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Tribromo melamine as novel and versatile catalyst for the formylation and acetylation of alcohols
Chinese Journal of Catalysis 35 (2014) 260–263
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r. c o m / l o c a t e / c h n j c
Article
Tribromo melamine as novel and versatile catalyst for the formylation and acetylation of alcohols Maryam Hajjami *, Arash Ghorbani‐Choghamarani, Zahra Karamshahi, Masoomeh Norouzi Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
A R T I C L E I N F O
A B S T R A C T
Article history: Received 23 September 2013 Accepted 13 November 2013 Published 20 February 2014
Keywords: Tribromo melamine Acetylation Formylation Alcohol Ethyl formate Acetic anhydride
Tribromo melamine has been found to be an efficient and green organocatalyst for the acetylation and formylation reactions of alcohols with acetic anhydride and ethyl formate at room temperature and under mild reaction conditions. © 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.
1. Introduction During the multistep synthesis of natural products, the effi‐ ciency of the synthetic protocol employed often depends large‐ ly on protection and deprotection of the functional groups. To this end, protecting groups have played a crucial role in the synthesis of complex natural products [1]. Acetylation and formylation of hydroxy groups are the most widely used trans‐ formations in organic synthesis [2–4]. Amongst protecting groups for alcohols, esters are the most important with acetate being the simplest and easiest to use. Acetylation is usually performed with reagents such as acetic anhydride or acetyl chloride in the presence of variety of acidic or basic catalysts [5]. Formylation is also a very important process in organic chemistry. O‐Formylation is the method of choice for protecting an alcoholic group in a complex synthetic sequence because deformylation can be affected selectively in the presence of
acetate or other ester protecting groups [6–8]. Several acetylation and formylation procedures for alcohols have been reported over the years [9–14], but these methods suffer from some disadvantages, such as heavy metal contami‐ nation, high temperature, formation of undesirable or toxic byproducts, expensive reagents, or long reaction times [15–18]. These issues stimulated us to research a simple, efficient, and safe catalyst for the acetylation and formylation of alcohols. In this regard, a group of compounds entitled N‐halo reagents is widely used in fine organic synthesis [19]. 2. Experimental Chemicals were purchased from Fluka, Merck, and Aldrich. The formylated and acetylated products were characterized by comparison of their spectral (IR, 1H NMR, and 13C NMR) and physical data with those of authentic samples.
* Corresponding author. Tel/Fax: +98‐8412227022; E‐mail: [email protected];[email protected] DOI: 10.1016/S1872‐2067(12)60748‐7 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 35, No. 2, February 2014
Maryam Hajjami et al. / Chinese Journal of Catalysis 35 (2014) 260–263
2.1. Formylation of 4‐tert‐butylbenzyl alcohol To the stirred mixture of 4‐tert‐butyl benzyl alcohol (1 mmol, 0.164 g) and ethyl formate (2 mL), tribromo melamine (0.1 mmol) was added without additional solvents. The result‐ ing mixture was stirred at room temperature for 30 min. The reaction was monitored by TLC. On completion of reaction, the product was extracted with CH2Cl2 (5 mL × 4). The organic layer was separated, dried over anhydrous Na2SO4 (1.5 g), and concentrated under reduced pressure. Finally, the organic sol‐ vents were evaporated, and 4‐tert‐butylbenzyl formate was obtained in 92% yield. The identity of the product was con‐ firmed by comparing the physical and spectral data with those of the known compound. 