Taming of superacids: PVP-triflic acid as an effective solid triflic acid equivalent for Friedel-Crafts hydroxyalkylation and acylation

Article abstract of DOI:10.1016/j.jfluchem.2014.08.020

The application of poly(4-vinylpyridine) supported trifluoromethanesulfonic acid (PVP-TfOH, 1:10) as a convenient solid superacid catalyst system in Friedel-Crafts reactions is described. In the presence of PVP-TfOH, one pot solvent-free synthesis of a wide variety of diarylacetic acid derivatives was achieved by Friedel-Crafts hydroxyalkylation reaction of glyoxylic acid with arenes under mild conditions. Acylation of both activated and deactivated aromatic compounds with acetyl chloride was also achieved using PVP-TfOH complex under solvent-free conditions at room temperature. As the polymer supported triflic acid was found to be a very efficient and an easy-to-handle solid acid, it can be a useful addition to environmentally more adaptable strong acid catalyst systems.

Full text of DOI:10.1016/j.jfluchem.2014.08.020

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Journal of Fluorine Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Taming of superacids: PVP-triflic acid as an effective solid triflic acid
equivalent for Friedel–Crafts hydroxyalkylation and acylation
*
G.K. Surya Prakash , Farzaneh Paknia, Aditya Kulkarni, Arjun Narayanan, Fang Wang,
*
Golam Rasul, Thomas Mathew , George A. Olah
Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, CA 90089-1661, United States
A R T I C L E I N F O
A B S T R A C T
Article history:
The application of poly(4-vinylpyridine) supported trifluoromethanesulfonic acid (PVP-TfOH, 1:10) as a
convenient solid superacid catalyst system in Friedel–Crafts reactions is described. In the presence of
PVP-TfOH, one pot solvent-free synthesis of a wide variety of diarylacetic acid derivatives was achieved
by Friedel–Crafts hydroxyalkylation reaction of glyoxylic acid with arenes under mild conditions.
Acylation of both activated and deactivated aromatic compounds with acetyl chloride was also achieved
using PVP-TfOH complex under solvent-free conditions at room temperature. As the polymer supported
triflic acid was found to be a very efficient and an easy-to-handle solid acid, it can be a useful addition to
environmentally more adaptable strong acid catalyst systems.
Received 23 June 2014
Accepted 28 August 2014
Available online xxx
Keywords:
Trifluoromethanesulfonic acid
PVP:triflic acid
Solid superacid
Hydroxyalkylation
Acylation
ß 2014 Elsevier B.V. All rights reserved.
1. Introduction
efficiently swollen by organic solvents are thus desired [5a]. Up to
now, several polymer bound Lewis acids and Brønsted acids have
The Friedel–Crafts reaction is one of the most fundamental and
useful reactions for C–C bond formation in organic chemistry
[1]. The Friedel–Crafts reaction generally requires Lewis or
Brønsted acid catalysts in large quantities, which quite often lead
to many difficulties. Many of these catalysts are generally corrosive
and difficult to recycle. Thus, there are still enormous demands for
clean and eco-friendly Friedel–Crafts processes. Recently, consid-
erable attention has been given towards the development of
Friedel–Crafts reactions heterogenously catalyzed by solid acid
catalysts such as zeolites, clays, Nafion-H, heteropolyacids (HPA),
etc [2]. In which the acidity is an intrinsic property of the
compounds and part of their chemical structure [3]. Nafion1-H (1),
a perfluoroalkanesulfonic acid resin, has been found to be a viable
solid acid catalyst with catalytic activity for many reactions giving
high selectivity [4]. As the solid catalyst is can be easily recycled,
the work-up of such reactions is usually very feasible. Therefore,
large scale synthesis of many useful products can be achieved with
significantly reduced cost. One major drawback of this catalyst is
its inefficient swelling by aprotic organic solvents, which generally
leads to low reaction rates. Polymer bound superacids that can be
been reported [5b]. It is believed that polystyrene bound super
Brønsted acid 2 is a strong carbon acid among known solid acids
[5]. Different types of polymer tethered Lewis acid catalysts
namely ‘‘immobilized’’ or ‘‘microencapsulated’’ Lewis acids such as
3 have been documented [6a]. New polymer supported acid
catalysts such as Cross-linked polystyrene-supported aluminum
triflate {Ps–Al(OTf)3} [6b], aluminum chloride immobilized on
cross-linked polyvinyl alcohol microspheres [6c], and poly(vinyl-
sulfonic acid)-grafted polystyrene [6c] have also been reported
recently (Fig. 1).
Our group observed that PVP {poly(4-vinylpridine)} is an
effective solid support for various gaseous and liquid acidic
reagents. The preparation of a polymer supported hydrogen
fluoride reagent, poly(4-vinylpyridinium) poly(hydrogen fluoride),
was previously reported by Olah et al. Pyridinium poly(hydrogen
fluoride) (PPHF, known as the Olah reagent) is an ionic liquid with a
high dielectric constant and has been used as a fluorinating agent
for alkenes, alkynes and alcohols [7]. Another Lewis acid complex,
PVP-SO2 was used as mild solid acid catalyst for three component
Strecker synthesis of
a-aminonitriles [8]. PVP-H2O2, a solid H2O2
equivalent, was exploited for ipso-hydroxylation of arylboronic
acids to phenols, selective oxidation of sulfides to sulfoxides
and conversion of ketones to gem-dihydroperoxides [9]. Trifluor-
omethanesulfonic acid (triflic acid) is a strong non-oxidizing
Brønsted superacid, extensively utilized in acid catalyzed synthetic
transformations. We have now immobilized triflic acid onto cross
*
Corresponding authors at: Loker Hydrocarbon Research Institute and Depart-
ment of Chemistry, University of Southern California, Los Angeles, CA 90089-1661,
United States. Tel.: +1 213 740 5984; Fax: +1 213 740 6679.
E-mail addresses: gprakash@usc.edu (G.K. Surya Prakash), tmathew@usc.edu
(T. Mathew).
http://dx.doi.org/10.1016/j.jfluchem.2014.08.020
0022-1139/ß 2014 Elsevier B.V. All rights reserved.
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Fig. 1. Polymer-bound superacids.
linked poly(4-vinylpyridine) expecting the formation of a stable
PVP-TfOH complex 4, which represents a convenient solid form of
triflic acid (Fig. 1).
