Synlett 2013; 24(9): 1113-1116
DOI: 10.1055/s-0033-1338386
letter
© Georg Thieme Verlag Stuttgart · New York

Benzylation of Aromatic Compounds Catalyzed by 3-Methyl-1-sulfonic Acid Imidazolium Tetrachloroaluminate and Silica Sulfuric Acid under Mild Conditions

Mohammad Ali Zolfigol*
a   Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran   Fax: +98(811)8257407   Email: mzolfigol@yahoo.com
,
Hooshang Vahedi
b   Department of Chemistry, Payame Noor University, PO Box 19395-4697, Teheran, Iran
,
Saeid Azimi
b   Department of Chemistry, Payame Noor University, PO Box 19395-4697, Teheran, Iran
,
Ahmad Reza Moosavi-Zare
c   Department of Chemistry, University of Sayyed Jamaleddin Asadabadi, Asadabad 6541835583, Iran
› Author Affiliations
Further Information

Publication History

Received: 01 February 2013

Accepted after revision: 24 March 2013

Publication Date:
16 April 2013 (online)

 


Abstract

In this work, efficient procedures for benzylation of a range of aromatic compounds by benzyl acetate in the presence of catalytic amounts of 3-methyl-1-sulfonic acid imidazolium tetrachloroaluminate ([Msim]AlCl4) or silica sulfuric acid (SSA) under mild conditions are described. Simple methodology, easy workup procedure, clean reaction and reusability of the catalyst are some advantages of this work.


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Diarylmethanes are an interesting group of bioactive compounds, and are also very important and useful in organic synthesis.[1] [2] [3] Catalytic systems used for the benzylation of aromatic compounds include HfO2–HfCl4,[3] aliquat 336,[4] phosphomolybdic acid supported silica gel,[5] TMSOTf,[6] organozinc and organoboron derivatives, HCl, H2SO4, MeSO3H, HOTf and HNTf2.[7] However, some of these procedures suffer from various drawbacks, such as complex workup and purification, production of significant amounts of waste materials, use of strongly acidic conditions, and occurrence of side reactions with poor yields.

In recent years, silica sulfuric acid (SSA), as one of the more important solid acid catalysts,[8] [9] [10] [11] [12] and 3-methyl-1-sulfonic acid imidazolium tetrachloroaluminate ([Msim]AlCl4), as a new sulfonic acid functionalized imidazolium salts (SAFIS) with interesting applications, have been reported (Figure [1]).[13] [14] [15]

Herein, we describe the use of SSA and [Msim]AlCl4 as catalysts for benzylation of a range of aromatic compounds under mild conditions to give diarylmethanes, and compare their catalytic activity in this reaction (Scheme [1]). The promising aspects of this methodology are its efficiency, high yield, cleaner reaction profile, and simplicity, rendering it an attractive process for the preparation of diarylmethanes.

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Figure 1
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Scheme 1The preparation of diarylmethanes catalyzed by [Msim]AlCl4 (method a) and SSA (method b)

To optimize the reaction conditions, we selected the reaction of anisole and benzyl acetate as a model reaction (Scheme [2]).

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Scheme 2Benzylation of anisole as model reaction

We observed that the best results were obtained using 5 mol% of [Msim]AlCl4 at 70 °C or 7 mol% of SSA at 80 °C (Table [1]).

Table 1 Effect of Different Amounts of the Catalyst and Temperature on the Reaction of Anisole with Benzyl Acetate under Solvent-Free Conditions

Catalyst

Catalyst (mol%)

Temp (°C)

Time (min)

Yielda (%)

[Msim]AlCl4

 1

70

 90

48

[Msim]AlCl4

 3

70

 90

60

[Msim]AlCl4

 5

70

 60

85

[Msim]AlCl4

 7

70

 60

85

[Msim]AlCl4

10

70

 60

85

[Msim]AlCl4

 5

60

120

40

[Msim]AlCl4

 5

80

 60

85

SSA

 1

80

120

51

SSA

 3

80

120

60

SSA

 5

80

 90

74

SSA

 7

80

 60

83

SSA

10

80

 60

83

SSA

 7

70

 90

69

SSA

 7

90

 60

83

a Isolated yield.

In a further study, the model reaction was tested with [Msim]AlCl in several solvents; the corresponding results are displayed in Table [2], indicating that the best result was obtained under solvent-free conditions.

