Trifluoromethylation of non-activated aldimines with trimethyl(trifluoromethyl)silane in the presence of tetramethylammonium fluoride: A closer look into the reaction route

Article abstract of DOI:10.1016/j.jfluchem.2007.07.005

The reactions of non-activated aldimines with trimethyl(trifluoromethyl)silane and 1 equiv. of tetramethylammonium fluoride proceed via the formation of tetramethylammonium amides which were identified by low-temperature ¹⁹F NMR experiments. Consecutive reactions of the salts formed in situ with electrophiles yielded trifluoromethylated amines. Fluoride elimination is observed in the absence of electrophilic substrates leading to the formation of difluoromethylated ketimines.

Full text of DOI:10.1016/j.jfluchem.2007.07.005

Journal of Fluorine Chemistry 129 (2008) 14–21
www.elsevier.com/locate/fluor
Trifluoromethylation of non-activated aldimines with
trimethyl(trifluoromethyl)silane in the presence of
tetramethylammonium fluoride: A closer look into the
reaction route
Nataliya V. Kirij a, Lesya A. Babadzhanova a, Valeria N. Movchun a,
b
b
Yurii L. Yagupolskii a, , Wieland Tyrra , Dieter Naumann ,
*
Hendrik T.M. Fischer b, Harald Scherer b
a Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya St., UA-02094 Kiev 94, Ukraine
b
¨ ¨ ¨ ¨
Institut fur Anorganische Chemie, Universitat zu Koln, Greinstrasse 6, D-50939 Koln, Germany
Received 1 June 2007; received in revised form 9 July 2007; accepted 12 July 2007
Available online 18 July 2007
Abstract
The reactions of non-activated aldimines with trimethyl(trifluoromethyl)silane and 1 equiv. of tetramethylammonium fluoride proceed via the
formation of tetramethylammonium amides which were identified by low-temperature 19F NMR experiments. Consecutive reactions of the salts
formed in situ with electrophiles yielded trifluoromethylated amines. Fluoride elimination is observed in the absence of electrophilic substrates
leading to the formation of difluoromethylated ketimines.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Trifluoromethylation; Amines; Aldimines; Alkylation; Silylation
1. Introduction
suggested to stabilize the intermediates [6]. An alternative
approach has been presented in 2005 by Motherwell and Storey
[7]. They achieved comparable results in conversion of imines
into the corresponding aryl(2,2,2-trifluoro-1-aryl-ethyl)amines
using the 1:1 adduct of trifluoroacetophenone and N,N-
The study and development of methods for the introduction
of fluorinated moieties into organic molecules to change their
properties by design is one of the challenges in synthetic
chemistry. Fluorine-containing physiologically active sub-
stances and the methodologies making them easily accessible
are of great interest. One of the general methods to obtain
trifluoromethyl containing amines is based on the addition of
the CF3 group to imine double bonds. However, only the
reactions of nucleophilic trifluoromethylation of activated
aldimines such as azirines [1], nitrones [2], imines of
hexafluoroacetone [3], N-(t-butylsulfinyl)imines [4] and sulfo-
nylimines [5] using Me3SiCF3 are mentioned in the literature.
In 1999 Blazejewski et al. showed that Me3SiCF3 also reacts
with non-activated aldimines but only in the presence of
trimethylsilylimidazole as an auxiliary reagent which is
dimethylamino(trimethyl)silane as
a
trifluoromethylating
reagent and 2-trimethylsiloxypyridine as an alternative to
trimethylsilylimidazol in conjunction with caesium fluoride as
initiator. Difluoromethyl containing ketimines are much more
inaccessible. The only method to synthesize these compounds
is based on the transformation of trifluoromethyl into
difluoromethyl groups, i.e. trifluoromethylated pyridines can
be converted into the difluoromethyl compounds by the
reaction of DBU (1,8-diazabicyclo[4,5,0]undec-7-ene) [8].
Uneyama et al. reported a method to obtain difluoroenamines
by C–F bond cleavage of trifluoromethylimines via the reaction
of elemental magnesium in the presence of chlorotrimethylsi-
lane; in a second reaction step these difluoroenamines were
converted into difluoromethyl imines with tetrabutylammo-
nium fluoride (TBAF) [9].