In continuation of our studies on superacid catalyzed Friedel–
Crafts reactions, we disclose the application of the new PVP-TfOH
(1:10) complex, the ‘‘immobilized’’ superacid as an efficient
catalyst for the hydroxyalkylation and acetylation of aromatic
compounds at room temperature.
and triflic acid reached to a 1:10 ratio (Scheme 1). The ratio 1:10 is
more preferred for its use as a catalyst because the addition of more
triflic acid resulted in a wet solid. The reagent PVP-TfOH (1:10)
contains 93% triflic acid by weight and was found to be a very
useful and efficient catalyst for the Friedel–Crafts reactions.
However, a less acidic form was obtained in a drier solid form if
the ratio is less than 1:10.
Poly(4-vinylpyridine) acts as a suitable solid phase reservoir for
triflic acid, making the complex more convenient and safer for use.
Although the light creamy colored polymer powder slightly fumes
when exposed to air, it can be stored in well sealed Nalgene bottles
in a refrigerator for months without the detectable loss of the
catalytic activity. The surface morphology of the polymer samples
was also determined through scanning electron microscope
(Fig. 2).
In addition to the SEM characterization, we have also performed
TGA analysis of PVP-TfOH (1:10). Initial weight loss of 87% at ꢁ80–
220 8C in the TGA diagram is probably due to the loss of loosely
bound triflic acid molecules which are distant from the pyridinium
center in the poly(triflic acid) chain. Additional 12% weight loss
occurred at ꢁ280–480 8C possibly due to the decomposition from
2. Results and discussion
2.1. Preparation and properties of poly(4-vinylpyridinium) poly(triflic
acid)
Poly(4-vinylpyridinium) poly(triflic acid) in the solid form, was
conveniently prepared from poly(4-vinylpyridine) and triflic acid.
Commercially available 2% cross linked poly(4-vinylpyridine) was
carefully added to triflic acid in small portions at ꢀ78 8C under
nitrogen in the absence of solvents and mixed thoroughly until
uniform complexation. A stable creamy white solid powder
(slightly wet) was obtained when the loading ratio of the polymer
Scheme 1. Preparation of poly(4-vinylpyridinium) poly(triflic acid).
Fig. 2. (a) Surface morphology of 2% cross linked poly(4-vinyl pyridine). (b) Surface morphology of poly(4-vinylpyridinium) poly(triflic acid) (1:10).
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Fig. 3. TGA data of PVP-triflic acid.
molecules closer to cationic center and the 1:1 pyridinium salt
form itself (Fig. 3). More than 99% of the polymer underwent
decomposition above 500 8C. The TGA analysis clearly showed that
the current solid polymeric triflic acid is much less volatile than
liquid triflic acid and thus more convenient to handle.
The solid polymeric triflic acid is less volatile than liquid triflic
acid and more convenient to handle, thus making the product
separation easier by simple filtration of the reaction mixture
followed by neutralization of the filtrate. Since the leaching of triflic
acid is inevitable during the reaction, a complete recycling of the
solid triflic acid reagent can be practically challenging. However, the
regeneration PVP-TfOH can still be feasible and achieved by treating
recovered solid PVP support with fresh triflic acid.
5–7 [13–16]. The compound 5 has shown anti-muscarinic, 5-HT2A
,
and anti-dopaminergic activity [13].
a
,
a
-Diphenylacetamide
derivative (6a) has been shown to act as a local anesthetic with
high selectivity for the type IIA sodium channels [14a–b],
and antioxidant activity of acetamide 6b has been studied [14c].
2,2-Diphenylethylamine 7a has also exhibited antidepressant
activity [15a]. Modafinil analogue 7b has also been synthesized
and evaluated for biological activity [15b] (Fig. 4).
2.2. Synthesis of diarylacetic acid derivatives through Friedel–Crafts
hydroxyalkylationreactionofareneswithglyoxylicacidusingPVP-TfOH
The acid catalyzed condensation of ketones and aldehydes with
aromatic compounds is described in the literature as the hydro-
xyalkylation reaction. [1,10]. Our group [11] and others [12] have
exploited hydroxyalkylation reaction for the synthesis of various
biologically active heteroaryl compounds. With the present
method, a wide variety of diarylacetic acid derivatives was
synthesized by the Friedel–Crafts hydroxyalkylation reaction of
glyoxylic acid using PVP-TfOH (1:10) as an acid catalyst (Scheme 2).
Diarylacetic acids have been used as valuable building blocks
for the synthesis of many biologically active compounds such as
Fig. 4. Biologically important compounds prepared from diphenylacetic acids
precursors.
Scheme 2. Synthesis of diarylacetic acid derivatives.
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Table
1
Reaction of glyoxylic acid with arenes in the presence PVP-TfOH.
Entry
1
Arenes
Time (h)
12
Products
Isolated yield (%)
79
COOH
H
10
2
3
7
4
92
95
CH3
COOH
H
H3C
CH3
p-p/regioisomers = 7:3
11
CH3 CO2H
CH3
CH3
H
H3C
CH3
CH3
CH3
12
4
4
94
CH3 CO2H
H
CH3
H3C
H3C
13
CH3
o,p-o,p/regioisomers = 9:1
5
6
6
92
47
F
COOH
H
F
F
14
p-p/regioisomers = 9:1
10
COOH
Cl
H
Cl
F
Cl
15
CO2H
p-p/regioisomers = 7:3
7
48
38
F
F
H
F
F
F
16
8
72
5
Cl
Cl
CO2H
Cl
H
Cl
17
Cl
Cl
There are limited studies on the synthesis diarylacetic acids,
which include, reduction of benzilic acid [17a], carboxylation of
diarylmethanol with carbon monoxide in H2SO4 [17b], Friedel–
excess amount of acid catalyst is necessary. PVP-TfOH was found to
be very efficient and the synthesis of various diarylacetic acid was
achieved in a one pot process. To demonstrate the usefulness and
effectivenessof PVP-TfOH as a solid acid catalyst, its catalytic activity
in hydroxyalkylation reactions was compared with commercial
TfOH. Tables 1 and 2 show that the catalytic activityof PVP-TfOH and
TfOH is essentially comparable in most cases. Similar catalytic
activity of TfOH and solid PVP-TfOH as acid catalysts is presumably
duetothefactthatalargeamountoftriflicacidislooselyboundinthe
polymeric chain by hydrogen bonding. Such property of PVP-TfOH
allows the acid easily accessible for catalytic action.
Crafts reaction of methyl
in the presence of a Lewis acid [17c] and reaction of
methylanilino)acetonitrile with benzophenone to form
a
-chloro-
a
-methoxyacetate with arenes
-(N-
-cyano
a
a
enamines followed by acidic hydrolysis [17d]. However, all these
methods have shown drawbacks such as the utilization of toxic
reagents, multistep procedures and poor yields. Reaction of
glyoxylic acid with electron-rich aromatics in the presence of
concentrated sulfuric acid, has also been reported [17e].