2.2. Acetylation of 3‐fluorobenzyl alcohol Tribromo melamine (0.1 mmol) was added to a solution of 3‐fluorobenzyl alcohol (0.126 g, 1 mmol) and acetic anhydride (0.204 g, 2 mmol) in dichloromethane (5 mL), and the reaction mixture was stirred at room temperature for 1 h (the progress of the reaction was monitored by TLC). On completion of the reaction, water (5 mL) and then 5% NaHCO3 (5 mL) was added to the mixture with stirring, and the product was extracted with CH2Cl2 (5 mL × 4). The organic layer was dried over anhy‐ drous Na2SO4 (1.5 g). Finally, the organic solvents were evapo‐ rated, and 3‐fluorobenzyl acetate was obtained in 86% yield. 3. Results and discussion Following our previous work in developing new methods for the protection of the hydroxy group [20–23], an effective procedure for the acetylation and formylation of alcohols with acetic anhydride and ethyl formate in the presence of catalytic amounts of tribromo melamine at room temperature (Scheme 1) has been developed. To find the optimal conditions for the formylation of alco‐ hols by this method, we selected 4‐bromobenzyl alcohol as a model substrate and treated it with ethyl formate in the pres‐ ence of different amounts of tribromo melamine at room tem‐ perature. We found that 0.05 equivalents of tribromo melamine gave the highest yield of the respective alkyl formate after 60 min at room temperature (Table 1, entry 5). The results clearly show that the tribromo melamine is effective for this transfor‐
EtOOCH, TBM solvent-free, rt
ROCOH + EtOH
ROH Ac2O, TBM CH2Cl2, rt
ROCOCH3 + CH3COOH BrHN
TBM = Tribromo melamine
N N
NHBr N
NHBr Scheme 1. Formylation and acetylation of alcohols.
Table 1 Optimization of the amount of tribromo melamine in the reaction of 4‐bromobenzyl alcohol with ethyl formate or acetic anhydride. Entry Catalyst amount (mmol) Yield a (%) 1 0.01 13 2 0.02 40 3 0.03 41 4 0.04 56 5 0.05 99 6 No catalyst Trace 7 0.01 22 8 0.02 28 9 0.03 30 10 0.04 57 11 0.05 95 12 No catalyst Trace Reaction conditions: 4‐bromobenzyl alcohol 1 mmol, ethyl formate 2 mL or acetic anhydride 2 mmol, room temperature. a Yields refer to isolated pure products.
mation, whereas, in its absence, the reaction fails to initiate even after 24 h (Table 1, entry 6). Additionally, 4‐bromobenzyl alcohol was used as a model substrate for acetylation (Table 1, entries 7–12). The reaction was monitored with different amounts of catalyst. Increasing the loading of tribromo mela‐ mine from 0.01 mmol to 0.05 mmol resulted in a considerable improvement of the yield from 22% to 95% (Table 1, entries 7 and 11). The acetylation reaction was also carried out in the absence of catalyst. Again, the reaction had not initiated after 24 h (Table 1, entry 12). To find the best solvent for the formylation, the model reac‐ tion was performed in a number of solvents, and moderate to poor yields of the corresponding alkyl formates were obtained (Table 2, entry 2–6). A far higher yield was obtained under solvent‐free conditions (Table 2, entry 1). The acetylation reaction was also investigated in various solvents; the model reaction consisted of 1 mmol of 4‐bromobenzyl alcohol with acetic anhydride (2 mmol) using 0.05 mmol of tribromo melamine as the catalyst (Table 2, entry Table 2 Effect of solvent on the conversion of 4‐bromobenzyl alcohol to the corresponding formate or acetate. Entry Solvent Time (min) Yield a (%) 1 Solvent‐free 1 h 99 2 Acetone 24 h 40 3 Dichloromethane 24 h 54 4 Acetonitrile 24 h 9 5 Ethyl acetate 24 h 58 6 Chloroform 24 h 23 7 Solvent‐free 240 96 8 Acetone 180 95 9 Dichloromethane 20 95 10 Acetonitrile 165 83 11 Ethyl acetate 202 99 12 Chloroform 106 97 Reaction conditions: substrate:ethyl formate/acetic anhydride = 1 mmol/2 mmol, catalyst 0.05 mmol, solvent 5 mL. a Yields refer to isolated pure products.
