Synthesis of trifluoromethyl-imines by solid acid/superacid catalyzed microwave assisted approach

Article abstract of DOI:10.1016/j.jfluchem.2007.01.011

A new solid acid/superacid catalyzed microwave assisted synthesis of trifluoromethyl-imines is described. Various α,α,α-trifluoromethylketones react readily with primary amines to produce the corresponding imines. Two different strategies have been employ

Full text of DOI:10.1016/j.jfluchem.2007.01.011

Journal of Fluorine Chemistry 128 (2007) 587–594
www.elsevier.com/locate/fluor
Synthesis of trifluoromethyl-imines by solid acid/superacid catalyzed
microwave assisted approach
Mohammed Abid a,b, Markku Savolainen b,1, Shainaz Landge a,b, Jinbo Hu c,
c
¨ ¨
G.K. Surya Prakash , George A. Olah , Bela Torok
c
a,b,
*
´
a Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Blvd., Boston, MA 02125-3393, USA
b Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA
c Donald P. and Katherine B. Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California,
University Park, 837 Bloom Walk, Los Angeles, CA 90089-1661, USA
Received 6 November 2006; received in revised form 22 January 2007; accepted 24 January 2007
Available online 2 February 2007
Abstract
A new solid acid/superacid catalyzed microwave assisted synthesis of trifluoromethyl-imines is described. Various a,a,a-trifluoromethylk-
etones react readily with primary amines to produce the corresponding imines. Two different strategies have been employed; one is the application
of microwave irradiation coupled with solvent-free solid acid catalysis. The other method, for highly deactivated substrates includes the use of a
pressure vessel at 175 8C temperature, with solid superacid catalysis. Using the solid acid K-10 montmorillonite or the superacidic perfluorinated
resinsulfonic acid Nafion-H, a wide variety of trifluoromethylated imines have been synthesized using the above methods. The products have been
isolated in good to excellent yields and high selectivities. This new environmentally friendly synthetic methodology provides significantly higher
yields than traditional methods during relatively short reaction times for the preparation of the target compounds.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Trifluoromethyl; Imine; Clay; Solid acids; Solid superacid; Catalysis; Microwave irradiation
1. Introduction
produce no waste. Several different types of solid acid catalysts
include: acidic clays, zeolites, silica-occluded heteropoly acids,
sulfonated polystyrenes (Dowex, Amberlyst) and polysiloxanes
(Deloxane), and various forms of perfluorinated sulfonic acid
ion exchange resins, such as Nafion-H1 [3].
Solid acids and solid superacids are among the most
important and widely used catalysts in industrial and laboratory
practice [1]. Traditionally, acid catalyzed reactions were carried
out using mineral acids (e.g. HCl, H2SO4, etc.), or Lewis acids
(AlCl3, TiCl4, etc.). However, due to the increasing awareness
of environmental impact and safety factors in laboratory and
industrial processes, solid acid alternatives have been devel-
oped [2]. Solid acid catalyzed processes are gradually replacing
most industrial acid catalyzed processes. These catalysts are
safer than mineral acids, easy to store and handle, the workup
procedure, namely the catalyst separation, is easy and they
One particularly important area of their application is the
synthesis of organofluorine compounds. Organofluorine chem-
istry has received extensive attention especially in the
pharmaceutical industry and in materials science due to the
unique properties of fluorinated compounds [4]. Trifluoro-
methylated compounds are of particular interest as the strong
electron-withdrawing effect of CF3 group contributes to a
number of biologically important molecular properties. For
example it results in significant increase in lipophilicity of the
molecule, which is a very important feature in drug delivery.
The different medicinal applications of fluorinated organic
molecules are widespread. Some of the most well known
fluorine containing drugs are Prozac1 (anti-depressant),
Diflucan1 (anti-fungal agent), Casodex1 (anti-cancer agent)
and Desflurane (inhalation anesthetic) [4]. Recent, new
* Corresponding author at: Department of Chemistry, University of Massa-
chusetts Boston, 100 Morrissey Blvd. Boston, MA 02125-3393, USA.
Fax: +1 617 287 6030.
¨ ¨
E-mail address: bela.torok@umb.edu (B. Torok).
1
Present address: Adolor Corporation, Exton, PA, USA.
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2007.01.011

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M. Abid et al. / Journal of Fluorine Chemistry 128 (2007) 587–594
application of organofluorine compounds, include their use as
potential therapeutics for HIV, cancer or Alzheimer’s disease.
Accordingly, the synthesis of these molecules is in great
demand [5] and the search for new biologically active
fluorinated compounds is in the forefront of organic and
medicinal chemistry [6]. Trifluoromethylated imines are
particularly important as precursor products or as building
blocks for the synthesis of biologically active molecules [7].
Unfortunately the synthesis of these compounds is relatively
difficult using traditional methods. One frequently used method
is the PTSA catalyzed condensation reaction of trifluoromethyl
ketones with various amines, such benzylamines or anilines.