With the present method, the Friedel–Crafts hydroxyalkylation
of various activated and deactivated aromatics with glyoxylic acid
was carried out using poly(4-vinylpyridinium) poly(triflic acid)
(1:10). Due to consumption of acid by coordination to the carboxyl
groupandformationofdistonicsuperelectrophilicdicationicspecies,
The efficiency of hydroxyalkylation depends on the degree of
activation of arenes. The reaction with electron-rich arenes
afforded the final products in a short period of time with high
yields (Entries 1–5, Table 1), whereas deactivated arenes generally
led to low yields (Entries 6–8, Table 1). Hydroxyalkylation reaction
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Table
2
Reaction of glyoxylic acid with arenes in the presence of triflic acid.
Entry
1
Arenes
Time (h)
5
Products
Isolated yield (%)
90
COOH
CH3
H
H3C
CH3
11
p-p/regioisomers = 7:3
2
3
4
4
95
93
CH3
CH3 CO2H
CH3
H
H3C
12
CH3
CH3
CH3
CH3 CO2H
H
CH3
H3C
CH3
H3C
13
o,p-o,p/regioisomers = 9:1
4
5
6
6
7
90
81
77
COOH
F
H
F
F
14
p-p/regioisomers = 9:1
Cl
F
COOH
H
Cl
Cl
15
p-p/regioisomers = 7:3
24
F
CO2H
F
H
F
16
F
F
7
72
24
40
Cl
Cl
CO2H
Cl
H
Cl
17
Cl
Cl
8
No reaction*
NO2
*
The reaction was carried out at 80 8C.
with highly deactivated arenes required longer period of time
resulting inlower yieldsof the products. Reactions of chlorobenzene,
difluorobenzene and dichlorobenzene with glyoxylic acid were
carried out, respectively, in 7 h, 24 h and 72 h at room temperature,
giving the final products in 81%, 38% and 5% yields, respectively
(Tables 1 and 2). Condensation of mono-substituted arenes with
glyoxylic acid gave rise to para-para’ substituted diarylacetic acids as
the major products along with other regioisomers.
[19]. Later, superelectrophilic activation was studied by Shudo [20]
and Klumpp [21] in the Friedel–Crafts hydroxyalkylation of 1,2-
dicarbonyl compounds with arenes. They also proposed the
formation of O,O-diprotonated 1,2-dicarbonyl species in superacidic
solution. On the basis of these results, it seemed plausible that the
glyoxylic acid might also serve as a superelectrophile in hydroxyalk-
yaltion reaction with arenes. In other words, the hydroxyalkylation
reaction involves the protonation of both carbonyl groups [18–21] to
produce superelectrophilic species with resonance structures III and
IV. The electrophilic attack on arene results in hydroxycarboxylicacid
(V). V can undergo further protonation to give dications resonance
structures VI and VII, which reacts with second arene to form the
corresponding gem-diaryl carboxylic acid product (Scheme 3).
2.3. The plausible mechanism for hydroxyalkylation
Since the initial proposal of superelectrophilic activation by Olah
[18], there has been significant interest in the chemistry of
superelectrophilic reactive intermediates. Superelectrophilic activa-
tion is proposed to occur in superacidic medium by protosolvation of
electrophiles to give highly reactive superelectrophilic species. Based
on spectroscopic evidence, Olah has previously suggested the
formation of O,O-diprotonated diketones in superacid medium
2.4. Friedel–Crafts acetylation of aromatics catalyzed by PVP-TfOH
The Friedel–Crafts acylation of aromatic compounds is the most
important one step route for the synthesis of aromatic ketones [1].
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Scheme 3. Plausible mechanism of superacid catalyzed Friedel–Crafts hydroxyalkylation reaction of glyoxylic acid with arenes through superelectrophilic activation.
yield of acetophenone was found to be similar (40–41%) inidicating
similar catalytic activity of PVP-TfOH to neat TfOH. The acetylation
of toluene, p-xylene and m-xylene in the presence of PVP-TfOH
gave the corresponding acetophenones in two hours at (60–73%)
yield (Entry 2–4). The Friedel–Crafts acylation of mesitylene with
acetyl chloride gave 23 in 69% yield (Entry 5). It is important to
note that aromatic ether can act as a good donor to form a complex
with acid catalyst, therefore diminishing the original activity of
both aromatic ether and catalyst [28]. However, the acylation of
anisole also underwent smoothly in 1.5 h to give a mixture of
corresponding ortho and para regioisomers in 89% yield (Entry 6,
Table 3). Furthermore, the reaction conditions are mild enough to
avoid any dealkylation of the ether group during acylation of
anisole [27j,29]. PVP-TfOH catalyzed acetylation of deactivated
arenes such as chlorobenzene and bromobenzene gave rise to
26a,b and 27a,b in 25% and 20% yields, respectively (Entries 8 and
9, Table 3). The acylation of mono-substituted arenes occurred
Fig. 5. A few important aromatic ketones.
Aromatic ketones, such as 2-benzoylthiophene 18, have been used as
photocatalysts [22]. Acetophenone 19 is a natural component of
berries, seafood, beef, and nuts. Similar aromatic ketones have also
been used as flavor ingredients. [23] Chalcone 20 and related
compounds have been found to be very active against the human
kidney carcinoma cells TK-10 and human colon adenocarcinoma cells
HT-29[24].Aromatic ketones have alsobeenused asprecursorsforthe
synthesis of a variety of pharmaceuticals, agrochemicals and natural
products [25]. Brasiliquinone B 21 is a cytotoxic benz[a]anthraqui-
none, which belongs to a large group of antibiotics commonly called
angucyclines (Fig. 5). The total synthesis of (ꢂ)-brasiliquinone B has
been achieved based on Friedel–Crafts acylation [26].
mainly at the para position in accordance with
a typical
electrophilic aromatic substitution reaction pathway. It should
be noted that increase in reaction time did not result in higher
yields but resulted in a mixture of unknown by-products. As
observed in earlier studies, low yields for these acetylation
reactions are probably due to ketene formation followed by
polymerization (Scheme 5) [30].
2.5. The plausible mechanism for acetylation
In most cases of the Friedel–Crafts acylation, an aromatic
compound undergoes electrophilic substitution reaction with a
carboxylic acid derivative (e.g. acid anhydride, acyl chloride, or the
acid itself) in the presence of a stoichiometric or excess amount of
acid catalysts. Various acid catalysts have been used for the Friedel–
Crafts acylation reactions such as methanesulfonic acid, [27a] triflic
acid [27b–d], Nafion1-H [27e], gallium triflate [27f], scandium
triflate[27g],zeolite[27h],heteropolysalt[27i],andzincoxide[27j].
