorate Jalal Albadi a,*, Masoumeh Abedini b, Nasir Iravani a a
Young Research Club, Gachsaran branch, Islamic Azad University, Gachsaran, Iran b Department of Chemistry, College of Science, University of Guilan, Rasht, Iran Received 24 August 2011 Available online 24 January 2012
Abstract A simple and efficient method for the selective iodination of various aromatic compounds by using potassium iodide in the presence of benzyltriphenylphosphonium perchlorate, is reported. This method provides several advantages such as good selectivity between ortho and para positions of aromatic compounds and high yields of the products. # 2011 Jalal Albadi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Benzyl triphenylphosphonium perchlorate; Iodination; Aromatic compound; Potassium iodide
Aryl iodides are important intermediates for the synthesis of various pharmaceutical and bioactive compounds. They can be used in Heck reactions as well as Still and Negishi cross couplings reactions and have found applications in numerous medicinally and industrially valuable product [1,2]. Due to the low reactivity of iodine, direct iodination of aromatic compounds is difficult and requires the presence of an activating agent such as oxidizing reagents to produce a strongly electrophilic I+ species. In addition, direct iodination by iodine, generates hydrogen iodide, which is corrosive, toxic and pollutes the environment. Various methods have been used for the iodination of aromatic compounds which of them CAN/I2 [3], 1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate/I2 [4], HIO3/I2 [5], N-iodosaccharin [6], NH4I/H2O2 [7], I2/O2/H5PV2Mo10O40 [8], NaI/cerium(IV) trihydroxide/SDS [9], ICl/In(OTf)3 [10], NaClO2/NaI/HCl [11], and KI/tert-butyl hydroperoxide [12], pyridinium iodochloride (PyICl) [13], potassium ferrate supported on montmorillonite [14], PVP-H2O2/KI or I2 [15]. However, in spite of their potential utility, the practical application of most of these reagents suffers from disadvantages such as harsh reaction conditions, low regioselectivity, the use of expensive or less easily available reagents, long reaction times, low yields and tedious work-up. Therefore, due to importance of aryliodides, introduction of new methods for the preparation of these compounds in terms of increase of the selectivity and also the yields of the para-products, potential simplicity, and short reaction times, is still in demand. 1. Experimental General: All products are known and therefore, their physical data are not reported. Products were identified by comparison of their spectral and physical data with those of the known samples. Chemicals were purchased from * Corresponding author. E-mail address: [email protected] (J. Albadi). 1001-8417/$ – see front matter # 2011 Jalal Albadi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2011.12.010
262
J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
Fluka, Merck, and Aldrich Chemical Companies. Benzyl triphenylphosphonium perchlorate, was prepared according to the previously reported same method [18]. General procedure for iodination of aromatic compounds: A mixture of aromatic compound (1 mmol), benzyl triphenylphosphonium perchlorate, (1 mmol) and potassium iodide (1 mmol) in acetonitrile (3 mL), was heated under reflux conditions. After completion of the reaction (monitored by TLC), the reaction mixture was filtered and poured into an aqueous sodium thiosulfate solution (1 mol/L) and extracted with dichloromethane (3 5 mL). The organic layer is dried over anhydrous calcium chloride. Evaporation of the solvent followed by recrystallization or column chromatography on silica gel gave the corresponding iodinated compounds in high yields (Table 1). Table 1 Iodination of aromatic compounds with KI in the presence of BTPPPC. Entry
Substrate
Product
OCH3
1
2
H3C
OCH3
Time(h)
Yield (%) a
I
OCH3
1
86
H3C
OCH3
2
80
OCH3
0.5
88
OCH3
1
87
OCH3
1.2
85
OCH3
2
83
0.5
88
OH
0.45
89
OH
0.5
85
1
90
I
I
OCH3
3
H3CO
H3CO
OCH3
4
I
CH3
CH
OCH3
5
I
Cl
6
Cl
Cl
Cl
OCH3
I
OH
7
I
I
OH
8
OH
H3C
H3C
OH
9
I
CH3
10
Cl
CH3 I
OH Cl
OH
CH3 CH3
J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
263
Table 1 (Continued ) Entry
Substrate
11
H3COC
Time(h)
Yield (%) a
3
75
3
77
4.5
80
6
78
1.2
87
OH
0.3
90
N(CH3)2
0.5
85
2
86
5
72
Product
H3COC
OH
OH I
12
I
OH NO2
O2N
OH NO2
OH
13
O2N
OH I
I
14
OH
O2N
OH
O 2N
NO2
15
NO2
OH
I
OH
Cl
Cl
16
OH
I
HO
17
HO
N(CH3)2
18
CH3
19
COOH
I
I
CH3
COOH I
a
Isolated yields.