The very strong electron withdrawing nature of the trifluor-
omethyl group stabilizes the tetrahedral hemiaminal inter-
mediate in the target reaction similarly to hemiacetals that can
be easily isolated [7e]. The same electron withdrawing effect
destabilizes the carbocationic intermediate. Since the thermo-
dynamic stability of the carbocationic intermediate is
significantly lower than that of the hemiaminal, the reaction
should be reasonably endothermic. To overcome this energy
barrier requires the use of high temperature or other non-
classical activation methods.
while reasonably decreasing the reaction time and also
minimizing the formation of undesirable byproducts. The
major advantages of this method are short reaction times, high
yields and selectivities and ease of work-up and isolation of
products.
2. Results and discussion
In response to the increasing industrial importance of
imines, much research is directed toward the development of
catalytic methods for their preparation. Many useful methods
have been developed for the synthesis of imines from the
corresponding carbonyl compounds and amines using both
traditional liquid and contemporary ‘‘green’’ solid acid
catalysts [10]. Effective synthesis of trifluoromethylated imines
from highly deactivated trifluoromethyl ketones, however, is
still an important challenge. Our goal was to develop an
efficient and at the same time, environmentally benign method
for the synthesis of the target compounds. The condensation of
1,1,1-trifluoroacetophenone with benzylamine has been
selected as a model reaction to optimize the process. For
comparison, the reaction has been carried out using a traditional
synthetic approach. Initially, the reaction was performed in
toluene using p-toluenesulfonic acid (PTSA) as a catalyst under
reflux conditions (110 8C) [11]. This reaction took place
extremely slowly providing moderate yield (ꢀ70%) after 7
days of reflux (Table 1). To improve the reaction rate we carried
out the reaction using the same reactants, catalyst and solvent in
a closed pressure tube at 175 8C. Despite the significant
increase in temperature the yield was only 25% after 24 h
(Table 1). This indicates the need for an alternative approach
that provides higher yield in a more reasonable time frame. Our
strategy was to apply solid acid catalysis instead of PTSA.
Over the past two decades, microwave assisted organic
synthesis has emerged as important area and attracted
significant attention as indicated by extensive number of
publications [8]. It is a convenient and time saving method,
which promotes the application of environmentally benign
approaches such as solvent free and heterogeneous catalytic
reaction conditions [9].
Herein, we describe a novel, environmentally benign
approach for the synthesis of a wide variety of a,a,a-
trifluoromethyl-imines. The combination of microwave irra-
diation and solid acid/superacid catalysis provides high yields
Table 1
Summary of experimental conditions and product yields in condensation of 1,1,1-trifluoroacetophenone with benzylamine
Catalyst
Method of heating
Other
Reaction time (h)
Yielda (%)
PTSA
PTSA
Nafion-H
Nafion-H
K-10
K-10
K-10
–
Reflux (110 8C)
175 8C
175 8C
Microwave irradiation, 175 8C
Microwave irradiation, 175 8C
Microwave irradiation, 175 8C
Microwave irradiation, 175 8C
175 8C
Toluene
168
24
75
24
80
50
50
5
Pressure tube, toluene
Pressure tube, toluene
A/Kb ratio = 1
48
0.5
Int. cooling, A/K ratio = 1
Ar flow, A/K ratio = 1
A/K ratio = 1.5
1.5
0.33
0.45
24
95
17
8
No solvent, pressure tube
A/K ratio = 1.5
–
Microwave irradiation, 175 8C
A/K ratio = 1.5
0.45
0.45
PTSA
A/K ratio = 1.5
22
a
GC-yield.
b
A/K—amine/ketone ratio.
Scheme 1. Solid acid catalyzed condensation of various amines and trifluoromethylated ketones.

M. Abid et al. / Journal of Fluorine Chemistry 128 (2007) 587–594
589
Table 2
Based on our experience, K-10 montmorillonite and the
superacidic perfluorinated resinsulfonic acid Nafion-H were
selected as catalysts (Scheme 1).
K-10 catalyzed microwave assisted synthesis of trifluoromethylated imines
from 1,1,1-trifluoroacetophenone and various amines at 175 8C
Both catalysts are well-known and widely used in a variety
of organic transformations [3,12]. K-10 montmorillonite is a
solid acid of moderate acid strength. Its Hammett constant is
H0 = À8, which is similar to that of concentrated HNO3. Its
high surface area (250 m2/g), however, makes it a useful and
active catalyst. Both its structural features [13] and synthetic
potential [12] have been extensively studied. In contrast,
Nafion-H, another widely studied solid acid, possesses very
strong acidity [3]. In fact, it is a solid superacid with a Hammett
constant of H0 = À12.2 [3]. The above model reaction has been
studied using these two catalysts under widely varied
experimental conditions. The results are summarized in
Table 1.
Entry
R
Time (min)
Yield (%)a
1
2
3
30
45
21
90
95
95
4
5
30
30
60
95
Beside the catalyst, the use of microwave irradiation and
high temperature reaction in a pressure tube vessel were the
most significant changes implemented. The microwave assisted
reactions have been carried out under solvent-free conditions.
The reactants and the catalyst were stirred in ether for 10 min,
and then the solvent was removed providing a dry mixture of
catalyst with reactants evenly distributed on its surface. This
mixture was placed into the microwave cavity and irradiated for
a specific time at constant temperature. It was observed that a
traditional reaction at 175 8C using Nafion-H as catalyst
resulted in only 5% improvement in yield, however, its use
significantly reduced reaction times. The Nafion-H catalyzed
microwave assisted reaction showed promise, unfortunately,
the catalyst formed a dark melt and completely lost activity.
