Unexpectedly high activity of Zn(OTf)2·6H2O in catalytic Friedel-Crafts acylation reaction

Article abstract of DOI:10.1080/00397910701750292

Zn(OTf)2·6H2O was used to promote Friedel-Crafts acylation of aromatics. The work describes the high activity and efficiency of Zn(OTf)2·6H2O in acylation of aromatics, and the catalyst has surpassed most metal triflates in dispensing when dried at high temperature under vacuum before use. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701750292

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Unexpectedly High Activity of
Zn(OTf)2 · 6H2O in Catalytic Friedel–Crafts
Acylation Reaction
Fei He a , Huayue Wu a , Jiuxi Chen a & Weike Su a b
a College of Chemistry and Materials Science, Wenzhou University, Wenzhou,
China
b College of Pharmaceutical Sciences, Zhejiang University of Technology,
Zhejiang Key Laboratory of Pharmaceutical Engineering, Hangzhou, China
Version of record first published: 18 Jan 2008.
To cite this article: Fei He, Huayue Wu, Jiuxi Chen & Weike Su (2008): Unexpectedly High Activity of
Zn(OTf)2 · 6H2O in Catalytic Friedel–Crafts Acylation Reaction, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 38:2, 255-264
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Synthetic Communicationsw, 38: 255–264, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701750292
Unexpectedly High Activity of
.
Zn(OTf)2 6H2O in Catalytic
Friedel–Crafts Acylation Reaction
Fei He,1 Huayue Wu,1 Jiuxi Chen,1 and Weike Su1,2
1College of Chemistry and Materials Science, Wenzhou University,
Wenzhou, China
2College of Pharmaceutical Sciences, Zhejiang University of Technology,
Zhejiang Key Laboratory of Pharmaceutical Engineering,
Hangzhou, China
.
Abstract: Zn(OTf)2 6H2O was used to promote Friedel–Crafts acylation of
.
aromatics. The work describes the high activity and efficiency of Zn(OTf)2 6H2O
in acylation of aromatics, and the catalyst has surpassed most metal triflates in dispen-
sing when dried at high temperature under vacuum before use.
.
Keywords: Friedel–Crafts acylation, high activity, Zn(OTf)2 6H2O
Despite of their broad utility in organic chemistry, the Friedel–Crafts
acylation reaction often needed stoichiometric or even excess of a convention-
al Lewis acid (LA) such as AlCl3.[1] The formation of a strong coordinate
oxygen–metal bond was the key.[2] Thus, the products (ketones) must be
obtained after aqueous workup because of the complex of LA with the
ketones (Scheme 1).
[3]
Although FeCl3 allowed the development of a catalytic cycle, drastic
conditions were often needed and led to side reactions. Stoichiometric zinc
Received March 18, 2007
Address correspondence to Weike Su, College of Pharmaceutical Sciences,
Zhejiang University of Technology, Zhejiang Key Laboratory of Pharmaceutial Engin-
eering, Hangzhou 310014, China. E-mail: suweike@zjut.edu.cn
255

256
F. He et al.
Scheme 1.
power[4] was described as a useful reagent for Friedel–Crafts acylation under
microwave irradiation. Because of thier importance in organic chemistry,
Friedel–Crafts reactions were well studied using other catalysts.[5] In recent
years, Kobayashi et al. found anhydrous rare-earth metal triflates[6] could
catalyze the Friedel–Crafts acylation reaction, even using a catalytic amount,
with good to excellent yields; later other metal triflates,[7] such as Hf(OTf)4,
Ga(OTf)3, Sb(OTf)3, and Sn(OTf)2, also demonstrated high catalytic activity
in the Friedel–Crafts acylation reaction. However, it is worth noting that
these metal triflates needed activation by drying for a few hours at high temp-
erature under vacuum immediately before use. The same anhydrous condition
was needed when aluminium[8] or ferric[9] hydrogensulfate was used as the
catalyst. Next, bismuth(III) derivatives[10] were found to be excellent
catalysts in the Friedel–Crafts acylation reaction. Among these derivatives,
.