* Corresponding author. Tel.: +380 44 559 0349; fax: +380 44 573 2643.
E-mail address: Yagupolskii@bpci.kiev.ua (Y.L. Yagupolskii).
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2007.07.005

N.V. Kirij et al. / Journal of Fluorine Chemistry 129 (2008) 14–21
15
Scheme 1.
In 2006 Prakash et al. reported a route to obtain trifluoro- and
difluoromethyl amines on a preparative scale [10] starting from
non-activated aldimines and trimethyl(trifluoromethyl)silane in
the presence of fluoride sources. Trifluoromethylated amines
are formed in high yields using catalytic amounts (5–15%) of
tetrabutylammonium triphenyldifluorosilicate (TBAT). The
authors pointed out that the reaction proceeds via the formation
of unstable silylated amines. The yields were determined
exclusively by NMR spectroscopic experiments. Using
0.5 equiv. of tetramethylammonium fluoride (TMAF) gave
product mixtures that contained difluoromethyl ketimines. One
of the ketimines was isolated in 34% yield; the others were
reduced to difluoromethyl amines.
The strong nucleophilic salts 2 react with electrophiles under
very mild conditions (À45 Æ 5 8C). Aqueous work-up of salts 2
converts them into the secondary amines 3 in 70–90% yields.
Amines 4 containing two CF3 groups bonded to the former
C=N carbon atom were detected in the 19F NMR spectra as by-
products; 4d was obtained from aldimine 1d in 25% yield and
characterized. Salts 2 react with methyl iodide and chloro-
trimethylsilane to form the tertiary amines 5 and the silylated
amines 6, respectively (Scheme 3). Compounds 3, 5, 6 were
isolated and fully characterized.
On the basis of these investigations, it is concluded that
silylated amines 6 are stable under neutral conditions but
desilylate easily in the presence of acids to form amines 3 and in
the presence of fluoride ions the difluoromethyl ketimines 7
(Scheme 4).
We mentioned the smooth reaction of Schiff bases with
Me3SiCF3 in a conference presentation in 2000 [11] and in
parallel with Prakash et al. [10], we studied the reactions of
non-activated aldimines with Me3SiCF3 in the presence of
[Me4N]F. We used 1 equiv. of fluoride and investigated the
reaction, putting more emphasis on the intermediates involved.
The elimination of a fluoride ion of the CF3 group of 2
accompanied by hydrogen atom migration occurs on warming
the salts 2 to room temperature yielding the ketimines 7
(Scheme 5).
2. Results and discussion
The reagent Me3SiCF3 reacts with aldimines 1 in the
presence of 1 equiv. of [Me4N]F in THF at À50 8C to form the
salts 2 (Scheme 1).
The salts 2c,d were characterized by low-temperature NMR
spectroscopic methods. In the 19F NMR spectrum of 2c at
À30 8C the CF3 group is detected at À72.0 ppm and the fluorine
atom in four-position of the aromatic ring at À143.5 ppm. This
signal is shifted by 25.7 ppm to higher field in comparison with
the parent aldimine 1c, indicating the presence of the free amide
in solution. Due to the delocalization of the negative charge
from the nitrogen atom into the aromatic ring, the following
canonical forms (I, II) should be assumed with the right hand
side being favoured (Scheme 2).
Scheme 3.
Scheme 2.
Scheme 4.
Scheme 5.

16
N.V. Kirij et al. / Journal of Fluorine Chemistry 129 (2008) 14–21
Table 1
Crystal data and structure refinement for 6a
Formula
C17H20F3NSi
Triclinic
Crystal system
Space group
P-1 (number 2)
Scheme 6.
Unit cell parameters
a (pm)
b (pm)
c (pm)
a (8)
862.7(2)
1331.1(4)
1563.8(4)
84.02(3)
b (8)
82.00(3)
g (8)
80.65(3)
V (106 pm3)
Z
1748.4(8)
4
D (g cmÀ3
)
1.229
Scheme 7.
m (Mo Ka) (mmÀ1
Crystal size (mm)
)
0.158
0.30 0.30 0.20
21,308(2.60–28.19)
680
Number of data collected (u range)
F (0 0 0)
This reaction pathway is implied to be intramolecular due to
the exclusive formation of CF2H containing compounds even
when the reactions were performed in carefully dried THF-d8.