Maryam Hajjami et al. / Chinese Journal of Catalysis 35 (2014) 260–263
Table 3 Formylation of alcohols. Entry Substrate 1 4‐Chlorobenzyl alcohol 2 Benzyl alcohol 3 4‐Fluorobenzyl alcohol 4 3‐Fluorobenzyl alcohol 5 2,4‐Dichlorobenzyl alcohol 6 4‐Nitrobenzyl alcohol 7 Benzhydrol 8 4‐t‐Butylbenzyl alcohol 9 4‐Bromobenzyl alcohol 10 3‐Pyridinmethanol Reaction conditions: alcohol 1 mmol, ethyl formate 2 mmol. a Yields refer to isolated pure products.
Catalyst amount (mmol) 0.05 0.05 0.20 0.20 0.15 0.20 0.15 0.10 0.05 0.05
Time (min) 80 30 44 48 70 120 55 30 60 180
Yield a (%) 97 99 98 96 99 50 93 92 99 23
Time (min) 45 15 50 60 12 95 60 40 20 80
Yield a (%) 99 99 99 86 84 97 93 98 95 86
Table 4 Acetylation of alcohols. Entry Substrate Catalyst amount (mmol) 1 2‐Chlorobenzyl alcohol 0.05 2 Benzyl alcohol 0.05 3 4‐Fluorobenzyl alcohol 0.10 4 3‐Fluorobenzyl alcohol 0.10 5 2,4‐Dichlorobenzyl alcohol 0.15 6 4‐Nitrobenzyl alcohol 0.20 7 Benzhydrol 0.10 8 4‐tert‐Butylbenzyl alcohol 0.10 9 4‐Bromobenzyl alcohol 0.05 10 3‐Pyridinmethanol 0.10 Reaction conditions: alcohol 1 mmol, acetic anhydride 2 mmol. a Yields refer to isolated pure products.
7–12). Dichloromethane was found to be most effective solvent giving high yield with comparatively low reaction time (Table 2, entry 9). Therefore, we employed these optimized conditions for the formylation (0.05 mmol tribromo melamine, solvent‐free) and acetylation (0.05 mmol tribromo melamine in dichloromethane as the solvent) of various alcohols into the corresponding for‐ mates (Table 3) and acetates (Table 4), respectively. Different types of alcohols, having both electron withdraw‐ ing and donating groups, were formylated with ethyl formate in the presence of a catalytic amount of tribromo melamine under solvent‐free conditions in good to high yields (Table 3, entries 1–9). Benzyl alcohols, phenols, and non‐benzyl alcohols groups
were subjected to the formylation reaction to investigate the chemoselectivity of the proposed system. The formylation of phenols and non‐benzyl alcohols did not occur under our con‐ ditions, and phenols or non‐benzyl hydroxyl groups remained unaffected during the reaction (Scheme 2). As can be seen in Table 4, both electron‐withdrawing and electron‐donating substituents on the alcohols could be em‐ ployed in the synthesis of acetates. Our experiments also indicated that non‐benzyl alcohols were not acetylated under these conditions. This catalytic acet‐ ylating system is also chemoselective so that the acetylation of benzyl alcohols was selective in the presence of phenols (Scheme 3). A possible mechanism of these reaction systems is shown in Scheme 4. O
O OCH
OH O OH + Et
+
H
O
TBM rt, solvent-free
+
OH
Br
Br
OCH
OCH
OH
H
TBM rt, solvent-free
+ Br 100%
Scheme 2. Chemoselectivity of formylation.
+ Ac2O
+ Br 0%
Br
Br
TBM rt, CH2Cl2
OCCH3
0% O
OCCH3
OH
O + Et
+
O
+ Br 100% O
Br
O
O
TBM rt, CH2Cl2
0%
100% OH
OH + Ac2O
+
OCH
Br
Br
OCCH3
OH
OCCH3 +
Br
Br
100%
0%
Scheme 3. Chemoselectivity of the acetylation.