Bi(OTf)3 4H2O received attention for its surprising catalytic activity in this
reaction. Even the inactive fluorobenzene could react with acylation reagents
.
and a catalytic amount of Bi(OTf)3 4H2O at high temperature with good yield.
.
However, we found that hexaaqua zinc triflate [Zn(OTf)2 6H2O] was an
efficient catalyst for title reaction. Although anhydrous Zn(OTf)2–catalyzed
benzoylation and acetylation of anisole in ionic liquid was reported,[11] our
experiment had many advantages such as simple operation, moderate
reaction condition, and good yields without drying the catalyst at high temp-
erature under vacuum before use.
Because zinc triflate is a strong and water-tolerant LA, it can be useful
even in practical and industrial applications. In addition, zinc metal was
available easily and more cheaply than many other metals. The preparation
[12]
.
of Zn(OTf)2 6H2O
was easier and simpler than other metal triflates. In
continuation of our interest in the Friedel–Crafts reaction,[13] we herein
describe a simple and practical method for Friedel–Crafts acylation
.
reaction using Zn(OTf)2 6H2O.
First, we tested the acylation reaction of furan and thiophenes with several
.
acylation reagents in the presence of Zn(OTf)2 6H2O and the results are sum-
marized in Table 1.
As can be seen in Table 1, the reaction of furan or thiophenes with
.
acylation reagents proceeded smoothly in the presence of Zn(OTf)2 6H2O,
but the reactions of thiophenes were a little quicker than those of furan, and
thus the yields of acylated thiophenes were higher under the same conditions.
In addition, it was obvious that aliphatic acyl chloride reacted with the sub-
strates quicker than aroyl chloride.
It was interesting that the substituent of halogen on the thiophene ring did
not affect the yields. For example, 2-chlorothiophene and 2-bromothiophene

.
High Activity of Zn(OTf)2 6H2O
257
Table 1. Friedel–Crafts acylation reaction of furan and thiophenes catalyzed by
.
Zn(OTf)2 6H2O
Entry
Y
X
R1
R2 Time (h) Product Yield (%)a
1
2
O
O
O
O
S
OCOCH3
Cl
CH3
CH3
H
H
4
4
4
8
4
4
4
8
4
4
4
3a
3a
3b
3c
3d
3d
3e
3f
75
85
86
78
84
89
89
82
87
88
88b
3
Cl
Cl
CH3CH2CH2
p-CH3C6H4
CH3
H
4
H
5
OCOCH3
H
6
S
Cl
Cl
Cl
Cl
Cl
Cl
CH3
H
7
S
CH3CH2
p-CH3C6H4
CH3
H
8
S
H
9
S
Cl
Br
Br
3g
3h
3h
10
11
S
CH3
CH3
S
aBazed on aromatics 1.5 mol of acylation reagent was used.
bYb(OTf)3 (5 mol%) was used as the catalyst.
were excellent substrates, which reacted with acetyl chloride quickly and
afforded good yields in 4h. In a contrast, 89% of 5-bromoacetylthiophene
was obtained when 5 mol% of anhydrous Yb(OTf)3 was used as the catalyst
under the same reaction condition (entry 11).
Another five-component heteroaromatic, N-methyl pyrrole, was
desirable. We next tested the Friedel–Crafts acylation reaction under
different conditions (Table 2). Nitromethane was the best solvent of this
reaction. The acylation of N-methyl pyrrole was much easier than other
hetero aromatics (including furan and thiophene), and high yield of
desirable acetylated and benzoylated products were obtained in 4h. A long-
chain alkyl acyl chloride, named octadecanoyl chloride (n-C17H35COCl),
was used in the reaction and 78% yield of acylated product was obtained in
nitromethane after 12 h at 508C.
Unfortunately, nicotinoyl chloride (pyridin-3-yl-COCl) afforded less than
10% yield of product. In this case, an insoluble white solid was obtained,
which was determined as a hydrochloric compound of pyridines (Scheme 2).
The effects of the solvents were obvious; the best was nitromethane and
the worst was carbon tetrachloride (Table 2, entry 11).
In the acylation of anisoles (Table 3), the reaction was slower than those
of electron-rich hetero aromatics. Acylated product 7 was dominant, and other
isomers were detected in very small parts.