With PVP-TfOH (1:10), the reaction of acetyl chloride with
various aromatics was carried out at room temperature to afford a
variety of acetophenone derivatives in good yields (Scheme 4). All
reactions were carried out using liquid arenes in excess, which also
act as the solvent. The results are summarized in Table 3.
A possible mechanism of acylation involves the protonation
of carbonyl group of acetyl chloride to form intermediates
I. Further protonation of acetyl cation I give rise to super-
electrophilic dicationic species II. The protonated acetyl cation
may directly react with arenes to give acetylated product
(Scheme 5). Possible formation of such activated intermediates
in strong acids have been earlier explored by Olah [31] and
Shudo [27b,32].
Fries rearrangement has also been successfully carried out
using PVP-TfOH. Fries rearrangement, is a well-known method for
the preparation of phenolic ketones through the arrangement of
phenolic esters by acid catalysts or photocatalysts. Phenyl acetate
was converted to para and ortho acetylated phenols in presence of
PVP-TfOH in good yields with higher para selectivity (Scheme 6)
though the yield is slightly diminished.
To compare the catalytic activity of supported acid catalyst with
the acid, the acetylation of benzene was carried out in the presence
of TfOH and PVP-TfOH. In both cases, in a period of three hours, the
Scheme 4. PVP-TfOH catalyzed acetylation of aromatics.
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Table
3
Acetylation of aromatics with acetyl chloride in presence of PVP-TfOH (1:10).
O
R
O
O
PVP-TfOH
RT
CH3
CH3
R
+
+
H3C
Cl
R
18
19-27
Entry
1
Arenes
Time (h)
3.0
Products
Isolated yield (%)
40
O
CH3
19
2
3
4
1.0
2.0
2.0
60
65
73
CH3
O
CH3 O
CH3
CH3
H3C
H3C
p/o regioisomers = 8:2
20b
20a
CH3
O
CH3
H3C
H3C
CH3
O
21
CH3
CH3
CH3
CH3
H3C
H3C
H3CO
F
22
5
6
7
6.0
1.5
2.0
69
89
39
H3C
CH3
O
CH3
CH3
CH3
23
OCH3
O
H3CO
O
CH3
CH3
24b
p/o regioisomers = 8:2
24a
F
F
O
O
CH3
CH3
p/o regioisomers = 9:1
25a
25b
8
9
6.0
6.0
25
20
Cl
Br
O
Cl
O
CH3
CH3
Cl
Br
p/o regioisomers = 8:2
26b
26a
27a
O
Br
O
CH3
CH3
p/o regioisomers = 7:3
27b
3. Theoretical study of mono- and diprotonation of glyoxylic
acid
0.95 [34]. Relative energies were computed at the MP2/cc-pVTZ//
MP2/cc-pVTZ + ZPE level. Computed energies are given in Table 4.
We have optimized the geometry of glyoxylic acid at the MP2/
cc-pVTZ level (Fig. 6). The structure 28 with C–C bond length of
Geometry optimizations were performed at the MP2/cc-pVTZ
level using the Gaussian 09 program [33]. Vibrational frequencies
at the MP2/cc-pVTZ//MP2/cc-pVTZ level were used to characterize
stationary points as minima (number of imaginary frequency
(NIMAG) = 0) or transition state (NIMAG) = 1) and to evaluate zero
point vibrational energies (ZPE), which were scaled by a factor of
˚
1.523 A was found to be the lowest energy structure. Isomeric
structure 29 was computed to be 1.2 kcal/mol less stable than
structure 1 at the MP2/cc-pVTZ//MP2/cc-pVTZ + ZPE level. O1-
protonated 30 and O3-protonated 31 were found to be the viable
minima for protonated glyoxylic acid at the MP2/cc-pVTZ level.
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O
-Cl-
H
H3C
C
O
H3C C O H
CH3
a
II
I
O
H3C
Cl
-Cl-
H
O
H
-H
CH3CO+
b
H2C
C
O
C C O
CH3 C CH2
C
O+
H
I
H2C
C
O
O
OH
OH
O
C
O+
C CH2
C
O+
CH3
CH3 C CH C CH
C CH2
polymerization
OH
O
O
O
n
n
Scheme 5. Possible mechanism of PVP-TfOH catalyzed acetylation of arenes.
4.1. Typical procedure for the preparation of poly(4-vinylpyridinium)
poly(triflic acid), PVP-TfOH (1:10)
2% Cross linked poly(4-vinylpyridine) (10.7 g, 0.1 mol) was
added under nitrogen to triflic acid (150 g, 1 mol) in a polyethylene
bottle. Since the reaction between PVP and triflic acid is highly
exothermic, triflic acid was added very slowly at ꢀ78 8C with
frequent shaking. Then the bottle was gradually warmed to the
room temperature and then stored in refrigerator. The resulting
creme white solid was formed to 93% by weight triflic acid and 7%
PVP (about 10 equivalent of triflic acid to each equivalent of
vinylpyridine unit).
Scheme 6. Fries rearrangement of phenyl acetate.
4.2. General procedure for the condensation reaction of glyoxylic acid
with aromatics, using PVP-TfOH(1:10) as the solid acid catalyst
Structure 30 was computed to be 2.9 kcal/mol more stable than
structure 31 at the MP2/cc-pVTZ//MP2/cc-pVTZ + ZPE level. The C–
The glyoxylic acid, 50% (0.6 g, 4 mmol), was mixed with arenes
(5 mL) in a Nalgene1 bottle and cooled to 0 8C. Then PVP-TfOH
(4.5 g, 28 mmol, 7 equivalents) was added slowly. The reaction
mixture was warmed up to room temperature and stirred over
specific period of time (Table 1). The reaction progress was
monitored by TLC (3:1 hexanes/ethyl acetate). After the reaction
was complete, the mixture was poured over ice (25 g), neutralized
with sodium bicarbonate, and extracted with diethyl ether
(3 ꢃ 15 mL). The organic extracts were combined, washed with
water and dried over anhydrous Na2SO4. The solvent was removed
by vaccum evaporation and crude products were purified by
column chromatography on silica gel (70–230 mesh) using
hexane/ethyl acetate (85:15) as eluent. The products were
characterized by spectral analysis and by comparing the spectral
˚
C bond length of 32 (1.542 A) was found to be significantly longer
˚
than that of 31 (1.513 A) indicating differences in charge
delocalization. The charge is localized (involving O1–C1–O2 atom)
in 30. On the other hand, the charge is delocalized (involving O3–
C2–C1–O1 atom) in 31. Diprotonated glyoxylic acid 32 was found
to be the lowest energy structure at the MP2/cc-pVTZ level.