Maryam Hajjami et al. / Chinese Journal of Catalysis 35 (2014) 260–263
Graphical Abstract Chin. J. Catal., 2014, 35: 260–263 doi: 10.1016/S1872‐2067(12)60748‐7 Tribromo melamine as novel and versatile catalyst for the formylation and acetylation of alcohols Maryam Hajjami *, Arash Ghorbani‐Choghamarani, Zahra Karamshahi, Masoomeh Norouzi Ilam University, Iran
EtOOCH, tribromo melamine
ROCOH + EtOH
Solvent-free, rt
BrHN
ROH
Tribromo melamine = Ac2O, tribromo melamine
ROCOCH3 + CH3COOH
CH2Cl2, rt
N N
NHBr N
NHBr
The acetylation and formylation of alcohols with acetic anhydride and ethyl formate in the presence of catalytic amounts of tribromo melamine at room temperature are described. O R1O
C
[2] Shirini F, Zolfigol M A, Mallakpour S. Russ J Org Chem, 2005, 41:
R2
R1= C2H5, CH3CO R2= CH3, H
625 [3] Shirini F, Zolfigol M A, Abedini M, Salehi P. Bull Korean Chem Soc,
2003, 24: 1683 [4] Lee C W, Hwang H Y, Jeong H M, Yoon U C, Chi K W. Synth Met,
2009, 159: 1820 BrHN
N N
NHBr O
N NHBr
R1O
C
Br HN
N N
R2
NHBr N
NHBr
[5] Niknam K, Saberi D. Tetrahedron Lett, 2009, 50: 5210 [6] Ram R N, Meher K N. Tetrahedron, 2002, 58: 2997 [7] Zolfigol M A, Chehardoli G, Dehghanian M, Niknam K, Shirini F,
Khoramabadi‐Zad A. J Chin Chem Soc, 2008, 55: 885 [8] Niknam K, Saberi D. Appl Catal A, 2009, 366: 220 [9] Ghorbani‐Choghamarani A, Akbaripanah Z. Chin Chem Lett, 2012,
23: 450 R OH R OCOR2 + R1OH
Scheme 4. Proposed mechanism for the acetylation and formylation.
[10] Singh A S, Bhanage B M, Nagarkar J M. Green Chem Lett Rev, 2012,
5: 27 [11] Zareyee D, Alizadeh P, Ghandali M S, Khalilzadeh M A. Chem Pap,
2013, 67: 713 [12] Iranpoor N, Firouzabadi H, Davan E E. Tetrahedron Lett, 2013, 54:
1813
4. Conclusions We have developed a new strategy for the acetylation and formylation of alcohols with acetic anhydride and ethyl formate in the presence of catalytic amounts of tribromo melamine at room temperature. Our method involves mild reaction condi‐ tions, using very simple and accessible starting materials and solvents, as well as an inexpensive and non‐toxic catalyst. Acknowledgements Financial support from the Ilam University, Ilam, Iran is gratefully acknowledged. References
[13] Rahmatpour A. C R Chim, 2012, 15: 1048 [14] Li G L, Zhao G. Synth Commun, 2013, 43: 34 [15] Habibi M H, Tangestaninejad S, Mirkhani V, Yadollahi B. Tetrahe‐
dron, 2001, 57: 8333 [16] Niknam K, Zolfigol M A, Saberi D, Khonbazi M. Chin J Chem, 2009,
27: 1548 [17] Mirkhani V, Tangestaninejad S, Moghadam M, Yadollahi B,
Alipanah L. Monatsh Chem, 2004, 135: 1257 [18] Iranpoor N, Firouzabadi H, Jamalian A. Tetrahedron Lett, 2005, 46:
7963 [19] Kolvari E, Ghorbani‐Choghamarani A, Salehi P, Shirini F, Zolfigol M
A. J Iran Chem Soc, 2007, 4: 126 [20] Hajjami M, Ghorbani‐Choghamarani A, Norouzi M. Chin J Catal,
2012, 33: 1661 [21] Ghorbani‐Choghamarani A, Norouzi M. Bull Korean Chem Soc,