258
F. He et al.
.
Table 2. Catalytic acylation of N-methyl pyrrole in the presence of Zn(OTf)2 6H2O
Entry
Acylation reagent
Time (h)
Product
Yield (%)a
1
2
3
4
5
Acetic anhydride
Acetyl chloride
4
4
5a
5a
5b
5c
5d
87
92
Benzoyl chloride
2-Phenyl acetyl chloride
Octadecanoyl chloride
(n-C17H35COCl)
8
86
89
78b
4
12
6
Nicotinoyl chloride
(pyridin-3-yl-COCl)
Acetic anhydride
Acetic anhydride
Acetic anhydride
Acetic anhydride
Acetic anhydride
24
5e
,10
7
8
4
4
4
4
4
5a
5a
5a
5a
5a
83c
78d
65e
61f
9
10
11
46g
aBazed on aromatics. 1.5 mol of acylation reagent was used.
bAt 508C for 12 h.
cIn acetonitrile.
dIn chloroform.
eIn dichloromethane.
fIn nitrobenzene.
gIn carbon tetrachloride.
.
In conclusion, we have found that Zn(OTf)2 6H2O was a excellent
catalyst of the Friedel–Crafts acylation reaction. The work described a
facile, simple operation, suitable in large-scale approaches for preparation
of aromatic ketones with good yields. The strongest point was the ability to
use it without drying at high temperature under vacuum before use.
EXPERIMENTAL
Mass spectra (ESI) were tested on a Thermo Finnagan LCQ Advantage
instrument. 1H NMR and 13C NMR spectra were recorded on a Varian
Scheme 2.

.
High Activity of Zn(OTf)2 6H2O
259
Table 3. Catalytic benzoylation and acetylation of anisoles
Entry
R4
R5
X
Time/h
Product
Yielda/%
1
2
3
4
5
o-CH3
o-CH3
o-CH3
m-CH3
m-CH3
CH3
CH3
ph
OCOCH3
8
8
8
8
8
7a
7a
7b
7c
7d
71
78
72
76
70
Cl
Cl
Cl
Cl
CH3
ph
aBased on anisole. 1.5 mol of acylation reagent was used.
400-MHz instrument using CDCl3 as the solvent with TMS as an internal
standard. IR spectra were recorded on a Avatar-370 infrared spectropho-
tometer. Melting points were determined on a digital melting-point
.
apparatus WRS-1B and are uncorrected. Zn(OTf)2 6H2O was prepared
according to the literature.[12]
General Procedure for Friedel–Crafts Acyaltion of Aromatics
To a solution of aromatic reagent (4 mmol) and acyaltion reagent (6 mmol) in
.
nitronmethane (5 ml), Zn(OTf)2 6H2O (0.4 mmol) was added successfully.
The mixture was stirred at room temperature for the given time, and it
slowly turned green or purple. After completion, it was treated with
saturated aqueous NaHCO3 (10 ml) and extracted with chloroform
(20 ml ꢀ 2). The combined organic solution was dried over anhydrous
MgSO4 and filtered. After it was concentrated in vacuum and purified by pre-
parative thin-layer chromatography (TLC), the corresponding product was
obtained. The regioselectivity also could be determined by the NMR analysis.
Data
2-Acetylfuran (3a)
1
Oil: H NMR (400 MHz, CDCl3) d 7.59 (dd, J ¼ 1.7, 0.7 Hz, 1H), 7.19 (dd,
J ¼ 3.5, 0.7 Hz, 1H), 6.54 (dd, J ¼ 3.5, 1.7 Hz, 1H), 2.49 (s, 3H); IR
(cm21) (neat) 1678.