2. Results and discussion In continuation of our research on the halogenations of aromatic compounds [16], we herein, report the highly efficient and selective iodination of aromatic compounds employing potassium iodide as the source of iodine and benzyltriphenylphosphonium perchlorate (BTPPPC), as the oxidant in acetonitrile as solvent (Scheme 1). At first, for the optimization of the reaction conditions, the iodination of anisole, using potassium iodide and BTPPPC in various solvents was examined. The best result was achieved by caring out the reaction of anisole, potassium iodide and BTPPPC (with 1:1:1 mol ratio) in acetonitrile under reflux conditions (Table 1, entry 1). A wide range of aromatic compounds, were successfully reacted to afford the desired iodinated products. Results show that
J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
264
R
R KI/BTPPPC CH3CN, reflux
I
Scheme 1.
compounds containing electron donating were found to be most reactive and converted to the corresponding monoiodinated products in shorter reaction times (Table 1, entries 1,3,7,17). However, the rate of reaction was slower when the ring contains an electron-withdrawing groups (Table 1, entries 12,14,15). It has been observed that chemoselective conversion of aromatic compounds to their para substituted products was achieved in excellent yield. When the paraposition was blocked, monoiodinated products were obtained over longer reaction times (Table 1, entry 2,6,11,13,14). Anisole gave mainly the para isomer as the major product in short reaction time (Table 1 entries 1). However 4-methyl anisole was iodinated after 2 h to afford 2-iodo-4-methylanisol (Table 1, entry 2). Phenol, ortho-cholorophenol, orthocresol and ortho-nitrophenol were quantitatively converted to the para iodinated products with respect to the hydroxyl groups in good yields (Table 1, entries 7,9,12,15). Plausible mechanism of the reaction is shown in Eq. (1), based on the literature [17], our observations and obtained results. 1: ArH þ KI þ PhCH2 PPh3 ClO4 ! ArI þ KOH þ PhCH2 PPh3 ClO3 or 2: KI þ pHCH2 PPh3 ClO4 ! KOI þ PhCH2 PPH3 ClO3 KOI þ ArH ! ArI þ KOH
(1)
In conclusion, we have described an efficient method for the iodination of aromatic compounds using KI and BTPPPC, under reflux conditions. Simple work-up, good chemoselectivity, high yields of the products and short reaction time will make this procedure a useful addition to the available methods. Acknowledgment We are thankful to the Gachsaran branch, Islamic Azad University, for the partial support of this work. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
A. Butler, J.V. Walker, Chem. Rev. 93 (1993) 1937. E.B. Merkushev, Synthesis (1988) 923. B. Das, M. Krishnaiah, K. Venkateswarlu, et al. Tetrahedron Lett. 48 (2007) 81. R. Badri, M. Gorjizadeh, Chin. Chem. Lett. 20 (2009) 1439. A. Vibhute, Sh. Mokle, K. Karamunge, et al. Chin. Chem. Lett. 21 (2010) 914. L. Bailey, S.C. Handy, Tetrahedron Lett. 52 (2011) 2413. N. Narender, K. Suresh Kumar Reddy, K.V.V. Krishna Mohan, et al. Tetrahedron Lett. 48 (2007) 6124. O.V. Branytska, R. Neumann, J. Org. Chem. 68 (2003) 9510. H. Firouzabadi, N. Iranpoor, A. Garzan, Adv. Synth. Catal. 347 (2005) 1925. R. Johnsson, A. Meijer, U. Ellervik, Tetrahedron 61 (2005) 11657. L. Lista, A. Pezzella, A. Napolitano, et al. Tetrahedron 64 (2008) 234. R. Rajender Reddy, M. Venkateshwar, C. Uma Maheswari, et al. Tetrahedron Lett. 51 (2010) 2170. S.V. Khansole, Sh Mokle, M.A. Sayyed, Y.B. Vibhute, J. Chin. Chem. Soc. 22 (2011) 1427. H. Keipour, M.A. Khalilzadeh, B. Mohtat, et al. Chin. Chem. Lett. 22 (2011) 1427. A.R. Pourali, M. Ghanei, Chin. J. Chem. 24 (2006) 1077. H. Tajik, I. Mohammadpoor-Baltork, J. Albadi, Synth. Commun. 37 (2007) 323. H. Adibi, A.R. Hajipour, M. Hashemi, Tetrahedron Lett. 48 (2007) 1255. A.R. Hajipour, S.E. Mallakpour, I. Mohammadpoor-Baltork, et al. Tetrahedron 58 (2002) 143.