Table 2 Reaction of Anisole with Benzyl Acetate Using [Msim]AlCl4 (5 mol%) in Different Solvents at Reflux

Entry

Solvent

Time (min)

Yielda (%)

1

EtOH

120

46

2

MeOH

120

34

3

MeCN

 90

15

4

CH2Cl2

 60

75

5

MeCOOEt

100

15

6b

 60

85

a Isolated yield.

b Reaction was carried out at 70 °C.

Subsequently we examined various aromatic substrates with benzyl acetate as electrophile under solvent-free conditions and with solvent using SSA or [Msim]AlCl4 as catalyst (Table [3]). In certain instances, reaction occurred in the absence of solvent (Table [3] entries 1–3, 7 and 8) and in others, CH2Cl2 was the reaction solvent. Substrates with electron-donating substituents gave high yields of benzylated products under mild conditions.

Mendoza et. al have reported benzylation of certain aromatic substrates using HOTf as a Brønsted acidic catalyst but indole was found to react poorly with the acid catalyst, leading to decomposition products and unreacted indole.[7] However, with our protocol, 3-benzyl indole was obtained in good yield using [Msim]AlCl4 or SSA as catalyst (Table [3], entry 6). Generally, our protocol is more efficient than previous methods;[16] with substrates possessing additional electron-donating groups, the yield increased and reaction time decreased (Table [3], entries 1 and 2) and, with phenol as substrate, the p-benzylphenol was produced rather than the o-benzylphenol. Furthermore, with indole, trimerization was not observed.[17]

Table 3 Synthesis of Diarylmethanes Using SSA and [Msim]AlCl4 as Catalyst

Entry

Nucleophile

Main product

Time (h)/ Yielda (%) {[Msim]AlCl4}

Time (h)/ Yielda (%) (SSA)

Time (h)/ Yielda,b (%)

1

1/93

1/89

1/86[7]

2

1/85

1/83

1/23[21] 5/80.3[18]

3

1.5/86

1.5/82

0.5/23[21]

4c

2/95

2/89

0.58/32[20] 6/65[19]

5c

2/89

2/80

 6c

3/87

3/80

18/69[16]

 7

2/86

2/81

40/63[3]

 8

2.5/92

3/87

40/87[3]

 9c,d

3/95

4/90

10c,e

3.5/90

4.5/86

a Isolated yield.

b Literature results compared with the presented results.

c These reactions were carried out in CH2Cl2 under reflux.

d Ratio of benzyl acetate to nucleophile was 4:1.

e Ratio of benzyl acetate to nucleophile was 2:1.

The recyclability of the catalyst was also investigated with the reaction of anisole and benzyl acetate as a model reaction. The reaction mixture was extracted with CH2Cl2 to separate products form the [Msim]AlCl4 or with ethanol to separate from the SSA. Subsequently, the catalyst was employed for a second cycle reaction. We observed that the catalytic activity of [Msim]AlCl4 (Table [4]) and SSA (Table [5]) was retained, within the limits of experimental error, for five and four successive runs, respectively.

Table 4 Reaction of Anisole and Benzyl Acetate in the Presence of Recycled [Msim]AlCl4 under Solvent-Free Conditions at 70 °C

Entry

Cycle

Time (min)

Yielda (%)

1

1st run

 60

85

2

2nd run

 80

80

3

3rd run

 90

73

4

4th run

115

67

5

5th run

120

61

a Isolated yield.

Table 5 Reaction of Anisole and Benzyl Acetate in the Presence of Recycled SSA under Solvent-Free Conditions at 80 °C

Entry

Cycle

Time (min)

Yielda (%)

1

1st run

 60

83

2

2nd run

 85

75

3

3rd run

100

68

4

4th run

130

60

a Isolated yield.

In summary, we have reported two new procedures[22] for the preparation of diarylmethanes by the benzylation of a range of aromatic compounds using 3-methyl-1-sulfonic acid imidazolium tetrachloroaluminate {[Msim]AlCl4} or silica sulfuric acid (SSA) as heterogeneous catalysts with high yields under mild conditions.


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Acknowledgement

The authors gratefully acknowledge partial support of this work by the Research Affairs Office of Bu-Ali Sina University (Grant number 32-1716: Development of Chemical Methods, Reagents and molecules), and the Center of Excellence in Development of Chemical Method (CEDCM), Hamedan, I. R. Iran.