2011, 32: 1399 [22] Ghorbani‐Choghamarani A, Norouzi M. Chin J Catal, 2011, 32:
595 [1] Hagiwara H, Morohashi K, Sakai H, Suzuki T, Ando M. Tetrahedron,
1998, 54: 5845
[23] Ghorbani‐Choghamarani A, Goudarziafshar H, Zamani P. Chin
Chem Lett, 2011, 22: 1207
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r. c o m / l o c a t e / c h n j c
Article
Tribromo melamine as novel and versatile catalyst for the formylation and acetylation of alcohols Maryam Hajjami *, Arash Ghorbani‐Choghamarani, Zahra Karamshahi, Masoomeh Norouzi Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
A R T I C L E I N F O
A B S T R A C T
Article history: Received 23 September 2013 Accepted 13 November 2013 Published 20 February 2014
Keywords: Tribromo melamine Acetylation Formylation Alcohol Ethyl formate Acetic anhydride
Tribromo melamine has been found to be an efficient and green organocatalyst for the acetylation and formylation reactions of alcohols with acetic anhydride and ethyl formate at room temperature and under mild reaction conditions. © 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.
1. Introduction During the multistep synthesis of natural products, the effi‐ ciency of the synthetic protocol employed often depends large‐ ly on protection and deprotection of the functional groups. To this end, protecting groups have played a crucial role in the synthesis of complex natural products [1]. Acetylation and formylation of hydroxy groups are the most widely used trans‐ formations in organic synthesis [2–4]. Amongst protecting groups for alcohols, esters are the most important with acetate being the simplest and easiest to use. Acetylation is usually performed with reagents such as acetic anhydride or acetyl chloride in the presence of variety of acidic or basic catalysts [5]. Formylation is also a very important process in organic chemistry. O‐Formylation is the method of choice for protecting an alcoholic group in a complex synthetic sequence because deformylation can be affected selectively in the presence of
acetate or other ester protecting groups [6–8]. Several acetylation and formylation procedures for alcohols have been reported over the years [9–14], but these methods suffer from some disadvantages, such as heavy metal contami‐ nation, high temperature, formation of undesirable or toxic byproducts, expensive reagents, or long reaction times [15–18]. These issues stimulated us to research a simple, efficient, and safe catalyst for the acetylation and formylation of alcohols. In this regard, a group of compounds entitled N‐halo reagents is widely used in fine organic synthesis [19]. 2. Experimental Chemicals were purchased from Fluka, Merck, and Aldrich. The formylated and acetylated products were characterized by comparison of their spectral (IR, 1H NMR, and 13C NMR) and physical data with those of authentic samples.