Using the thermally stable K-10 as catalysts, the reaction gave
nearly quantitative yield (95%) in very short time of irradiation
(25 min). It is worth noting that both K-10 and Nafion-H are
strong acids; however, the density of the acid centers is
relatively low. Depending on the accessibility of the acid center
to individual substrates, the amount of available acid centers
varies between 1–5 mmol/kg (based on ion-exchange capa-
cities) [3,12,13]. It means, for instance, that the 0.5 g K-10 used
had about 5–25 Â 10À4 mmol acid centers compare to 1–
1.5 mmol reactants. As such, these materials, although used in
relatively large amount are still considered as catalysts. Based
on the results obtained under optimized reaction conditions, the
scope of the microwave-assisted approach has been extended
by using 1,1,1-trifluoroacetophenone and wide selection of
substituted amines as reaction partners. The results are
summarized in Table 2.
6
7
50
30
90
95
8
9
30
20
91
95
10
30
92
a
Isolated yields.
on this comparison the products have been identified as (E)-
isomers throughout this study.
These results certainly initiated studies on wide variety of
trifluoromethyl ketones and amines, as well. Table 3 summarizes
the results obtained in the condensation of aryl-trifluoromethyl
ketoneswith methylbenzylamineando-methylaniline. InTable 4
the scope of the reaction was further widened using aryl- and
alkyl-trifluoromethyl ketones, ethyl 3,3,3-trifluoroacetoacetate
with o-phenylenediamines.
Tables 3 and 4 indicate that the reaction can be carried out
effectively with a diverse group of trifluoromethyl ketones and
amines. The yields range from good to excellent during short
reaction times. Several sensitive substrates such as 2-
trifluoroacetylpyrrole and 2-trifluoroacetylthiophene, which
tend to polymerize under strongly acidic conditions readily
underwent condensation under the relatively mild solid acid/
microwave conditions. Ethyl trifluoroacetoacetate and other
trifluoromethyl ketones provided the cyclic products in
excellent yields and selectivity with two types of phenylene-
diamines in very short reaction times (Table 4). The cyclization
reaction occurred between the second amino and the ethoxy
groups. It is also clear that despite the presence of two amino
The data indicate that trifluoroacetophenone readily under-
goes condensation with a wide variety of amines including
benzylamine and aniline derivatives providing yields mostly
higher than 90%. During the reaction the desired products were
formed exclusively, with no byproduct formation. Analysis of
the products by both capillary gas chromatography and 19F
NMR spectroscopy indicated the formation of a single isomeric
product instead of the mixture of two stereoisomers. Many of
these products have already been synthesized and described in
the literature [14]. We have used this method to synthesize
authentic compounds and compare them to our products. Based

590
M. Abid et al. / Journal of Fluorine Chemistry 128 (2007) 587–594
Table 3
selectivity is exclusive for the corresponding cyclic product
even after extended period of irradiation. Most likely one amino
group activates the other one through the continuous
conjugation and increases the nucleophilicity of the reacting
amino group. Hence, the reaction rates are significantly higher
than that of other amines regardless of the ketone used. After
the condensation, the strongly electron withdrawing effect of
CF3 will dominate and deactivate the remaining amino group
toward condensation.
K-10 catalyzed microwave assisted synthesis of trifluoromethylated imines
from trifluoromethyl ketones and various amines at 175 8C
We have also studied the possible reuse of the K-10
montmorillonite. The catalyst appeared to be active even after
the fifth consecutive run, although we have observed a gradual
decrease in product yields. It is most likely due to the formation
of irreversibly adsorbed carbonaceous deposits on the catalyst,
which can be removed by high temperature (ꢀ300 8C) aerobic
heat treatment.
Entry
R
Amine
Time (min)
Yield (%)a
1
2
3
a
b
a
36
30
50
85
87
95
During these studies we have observed that few CF3-
ketones, such as 9-trifluoroacetyl-anthracene, 1-trifluoroace-
tylnaphthalene and 3-trifluorocetylindole have shown strong
resistance toward reaction. Only 1-trifluoroacetylnaphthalene
underwent K-10 catalyzed reaction with a vast excess of amine
and much longer irradiation period. The remaining two ketones
are so deactivated that they do not show any product formation
even after excess amine or extended time of irradiation. The use
of the solid superacidic perfluorinated resinsulfonic acid,
Nafion-H, partially overcame the problem of reactant
deactivation. As Nafion-H appeared to be unstable under
microwave irradiation (Table 1), the reactants and Nafion-H
were mixed in toluene and heated up in a pressure tube to
175 8C by conventional heating. Nafion-H under these
condition provided some product formation but in only low
yields in the case of trifluoroacetylnaphthalene and indole,
respectively. In the case of trifluoroacetylnaphthalene a
subsequent isomerization has also been observed. With 9-
trifluoroacetylanthracene the product was obtained in traces
only. It is very likely that the presence of an orthogonal C–H
bond, e.g. at the naphthyl 8-position interferes with the
stabilization of the imine form, leading to an increased stability
of the tetrahedral intermediate. The important role of this
interaction is clearly supported by the data, that trifluoroace-
tylnaphthalene with one such interaction gives low yield, while
9-trifluoroacetylanthracene with two such interactions gave the
product only in traces.