Ketimines 7 are formed in 65–75% yields as mixtures of E-
and Z-isomers. The resulting 2D NOESY spectrum shows cross
correlations between the two equilibrating structures, for
example between the corresponding H-2,6 resonances (phenyl
group bond to carbon/phenyl group bond to nitrogen) in the E-
isomer (d 7.29/6.79) and the Z-isomer (d 8.15/6.94) of 7a. The
ratios vary significantly depending on the polarity of the solvent
used. Imines 7 are stable under neutral conditions but hydrolyze
easily under aqueous work-up in the presence of acids or
[Me4N]F giving difluoromethyl ketones 8 and anilines 9
(Scheme 6).
Maximum, minimum transmission
R1, wR2 [I > 2s(I)]
0.9857, 0.9073
0.0464, 0.0686
0.142, À0.146
Maximum, minimum residual electron
density (eÁ10À6 pm)
CCDC [24]
644,041
Table 2
Selected bond lengths (pm) and angles (8) for the two independent molecules of
6a with estimated standard deviations in parantheses
Molecule 1
Molecule 2
Si1–N1
175.2(4)
143.8(6)
144.6(8)
151.6(9)
150.7(9)
133.8(9)
131.7(8)
133.6(9)
120.8(4)
117.4(3)
118.4(4)
117.0(5)
112.0(5)
105.4(6)
107.15)
Si2–N2
174.4(4)
147.4(8)
145.8(6)
148.8(7)
151.7(9)
132.5(9)
132.7(9)
132.0(7)
121.7(3)
118.3(3)
117.5(4)
115.7(4)
112.1(5)
105.4(6)
107.5(5)
105.8(6)
N1–C108
N2–C208
N1–C1
N2–C2
The ketimine 7b was an exception. Aqueous work-up
yielded compound 10 in 42% yield together with the products
of hydrolysis (Scheme 7).
C1–C101
C2–C201
C1–C107
C2–C207
C107–F11
C207–F21
Compound 7c was taken as an example to show that
ketimines also react with Me3SiCF3 in the presence of
1 equiv. of [Me4N]F to form amines with trifluoromethyl-
and difluoromethyl groups bond to the same carbon atom
(Scheme 8).
C107–F12
C207–F22
C107–F13
C207–F23
Si1–N1–C1
Si1–N1–C108
C108–N1–C1
N1–C1–C101
N1–C1–C107
F11–C107–F12
F12–C107–F13
F13–C107–F11
Si2–N2–C2
Si2–N2–C208
C208–N2–C2
N2–C2–C201
N2–C2–C207
F21–C207–F22
F22–C207–F23
F23–C207–F21
The reaction conditions and treatment of the reaction
mixture were analogous to that of the conversion of aldimines 1
to amines 3. Amine 11 was isolated in 78% yield and fully
characterized.
105.0(5)
2.1. The crystal structure of phenyl-(2,2,2-trifluoro-1-
phenyl-ethyl)-trimethylsilanylamine (6a)
are found in the expected range and are comparable with those
determined for related compounds (e.g. 12) although examples
for comparison are rare. In the packing the molecules are well
separated without significant intermolecular contacts.
¯
Compound 6a crystallizes in the triclinic space group P1
(no. 2) (Table 1). In the unit cell, two independent molecules are
found (Table 2; Figs. 1 and 2). The two independent molecules
exhibit identical structural motifs and differ only slightly in
their interatomic distances and angles. Bond lengths and angles
Within both molecules two chiral atoms (N1 and C1 as well
as N2 and C2) with (R,R)-configuration are found. As expected
the centre of inversion generates two molecules with
Scheme 8.

N.V. Kirij et al. / Journal of Fluorine Chemistry 129 (2008) 14–21
17
ments. The reactions of the salts 2 formed in situ with water,
methyl iodide and chlorotrimethylsilane led to secondary and
tertiary amines. The conditions of selective conversion of the
salts 2 into ketimines containing difluoromethyl group were
elaborated.