* Corresponding author. Tel/Fax: +98‐8412227022; E‐mail: [email protected];[email protected] DOI: 10.1016/S1872‐2067(12)60748‐7 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 35, No. 2, February 2014
Maryam Hajjami et al. / Chinese Journal of Catalysis 35 (2014) 260–263
2.1. Formylation of 4‐tert‐butylbenzyl alcohol To the stirred mixture of 4‐tert‐butyl benzyl alcohol (1 mmol, 0.164 g) and ethyl formate (2 mL), tribromo melamine (0.1 mmol) was added without additional solvents. The result‐ ing mixture was stirred at room temperature for 30 min. The reaction was monitored by TLC. On completion of reaction, the product was extracted with CH2Cl2 (5 mL × 4). The organic layer was separated, dried over anhydrous Na2SO4 (1.5 g), and concentrated under reduced pressure. Finally, the organic sol‐ vents were evaporated, and 4‐tert‐butylbenzyl formate was obtained in 92% yield. The identity of the product was con‐ firmed by comparing the physical and spectral data with those of the known compound. 2.2. Acetylation of 3‐fluorobenzyl alcohol Tribromo melamine (0.1 mmol) was added to a solution of 3‐fluorobenzyl alcohol (0.126 g, 1 mmol) and acetic anhydride (0.204 g, 2 mmol) in dichloromethane (5 mL), and the reaction mixture was stirred at room temperature for 1 h (the progress of the reaction was monitored by TLC). On completion of the reaction, water (5 mL) and then 5% NaHCO3 (5 mL) was added to the mixture with stirring, and the product was extracted with CH2Cl2 (5 mL × 4). The organic layer was dried over anhy‐ drous Na2SO4 (1.5 g). Finally, the organic solvents were evapo‐ rated, and 3‐fluorobenzyl acetate was obtained in 86% yield. 3. Results and discussion Following our previous work in developing new methods for the protection of the hydroxy group [20–23], an effective procedure for the acetylation and formylation of alcohols with acetic anhydride and ethyl formate in the presence of catalytic amounts of tribromo melamine at room temperature (Scheme 1) has been developed. To find the optimal conditions for the formylation of alco‐ hols by this method, we selected 4‐bromobenzyl alcohol as a model substrate and treated it with ethyl formate in the pres‐ ence of different amounts of tribromo melamine at room tem‐ perature. We found that 0.05 equivalents of tribromo melamine gave the highest yield of the respective alkyl formate after 60 min at room temperature (Table 1, entry 5). The results clearly show that the tribromo melamine is effective for this transfor‐
EtOOCH, TBM solvent-free, rt
ROCOH + EtOH
ROH Ac2O, TBM CH2Cl2, rt
ROCOCH3 + CH3COOH BrHN
TBM = Tribromo melamine
N N
NHBr N
NHBr Scheme 1. Formylation and acetylation of alcohols.
Table 1 Optimization of the amount of tribromo melamine in the reaction of 4‐bromobenzyl alcohol with ethyl formate or acetic anhydride. Entry Catalyst amount (mmol) Yield a (%) 1 0.01 13 2 0.02 40 3 0.03 41 4 0.04 56 5 0.05 99 6 No catalyst Trace 7 0.01 22 8 0.02 28 9 0.03 30 10 0.04 57 11 0.05 95 12 No catalyst Trace Reaction conditions: 4‐bromobenzyl alcohol 1 mmol, ethyl formate 2 mL or acetic anhydride 2 mmol, room temperature. a Yields refer to isolated pure products.
mation, whereas, in its absence, the reaction fails to initiate even after 24 h (Table 1, entry 6). Additionally, 4‐bromobenzyl alcohol was used as a model substrate for acetylation (Table 1, entries 7–12). The reaction was monitored with different amounts of catalyst. Increasing the loading of tribromo mela‐ mine from 0.01 mmol to 0.05 mmol resulted in a considerable improvement of the yield from 22% to 95% (Table 1, entries 7 and 11). The acetylation reaction was also carried out in the absence of catalyst. Again, the reaction had not initiated after 24 h (Table 1, entry 12). To find the best solvent for the formylation, the model reac‐ tion was performed in a number of solvents, and moderate to poor yields of the corresponding alkyl formates were obtained (Table 2, entry 2–6). A far higher yield was obtained under solvent‐free conditions (Table 2, entry 1). The acetylation reaction was also investigated in various solvents; the model reaction consisted of 1 mmol of 4‐bromobenzyl alcohol with acetic anhydride (2 mmol) using 0.05 mmol of tribromo melamine as the catalyst (Table 2, entry Table 2 Effect of solvent on the conversion of 4‐bromobenzyl alcohol to the corresponding formate or acetate. Entry Solvent Time (min) Yield a (%) 1 Solvent‐free 1 h 99 2 Acetone 24 h 40 3 Dichloromethane 24 h 54 4 Acetonitrile 24 h 9 5 Ethyl acetate 24 h 58 6 Chloroform 24 h 23 7 Solvent‐free 240 96 8 Acetone 180 95 9 Dichloromethane 20 95 10 Acetonitrile 165 83 11 Ethyl acetate 202 99 12 Chloroform 106 97 Reaction conditions: substrate:ethyl formate/acetic anhydride = 1 mmol/2 mmol, catalyst 0.05 mmol, solvent 5 mL. a Yields refer to isolated pure products.