260
F. He et al.
2-Butyrylfuran (3b)
1
Oil: H NMR (400 MHz, CDCl3) d 7.58 (dd, J ¼ 1.8, 0.7 Hz, 1H), 7.19 (dd,
J ¼ 3.7, 0.7 Hz, 1H), 6.54 (dd, J ¼ 3.7, 1.8 Hz, 1H), 2.80 (m, 2H), 1.75
(m, 2H), 0.99 (m, 3H); IR (cm21) (neat) 1675.
p-Methylbenzoylfuran (3c)
Oil: 1H NMR (400 MHz, CDCl3) d 7.90 (d, J ¼ 7.6 Hz, 2H), 7.69 (dd,
J ¼ 1.7, 0.7 Hz, 1H), 7.28 (d, J ¼ 7.6 Hz, 2H), 7.21 (dd, J ¼ 3.4, 0.7 Hz,
1H), 6.59 (dd, J ¼ 3.4, 1.7 Hz, 1H), 2.44 (s, 3H); IR (cm21) (neat) 1655.
2-Acetylthiophene (3d)
1
Oil: H NMR (400 MHz, CDCl3) d 7.71 (dd, J ¼ 4.0, 1.0 Hz, 1H), 7.64 (dd,
J ¼ 5.0, 1.0 Hz, 1H), 7.14 (dd, J ¼ 5.0, 4.0 Hz, 1H), 2.57 (s, 3H); IR
(cm21) (neat) 1662.
2-Propionylthiophene (3e)
1
Oil: H NMR (400 MHz, CDCl3) d 7.72 (dd, J ¼ 3.8, 1.0 Hz, 1H), 7.62 (dd,
J ¼ 4.8, 1.0 Hz, 1H), 7.12 (dd, J ¼ 4.8, 3.8 Hz, 1H), 2.94 (m, 2H), 1.23
(t, J ¼ 7.2 Hz, 3H); IR (cm21) (neat) 1668.
2-p-Methylbenzoylthiophene (3f)
1
Red solid: mp 70–728C (lit.[14] 728C); H NMR (400 MHz, CDCl3) d 7.79
(d, J ¼ 8 Hz, 2H), 7.69 (dd, J ¼ 4.2, 1.0 Hz, 1H), 7.64 (dd, J ¼ 5.0, 1.0 Hz,
1H), 7.29 (d, J ¼ 8 Hz, 2H), 7.14 (dd, J ¼ 5.0, 4.2 Hz, 1H), 2.44 (s, 3H); IR
(cm21) (neat) 1634.
5-Chloro-2-acetylthiophene (3g)
[15]
1
Yellow solid: mp 45–468C (lit.
45.5–468C); H NMR (CDCl3) d 7.41
(d, J ¼ 4.6 Hz, 1H), 7.01 (d, J ¼ 4.6 Hz, 1H), 2.46 (s, 3H); IR (cm21) 1655.
5-Bromo-2-acetylthiophene (3h)
1
Yellow solid: mp 92–948C (lit.[15] 94.5–958C); H NMR (CDCl3) d 7.43
(d, J ¼ 4.8 Hz, 1H), 7.10 (d, J ¼ 4.8 Hz, 1H), 2.50 (s, 3H); IR (cm21) 1650.

.
High Activity of Zn(OTf)2 6H2O
261
N-Methyl-2-acetylpyrrole (5a)
1
Oil: H NMR (400 MHz, CDCl3) d 6.94 (dd, J ¼ 4.0, 1.6 Hz, 1H), 6.79
(t, J ¼ 2.4 Hz, 1H), 6.11 (dd, J ¼ 4.0, 2.4 Hz, 1H), 3.93 (s, 3H), 2.43
(s, 3H); IR (cm21) (neat) 1645.
N-Methyl-2-benzoylpyrrole (5b)
1
Oil: H NMR (400 MHz, CDCl3) d 7.79–7.82 (m, 2H), 7.26–7.55 (m, 3H),
6.92 (dd, J ¼ 3.8, 1.6 Hz, 1H), 6.74 (t, J ¼ 2.4 Hz, 1H), 6.16 (dd, J ¼ 3.8,
2.4 Hz, 1H), 4.03 (s, 3H); IR (cm21) (neat) 1650.
N-Methyl-2-(a-phenyl)acetylpyrrole (5c)
1
Oil: H NMR (400 MHz, CDCl3) d 7.22–7.34 (m, 5H), 7.09 (dd, J ¼ 3.8,
1.7 Hz, 1H), 6.82 (t, J ¼ 2.4 Hz, 1H), 6.14 (dd, J ¼ 3.8, 2.4 Hz, 1H), 4.07
(s, 2H), 3.91 (s, 3H); IR (cm21) (neat) 1646.