4. Experimental
4.1. General
All reactions were carried out in a dry argon (or nitrogen)
atmosphere using Schlenk techniques. Me3SiCF3 was pur-
chased from ABCR, all aldehydes, anilines, Me3SiCl from
Aldrich. [Me4N]F [13] was synthesized according to a literature
procedure. All solvents were purified according to literature
procedures [14].
NMR spectra were recorded with the Bruker spectrometers
AC 200 (1H at 200 MHz, 19F at 188.14 MHz, 13C at
50.32 MHz), Avance II 300 (19F at 282.4 MHz, 13C at
75.5 MHz, 29Si at 59.6 MHz), Avance 400 (1H at 400 MHz,
13C at 100.6 MHz), Avance DRX 500 (1H at 500 MHz, 13C at
125.77 MHz) and the Varian spectrometer VXR-300 (1H at
300 MHz). Chemical shifts are given in ppm relative to Me4Si
(1H, 13C, 29Si) and CCl3F (19F) as external standards. J-values
are given in Hz. Assignments were made on the basis of
different 2D NMR experiments. EI mass spectra were run on a
Finnigan MAT 95 spectrometer (20 eV). Melting points were
measured in one-end open glass capillaries and are uncorrected.
CHNF-analyses were performed with the apparatus HEKAtech
Euro EA 3000 and Analytikjena Spekol 1100.
Fig. 1. ORTEP plot of one molecule of 6a with the labeling scheme (thermal
ellipsoids at the 50% probability level, cf. Table 2).
Crystal structure determination. The compound forms
single crystals which were sealed in glass capillaries and the
suitability was checked with the help of an IP-diffractometer
(STOE IPDS I). The same device was used to collect the
reflection data of the respective best specimen using graphite-
monochromated Mo Ka radiation (71.073 pm). The data were
corrected for Lorentz and polarization effects. The programs
used in this work are Stoe’s X-area [15], including X-RED [16]
and X-shape [17] for data reduction and numerical absorption
correction, and SIR-97 [18] and SHELXL-97 [19] for structure
solution and refinement. All hydrogen atoms were placed in
idealized positions and constrained to ride on their parent atom.
The last cycles of refinement included atomic positions for
all the atoms, anisotropic thermal parameters for all the
non-hydrogen atoms and isotropic thermal parameters for all
of the hydrogen atoms. Intensity data for details of crystal
data and structure refinement parameters are summarised in
Table 1; cf. [24].
Fig. 2. View of the unit cell of 6a along the b-axis.
(S,S)-configuration in the unit cell additionally giving two
enantiomeric pairs of molecules.
4.2. Preparative procedures
4.2.1. Benzylidene-phenyl-amines (1a–d)
Benzylidene-phenyl-amines (1a–d) were synthesised
according to literature procedures [20].
3. Conclusion
The reaction of aldimines with Me3SiCF3 and 1 equiv. of
[Me4N]F proceeds via the formation of the salts 2 which were
identified by low-temperature 19F NMR spectroscopic experi-
4.2.1.1. Benzylidenephenylamine (1a). Yield: 83%; colour-
less solid; mp 51–52 8C (lit. [20] mp 52 8C).

18
N.V. Kirij et al. / Journal of Fluorine Chemistry 129 (2008) 14–21
4.2.1.2. Benzylidene(3-fluorophenyl)amine (1b). Yield: 87%;
1
2.2 Hz , ArH), 6.45 (2H, m, ArH), 7.09 (1H, dm, J = 6.5 Hz,
ArH), 7.42 (5H, m, ArH); 19F NMR (188.14 MHz, CD2Cl2): d
À73.9 (3F, d, 3JFH = 7.4 Hz, CF3), À113.5 (1F, br s); 13C {1H}
yellow liquid; bp 106–108 8C/0.04 Torr. H NMR (300 MHz,
acetone-d6): d 7.0–7.15 (3H, m, ArH), 7.4–7.6 (4H, m, ArH),
8.09 (2H, m, ArH), 8.62 (1H, s); 19F NMR (188.14 MHz,
acetone-d6): d À113.1 (s); 13C NMR spectral data (lit. [21]).