4
5
b
60
88
a
78
69
53
90
6
b
a
Isolated yields.
groups in phenylenediamines, only one is able to react to form
imine with simple trifluoromethyl ketones, the other amino
group becomes highly deactivated. Thus, the first reaction
proceeds with high rate, then cyclization takes place, the
Table 4
K-10 catalyzed microwave assisted condensation of various trifluoromethyl-
ketones and a ketoester with o-phenylenediamines at 175 8C
Entry
R1
R2
Time (min)
Yield (%)a
The reaction follows the regular mechanism of acid
catalyzed condensation reactions. The CF3 moiety has a very
strong electron withdrawing character, and coupled with the
carbonyl oxygen’s electron withdrawing nature, the carbonyl C
carries a strong partial positive charge that is significantly
greater than that of a ketone without a-CF3 group. This
enhanced d+ charge, in fact, activate the first step in the
mechanism, namely the nucleophilic attack on the C providing
the highlighted intermediate. However, the subsequent proto-
nation and water elimination of the key intermediate is not
favored as the strong electron withdrawing effect of CF3
destabilizes the carbocationic intermediate (Scheme 2). As a
result, the water elimination is the rate-determining step of the
condensation reaction in the case of trifluoromethyl ketones.
1
2
3
4
H
1
2
1
2
95
90
92
82
CH3
H
CH3
5
6
7
8
CH2COOEt
CH2COOEt
CH3
H
1
1
1
3
90
92
88
90
CH3
H
CH3
CH3
a
Isolated yields.

M. Abid et al. / Journal of Fluorine Chemistry 128 (2007) 587–594
591
Scheme 2. The strongly deactivated dehydration step during the condensation of trifluoromethyl ketones with primary amines.
3. Conclusion
preparative reactions. After satisfactory conversion, ether was
added to the cold mixture, and the product was separated from
catalyst by filtration. The products have been isolated as
crystals or oils and purified by flash chromatography.
In conclusion, a novel, effective solid acid/superacid
catalyzed, economic and environmentally benign method for
synthesis of novel trifluoromethylated Schiff bases have been
developed. The combination of microwave irradiation and solid
acid catalysis greatly reduced reaction time, while improving
the yields and making the synthesis of a diverse group of CF3
imines possible. The short reaction time, mostly solvent-free
reaction conditions, ease of product isolation, and the safe
nature of the catalysts make the process an attractive alternative
for the synthesis of trifluoromethyl-imines in an environmen-
tally benign manner.
4.2. General procedure for synthesis of trifluoromethylated
imines using Nafion-H catalysis in a pressure tube
Trifluoromethylated ketone (1.0 mmol), amine (2.0 mmol)
were dissolved with 2 mL of toluene in a Teflon screw-cap
pressure tube and then Nafion-H (1 g) was added. The reaction
mixture was then immersed into an oil bath preheated to
175 8C. The reaction mixture was stirred by magnetic stirrer
and during optimization the progress was monitored by TLC,
then the optimized times were used for preparative reactions.
After satisfactory conversion, the product was separated from
catalyst by filtration. The solvent was removed under vacuum.
The oily residue was purified by flash chromatography to obtain
the pure product.
4. Experimental
All trifuoromethyl ketones, and amines were purchased
from Aldrich and used without further purification. K-10 was a
Fluka product. Nafion-H was purchased from Aldrich as a
potassium salt and was acidified by successive treatments with
HCl and HNO3 according to the literature [3e]. The CDCl3 used
as solvent for NMR studies and the CFCl3, used as reference
compound in 19F NMR measurements were obtained form
Aldrich. Other solvents used in synthesis were Fisher products
with a minimum purity of 99.5%.
4.3. Product characterization
4.3.1. N-[2,2,2-Trifluoro-1-phenylethylidene]aniline
(Table 2, Entry-1)
Ref. [7(i)], 1H NMR (399.81 MHz, CDCl3), d (ppm) 8.07 (d,
J = 8 Hz, 1H), 7.54 (t, J = 8 Hz, 1H), 7.26 (m, 5H), 7.02 (t,
J = 7.6 Hz, 1H), 6.72 (d, J = 7.6 Hz, 2H); 13C NMR
(100.53 MHz, CDCl3), d (ppm) 146.1, 130.4, 129.4, 128.9,
128.8, 128.7, 125.5, 120.7; 19F NMR (376.19 MHz, CDCl3,
CFCl3-Ref), d (ppm) À70.4 (s, 3F). MS-C14H10F3N (249), m/z
(%): 249 (M+, 25), 180 (100), 77 (60).
1
The H, 13C and 19F spectra were obtained on a 400 MHz
superconducting Varian Innova 400 NMR spectrometer, in
CDCl3 solvent with tetramethylsilane or the residual solvent
signal of CDCl3 as internal standards. CFCl3 was used as
internal standard for 19F signals. The temperature was 25 8C
(accuracy Æ1 8C) and controlled by the Varian control unit.
The mass spectrometric identification of the products have been
carried out by a Shimadzu QP5050 gas chromatograph-mass
spectrometer system (70 eVelectron impact ionization) using a
30 m long DB-5 type column (J&W Scientific).