Maryam Hajjami et al. / Chinese Journal of Catalysis 35 (2014) 260–263
Table 3 Formylation of alcohols. Entry Substrate 1 4‐Chlorobenzyl alcohol 2 Benzyl alcohol 3 4‐Fluorobenzyl alcohol 4 3‐Fluorobenzyl alcohol 5 2,4‐Dichlorobenzyl alcohol 6 4‐Nitrobenzyl alcohol 7 Benzhydrol 8 4‐t‐Butylbenzyl alcohol 9 4‐Bromobenzyl alcohol 10 3‐Pyridinmethanol Reaction conditions: alcohol 1 mmol, ethyl formate 2 mmol. a Yields refer to isolated pure products.
Catalyst amount (mmol) 0.05 0.05 0.20 0.20 0.15 0.20 0.15 0.10 0.05 0.05
Time (min) 80 30 44 48 70 120 55 30 60 180
Yield a (%) 97 99 98 96 99 50 93 92 99 23
Time (min) 45 15 50 60 12 95 60 40 20 80
Yield a (%) 99 99 99 86 84 97 93 98 95 86
Table 4 Acetylation of alcohols. Entry Substrate Catalyst amount (mmol) 1 2‐Chlorobenzyl alcohol 0.05 2 Benzyl alcohol 0.05 3 4‐Fluorobenzyl alcohol 0.10 4 3‐Fluorobenzyl alcohol 0.10 5 2,4‐Dichlorobenzyl alcohol 0.15 6 4‐Nitrobenzyl alcohol 0.20 7 Benzhydrol 0.10 8 4‐tert‐Butylbenzyl alcohol 0.10 9 4‐Bromobenzyl alcohol 0.05 10 3‐Pyridinmethanol 0.10 Reaction conditions: alcohol 1 mmol, acetic anhydride 2 mmol. a Yields refer to isolated pure products.
7–12). Dichloromethane was found to be most effective solvent giving high yield with comparatively low reaction time (Table 2, entry 9). Therefore, we employed these optimized conditions for the formylation (0.05 mmol tribromo melamine, solvent‐free) and acetylation (0.05 mmol tribromo melamine in dichloromethane as the solvent) of various alcohols into the corresponding for‐ mates (Table 3) and acetates (Table 4), respectively. Different types of alcohols, having both electron withdraw‐ ing and donating groups, were formylated with ethyl formate in the presence of a catalytic amount of tribromo melamine under solvent‐free conditions in good to high yields (Table 3, entries 1–9). Benzyl alcohols, phenols, and non‐benzyl alcohols groups
were subjected to the formylation reaction to investigate the chemoselectivity of the proposed system. The formylation of phenols and non‐benzyl alcohols did not occur under our con‐ ditions, and phenols or non‐benzyl hydroxyl groups remained unaffected during the reaction (Scheme 2). As can be seen in Table 4, both electron‐withdrawing and electron‐donating substituents on the alcohols could be em‐ ployed in the synthesis of acetates. Our experiments also indicated that non‐benzyl alcohols were not acetylated under these conditions. This catalytic acet‐ ylating system is also chemoselective so that the acetylation of benzyl alcohols was selective in the presence of phenols (Scheme 3). A possible mechanism of these reaction systems is shown in Scheme 4. O
O OCH
OH O OH + Et
+
H
O
TBM rt, solvent-free
+
OH
Br
Br
OCH
OCH
OH
H
TBM rt, solvent-free
+ Br 100%
Scheme 2. Chemoselectivity of formylation.