N-Methyl-2- octadecanoylpyrrole (5d)
Solid: mp 58–618C. 1H NMR (400 MHz, CDCl3) d 6.95 (dd, J ¼ 4.0, 2.0 Hz,
1H), 6.79 (t, J ¼ 2.0 Hz, 1H), 6.12 (dd, J ¼ 4.0, 2.0 Hz, 1H), 3.91 (s, 3H), 2.75
(t, J ¼ 7.6 Hz, 2H), 1.66–1.70 (m, 2H), 0.88–1.31 (m, 31H); (ESI) MS 348.2
(M þ 1)þ; IR (cm21) (neat) 1666.
3-Methyl-4-methoxylacetophenone (7a)
1
Oil: H NMR (400 MHz, CDCl3) d 7.76–7.81 (m, 2H), 6.83 (d, J ¼ 8.4 Hz,
1H), 3.88 (s, 3H), 2.55 (s, 3H), 2.24 (s, 3H); IR (cm21) (neat) 1649.
3-Methyl-4-methoxylbenzoylphenone (7b)
1
Solid: mp 75–788C (lit.[16] 79.5–80.58C). H NMR (400 MHz, CDCl3) d
7.79–7.83 (m, 2H), 7.75–7.80 (m, 2H), 7.26–7.55 (m, 3H), 6.81
(d, J ¼ 8.4 Hz, 1H), 3.88 (s, 3H), 2.32 (s, 3H); IR (cm21) (neat) 1643.
2-Methyl-4-methoxylacetophenone (7c)
1
Oil: H NMR (400 MHz, CDCl3) d 7.70–7.72 (m, 1H), 6.69–6.74 (m, 2H),
3.80 (s, 3H), 2.54 (s, 3H), 2.50 (s, 3H); IR (cm21) (neat) 1647.
2-Methyl-4-methoxylbenzoylphenone (7d)
Solid: mp 72–74 8C (lit.[17] bp 219–2218C/23 mmHg). 1H NMR (400 MHz,
CDCl3) d 7.74–7.78 (m, 2H), 7.51–7.53 (m, 1H), 7.39–7.44 (m, 2H), 7.32

262
F. He et al.
(d, J ¼ 8.4 Hz, 1H), 6.79–6.81 (m, 1H), 6.70–6.73 (m, 1H), 3.82 (s, 3H), 2.41
(s, 3H); IR (cm21) (neat) 1651.
ACKNOWLEDGMENT
We are grateful to the National Natural Science Foundation of China (Grant
Nos. 20476098 and 20676123) for financial support.
REFERENCES
1. (a) Olah, G. A. Friedel-Crafts and Related Reaction; Wiley-Interscience:
New York, 1963–1964, Vols. 1–4; (b) Olah, G. A. Friedel-Crafts Chemistry;
Wiley-Interscience: New York, 1973.
2. Chevrier, B.; Weiss, R. Structures of the intermediate complexes in Friedel–Crafts
acylations. Angew. Chem. Int. Ed. Eng. 1974, 13, 1–10.
3. (a) Pearson, D. E.; Buehler, C. A. Friedel–Crafts acylations with little or no
catalyst. Synthesis 1972, 533–542; (b) Effenberger, F.; Steegmuller, D.;
Null, V.; Ziegler, T. Intramolekulare Friedel-Crafts Acylierung von N-phthaloyl-
substitutierten Aryl-undomophenylalanylchloriden. Chem. Ber. 1988, 121,
125–130.
4. Paul, S.; Nanda, P.; Gupta, R.; Loupy, A. Zinc-mediated Friedel–Crafts acylation
in solvent-free conditions under microwave irradiation. Synthesis 2003, 18,
2877–2881.
5. (a) Huang, A. P.; Liu, X. Y.; Li, L. H.; Wu, X. L.; Liu, W. M.; Liang, Y. M.