4.3.2. 1-Phenyl-N-[2,2,2-trifluoro-1-
phenylethylidene]methylamine (Table 2, Entry-2)
Ref. [14(a)], 1H NMR (399.81 MHz, CDCl3), d (ppm) 8.07 (d,
J = 8 Hz, 1H), 7.36 (m, 4H), 7.26 (m, 5H), 4.60 (s, 2H); 13C NMR
(100.53 MHz, CDCl3), d (ppm) 138.2, 130.4, 129.1, 128.9,
128.8, 127.8, 127.8, 127.4, 57.0;19F NMR(376.19 MHz, CDCl3,
CFCl3-Ref), d (ppm) À71.3 (s, 3F). MS-C15H12F3N (263), m/z
(%): 263 (M+, 15), 194 (100), 159 (25), 91 (20).
4.1. General procedure for the synthesis of
trifluoromethylated imines by microwave assisted K-10
montmorillonite catalyzed condensation of trifluoromethyl
ketones with primary amines
Trifluoromethyl ketone (1.0 mmol), amine (1.5 mmol) were
dissolved in 3 mL of ether in a round-bottomed flask then K-10
(500 mg) was added. After 5 min stirring the solvent was
evaporated under reduced pressure to get the dry mixture of
reactants adsorbed on the catalyst’s surface. The dry mixture
was transferred to a reaction tube and irradiated in the
microwave reactor (CEM Discover Benchmate) at 175 8C.
During optimization the progress of the reaction was monitored
by TLC and GCMS, then the optimized times were used for
4.3.3. 2-Methyl-N-[2,2,2-trifluoro-1-
phenylethylidene]aniline (Table 2, Entry-3)
1
Ref. [7(j)], H NMR (399.81 MHz, CDCl3), d (ppm) 7.18
(m, 5H), 6.92 (t, J = 3 Hz, 2H), 6.39 (d, J = 7.6 Hz, 2H), 2.18 (s,
3H); 13C NMR (100.53 MHz, CDCl3), d (ppm) 130.3, 130.2,
129.0, 128.4, 128.2, 126.1, 125.1, 118.4, 118.0, 94.4, 17.7; 19
F
NMR (376.19 MHz, CDCl3, CFCl3-Ref), d (ppm) À69.9 (s,
3F). MS-C15H12F3N (263), m/z (%): 263 (M+, 30), 194 (100),
91 (50).

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M. Abid et al. / Journal of Fluorine Chemistry 128 (2007) 587–594
4.3.4. 4-Methyl-N-[2,2,2-trifluoro-1-
4.3.10. N-[2,2,2-Trifluoro-1-phenylethylidene]naphth-2-yl-
amine (Table 2, Entry-10)
phenylethylidene]aniline (Table 1, Entry-4)
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.20 (m, 5H),
6.98 (t, J = 3 Hz, 2H), 6.45 (t, J = 7.6 Hz, 2H), 2.25 (s, 3H).
13C NMR (100.53 MHz, CDCl3), d (ppm) 130.9, 130.2, 129.2,
128.2, 128.0, 126.1, 125.5, 118.9, 118.0, 91.3, 19.1, 19F NMR
(376.19 MHz, CDCl3, CFCl3-Ref), d (ppm) À70.0 (s, 3F).
MS-C15H12F3N (263), m/z (%): 263 (M+, 40), 194 (100), 91
(30).
1H NMR (399.81 MHz, CDCl3), d (ppm) 8.07 (dd, J = 7.6,
0.8 Hz, 2H), 7.67 (m, 5H), 7.41 (m, 3H), 6.87 (dd, J = 2.0,
8.4 Hz, 2H); 13C NMR (100.53 MHz, CDCl3), d (ppm) 144.8,
135.7, 133.7, 131.4, 130.5, 130.3, 130.2, 130.1, 129.3, 128.9,
128.8, 128.0, 127.9, 126.7, 125.7, 120.6, 118.4; 19F NMR
(376.19 MHz, CDCl3, CFCl3-Ref), d (ppm) À70.2 (s, 3F). MS-
C18H12F3N (299), m/z (%): 299 (M+, 50), 230 (100), 127 (95).
4.3.11. N-[1-Benzyl-2,2,2-trifluoroethylidene]-1-
4.3.5. 4-Methoxy-N-[2,2,2-trifluoro-1-
phenylethylamine (Table 3, Entry-1)
phenylethylidene]aniline (Table 2, Entry-5)
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.27 (m, 10H),
5.28 (s, 2H), 4.83 (q, J = 6.4 Hz, 1H), 1.41 (d, J = 6.4 Hz, 3H);
13C NMR (100.53 MHz, CDCl3), d (ppm) 129.1, 128.7, 128.4,
127.4, 127.2, 126.6, 60.4, 33.3, 24.6; 19F NMR (376.19 MHz,
CDCl3, CFCl3-Ref), d (ppm) À72.6 (s, 3F). MS-C17H16F3N
(291), m/z (%): 291 (M+, 10), 187 (25), 105 (100), 77 (10).