Protonation of 28 to form 30 was calculated to be exothermic by
170.0 kcal/mol. Further protonation of 30 to form 32 was also
found to be exothermic by 45.0 kcal/mol. Diprotonated glyoxylic
acid 33 was also found to be a minimum. However, structure 33 is
significantly less stable than structure 32 by 16.2 kcal/mol.
4. Experimental
Unless otherwise mentioned, all chemicals were purchased
from commercial sources. PVP-TfOH was prepared by the method
described below. 1H, 13C, and 19F NMR spectra were recorded on
varian NMR at 400 MHz. 1H NMR chemical shifts were determined
relative to internal tetramethylsilane at 0.0 ppm, 13C NMR
chemical shifts were determined relative to 13C signal of CDCl3
at 77.0 ppm. 19F NMR chemical shifts were determined relative to
internal CFCl3 at 0.0 ppm. GC–MS spectra were recorded on a
ThermoFinnigan Mass (EI) spectrometer. HRMS data were
obtained from a high resolution Micromass GCT (GC–MS TOF)
spectrometer at Mass Spectrometry Facility, Department of
Chemistry, University of Arizona.
Table
4
Total energies (-au), ZPEa and relative energiesb.
Structure
Total energy
ZPE (kcal/mol)
Relative energy (kcal/mol)
28
29
30
31
32
33
ꢀ302.60282
ꢀ302.60051
ꢀ302.88508
ꢀ302.88100
ꢀ302.96810
ꢀ302.94030
26.1
25.8
33.2
33.5
40.3
39.0
215.0
216.2
45.0
47.9
0.0
16.2
a
Zero point vibrational energies (ZPE) at MP2/cc-pvtz//MP2/cc-pvtz level of
theory scaled by a factor of 0.95.
b
Relative energy at MP2/cc-pVTZ//MP2/cc-pVTZ level with ZPE correction.
Please cite this article in press as: G.K.S. Prakash, et al., J. Fluorine Chem. (2014), http://dx.doi.org/10.1016/j.jfluchem.2014.08.020

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G.K.S. Prakash et al. / Journal of Fluorine Chemistry xxx (2014) xxx–xxx
9
Fig. 6. MP2/cc-pVTZ calculated structures of 28–33.
data with those of the authentic samples (in the case of known
compounds). Some of the reactions were also repeated in presence
of TfOH (7 equivalents, Table 2). Since dichlorobenzene is a solid
aromatic compound, it was dissolved in dichloromethane and the
solution was used in the reaction.
2,2-Bis(20,40-dimethylphenyl)acetic acid (13) [38,39]: 1H NMR
(400 MHz, CDCl3):
d
2.22 (s, 6H), 2.29 (s, 6H), 5.24 (s,1H), 6.97–7.00
19.5, 21.0,
(m, 6H), 10.79 (br, 1H); 13C NMR (100 MHz, CDCl3):
d
50.1, 126.9, 128.1, 131.4, 132.9, 136.2, 137.0, 179.2; GC–MS (EI), m/
z, 268.05 (M+).
2,2-Bis(40-fluorophenyl)acetic acid (14) [37,40]: 1H NMR
4.3. General procedure for the PVP-TfOH catalyzed reactions of acetyl
chloride with arenes
(400 MHz, CDCl3): d 5.00 (s, 1H), 7.00–7.04 (m, 4H), 7.25–7.29
(m, 4H), 10.36 (br, 1H); 13C NMR (100 MHz, CDCl3):
d
55.3, 115.7 (d,
3
4
2JC–F = 21.4 Hz), 130.2 (d, JC–F = 7.6 Hz), 133.4 (d, JC–F = 3.1 Hz),
1
Acetyl chloride (20 mmol, 1.57 g) was added to arene (50 mmol)
in a Nalgene1 bottle. The solution was cooled to 0 8C and then PVP-
TfOH (1:10) complex (4.81 g, 30 mmol) was added slowly. The
mixture was stirred at 0 8C and gradually allowed to warm up to
room temperature and continued for specific period of time
(Table 3). Reaction of benzene (50 mmol) with acetylchloride
(20 mmol, 1.57 g) was repeated in presence of pure TfOH (30 mmol)
for comparison. Progress of the reactions was monitored by TLC (4:1
hexane/ethyl acetate). After the reaction was complete the reaction
mixture was carefully filtered into ice water, neutralized with
solution of sodium bicarbonate, and extracted with diethyl ether
(3 ꢃ 15 mL). The organic extracts were combined, washed with
water and dried over anhydrous Na2SO4. The solvent was removed
by vacuum evaporation and crude products were purified with
column chromatography using silica gel and hexane/ethyl acetate
(85:15) as eluent. All products were characterized by comparing the
spectral data with those of the authentic samples.
162.2 (d, JC–F = 247.2 Hz), 178.5; 19F NMR (376 MHz, CDCl3):
d
ꢀ115.0 (m); GC–MS (EI), m/z, 248.05 (M+).
2,2-Bis(chlorophenyl)acetic acids (15) [37,40]: A mixture was
obtained with para–para isomer as a major product along with
other regioisomers. 1H NMR (400 MHz, CDCl3):
d
4.97 (s, 1H), 5.48
(s, 1H), 7.22–7.25 (m, 7H), 7.29–7.33 (m, 9H), 10.86 (brs, 2H); 13C
NMR (100.5 MHz, CDCl3): 55.33, 55.82, 127.33, 129.20, 129.32,
d
129.95, 130.07, 130.159, 130.61, 134.01, 134.50, 135.00, 135.59,
136.06, 177.97, 178.26; GC–MS (EI), m/z, 280.20 (M+).
2,2-Bis(20,50-difluorophenyl)acetic acid (16): 1H NMR (400 MHz,
CDCl3):
(100 MHz, CDCl3):
d
5.50 (s, 1H), 6.95–7.10 (m, 6H), 10.10 (br, 1H); 13C NMR
2
d
43.3, 116.2–117.0 (m),124.9 (dd, JC–
F = 17.9 Hz, 3JC–F = 8.0 Hz),156.44 (dd, 1JC–F = 243.4 Hz, 4JC–
F = 2.7 Hz), 158.6 (dd, JC–F = 243.4 Hz, JC–F = 2.3 Hz); 19F NMR
1
4
(376 MHz, CDCl3):
d
ꢀ118.0 (m), ꢀ122.4 (m); GC–MS (EI), m/z,
284.15 (M+); HRMS (ESI), m/z calcd for C13H7F4 (M+—45) 239.0484,
observed 239.0476.