Anal. Calcd for C13H10FN: C, 78.4; H, 5.1; F, 9.5; N, 7.0.
Found: C, 78.6; H, 5.3; F, 9.4; N, 6.8.
2
NMR (125.77 MHz, CD2Cl2): d 60.2 (1C, q, JCF = 30.4 Hz,
2
CCF3), 100.7 (1C, d, JCF = 25.5 Hz), 105.5 (1C, d,
4
2JCF = 23 Hz), 109.7 (1C, d, JCF = 2.4 Hz), 125.0 (1C, q,
1JCF = 285.4 Hz, CF3), 127.9, 129.0 (2C), 129.4 (2C), 130.5
3
(1C, d, JCF = 10 Hz), 133.5, 147.3 (1C, d, JCF = 10.5 Hz),
3
1
4.2.1.3. (4-Fluorophenyl)(4-methylbenzylidene)amine
(1c). Yield: 89%; yellow solid; mp 67–69 8C (lit. [22] mp
68 8C). 1H NMR (200 MHz, CDCl3): d 2.41 (3H, s, CH3), 7.00–
7.35 (6H, m, ArH), 7.79 (2H, d, J = 8 Hz, ArH), 8.39 (1H, s);
19F NMR spectral data (lit. [22]); 13C {1H} NMR (50.32 MHz,
CDCl3): d 21.6 (CH3), 115.8 (2C, d, 2JCF = 22 Hz), 122.3 (2C,
163.8 (1C, d, JCF = 236.3 Hz); EIMS: m/z (%) = 269 [M]+
(80), 200 [M-CF3]+ (100). Anal. Calcd for C14H11F4N: C, 62.4;
H, 4.1; F, 28.2; N, 5.2. Found: C, 61.8; H, 4.4; F, 28.6; N, 4.9.
4.2.3.3. (4-Fluorophenyl)-(2,2,2-trifluoro-1-p-tolyl-ethyl)a-
mine (3c). Yield: 72%; yellow liquid; bp 155–156 8C/
0.03 Torr. 1H NMR (200 MHz, CD2Cl2): d 2.38 (3H, s,
CH3), 4.38 (1H, br d, J = 6.4 Hz, NH), 4.90 (1H, qd, J = 7.4,
6.4 Hz, CH), 6.65 (2H, m, ArH), 6.92 (2H, t, J = 8.8 Hz, ArH),
7.46 (4H, dd J = 24.6, 8 Hz, ArH); 19F NMR (188.14 MHz,
CD2Cl2): d À74.8 (3F, d, 3JFH = 7.4 Hz, CF3), À126.8 (1F, m);
13C {1H} NMR (50.32 MHz, CD2Cl2): d 21.5 (CH3), 61.1 (1C,
3
d, JCF = 7.8 Hz), 128.7 (2C), 129.5 (2C), 133.5, 141.9, 148.1
(d, 4JCF = 2 Hz), 160.0 (C = N), 161.0 (d, 1JCF = 244 Hz). Anal.
Calcd for C14H12FN: C, 78.8; H, 5.7; F, 8.9; N, 6.6. Found: C,
78.6; H, 5.4; F, 9.0; N, 6.7.
4.2.1.4. (4-Dimethylaminophenyl)(4-fluorobenzylidene)amine
(1d). Yield: 79%; yellow solid; mp 136–137 8C (lit. [22] mp
137 8C). 19F NMR spectral data (lit. [22]); 1H, 13C NMR
spectral data (lit. [23]).
2
3
q, JCF = 29.8 Hz, CCF3), 115.5 (2C, d, JCF = 7.5 Hz), 116.1
2
(2C, d, JCF = 22.6 Hz), 125.7 (1C, q, JCF = 281.9 Hz, CF3),
4
128.2 (2C), 130.0 (2C), 131.2 (1C, d, JCF = 2 Hz), 139.8,
1
1
142.4, 157.0 (1C, d, JCF = 236.7 Hz); EIMS: m/z (%) = 283
4.2.2. Synthesis of the salts (2a–d)
[M]+ (75), 214 [M-CF3]+ (100), 173 [M-NHC6H4F]+ (16). Anal.