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.29 (m, 5H),
7.22 (m, 2H), 6.71 (m, 2H), 3.72 (s, 3H); 13C NMR
(100.53 MHz, CDCl3), d (ppm) 157.9, 139.8, 130.9, 130.2,
128.9, 128.7, 123.5, 114.1, 55.8; 19F NMR (376.19 MHz,
CDCl3, CFCl3-Ref), d (ppm) À70.4 (s, 3F). MS-C15H12F3NO
(279), m/z (%): 279 (M+, 30), 210 (100), 195 (15), 167 (15),
105 (10), 77 (20).
4.3.12. N-[1-Benzyl-2,2,2-trifluoroethylidene]-2-
methylaniline (Table 3, Entry-2)
4.3.6. 3-(Trifluoromethyl)-N-[2,2,2-trifluoro-1-
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.18 (m, 9H), 2.27
(s, 2H), 1.24 (s, 3H); 13C NMR (100.53 MHz, CDCl3), d (ppm)
135.1, 133.5, 130.5, 129.6, 128.8, 128.4, 126.8, 120.7, 114.7,
59.8, 17.8; 19F NMR (376.19 MHz, CDCl3, CFCl3-Ref), d
(ppm) À70.5 (s, 3F). MS-C16H14F3N (277), m/z (%): 277 (M+,
75), 262 (10), 208 (40), 186 (100), 166 (30), 91 (60).
phenylethylidene]aniline (Table 2, Entry-6)
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.30 (m, 5H), 7.02
(s, 1H), 6.86 (m, 2H); 13C NMR (100.53 MHz, CDCl3), d (ppm)
147.7, 131.4, 130.8, 129.6, 129.5, 129.3, 128.9, 128.7, 123.8,
122.2, 122.0, 118.0; 19F NMR (376.19 MHz, CDCl3, CFCl3-
Ref), d (ppm) À63.4 (s, 3F), À70.62 (s, 3F). MS-C15H8F6N
(317), m/z (%): 317 (M+, 20), 248 (100), 145 (40).
4.3.13. 1-Phenyl-N-[2,2,2-trifluoro-1-(1H-pyrrol-2-
yl)ethylidene]ethylamine (Table 3, Entry-3)
4.3.7. 4-Chloro-N-[2,2,2-trifluoro-1-
1H NMR (399.81 MHz, CDCl3), d (ppm) 8.40 (s, 1H), 7.34
(m, 5H), 6.91 (m, 1H), 6.61 (m, 1H), 6.29 (m, 1H), 5.01 (q,
J = 6.4 Hz, 1H), 2.15 (d, J = 6.4 Hz, 3H); 13C NMR
(100.53 MHz, CDCl3), d (ppm) 129.1, 128.7, 127.4, 127.3,
126.6, 126.2, 122.5, 121.7, 115.9, 110.1, 60.1, 24.9; 19F NMR
(376.19 MHz, CDCl3, CFCl3-Ref), d (ppm) À69.4 (s, 3F). MS-
C14H13F3N2 (266), m/z (%): 266 (M+, 10), 251 (15), 105 (100),
77 (20).
phenylethylidene]aniline (Table 2, Entry-7)
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.35 (m, 5H), 7.00
(m, 2H), 6.68 (m, 2H). 13C NMR (100.53 MHz, CDCl3), d
(ppm) 130.7, 129.8, 129.2, 128.8, 128.4, 128.3, 122.2; 19F
NMR (376.19 MHz, CDCl3, CFCl3-Ref); d (ppm) À70.0 (s,
3F). MS-C14H9F3ClN (283), m/z (%): 283 (M+, 30), 214 (100),
111 (30), 75 (25).
4.3.8. 4-Fluoro-N-[2,2,2-trifluoro-1-
4.3.14. 2-Methyl-N-[2,2,2-trifluoro-1-(1H-pyrrol-2-
yl)ethylidene]aniline (Table 3, Entry-4)
phenylethylidene]aniline (Table 2, Entry-8)
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.35 (m, 5H), 6.91
(m, 2H), 6.65 (m, 2H). 13C NMR (100.53 MHz, CDCl3), d
(ppm) 130.5, 128.9, 128.7, 122.8, 122.8, 119.1, 116.3, 115.8,
115.7, 19F NMR (376.19 MHz, CDCl3, CFCl3-Ref), d (ppm)
À70.6 (s, 3F). MS-C14H9F4N (267), m/z (%): 267 (M+, 25), 198
(100), 95 (40), 75 (15).
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.91 (s, 1H), 7.26
(m, 2H), 7.11 (t, J = 7.6 Hz, 2H), 6.78 (t, J = 8 Hz, 1H), 6.70 (q,
J = 1.2 Hz, 1H), 6.17 (quin, J = 2.4 Hz, 1H), 2.05 (s, 3H); 13
C
NMR (100.53 MHz, CDCl3), d (ppm) 131.7, 127.7, 126.2,
125.0, 124.4, 117.3, 110.2, 29.8; 19F NMR (376.19 MHz,
CDCl3, CFCl3-Ref), d (ppm) À67.6 (s, 3F). MS-C13H11F3N2
(252), m/z (%): 252 (M+, 30), 237 (100), 183 (50), 91 (60), 65
(45).
