Accepted ManuscriptErbium trifluoromethanesulfonate catalyzed Friedel–Crafts acylation using ar-omatic carboxylic acids as acylating agents under monomode-microwave irra-diation Phuong
Trang 1Accepted Manuscript
Erbium trifluoromethanesulfonate catalyzed Friedel–Crafts acylation using
ar-omatic carboxylic acids as acylating agents under monomode-microwave
irra-diation
Phuong Hoang Tran, Poul Erik Hansen, Hai Truong Nguyen, Thach Ngoc Le
DOI: http://dx.doi.org/10.1016/j.tetlet.2014.12.038
Please cite this article as: Hoang Tran, P., Erik Hansen, P., Truong Nguyen, H., Ngoc Le, T., Erbium trifluoromethanesulfonate catalyzed Friedel–Crafts acylation using aromatic carboxylic acids as acylating agents
under monomode-microwave irradiation, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet 2014.12.038
This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers
we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Trang 2
Graphical Abstract
Erbium trifluoromethanesulfonate catalyzed
Friedel-Crafts acylation using aromatic
carboxylic acids as acylating agents under
monomode-microwave irradiation
Phuong Hoang Tran, Poul Erik Hansen, Hai Truong Nguyen, Thach Ngoc Le
Leave this area blank for abstract info
Trang 3
Tetrahedron Letters
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
Erbium trifluoromethanesulfonate catalyzed Friedel–Crafts acylation using aromatic carboxylic acids as acylating agents under monomode-microwave irradiation
Phuong Hoang Trana, Poul Erik Hansenb, Hai Truong Nguyena, Thach Ngoc Lea, *
a Department of Organic Chemistry, Faculty of Chemistry, University of Science, Vietnam National University-Hochiminh City 70000, Vietnam
b
Department of Science, Systems and Models, Roskilde University, POB 260, Roskilde DK-4000, Denmark
———
Keywords: erbium triflate, aryl ketone, microwave irradiation, Friedel–Crafts acylation, aromatic carboxylic acid
*
Corresponding author E-mail: lenthach@yahoo.com
The Friedel–Crafts acylation is an important route to prepare aromatic ketones, which are useful precursors in the synthesis of
traditional reaction is extremely sensitive to water, it must be carried out under a dry atmosphere, using anhydrous substrates and
in place of acid chlorides because the use of carboxylic acids as acylating agents produces water as the sole by-product Therefore, acylation using a carboxylic acid can shorten the synthetic route and is environmentally preferable Friedel-Crafts
are often required
acidity and exhibit high tolerance towards water, and those that do not require special handling are effective catalysts in Friedel–
ketones have been prepared by Friedel–Crafts acylation of aromatic compounds with acid chlorides and acid anhydrides
and co-workers reported the C-acylation of phenol and naphthol derivatives using carboxylic acids as the acylating reagents in
solvents and long reaction times were required Matsushita et al improved the Friedel–Crafts acylation of aromatic compounds
Article history:
Received
Received in revised form
Accepted
Available online
Erbium trifluoromethanesulfonate is found to be a good catalyst for the Friedel–Crafts acylation of arenes containing electron-donating substituents using aromatic carboxylic acids as the acylating agents under microwave irradiation An effective, rapid and waste-free method allows the preparation a wide range of aryl ketones in good yields and in short reaction times with minimum amounts of waste
2014 Elsevier Ltd All rights reserved
Keywords:
Erbium triflate
Aryl ketone
Microwave irradiation
Friedel–Crafts acylation
Aromatic carboxylic acid
Trang 4
Tetrahedron
2
Crafts reaction, the long reaction time and presence of perfluoroalkanoic anhydride were disadvantageous
Friedel–Crafts benzoylation using benzoyl chloride as the acylating agent catalyzed by bismuth triflate under microwave
Friedel–Crafts acylation with aromatic carboxylic acids in the presence of metal triflates under microwave irradiation This is the first application of erbium triflate in Friedel–Crafts acylations with aromatic carboxylic acids as acylating agents The use of microwave irradiation resulted in short reaction times and improved yields of products This is also the first time that microwave irradiation has been applied in the Friedel–Crafts acylation using carboxylic acids catalyzed by a metal triflate