2,2-Diphenylacetic acid (10) [35,36]: 1H NMR (400 MHz, CDCl3):
2,2-Bis(20,50-dichlorophenyl)acetic acid (17): 1H NMR (400 MHz,
d
5.04 (s, 1H), 7.25–7.33 (m, 10H), 11.37 (brs, 1H); GC–MS (EI), m/z,
212.00 (M+).
2,2-Bis(methylphenyl)acetic acids (11) [37–39]: A mixture with
para–para isomer as a major product along with other regioi-
somers. 1H NMR (400 MHz, CDCl3):
2.28 (s, 6H), 2.30 (s, 6H), 4.96
(s, 1H), 5.18 (s,1H), 7.11 (d, J = 7.63 Hz, 7H), 7.17–7.21 (m, 8H),
7.26–7.29 (m, 1H) 11.30 (brs, 2H); 13C NMR (100.5 MHz, CDCl3):
CDCl3):
J = 2.4 Hz, 2H), 7.38 (d, J = 8.5 Hz, 2H), 9.37 (br, 1H); 13C NMR
(100 MHz, CDCl3): 51.2, 129.6, 129.7, 131.1, 133.0, 133.2, 135.5,
175.9; GC–MS (EI), m/z, 305.95 (M+—44); HRMS (ESI), m/z calcd for
13H8Cl4 (M—44) 303.9380, observed 303.9369.
d 5.80 (s, 1H), 7.12 (d, J = 2.3 Hz, 2H), 7.28 (dd, J = 8.5 Hz,
d
d
C
d
5. Conclusions
19.78, 21.01, 53.28, 56.25, 126.22, 127.47, 128.04, 128.45, 128.80,
129.29, 130.67, 134.20 135.09, 136.40 137.08, 179.26, 179.30; GC–
MS (EI), m/z, 239.55 (M+).
A novel solid superacidic system, poly(4-vinylpyridinium)
poly(triflic acid) (PVP-TfOH) was developed by immobilization
of triflic acid on poly(4-vinylpyridine). Being much safer to handle,
the polymer supported triflic acid was found to be very convenient
and effective solid acid catalyst for Friedel–Crafts hydroxyalkyla-
tion and acetylation reactions. One pot solvent-free synthesis of
wide variety of diarylacetic acids in high yields can be achieved by
2,2-Bis(20,50-dimethylphenyl)acetic acid (12) [38,39]: 1H NMR
(400 MHz, CDCl3):
7.00 (dd, J = 7.7 Hz, J = 1.1 Hz, 2H), 7.07 (d, J = 7.8 Hz, 2H), 10.82 (br,
1H); 13C NMR (100 MHz, CDCl3):
19.1, 21.2, 50.8, 128.2, 128.9,
130.4, 133.3, 135.5, 135.6, 178.9; GC–MS (EI), m/z, 268.25 (M+).
d2.21(s, 6H), 2.26(s, 6H), 5.27(s,1H), 6.91(s, 2H),
d
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G Model
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10
G.K.S. Prakash et al. / Journal of Fluorine Chemistry xxx (2014) xxx–xxx
(c) Z. Wang, B. Gao, J. Mol. Catal. A: Chem. 330 (2010) 35–40;
(d) T. Okayasu, K. Saito, H. Nishide, M. Hearn, Green Chem. 12 (2010) 1981–1989.
[7] (a) G.A. Olah, X.-Y. Li, Q. Wang, G.K.S. Prakash, Synthesis (1993) 693–699;
(b) G.A. Olah, X.-Y. Li, Synlett (1990) 267–268;
Friedel–Crafts hydroxyalkylation of arenes with glyoxilic acid by
using the polymer supported triflic acid complex as a convenient
solid triflic acid equivalent. Furthermore, an efficient solvent free
procedure for Friedel–Crafts acylation of aromatic compounds
using PVP-TfOH is also described. The advantages of this protocol
include easy handling and use of a solid acid catalyst, mild
reaction conditions, short reaction time and eliminating the need
for solvents. Poly(triflic acid) complex may find wide application as
a convenient solid superacid system for many organic transforma-
tions. Taming of superacids such as triflic acid is attained by
immobilizationonpoly(4-vinylpyridine)thussignificantlyreducing
the volatility and making the catalyst more environment friendly
and essentially making a step closer towards a green protocol.
(c) G.A. Olah, T. Mathew, A. Goeppert, B. To¨ro¨k, I. Bucsi, X.-Y. Li, Q. Wang, E.R.
Marinez, P. Batamack, R. Aniszfeld, G.K.S. Prakash, J. Am. Chem. Soc. 127 (2005)
5964–5969.
[8] G.A. Olah, T. Mathew, C. Panja, K. Smith, G.K.S. Prakash, Catal. Lett. 114 (2007) 1–7.
[9] (a) G.K.S. Prakash, S. Chacko, C. Panja, T.E. Thomas, L. Gurung, G. Rasul, T. Mathew,
G.A. Olah, Adv. Synth. Catal. 351 (2009) 1567–1574;
(b) G.K.S. Prakash, S. Chacko, C. Panja, T. Mathew, G.A. Olah, Abstracts of Papers,
230th ACS National Meeting, Aug. 28–Sept. 1, 2005, Washington, DC, United
States, 2005;
(c) G.K.S. Prakash, A. Shakhmin, K.E. Glinton, S. Rao, T. Mathew, G.A. Olah, Green
Chem. 16 (2014), http://dx.doi.org/10.1039/c4gc00586d.
[10] J. March, Advanced Organic Chemistry, fourth ed., Wiley, New York, NY, 1992.
[11] G.K.S. Prakash, F. Paknia, S. Chacko, T. Mathew, G.A. Olah, Heterocycles 76 (2008)
783–799.
[12] (a) D.A. Klumpp, Y. Zhang, D. Do, R. Kartika, Appl. Catal., A: Gen. 336 (2008) 128–
132;
Statement of significance
(b) D.A. Klumpp, M. Garza, A. Jones, S. Mendoza, J. Org. Chem. 64 (1999) 6702–
6705;
(c) D.A. Klumpp, P.J. Kindelin, A. Li, Tetrahedron Lett. 46 (2005) 2931–2935;
(d) D.A. Klumpp, M. Garza, G.V. Sanchez, S. Lau, S. Leon, J. Org. Chem. 65 (2000)
8997–9000;
(e) A.S. Gothelf, T. Hansen, K.A. Jorgensen, J. Chem. Soc., Perkin Trans. 1 (2001)
854–860;
The solid poly(4-vinylpyridine)-triflic acid (1:10) complex acts
as an effective solid equivalent of superacidic triflic acid without
significant loss of its catalytic activity. Both Friedel–Crafts
hydroxyalkylation and acetylation reactions are shown to be
effectively catalyzed by PVP-TfOH system. Application of this
complex in organic reactions allows storage and handling safer and
make the reactions more convenient compared to liquid triflic acid.