4.3.9. 1-Phenyl-N-[2,2,2-trifluoro-1-
phenylethylidene]ethylamine (Table 2, Entry-9)
1
Ref. [7(d)], H NMR (399.81 MHz, CDCl3), d (ppm) 7.46
4.3.15. 1-Phenyl-N-[2,2,2-trifluoro-1-(2-
(m, 5H), 7.25 (m, 5H), 4.53 (q, J = 6.4 Hz, 1H), 1.43 (dd,
J = 6.4 Hz, 3H, CH3); 13C NMR (100.53 MHz, CDCl3), d
(ppm) 143.7, 130.5, 130.0, 128.7, 128.6, 127.6, 127.2, 126.4,
51.9, 24.5; 19F NMR (376.19 MHz, CDCl3, CFCl3-Ref), d
(ppm) À71.5 (s, 3F). MS-C16H14F3N (277), m/z (%): 277 (M+,
10), 193 (5), 105 (100), 77 (20).
thiophenyl)ethylidene]ethylamine (Table 3, Entry-5)
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.55 (m, 2H), 7.34
(m, 5H), 7.18 (m, 1H), 7.11 (m, 1H), 4.90 (q, J = 6.8 Hz, 1H),
1.55 (d, J = 6.8 Hz, 3H); 13C NMR (100.53 MHz, CDCl3), d
(ppm) 144.1, 136.2, 132.1, 129.5, 128.9, 127.2, 126.5, 121.1,
61.1, 24.5; 19F NMR (376.19 MHz, CDCl3, CFCl3-Ref), d

M. Abid et al. / Journal of Fluorine Chemistry 128 (2007) 587–594
593
(ppm) À71.0 (s, 3F). MS-C14H12F3NS (283), m/z (%): 283 (M+,
4.3.21. 2-Carbetoxymethylene-2-
10), 199 (20), 105 (100), 77 (15).
(trifluoromethyl)benzimidazoline (Table 4, Entry-5)
m.p. 68.1–70.2 8C. 1H NMR (399.81 MHz, CDCl3), d (ppm)
6.67–6.73 (m, 2H), 6.59–6.64 (m, 2H), 4.62 (bs, 2H), 4.10 (q,
J = 7.2 Hz, 2H), 2.84 (s, 2H), 1.14 (t, J = 7.2 Hz, 3H). 13C NMR
(100.53 MHz, CDCl3), d (ppm) 168.6, 137.9, 128.2, 125.4,
122.5, 121.1, 109.8, 81.0, 80.7, 61.8, 39.2, 14.0, 19F NMR
(376.19 MHz, CDCl3, CFCl3-Ref), d (ppm) À85.1 (s, 3F). MS-
C12H13F3N2O2 (274), m/z (%): 274 (M+, 15), 245 (5), 205 (50),
187 (45), 177 (25), 159 (50), 131 (100), 104 (10), 77 (10).
4.3.16. 2-Methyl-N-[2,2,2-trifluoro-1-(2-
thiophenyl)ethylidene]aniline (Table 3, Entry-6)
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.58 (m, 2H), 7.45
(m, 1H), 7.18 (m, 2H), 7.01 (m, 1H), 6.62 (m, 1H), 2.04 (s, 3H);
13C NMR (100.53 MHz, CDCl3), d (ppm) 147.2, 133.5, 133.1,
131.2, 129.5, 127.3, 126.8, 125.4, 119.5, 17.5; 19F NMR
(376.19 MHz, CDCl3, CFCl3-Ref), d (ppm) À68.0 (s, 3F). MS-
C13H10F3NS (269), m/z (%): 269 (M+, 50), 200 (100), 167 (35),
91 (50), 65 (45).
4.3.22. 2-Carbethoxymethylene-5-methyl-2-
(trifluoromethyl)benzimidazoline (Table 4, Entry-6)
m.p. 56.0–58.1 8C. 1H NMR (399.81 MHz, CDCl3), d (ppm)
6.42–6.56 (m, 3H), 4.10 (q, J = 7.2 Hz, 2H), 2.83 (s, 2H), 2.19
(s, 3H), 1.15 (t, J = 7.2 Hz, 3H). 13C NMR (100.53 MHz,
CDCl3), d (ppm) 168.4, 138.0, 135.3, 130.7, 130.5, 125.2,
121.0, 110.7, 109.6, 61.6, 38.9, 21.0, 13.8, 19F NMR
(376.19 MHz, CDCl3, CFCl3-Ref), d (ppm) À85.2 (s, 3F).
MS-C13H15F3N2O2 (288), m/z (%): 288 (M+, 40), 259 (10), 219
(100), 201 (70), 191 (40), 181 (15), 145 (90), 104 (10), 77
4.3.17. 2-Phenyl-2-(trifluoromethyl)benzimidazoline
(Table 4, Entry-1)
Ref. [7(j)], m.p. 94.3–95.9 8C. 1H NMR (399.81 MHz,
CDCl3), d (ppm) 7.59–7.63 (m, 2H), 7.39–7.46 (m, 4H), 6.66–
6.98 (m, 3H), 4.42 (bs, 2H). 13C NMR (100.53 MHz, CDCl3),
d (ppm) 138.5, 137.8, 135.7, 130.3, 130.1, 129.6, 129.0,
126.1, 121.3, 118.3, 110.2, 110.1, 19F NMR (376.19 MHz,
CDCl3, CFCl3-Ref), d (ppm) À82.9 (s, 3F). MS-C14H11F3N2
(264), m/z (%): 264 (M+, 10), 243 (5), 223 (5), 195 (100), 92
(30), 65 (20).