yield However, all attempts to reduce the amount of catalyst led to lower yields and no reaction took place in the absence of a
more effective than other metal triflates giving the highest yield (78%) However, gadolinium triflate was also efficient, while other rare-earth triflates proved to be less effective (46–60%) Surprisingly, bismuth triflate, a good catalyst for the Friedel– Crafts acylation with acyl chlorides and acid anhydrides, gave a poor yield in the present method LiOTf was the least active catalyst affording only a 3% yield The combination of erbium triflate and microwave irradiation under solvent-free conditions
methyl benzoate and phenyl benzoate generated from demethylation/esterification of anisole The failure of some of the rare earth metals is due to the formation of these products rather than 4-methoxybenzophenone (see Figure 1)
With optimized conditions in hand, we next investigated the Friedel–Crafts acylation of anisole using aromatic carboxylic acids containing both electron-withdrawing and electron-donating substituents Anisole was chosen, as this substrate has been
predominantly (95%) and 2-chlorobenzoic acid was the best acylating agent using the above-mentioned conditions On the other hand, the use of 4-methoxybenzoic acid, 2-phenylbenzoic and 2-naphthoic acid gave low yields in the acylation of anisole (Table
In all cases, the formation of a certain amount of side products was observed: phenyl and methyl benzoate and minor amounts of
demethylation/alkylation pathways Attempted use of 2-biphenylcarboxylic acid gave fluorenone as the major product, which is the reason behind the low yield of the desired product (Table 2, entry 8)
In order to understand the potential and limitations of the erbium triflate reactivity, many other aromatic compounds were examined (Table 3) We found that the benzoylation is useful for aromatic compounds containing one electron-donating
substituent, such as anisole and thioanisole (Table 3, entries 1 and 6) Benzoylation occurs exclusively at the para position with good selectivity (>95%) However, in cases where the para position is blocked (Table 3, entry 4), an o-benzoylated product was
obtained For aromatic compounds containing two electron-donating groups such as 1,2-dimethoxybenzene (veratrole), 1,3-dimethoxybenzene and 1,4-1,3-dimethoxybenzene, the corresponding benzoylated products were obtained in lower yields (Table 3,
entries 2, 3 and 4) because of the predominant demethylation side reaction Steric hindrance clearly played a role as very little
o-substitution occurs for anisole However, this was not the explanation for veratrole (Table 3, entry 2) and it appears that the electron-withdrawing power also plays a role This is further supported by the fact that the reaction does not take place with
halobenzenes Furthermore, p-nitrotoluene decomposes under microwave irradiation at high temperature
Good yields of products were obtained when an excess of anisole or thioanisole was used as the starting material (mole ratio = 5:1) However, the use of excess starting material resulted in lower yields in the benzoylation of alkylbenzenes and dimethoxybenzenes Therefore, we investigated the mole ratio of starting material and benzoic acid Interestingly, the yield of the aromatic ketone was increased when the mole ratio of the starting material and benzoic acid was 1:2 The results are summarized
in Table 4 The substrate scope could be extended to alkylbenzenes which gave rise to the corresponding ketones with good
regioselectivities Thioanisole was benzoylated in 95% yield with 94% regioselectivity at the p-position (Table 4, entry 1)
Mono-, di- and tri-alkylbenzenes were also benzoylated in excellent yields and with good regioselectivities (Table 4, entries 2-9) Fluorene was benzoylated at the 2-position in 80% yield (Table 4, entry 10) It is noteworthy that naphthalene and anthracene (without electron-donating substituents) were also benzoylated in good yields (Table 4, entries 11 and 12) However, this method was not efficient for the Friedel–Crafts benzoylation of anisole and dimethoxybenzenes because of the demethylation of aryl methyl ethers when two equivalents of benzoic acid was used In the case of anisole, by-products such as phenol, methyl benzoate and phenyl benzoate were obtained as major products from the demethylation Previously, demethylation was observed