  • References and Notes

  • 1 Choudary BM, Mulukutla RS, Klabunde KJ. J. Am. Chem. Soc. 2003; 125: 2020
  • 2 Martínez AG, Barcina JO, Heras Md. R. C, Cerezo ÁD. F. Org. Lett. 2000; 2: 1377
  • 3 Zhang CY, Gao XQ, Zhang JH, Peng XJ. Chin. Chem. Lett. 2009; 20: 913
  • 4 Yang H.-M, Lin C.-L. J. Mol. Catal. A: Chem. 2003; 206: 67
  • 5 Yadav JS, Reddy BV. S, Reddy AS. J. Mol. Catal. A: Chem. 2008; 280: 219
  • 6 Theerthagiri P, Lalitha A. Tetrahedron Lett. 2010; 51: 5454
  • 7 Mendoza O, Rossey G, Ghosez L. Tetrahedron Lett. 2011; 52: 2235
  • 8 Mohammadpoor-Baltork I, Moghadam M, Tangestaninejad S, Mirkhani V, Mohammadiannejad-Abbasabadi K, Zolfigol MA. Compt. Rend. Chim. 2011; 14: 934
  • 9 Veisi H. Tetrahedron Lett. 2010; 51: 2109
  • 10 Shirini F, Sadeghzadeh P, Abedini M. Chin. Chem. Lett. 2009; 20: 1457
  • 11 Zolfigol MA. Tetrahedron 2001; 57: 9509
  • 12 Khalafi-Nezhad A, Parhami A, Soltani Rad MN, Zolfigol MA, Zare A. Tetrahedron Lett. 2007; 48: 5219
  • 13 Zolfigol MA, Kazaei A, Moosavi-Zare AR. J. Org. Chem. 2012; 77: 3640
  • 14 Zolfigol MA, Khazaei A, Moosavi-Zare AR, Zare A, Khakyzadeh V. Appl. Catal. A: Gen. 2011; 400: 70
  • 15 Zolfigol MA, Khazaei A, Moosavi-Zare AR, Zare A. Org. Prep. Proced. Int. 2012; 42: 95
  • 16 Zhu Y, Rawal VH. J. Am. Chem. Soc. 2011; 134: 111
  • 17 Valentine RA, Whyte A, Awaga K, Robertson N. Tetrahedron Lett. 2012; 53: 657
  • 18 Silva M, Costa C, Pinto M, Lachter E. Reactive Polymers 1995; 25: 55
  • 19 Podder S, Roy S. Tetrahedron 2007; 63: 9146
  • 20 Guo Q, Li L, Chen L, Wang Y, Ren S, Shen B. Energy Fuels 2009; 23: 51
  • 21 Keglevich G, Balint E, Karsai E, Grün A, Balint M, Greiner S. Tetrahedron Lett. 2008; 49: 5039
  • 22 General Procedure for the Synthesis of Diarylmethanes Using [Msim]AlCl4 : To a mixture of aromatic substrate (1 mmol) and benzyl acetate (1 mmol) was added [Msim]AlCl4 (0.017 g, 5 mol%) and the mixture was heated to 70 °C for the appropriate time (Table 3). After completion of the reaction, as monitored by TLC, the reaction mixture was cooled to r.t. and CH2Cl2 (2–5 mL) was added to separate the catalyst. After filtration, the pure product was obtained using plate chromatography on silica gel with n-hexane–EtOAc (10:2) as eluent. Note: In some cases, the reaction was carried out in CH2Cl2 (5 mL) at reflux (Table 3, entries 4–6, 9 and 10). General Procedure for the Synthesis of Diarylmethanes Using SSA: To a mixture of aromatic substrate (1 mmol), and benzyl acetate (1 mmol), silica sulfuric acid (0.054 g, 7 mol%) was added and the mixture was heated to 80 °C for the appropriate time (Table 3). After completion of the reaction, as monitored by TLC, the reaction mixture was cooled to r.t. Absolute EtOH (2–5 mL) was added and the mixture was filtered to separate the catalyst. The pure product was obtained using plate chromatography on silica gel with n-hexane–EtOAc (10:2) as eluent. Note: In some cases, the reaction was carried out in CH2Cl2 (5 mL) at reflux (Table 3, entries 4–6, 9 and 10).