4.3.23. 2-Methyl-2-(trifluoromethyl)benzimidazoline
(Table 4, Entry-7)
1
m.p. 110.7–112.3 8C. H NMR (399.81 MHz, CDCl3), d
4.3.18. 5-Methy-2-phenyl-2-
(ppm) 6.68–6.74 (m, 2H), 6.58–6.63 (m, 2H), 3.90 (bs, 2H),
1.63 (q, J = 1.2 Hz, 3H). 13C NMR (100.53 MHz, CDCl3), d
(ppm) 138.3, 129.0, 126.1, 123.3, 121.0, 109.8, 79.9, 79.6, 22.4,
19F NMR (376.19 MHz, CDCl3, CFCl3-Ref), d (ppm) À86.4 (s,
3F). MS-C9H9F3N2 (202), m/z (%): 202 (M+, 10), 187 (5), 167
(10), 133 (100), 92 (40), 66 (15).
(trifluoromethyl)benzimidazoline (Table 4, Entry-2)
m.p. 95.3–96.8 8C. 1H NMR (399.81 MHz, CDCl3), d (ppm)
7.61 (d, J = 7.6 Hz, 2H), 7.36–7.48 (m, 3H), 6.52–6.62 (m, 3H),
4.42 (bs, 2H) 2.22 (s, 3H). 13C NMR (100.53 MHz, CDCl3), d
(ppm) 138.8, 137.9, 135.9, 131.1, 130.1, 129.6, 129.3, 128.8,
125.9, 121.2, 110.9, 110.0, 21.0, 19F NMR (376.19 MHz,
CDCl3, CFCl3-Ref), d (ppm) À83.0 (s, 3F). MS-C15H13F3N2
(278), m/z (%): 278 (M+, 10), 257 (5), 237 (5), 209 (100), 104
(30), 77 (15).
4.3.24. 2,5-Dimethyl-2-(trifluoromethyl)benzimidazoline
(Table 4, Entry-8)
1H NMR (399.81 MHz, CDCl3), d (ppm) 6.53 (d, J = 0.8 Hz,
2H, Ar), 6.43–6.46 (m, 1H, Ar), 3.78 (bs, 2H, NH2), 2.21 (s, 3H,
CH3), 1.63 (q, J = 1.2 Hz, 3H, CH3). 13C NMR (100.53 MHz,
CDCl3), d (ppm) 138.5, 135.7, 130.6, 120.8, 110.6, 109.6, 79.8,
79.5, 21.1, 21.0, 19F NMR (376.19 MHz, CDCl3, CFCl3-Ref), d
(ppm) À86.5 (s, 3F). MS-C10H11F3N2 (216), m/z (%): 216 (M+,
40), 201 (10), 181 (10), 147 (100), 131 (15), 106 (15), 90 (10).
4.3.19. 2-Benzyl-2-(trifluoromethyl)benzimidazoline
(Table 4, Entry-3)
m.p. 44.2–46.0 8C. 1H NMR (399.81 MHz, CDCl3), d (ppm)
7.86–7.92 (m, 1H), 7.25–7.42 (m, 6H), 7.06–7.12 (m, 2H), 5.52
(s, 2H), 4.02 (bs, 2H). 13C NMR (100.53 MHz, CDCl3), d (ppm)
141.4, 135.8, 135.0, 129.8, 129.2, 128.4, 128.1, 126.5, 125.7,
124.0, 121.9, 111.3, 48.6, 19F NMR (376.19 MHz, CDCl3,
CFCl3-Ref), d (ppm) À61.9 (s, 3F). MS-C15H13F3N2 (278), m/z
(%): 278 (M+, 5), 209 (10), 187 (100), 167 (30), 116 (10), 91
(75).
Acknowledgements
Financial support provided by Michigan Technological
University, University of Massachusetts Boston, Loker
Hydrocarbon Research Institute (USC), the National Institute
of Health (R-15 AG025777-02, B. T.) and the ACS Petroleum
Research Fund (B. T.) is gratefully acknowledged.
4.3.20. 5-Methyl-2-benzyl-2-
(trifluoromethyl)benzimidazoline (Table 4, Entry-4)
1H NMR (399.81 MHz, CDCl3), d (ppm) 7.84–7.91 (m, 1H),
7.22–7.39 (m, 5H), 7.06–7.12 (m, 2H), 5.49 (s, 2H), 4.10 (bs,
2H), 2.21 (s, 3H). 13C NMR (100.53 MHz, CDCl3), d (ppm)
138.4, 135.6, 135.2, 130.2, 128.2, 127.4, 127.2, 125.2, 121.0,
123.0, 110.4, 110.1, 48.4, 21.1, 19F NMR (376.19 MHz, CDCl3,
CFCl3-Ref), d (ppm) À61.7 (s, 3F). MS-C16H15F3N2 (292), m/z
(%): 292 (M+, 10), 273 (5), 251 (5), 223 (15), 201 (100), 181
(15), 91 (50).
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