in the presence of benzoic acid
Trang 5
The carboxylic acid scope was also extended to ortho-substituted benzoic acids and 2-naphthoic acid in the Friedel–Crafts acylation of toluene and mesitylene (Table 5) o-Halobenzoic acids were reactive in the benzoylation of toluene and mesitylene
o-Toluic acid also gave a good yield (Table 5, entries 4 and 10) 2-Naphthoic acid afforded only a 55% yield in the case of
toluene (Table 5, entry 6), but gave an 80% yield with mesitylene (Table 5, entry 12)
This method was not effective for aliphatic carboxylic acids with chain lengths of 2 to 6 carbons
Interestingly, the use of erbium triflate was successful in Friedel–Crafts acylations of activated aromatic compounds with aromatic carboxylic acids under microwave irradiation The recycling of erbium triflate was also studied and the catalyst could
be easily recovered and reused in the benzoylation of anisole, toluene and mesitylene without any significant loss of the catalytic activity over three consecutive cycles (Scheme 1)
In conclusion, a green method for the Friedel–Crafts acylation of aromatic compounds employing erbium triflate and aromatic carboxylic acids under microwave irradiation has been developed The method gives products in good yields over short reaction times without the use of metal halides or acid chlorides Additionally, the easy recycling of erbium triflate is convenient to apply
in large-scale synthesis The microwave irradiation assisted Friedel–Crafts acylations are accomplished in short times (20-30 min) and have widened the substrate scope to alkylbenzenes, naphthalene and anthracene
Acknowledgments
We are grateful to the Vietnam National University - Hochiminh City (Grant No C2014-18-08) and the Hochiminh Department of Science and Technology (Grant No 355/2013/HĐ-SKHCN) Toshiba is also thanked for a PhD Student Award We thank Prof Fritz Duus (Roskilde University, Denmark), Dr Hien Quang Do (Caltech, USA) and Khiem Duy Nguyen Chau MSc (University of Minnesota Duluth, USA) for their help
References and notes
1 (a) Whitehead, A J.; Ward, R A.; Jones, M F Tetrahedron Lett 2007, 48, 911-913; (b) Shuju, G.; Jing, L.; Ting, L.; Dayong, S.; Lijun, H Chin J Oceanol Limnol 2011, 29, 68-74; (c) Mizuno, M.; Inagaki, A.; Yamashita, M.; Soma, N.; Maeda, Y.; Nakatani, H Tetrahedron 2006, 62, 4065-4070; (d) Rajitha, C.; Dubey, P K.; Sunku, V.; Piedrafita, F J.; Veeramaneni, V R.; Pal, M Eur J Med Chem 2011, 46, 4887-4896; (e) Yadav, G D.; George, G Microporous
Mesoporous Mater 2006, 96, 36-43
2 Olah, G A Friedel-Crafts Chemistry; John Wiley and Sons: New York, 1973
3 (a) Kobayashi, S.; Sugiura, M.; Kitagawa, H Chem Rev 2002, 102, 2227-2302; (b) Nguyen, V T A.; Duus, F.; Le, T
N Asian J Org Chem 2014, 3, 963-968
4 Sartori, G.; Maggi, R Advances in Friedel-Crafts Acylation Reactions: Catalytic and Green Processes; Taylor &
Francis: Boca Raton, 2010
5 (a) Singh, A P.; Pandey, A K J Mol Catal A: Chem 1997, 123, 141-147; (b) De Castro, C.; Primo, J.; Corma, A J
Mol Catal A: Chem 1998, 134, 215-222; (c) Lezcano-González, I.; Vidal-Moya, J A.; Boronat, M.; Blasco, T.;
Corma, A Angew Chem 2013, 125, 5242-5245; (d) Bai, G.; Han, J.; Zhang, H.; Liu, C.; Lan, X.; Tian, F.; Zhao, Z.; Jin, H RSC Adv 2014, 4, 27116-27121; (e) Yamashita, H.; Mitsukura, Y.; Kobashi, H J Mol Catal A: Chem 2010,
327, 80-86
6 Chiche, B.; Finiels, A.; Gauthier, C.; Geneste, P J Mol Catal 1987, 42, 229-235
7 Ranu, B C.; Ghosh, K.; Jana, U J Org Chem 1996, 61, 9546-9547
8 Firouzabadi, H.; Iranpoor, N.; Nowrouzi, F Tetrahedron Lett 2003, 44, 5343-5345
9 Savari, M H.; Sharghi, H Synthesis 2004, 2165-2168
10 Zarei, A.; Hajipour, A R.; Khazdooz, L Tetrahedron Lett 2008, 49, 6715-6719
11 Khodaei, M M.; Alizadeh, A.; Nazari, E Tetrahedron Lett 2007, 48, 4199-4202
13 Lu, J.; Zhang, H.; Chen, X.; Liu, H.; Jiang, Y.; Fu, H Adv Synth Catal 2013, 355, 529-536