Antimony(V) chloride–benzyltriethylammonium chloride complex as an
efficient catalyst for Friedel–Crafts acylation reactions. Adv. Synth. Catal. 2004,
346, 599–602; (b) Fu¨rstner, A.; Voigtlalnder, D.; Schrader, W.; Giebel, D.;
Reetz, M. T. A “hard/soft” mismatch enables catalytic Friedel–Crafts acylations.
Org. Lett. 2001, 3, 417–420; (c) Singh, R. P.; Kamble, R. M.; Chandra, K. L.;
Saravanan, P.; Singh, V. K. An efficient method for aromatic Friedel–Crafts alky-
lation, acylation, benzoylation, and sulfonylation reactions. Tetrahedron 2001, 57,
241–247; (d) Nishamol, K.; Rehna, K. S.; Sugunan, S. Liquid-phase Friedel–
Crafts benzoylation of benzene using CuxMn(1-x)Fe2O4 special catalysts. React.
Kinet. Catal. Lett. 2004, 81, 229–234; (e) Luiz, M. C.; Walter, A., Jr.;
´
Angelica, R. E. G.; Leila, M. G. A.; Heloysa, M. C. A. Friedel–Crafts acylation
of anisole with acetic anhydride over silica-supported heteropolyphosphotungstic
acid (HPW/SiO2). J. Mol. Catal. A: Chem. 2004, 209, 189–197;
¨
(f) Valkenberg, M. H.; deCastro, C.; Holderich, W. F. Friedel–Crafts acylation
of aromatics catalysed by supported ionic liquids. Appl. Catal. A: General 2001,
215, 185–190; (g) Gathergood, N.; Zhuang, W.; Jørgensen, K. A. Catalytic enan-
tioselective Friedel–Crafts reactions of aromatic compounds with Glyoxylate: A
simple procedure for the synthesis of optically active aromatic mandelic acid
esters. J. Am. Chem. Soc. 2000, 122, 12517–12522; (h) Fanny, D.;
Denise, B. B.; Alain, D.; Jean, R. D.; Jean, M. B. Lanthanide bis(trifluoromethyl-
sulfonyl)amides vs. trifluoromethylsulfonates as catalysts for Friedel–Crafts acy-
lations. J. Mol. Catal. A: Chem. 2002, 188, 97–104; (i) Bartoli, G.; Bosco, M.;
Marcantoni, E.; Massaccesi, M.; Rinaldi, S.; Sambri, L. LiClO4–acyl anhydrides

.
High Activity of Zn(OTf)2 6H2O
263
complexes as powerful acylating reagents of aromatic compounds in solvent free
conditions. Tetrahedron Lett. 2002, 43, 6331–6333; (j) Melero, J. A.;
Grieken, R. V.; Morales, G.; Nuno, V. Friedel–Crafts acylation of aromatic
compounds over arenesulfonic containing mesostructured SBA-15 materials.
Catal. Commun. 2004, 5, 131–136; (k) Choudhary, V. R.; Jana, S. K.;
Kiran, B. P. Highly active Si-MCM-41-supported Ga2O3 and In2O3 catalysts for
Friedel–Crafts-type benzylation and acylation reactions in the presence or
absence of moisture. J. Catal. 2000, 192, 257–261; (l) Choudhary, V. R.;
Jana, S. K. Highly active and low moisture sensitive supported thallium oxide
catalysts for Friedel–Crafts-type benzylation and acylation reactions: Strong
thallium oxide–support interactions. J. Catal. 2001, 201, 225–235;
(m) Firouzabadi, H.; Iranpoor, N.; Nowrouzi, F. Solvent-free Friedel–Crafts
acylation of aromatic compounds with carboxylic acids in the presence of trifluor-
oacetic anhydride and aluminum dodecatungstophosphate. Tetrahedron Lett.
2003, 44, 5343–5345; (n) Barrett, G. M.; Bouloc, N.; Braddorck, D. C.;
Chadwick, D.; Henderson, D. A. A highly active yetterbium(III) methide
complex for truly catalytic Friedel–Crafts acylation reactions. Synlett 2002, 10,
1653–1656.