  • References and Notes

  • 1 Choudary BM, Mulukutla RS, Klabunde KJ. J. Am. Chem. Soc. 2003; 125: 2020
  • 2 Martínez AG, Barcina JO, Heras Md. R. C, Cerezo ÁD. F. Org. Lett. 2000; 2: 1377
  • 3 Zhang CY, Gao XQ, Zhang JH, Peng XJ. Chin. Chem. Lett. 2009; 20: 913
  • 4 Yang H.-M, Lin C.-L. J. Mol. Catal. A: Chem. 2003; 206: 67
  • 5 Yadav JS, Reddy BV. S, Reddy AS. J. Mol. Catal. A: Chem. 2008; 280: 219
  • 6 Theerthagiri P, Lalitha A. Tetrahedron Lett. 2010; 51: 5454
  • 7 Mendoza O, Rossey G, Ghosez L. Tetrahedron Lett. 2011; 52: 2235
  • 8 Mohammadpoor-Baltork I, Moghadam M, Tangestaninejad S, Mirkhani V, Mohammadiannejad-Abbasabadi K, Zolfigol MA. Compt. Rend. Chim. 2011; 14: 934
  • 9 Veisi H. Tetrahedron Lett. 2010; 51: 2109
  • 10 Shirini F, Sadeghzadeh P, Abedini M. Chin. Chem. Lett. 2009; 20: 1457
  • 11 Zolfigol MA. Tetrahedron 2001; 57: 9509
  • 12 Khalafi-Nezhad A, Parhami A, Soltani Rad MN, Zolfigol MA, Zare A. Tetrahedron Lett. 2007; 48: 5219
  • 13 Zolfigol MA, Kazaei A, Moosavi-Zare AR. J. Org. Chem. 2012; 77: 3640
  • 14 Zolfigol MA, Khazaei A, Moosavi-Zare AR, Zare A, Khakyzadeh V. Appl. Catal. A: Gen. 2011; 400: 70
  • 15 Zolfigol MA, Khazaei A, Moosavi-Zare AR, Zare A. Org. Prep. Proced. Int. 2012; 42: 95
  • 16 Zhu Y, Rawal VH. J. Am. Chem. Soc. 2011; 134: 111
  • 17 Valentine RA, Whyte A, Awaga K, Robertson N. Tetrahedron Lett. 2012; 53: 657
  • 18 Silva M, Costa C, Pinto M, Lachter E. Reactive Polymers 1995; 25: 55
  • 19 Podder S, Roy S. Tetrahedron 2007; 63: 9146
  • 20 Guo Q, Li L, Chen L, Wang Y, Ren S, Shen B. Energy Fuels 2009; 23: 51
  • 21 Keglevich G, Balint E, Karsai E, Grün A, Balint M, Greiner S. Tetrahedron Lett. 2008; 49: 5039
  • 22 General Procedure for the Synthesis of Diarylmethanes Using [Msim]AlCl4 : To a mixture of aromatic substrate (1 mmol) and benzyl acetate (1 mmol) was added [Msim]AlCl4 (0.017 g, 5 mol%) and the mixture was heated to 70 °C for the appropriate time (Table 3). After completion of the reaction, as monitored by TLC, the reaction mixture was cooled to r.t. and CH2Cl2 (2–5 mL) was added to separate the catalyst. After filtration, the pure product was obtained using plate chromatography on silica gel with n-hexane–EtOAc (10:2) as eluent. Note: In some cases, the reaction was carried out in CH2Cl2 (5 mL) at reflux (Table 3, entries 4–6, 9 and 10). General Procedure for the Synthesis of Diarylmethanes Using SSA: To a mixture of aromatic substrate (1 mmol), and benzyl acetate (1 mmol), silica sulfuric acid (0.054 g, 7 mol%) was added and the mixture was heated to 80 °C for the appropriate time (Table 3). After completion of the reaction, as monitored by TLC, the reaction mixture was cooled to r.t. Absolute EtOH (2–5 mL) was added and the mixture was filtered to separate the catalyst. The pure product was obtained using plate chromatography on silica gel with n-hexane–EtOAc (10:2) as eluent. Note: In some cases, the reaction was carried out in CH2Cl2 (5 mL) at reflux (Table 3, entries 4–6, 9 and 10).

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Figure 1
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Scheme 1The preparation of diarylmethanes catalyzed by [Msim]AlCl4 (method a) and SSA (method b)
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Scheme 2Benzylation of anisole as model reaction