14 Fukuyama, T.; Maetani, S.; Miyagawa, K.; Ryu, I Org Lett 2014, 16, 3216-3219
15 (a) Kobayashi, S.; Iwamoto, S Tetrahedron Lett 1998, 39, 4697-4970; (b) Kobayashi, S.; Manabe, K Pure Appl
Chem 2000, 72, 1373-1380; (c) Koshima, H.; Kabota, M., Synth Commun 2003, 33, 3983-3988; (d) Tran, P H.; Duus,
F.; Le, T N Tetrahedron Lett 2012, 53, 222-224
16 (a) Hachiya, I.; Moriwaki, M.; Kobayashi, S Tetrahedron Lett 1995, 36, 409-412; (b) Desmurs, J R.; Labrouillère, M.; Roux, C L.; Gaspard, H.; Laporterie, A.; Dubac, J Tetrahedron Lett 1997, 38, 8871-8874; (c) Leonard, N M.; Wielan,
L C.; Mohan, R S Tetrahedron 2002, 58, 8373-8397; (d) Prakash, G K S.; Yan, P.; Török, B.; Bucsi, I.; Tanaka, M.;
Appl Catal A 2006, 306, 159-164; (f) Ghosh, R.; Maiti, S J Mol Catal 2007, 264, 1-8
17 Kobayashi, S.; Moriwaki, M.; Hachiya, I Tetrahedron Lett 1996, 37, 4183-4186
18 (a) Kawamura, M.; Cui, D M; Hayashi, T.; Shimada, S Tetrahedron Lett 2003, 44, 7715-7717; (b) Kawamura, M.; Cui, D M; Hayashi, T.; Shimada, S Tetrahedron 2006, 62, 9201-9209
19 Matsushita, Y.; Sugamoto, K.; Matsui, T Tetrahedron Lett 2004, 45, 4723-4727
Trang 6
Tetrahedron
4
20 Jin, C.; Li, J.; Su, W J Chem Res 2009, 607-611
21 Parvanak-Boroujeni, K.; Parvanak, K J Serb Chem Soc 2011, 76, 155-163
22 Loupy, A., Microwaves in Organic Synthesis; Wiley-VCH: Weinheim, 2006
23 (a) Gronnow, M J.; Macquarrie, D J.; Clark, J H; Ravenscroft, P J Mol Catal A 2005, 231, 47-51; (b) Gopalakrishnan, M.; Sureshkumar, P.; Kanagarajan, V.; Thanusu, J Catal Commun 2005, 6, 753-756; (c) Deng, W.;
Xu, Y.; Guo, Q X Chin Chem Lett 2005, 16, 327-330; (d) Flores, K O V.; de Aguiar, A P.; de Aguiar, M R M P.;
de Santa Maria, L C Mater Lett 2007, 61, 1190-1196; (e) Berardi, S.; Conte, V.; Fiorani, G.; Floris, B.; Galloni, P J
Organomet Chem 2008, 693, 3015-3020 (f) Wine, G.; Vanhaecke, E.; Ivanova, S.; Ziessel, R.; Pham-Huu, C Catal Commun 2009, 10, 477-480; (g) Mahdi, J.; Ankati, H.; Gregory, J.; Tenner, B.; Biehl, E R Tetrahedron Lett 2011, 52,
2594-2596 (h) Bai, G.; Li, T.; Yang, Y.; Zhang, H.; Lan, X.; Li, F.; Han, J.; Ma, Z.; Chen, Q.; Chen, G Catal
Commun 2012, 29, 114-117; (i) Chandra Shekara, B M.; Jai Prakash, B S.; Bhat, Y S J Catal 2012, 290, 101-107;
(j) Perrier, A.; Keller, M.; Caminade, A.-M.; Majoral, J.-P.; Ouali, A Green Chem 2013, 15, 2075-2080; (k) Reddy, K
P.; Venkateswarlu, M Tetrahedron Lett 2014, 55, 1756-1759
24 Tran, P H.; Hansen, P E.; Pham, T T.; Huynh, V T.; Huynh, V H.; Thi Tran, T D.; Huynh, T V.; Le, T N Synth
Commun 2014, 44, 2921-2929
25 The reactions were carried out with a CEM Discover oven, which offers microwave synthesis with safe pressure regulation, using a 10 mL pressurized glass tube fitted with a Teflon-coated septum and a vertically-focused IR temperature sensor controlling the reaction temperature
evaporator The crude product was purified by flash chromatography (n-hexane, then 10% EtOAc in n-hexane) to give
4-methoxybenzophenone (0.153 g, 72% yield) The purity and identity of the product were confirmed by GC-FID, and
26 (a) Ross, J.; Xiao, J Green Chem 2002, 4, 129-133; (b) Gmouh, S.; Yang, H.; Vaultier, M Org Lett 2003, 5,
2219-2222; (c) Goodrich, P.; Hardacre, C.; Mehdi, H.; Nancarrow, P.; Rooney, D W.; Thompson, J M Ind Eng Chem Res
2006, 45, 6640-6647; (d) Zayed, F.; Greiner, L.; Schulz, P S.; Lapkin, A.; Leitner, W Chem Commun 2008, 79-81
27 Su, W.; Jin, C Synth Commun 2004, 34, 4199-4205
Trang 7
Figure 1 Effect of side-products on the yield: (a) ratio of methyl benzoate to 4-methoxybenzophenone, (b) ratio of
phenyl benzoate to 4-methoxybenzophenone
Trang 8
anisole (5 mmol),
benzoic acid (1 mmol)
220 oC, 30 min
mesitylene (1 mmol) benzoic acid (2 mmol)
180 oC, 20 min
toluene (1 mmol) benzoic acid (2 mmol)
180oC, 20 min
Scheme 1 Recycling of erbium triflate over three consecutive cycles under microwave irradiation
Trang 9
Table 1 Reaction of anisole and benzoic acid catalyzed by metal triflates under microwave irradiation at 220 C over 30 min.a
a
Anisole (5 mmol), benzoic acid (1 mmol)
Yields were determined by GC analysis
c Isolated yield in parentheses
Trang 10
Table 2 Benzoylation of anisole with aromatic carboxylic acids catalyzed by Er(OTf)3 under microwave irradiation