Chinese Chemical Letters 23 (2012) 261–264 www.elsevier.com/locate/cclet
Regioselective iodination of aromatic compounds with potassium iodide in the presence of benzyltriphenylphosphonium perchlorate Jalal Albadi a,*, Masoumeh Abedini b, Nasir Iravani a a
Young Research Club, Gachsaran branch, Islamic Azad University, Gachsaran, Iran b Department of Chemistry, College of Science, University of Guilan, Rasht, Iran Received 24 August 2011 Available online 24 January 2012
Abstract A simple and efficient method for the selective iodination of various aromatic compounds by using potassium iodide in the presence of benzyltriphenylphosphonium perchlorate, is reported. This method provides several advantages such as good selectivity between ortho and para positions of aromatic compounds and high yields of the products. # 2011 Jalal Albadi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Benzyl triphenylphosphonium perchlorate; Iodination; Aromatic compound; Potassium iodide
Aryl iodides are important intermediates for the synthesis of various pharmaceutical and bioactive compounds. They can be used in Heck reactions as well as Still and Negishi cross couplings reactions and have found applications in numerous medicinally and industrially valuable product [1,2]. Due to the low reactivity of iodine, direct iodination of aromatic compounds is difficult and requires the presence of an activating agent such as oxidizing reagents to produce a strongly electrophilic I+ species. In addition, direct iodination by iodine, generates hydrogen iodide, which is corrosive, toxic and pollutes the environment. Various methods have been used for the iodination of aromatic compounds which of them CAN/I2 [3], 1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate/I2 [4], HIO3/I2 [5], N-iodosaccharin [6], NH4I/H2O2 [7], I2/O2/H5PV2Mo10O40 [8], NaI/cerium(IV) trihydroxide/SDS [9], ICl/In(OTf)3 [10], NaClO2/NaI/HCl [11], and KI/tert-butyl hydroperoxide [12], pyridinium iodochloride (PyICl) [13], potassium ferrate supported on montmorillonite [14], PVP-H2O2/KI or I2 [15]. However, in spite of their potential utility, the practical application of most of these reagents suffers from disadvantages such as harsh reaction conditions, low regioselectivity, the use of expensive or less easily available reagents, long reaction times, low yields and tedious work-up. Therefore, due to importance of aryliodides, introduction of new methods for the preparation of these compounds in terms of increase of the selectivity and also the yields of the para-products, potential simplicity, and short reaction times, is still in demand. 1. Experimental General: All products are known and therefore, their physical data are not reported. Products were identified by comparison of their spectral and physical data with those of the known samples. Chemicals were purchased from * Corresponding author. E-mail address: [email protected] (J. Albadi). 1001-8417/$ – see front matter # 2011 Jalal Albadi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2011.12.010
262
J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
Fluka, Merck, and Aldrich Chemical Companies. Benzyl triphenylphosphonium perchlorate, was prepared according to the previously reported same method [18]. General procedure for iodination of aromatic compounds: A mixture of aromatic compound (1 mmol), benzyl triphenylphosphonium perchlorate, (1 mmol) and potassium iodide (1 mmol) in acetonitrile (3 mL), was heated under reflux conditions. After completion of the reaction (monitored by TLC), the reaction mixture was filtered and poured into an aqueous sodium thiosulfate solution (1 mol/L) and extracted with dichloromethane (3 5 mL). The organic layer is dried over anhydrous calcium chloride. Evaporation of the solvent followed by recrystallization or column chromatography on silica gel gave the corresponding iodinated compounds in high yields (Table 1). Table 1 Iodination of aromatic compounds with KI in the presence of BTPPPC. Entry
Substrate
Product
OCH3
1
2
H3C
OCH3
Time(h)
Yield (%) a
I
OCH3
1
86
H3C
OCH3
2
80
OCH3
0.5
88
OCH3
1
87
OCH3
1.2
85
OCH3
2
83
0.5
88
OH
0.45
89
OH
0.5
85
1
90
I
I
OCH3
3
H3CO
H3CO
OCH3
4
I
CH3
CH
OCH3
5
I
Cl
6
Cl
Cl
Cl
OCH3
I
OH
7
I
I
OH
8
OH
H3C
H3C
OH
9
I
CH3
10
Cl
CH3 I
OH Cl
OH
CH3 CH3
J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
263
Table 1 (Continued ) Entry
Substrate
11
H3COC
Time(h)
Yield (%) a
3
75
3
77
4.5
80
6
78
1.2
87
OH
0.3
90
N(CH3)2
0.5
85
2
86
5
72
Product
H3COC
OH
OH I
12
I
OH NO2
O2N
OH NO2
OH
13
O2N
OH I
I
14
OH
O2N
OH
O 2N
NO2
15
NO2
OH
I
OH
Cl
Cl
16
OH
I
HO
17
HO
N(CH3)2
18
CH3
19
COOH
I
I
CH3
COOH I
a
Isolated yields.