+ Ac2O
+ Br 0%
Br
Br
TBM rt, CH2Cl2
OCCH3
0% O
OCCH3
OH
O + Et
+
O
+ Br 100% O
Br
O
O
TBM rt, CH2Cl2
0%
100% OH
OH + Ac2O
+
OCH
Br
Br
OCCH3
OH
OCCH3 +
Br
Br
100%
0%
Scheme 3. Chemoselectivity of the acetylation.
Maryam Hajjami et al. / Chinese Journal of Catalysis 35 (2014) 260–263
Graphical Abstract Chin. J. Catal., 2014, 35: 260–263 doi: 10.1016/S1872‐2067(12)60748‐7 Tribromo melamine as novel and versatile catalyst for the formylation and acetylation of alcohols Maryam Hajjami *, Arash Ghorbani‐Choghamarani, Zahra Karamshahi, Masoomeh Norouzi Ilam University, Iran
EtOOCH, tribromo melamine
ROCOH + EtOH
Solvent-free, rt
BrHN
ROH
Tribromo melamine = Ac2O, tribromo melamine
ROCOCH3 + CH3COOH
CH2Cl2, rt
N N
NHBr N
NHBr
The acetylation and formylation of alcohols with acetic anhydride and ethyl formate in the presence of catalytic amounts of tribromo melamine at room temperature are described. O R1O
C
[2] Shirini F, Zolfigol M A, Mallakpour S. Russ J Org Chem, 2005, 41:
R2
R1= C2H5, CH3CO R2= CH3, H
625 [3] Shirini F, Zolfigol M A, Abedini M, Salehi P. Bull Korean Chem Soc,
2003, 24: 1683 [4] Lee C W, Hwang H Y, Jeong H M, Yoon U C, Chi K W. Synth Met,
2009, 159: 1820 BrHN
N N
NHBr O
N NHBr
R1O
C
Br HN
N N
R2
NHBr N
NHBr
[5] Niknam K, Saberi D. Tetrahedron Lett, 2009, 50: 5210 [6] Ram R N, Meher K N. Tetrahedron, 2002, 58: 2997 [7] Zolfigol M A, Chehardoli G, Dehghanian M, Niknam K, Shirini F,
Khoramabadi‐Zad A. J Chin Chem Soc, 2008, 55: 885 [8] Niknam K, Saberi D. Appl Catal A, 2009, 366: 220 [9] Ghorbani‐Choghamarani A, Akbaripanah Z. Chin Chem Lett, 2012,
23: 450 R OH R OCOR2 + R1OH
Scheme 4. Proposed mechanism for the acetylation and formylation.
[10] Singh A S, Bhanage B M, Nagarkar J M. Green Chem Lett Rev, 2012,
5: 27 [11] Zareyee D, Alizadeh P, Ghandali M S, Khalilzadeh M A. Chem Pap,
2013, 67: 713 [12] Iranpoor N, Firouzabadi H, Davan E E. Tetrahedron Lett, 2013, 54:
1813
4. Conclusions We have developed a new strategy for the acetylation and formylation of alcohols with acetic anhydride and ethyl formate in the presence of catalytic amounts of tribromo melamine at room temperature. Our method involves mild reaction condi‐ tions, using very simple and accessible starting materials and solvents, as well as an inexpensive and non‐toxic catalyst. Acknowledgements Financial support from the Ilam University, Ilam, Iran is gratefully acknowledged. References
[13] Rahmatpour A. C R Chim, 2012, 15: 1048 [14] Li G L, Zhao G. Synth Commun, 2013, 43: 34 [15] Habibi M H, Tangestaninejad S, Mirkhani V, Yadollahi B. Tetrahe‐
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