Therefore, the complex will find wide applications as a solid
reservoir of triflic acid in superacid catalysis.
(f) M. Abid, B. Torok, Adv. Synth. Catal. 347 (2005) 1797–1803;
(g) J. Zhang, P.G. Blazecka, T.T. Curran, Tetrahedron Lett. 48 (2007) 2611–2615.
[13] R.K. Singh, S. Jain, N. Sinha, A. Mehta, F. Naqvi, A.K. Agarwal, N. Anand, Tetrahe-
dron Lett. 48 (2007) 545–548.
[14] (a) I. Roufos, S.J. Hays, D.J. Dooley, R.D. Schwarz, G.W. Campbell, A.W. Probert,
J. Med. Chem. 37 (1994) 268–274 (and the references therein);
(b) I. Roufos, S. Hays, R.D. Schwarz, J. Med. Chem. 39 (1996) 1514–1520;
(c) G. Autore, A. Caruso, S. Marzocco, B. Nicolaus, C. Palladino, A. Pinto, A. Popolo,
M.S. Sinicropi, G. Tommonaro, C. Saturnino, Molecules 15 (2010) 2028–2038.
[15] (a) B.E. Maryanoff, S.O. Nortey, J.F. Gardocki, J. Med. Chem. 27 (1984) 1067–1071;
(b) C. De Risi, L. Ferraro, G.P. Pollini, S. Tanganelli, F. Valente, A.C. Veronese,
Bioorg. Med. Chem. 16 (2008) 9904–9910.
Acknowledgement
Financial support of our work by the Loker Hydrocarbon
Research Institute is gratefully acknowledged.
[16] (a) F. Picard, E. Baston, W. Reichert, R.W. Hartmann, Bioorg. Med. Chem. 8 (2000)
1479–1487;
(b) F. Picard, S. Barassin, A. Mokhtarian, R.W. Hartmann, J. Med. Chem. 45 (2002)
3406–3417;
(c) J. Charton, S. Girault-Mizzi, M.A. Debreu-Fontaine, F. Foufelle, I. Hainault, J.G.
Bizot-Espiard, D.H. Caignard, C. Sergheraert, Bioorg. Med. Chem. 14 (2006) 4490–
4518;
Appendix A. Supplementary data
(d) R.S. Dothager, K.S. Putt, B.J. Allen, B.J. Leslie, V. Nesterenko, P.J. Hergenrother, J.
Am. Chem. Soc. 127 (2005) 8686–8696;
(e) M. Graffner-Nordberg, K. Kolmodin, J. Aqvist, S.F. Queener, A. Hallberg, Eur. J.
Pharm. Sci. 22 (2004) 43–54;
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jfluchem.
2014.08.020.
(f) C. Kaiser, C.J. Spagnuolo, T.C. Adams, V.H. Audia, A.C. Dupont, H. Hatoum, V.C.
Lowe, J.C. Prosser, B.L. Sturm, L. Noronha-Blob, J. Med. Chem. 35 (1992) 4415–
4424.
References
[17] (a) P. Strazzolini, A.G. Giumanini, G. Verardo, Synth. Commun. 17 (1987) 1919–
1928 (and references therein);
[1] (a) G.A. Olah, Friedel–Crafts and Related Reactions, vol. 2, Part I Ed., John Wiley &
Sons, New York, NY, 1964;
(b) Y. Takahashi, N. Yoneda, H. Nagai, Chem. Lett. (1985) 1733–1734;
(c) M.J. Earle, R.A. Fairhurst, H. Heaney, Tetrahedron Lett. 32 (1991) 6171–6174;
(d) K. Takahashi, K. Shibasaki, K. Ogura, H. Iida, J. Org. Chem. 48 (1983) 3566–
3569;
(b) G.A. Olah, Friedel–Crafts Chemistry, Wiley Interscience, New York, NY, 1973.
[2] (a) G. Sartori, R. Maggi, Chem. Rev. 106 (2006) 1077–1104;
(b) I.V. Kozhevnikov, Appl. Catal., A: Gen. 256 (2003) 3–18;
(c) T. Okayasu, K. Saito, H. Nishide, M.T.W. Hearn, Green Chem. 12 (2010) 1981–
1989;
(e) J. Tang, R. Zhang, J. Shen, Synth. Met. 155 (2005) 100–104.
[18] (a) R.R. Naredla, D.A. Klumpp, Chem. Rev. 113 (2013) 6905–6948;
(b) G.A. Olah, D.A. Klumpp, Superelectrophiles and Their Chemistry, Wiley-
Interscience, Hoboken, NJ, 2008;
(c) G.A. Olah, D.A. Klumpp, Acc. Chem. Res. 37 (2004) 211–220.
[19] G.A. Olah, M. Calin, J. Am. Chem. Soc. 90 (1968) 4672–4675.
[20] T. Yamazaki, S.-i. Saito, T. Ohwada, K. Shudo, Tetrahedron Lett. 36 (1995) 5749–
5752.
[21] D.A. Klumpp, S. Lau, M. Garza, B. Schick, K. Kantardjieff, J. Org. Chem. 64 (1999)
7635–7637.
[22] J. Perez-Prieto, R.E. Galian, M.C. Morant-Minana, ChemPhysChem 7 (2006) 2077–
2080.
[23] T.B. Adams, M.M. McGowen, M.C. Williams, S.M. Cohen, V.J. Feron, J.I. Goodman,
L.J. Marnett, I.C. Munro, P.S. Portoghese, R.L. Smith, W.J. Waddell, Food Chem.
Toxicol. 45 (2007) 171–180.
[24] M. Cabrera, M. Simoens, G. Falchi, M.L. Lavaggi, O.E. Piro, E.E. Castellano, A. Vidal,
A. Azqueta, A. Monge, A.L. Cerain, G. Sagrera, G. Seoane, H. Cerecettoa, M.
Gonzaleza, Bioorg. Med. Chem. 15 (2007) 3356–3367.
[25] (a) K. Nakamura, R. Yamanaka, T. Matsuda, T. Harada, Tetrahedron: Asymmetry
14 (2003) 2659–2681;
(b) E.B. Kurbanoglu, K. Zilbeyaz, N.I. Kurbanogluc, M. Taskin, Tetrahedron:
Asymmetry 18 (2007) 1529–1532.
[26] M.L. Patil, H.B. Borate, D.E. Ponde, V.H. Deshpande, Tetrahedron 58 (2002) 6615–
6620.