2. Results and discussion In continuation of our research on the halogenations of aromatic compounds [16], we herein, report the highly efficient and selective iodination of aromatic compounds employing potassium iodide as the source of iodine and benzyltriphenylphosphonium perchlorate (BTPPPC), as the oxidant in acetonitrile as solvent (Scheme 1). At first, for the optimization of the reaction conditions, the iodination of anisole, using potassium iodide and BTPPPC in various solvents was examined. The best result was achieved by caring out the reaction of anisole, potassium iodide and BTPPPC (with 1:1:1 mol ratio) in acetonitrile under reflux conditions (Table 1, entry 1). A wide range of aromatic compounds, were successfully reacted to afford the desired iodinated products. Results show that
J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
264
R
R KI/BTPPPC CH3CN, reflux
I
Scheme 1.
compounds containing electron donating were found to be most reactive and converted to the corresponding monoiodinated products in shorter reaction times (Table 1, entries 1,3,7,17). However, the rate of reaction was slower when the ring contains an electron-withdrawing groups (Table 1, entries 12,14,15). It has been observed that chemoselective conversion of aromatic compounds to their para substituted products was achieved in excellent yield. When the paraposition was blocked, monoiodinated products were obtained over longer reaction times (Table 1, entry 2,6,11,13,14). Anisole gave mainly the para isomer as the major product in short reaction time (Table 1 entries 1). However 4-methyl anisole was iodinated after 2 h to afford 2-iodo-4-methylanisol (Table 1, entry 2). Phenol, ortho-cholorophenol, orthocresol and ortho-nitrophenol were quantitatively converted to the para iodinated products with respect to the hydroxyl groups in good yields (Table 1, entries 7,9,12,15). Plausible mechanism of the reaction is shown in Eq. (1), based on the literature [17], our observations and obtained results. 1: ArH þ KI þ PhCH2 PPh3 ClO4 ! ArI þ KOH þ PhCH2 PPh3 ClO3 or 2: KI þ pHCH2 PPh3 ClO4 ! KOI þ PhCH2 PPH3 ClO3 KOI þ ArH ! ArI þ KOH
(1)
In conclusion, we have described an efficient method for the iodination of aromatic compounds using KI and BTPPPC, under reflux conditions. Simple work-up, good chemoselectivity, high yields of the products and short reaction time will make this procedure a useful addition to the available methods. Acknowledgment We are thankful to the Gachsaran branch, Islamic Azad University, for the partial support of this work. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
A. Butler, J.V. Walker, Chem. Rev. 93 (1993) 1937. E.B. Merkushev, Synthesis (1988) 923. B. Das, M. Krishnaiah, K. Venkateswarlu, et al. Tetrahedron Lett. 48 (2007) 81. R. Badri, M. Gorjizadeh, Chin. Chem. Lett. 20 (2009) 1439. A. Vibhute, Sh. Mokle, K. Karamunge, et al. Chin. Chem. Lett. 21 (2010) 914. L. Bailey, S.C. Handy, Tetrahedron Lett. 52 (2011) 2413. N. Narender, K. Suresh Kumar Reddy, K.V.V. Krishna Mohan, et al. Tetrahedron Lett. 48 (2007) 6124. O.V. Branytska, R. Neumann, J. Org. Chem. 68 (2003) 9510. H. Firouzabadi, N. Iranpoor, A. Garzan, Adv. Synth. Catal. 347 (2005) 1925. R. Johnsson, A. Meijer, U. Ellervik, Tetrahedron 61 (2005) 11657. L. Lista, A. Pezzella, A. Napolitano, et al. Tetrahedron 64 (2008) 234. R. Rajender Reddy, M. Venkateshwar, C. Uma Maheswari, et al. Tetrahedron Lett. 51 (2010) 2170. S.V. Khansole, Sh Mokle, M.A. Sayyed, Y.B. Vibhute, J. Chin. Chem. Soc. 22 (2011) 1427. H. Keipour, M.A. Khalilzadeh, B. Mohtat, et al. Chin. Chem. Lett. 22 (2011) 1427. A.R. Pourali, M. Ghanei, Chin. J. Chem. 24 (2006) 1077. H. Tajik, I. Mohammadpoor-Baltork, J. Albadi, Synth. Commun. 37 (2007) 323. H. Adibi, A.R. Hajipour, M. Hashemi, Tetrahedron Lett. 48 (2007) 1255. A.R. Hajipour, S.E. Mallakpour, I. Mohammadpoor-Baltork, et al. Tetrahedron 58 (2002) 143.