6. Kobayashi, S.; Sugiura, M.; Kitagawa, H.; Lam, W. W. L. Rare-earth metal
triflates in organic synthesis. Chem. Rev. 2002, 102, 2227–2302.
7. (a) Hachiya, I.; Moriwaki, M.; Kobayashi, S. Hafnium(IV) trifluoromethane sulf
onate, an efficient catalyst for the Friedel–Crafts acylation and alkylation
reactions. Bull. Chem. Soc. Jpn. 1995, 68, 2053–2060; (b) Komoto, I.;
Matsuo, J. I.; Kobayashi, S. Catalytic Friedel–Crafts acylation of heteroaromatics.
Topics Catal. 2002, 19, 43–47; (c) Prakash, G. K. S.; Yan, P.; Torok, B.; Bucsi, I.;
Tanaka, M.; Olah, G. A. Gallium(III) trifluormethanesulfonate: A water-tolerant,
reusable Lewis acid catalyst for Friedel–Crafts reactions. Catal. Lett. 2003, 85,
1–6.
8. Salehi, P.; Khodaei, M. M.; Zolfigol, M. A.; Sirouszadehy, S. Catalytic Friedel–
Crafts acylation of alkoxybenzenes mediated by aluminum hydrogensulfate in
solution and solvent-free conditions. Bull. Chem. Soc. Jpn. 2003, 76, 1863–1864.
9. Salehi, P.; Khodaei, M. M.; Zolfigol, M. A.; Zeinoldini, S. Catalytic Friedel–
Crafts acylation of alkoxy benzenes by ferric hydrogensulfate. Synth. Commun.
2003, 33, 1367–1373.
10. (a) Repichet, S.; Leroux, C.; Roques, N.; Dubac, J. BiCl3-catalyzed Friedel–Crafts
acylation reactions: Bismuth(III) oxychloride as a water insensitive recyclable pro-
catalyst. Tetrahedron Lett 2003, 44, 2037–2040; (b) Gmouh, S.; Yang, H.;
Vaultier, M. Boc-diol as a photolabile protecting group for aldehydes and
ketones. Org. Lett. 2003, 5, 2219–2122; (c) Repichet, S.; Roux, C. L.;
Dubac, J.; Desmurs, J. R. Bismuth(III) trifluoromethanesulfonate: A chameleon
catalyst for the Friedel–Crafts acylation. Eur. J. Org. Chem. 1998, 2743–2746;
(d) Desmurs, J. R.; Labrouillere, M.; Roux, C. L.; Gaspard, H.; Laporterie, A.;
Dubac, J. Surprising catalytic activity of bismuth (III) triflate in the Friedel–
Crafts acylation reaction. Tetrahedron Lett. 1997, 38, 8871–8874.
11. Ross, J.; Xiao, J. Friedel–Crafts acylation reactions using metal triflates in ionic
liquid. Green Chem. 2002, 4, 129–133.
12. Chinh, N.; Jeffrey, C. B.; Donald, A. P. Crystal structure and thermogravimetric
analysis of hexaaquazinc triflate. Struct. Chem. 2004, 15, 89–94.
13. Su, W. K.; Jin, C. Ytterbium(III) trifluoromethanesulfonate catalysed Friedel–
Crafts acylation of substituted thiophenes. J. Chem. Rese., Synop. 2003, 694–695.

264
F. He et al.
14. Spurlock, J. J. Hydantoins as anticonvulsants, I: 5-R-5-(2-Thienyl)-hydantoins.
J. Am. Chem. Soc. 1953, 75, 1115–1117.
15. Farrar, M. W.; Levine, R. Condensations effected by boron fluoride complexes.
The acylation of certain substituted thiophenes and furans. J. Am. Chem. Soc.
1950, 72, 3695–3698.
16. Yamada, O.; Kurozumi, A.; Ishida, S.; Futatsuya, F.; Ito, K.; Yamamoto, H. Plant
growth regulants. US Pat. 3873304, 1975, Chem. Abst. 78, 147571f.
17. Stadnikov, G. L.; Barysheva, A. Acylation and alkylation of some compounds of
the aromatic series in the presence of tin tetrachloride. Chem. Abst. 1928, 61B,
1996–1999.