(d) S.K. Jana, Catal. Surv. Asia 2 (2006) 98–109;
(e) K. Omata, Appl. Catal., A: Gen. 407 (2011) 112–117;
(f) K.-I. Shimizua, A. Satsumav, Energy Environ. Sci. 4 (2011) 3140–3153.
[3] G.A. Olah, G.K.S. Prakash, A. Molna´r, J. Sommer, Superacid Chemistry, John Wiley
& Sons, Inc., Hoboken, NJ, 2009.
[4] (a) G.A. Olah, R. Malhotra, S.C. Narang, J.A. Olah, Synthesis (1978) 672–673;
(b) G.A. Olah, P.S. Iyer, G.K.S. Prakash, Synthesis (1986) 513–531;
(c) G.K.S. Prakash, T. Mathew, S. Krishnaraj, E.R. Marinez, G.A. Olah, Appl. Catal., A:
Gen. 181 (1999) 283–288;
(d) M. Hachoumy, T. Mathew, E.C. Tongco, Y.D. Vankar, G.K.S. Prakash, G.A. Olah,
Synlett (1999) 363–365;
(e) G.A. Olah, T. Mathew, M. Farnia, G.K.S. Prakash, Synlett (1999) 1067–1068;
(f) G.A. Olah, T. Mathew, G.K.S. Prakash, Chem. Commun. (2001) 1696–1697;
(g) G.K.S. Prakash, H. Vaghoo, C. Panja, A. Molna´r, T. Mathew, G.A. Olah, Synthesis
(2008) 897–902;
(h) G.K.S. Prakash, G. Fogassy, G.A. Olah, Catal. Lett. 138 (2010) 155–159;
(i) G.K.S. Prakash, K.E. Glinton, C. Panja, L. Gurung, P.T. Battamack, B. To¨ro¨k, T.
Mathew, G.A. Olah, Tetrahedron Lett. 53 (2012) 607–611.
[5] (a) K. Ishihara, A. Hasegawa, H. Yamamoto, Angew. Chem. Int. Ed. Engl. 40 (2001)
4077–4079;
(b) Y. Yin, G. Zhao, G.L. Li, Tetrahedron 61 (2005) 12042–12052 (and references
therein).
[6] (a) S. Kobayashi, S. Nagayama, J. Am. Chem. Soc. 120 (1998) 2985–2986;
(b) K.P. Boroujeni, K. Parvanak, J. Serb. Chem. Soc. 76 (2011) 155–163;
[27] (a) V. Premasagar, V.A. Palaniswamy, E.J. Eisenbraun, J. Org. Chem. 46 (1981)
2974–2976;
Please cite this article in press as: G.K.S. Prakash, et al., J. Fluorine Chem. (2014), http://dx.doi.org/10.1016/j.jfluchem.2014.08.020

G Model
FLUOR-8412; No. of Pages 11
G.K.S. Prakash et al. / Journal of Fluorine Chemistry xxx (2014) xxx–xxx
11
(b) Y. Sato, M. Yato, T. Ohwada, S. Saito, K. Shudo, J. Am. Chem. Soc. 117 (1995)
3037–3043;
[31] (a) G.A. Olah, A. Germain, H.C. Lin, D. Forsyth, J. Am. Chem. Soc. 97 (1975) 2928–
2929;
(c) F. Effenberger, G. Epple, Angew. Chem. Int. Ed. 11 (1972) 299–300;
(d) F. Effenberger, G. Epple, Angew. Chem. Int. Ed. 11 (1972) 300–301;
(e) T. Yamato, C. Hideshima, G.K.S. Prakash, G.A. Olah, J. Org. Chem. 56 (1991)
3955–3957;
(f) G.K.S. Prakash, P. Yan, B. To¨ro¨k, I. Bucsi, M. Tanaka, G.A. Olah, Catal. Lett. 85
(2003) 1–6;
(g) Y. Matsushita, K. Sugamoto, T. Matsui, Tetrahedron Lett. 45 (2004) 4723–
4727;
(h) B. Chiche, A. Finiels, C. Gauthier, P. Geneste, J. Graille, D. Pioch, J. Org. Chem. 51
(1986) 2128–2130;
(b) G.A. Olah, Angew. Chem. Int. Ed. 32 (1993) 767–788.
[32] T. Ohwada, N. Yamagata, K. Shudo, J. Am. Chem. Soc. 113 (1991) 1364–1373.
[33] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery, T. Vreven, K.N. Kudin, J.C. Burant, et al., Gaussian 09, Revision
A.02, Gaussian, Inc., Wallingford, CT, 2009.
[34] J.B. Foresman, A. Frisch, Exploring Chemistry with Electronic Structure Methods,
Gaussian Inc., Pittsburgh, 1996, pp. 1–64.
[35] J.E. Miline, T. Storz, J.T. Colyer, O.R. Thiel, M.D. Seran, R.D. Larsen, J.A. Murry, J. Org.
Chem. 76 (2011) 9519–9524.
[36] C. Schnabel, K. Sterz, H. Mueller, J. Rehbein, M. Wiese, M. Hiersemann, J. Org.
Chem. 76 (2011) 512–522.
[37] J.R. Coats, J.W. Williams, C. Chang, A.H. Lee, R.L. Metcalf, Environ. Toxicol. Chem. 8
(1989) 45–52.
[38] Y. Iwakura, F. Toda, M. Kosugi, Y. Torii, J. Org. Chem. 36 (1970) 3990–3992.
[39] (a) R.C. Fuson, M.L. Ward, J. Am. Chem. Soc. 68 (1946) 521–522;
(b) G. Werber, F. Buccheri, Gaz. Chim. Ital. 96 (1966) 465–474.
[40] Y. Takahashi, N. Yoneda, H. Nagai, Chem. Lett. 11 (1985) 1733–1734.
(i) K. Shimizu, K. Niimi, A. Satsuma, Catal. Commun. 9 (2008) 980–983;
(j) M.H. Sarvari, H. Sharghi, J. Org. Chem. 69 (2004) 6953–6956.
[28] G. Sartori, R. Maggi, Chem. Rev. 106 (2006) 1077–1104.
[29] G.P. Schiemenz, U. Schmidt, Liebigs Ann. Chem. (1976) 1514–1519.
[30] (a) G.A. Olah, R. Malhotra, S.C. Narang, J.A. Olah, Synthesis (1978) 672–673;
(b) G.A. Olah, E. Zadok, R. Edler, D.H. Adamson, W. Kasha, G.K.S. Prakash, J. Am.
Chem. Soc. 111 (1989) 9123–9125.
Please cite this article in press as: G.K.S. Prakash, et al., J. Fluorine Chem. (2014), http://dx.doi.org/10.1016/j.jfluchem.2014.08.020