Calcd for C15H13F4N: C, 63.6; H, 4.6; F, 26.8; N, 4.9. Found: C,
64.1; H, 4.4; F, 27.1; N, 4.7.
To a solution of the corresponding imine (1a–d) (5.1 mmol)
and trimethyl(trifluoromethyl)silane (Me3SiCF3) (1.1 g,
7.6 mmol) in THF (25 mL) at À60 8C tetramethylammonium
fluoride ([Me4N]F) (0.64 g, 6.9 mmol) was added in small
portions over a period of 90 min. The mixture was stirred for
2 h at À50 Æ 5 8C.
4.2.3.4. (4-Fluorophenyl)-[2,2,2-trifluoro-1-(4-dimethylami-
nophenyl)-ethyl]-amine (3d). Yield: 65%; yellow liquid; bp
148 8C/0.02 Torr. 1H NMR (200 MHz, CD2Cl2): d 2.96 (6H, s,
CH3), 4.30 (1H, br d, J = 7.2 Hz, NH), 4.78 (1H, qd, J = 7.4,
7.2, Hz, CH), 6.67 (4H, m, ArH), 6.89 (2H, t, J = 8.8 Hz, ArH),
7.29 (2H, d, J = 8.4 Hz, ArH); 19F NMR (188.14 MHz,
4.2.2.1. Tetramethylammonium (4-fluorophenyl)(2,2,2-tri-
fluoro-1-p-tolyl-ethyl)amide (2c). 19F NMR (188.14 MHz,
3
3
THF, À30 8C): d À72.0 (3F, d, JFH = 7.4 Hz, CF3), À143.5
CD2Cl2): d À74.9 (3F, d, JFH = 7.4 Hz, CF3), À126.9 (1F,
(1F, br s).
m); 13C {1H} NMR (50.32 MHz, CD2Cl2): d 40.4 (CH3), 60.9
2
(1C, q, JCF = 29.6 Hz, CCF3), 112.6 (2C), 115.5 (2C, d,
4.2.2.2. Tetramethylammonium (4-fluorophenyl)-[2,2,
2-trifluoro-1-(4-dimethylaminophenyl)-ethyl]amide (2d). 19F
3JCF = 7.5 Hz), 116.1 (2C, d, 2JCF = 22.7 Hz), 121.0, 126.0 (1C,
1
q, JCF = 281.7 Hz, CF3), 128.9 (2C), 142.7 (1C, d,
1
NMR (188.14 MHz, THF, À30 8C):
d
À72.0 (3F, d,
4JCF = 2.1 Hz), 151.5, 157.0 (1C, d, JCF = 236.3 Hz); EIMS:
3JFH = 7.4 Hz, CF3), À145.2 (1F, br s).
m/z (%) = 312 [M]+ (32), 297 [M-CH3]+ (15), 243 [M-CF3]+
(10), 217 [M-C6H4F]+ (15), 202 [M-NHC6H4F]+ (100). Anal.
Calcd for C16H16F4N2: C, 61.5; H, 5.2; F, 24.3; N, 9.0. Found:
C, 61.1; H, 5.4; F, 23.9; N, 8.7.
4.2.3. Hydrolysis of salts (2a–d)
To a solution of corresponding salt (2a–d) at À45 Æ 5 8C
H2O (5 mL) was added and the amines obtained were extracted
with Et2O (2Â 10 mL). The extracts were washed with H2O
(5 mL), dried (MgSO4) and purified by vacuum distillation.
4.2.3.5. (4-Fluorophenyl)-[1,1,1,3,3,3-hexafluoro-2-(4-di-
methylaminophenyl)propyl]amine (4d). Purified by silica gel
column chromatography, Rf 0.8 (hexane: benzene = 4:1).
1
4.2.3.1. Phenyl-(2,2,2-trifluoro-1-phenyl-ethyl)amine
(3a). Yield: 89%; yellow liquid; bp 65–67 8C/0.04 Torr (lit.
Yield: 25%; yellow oil. H NMR (200 MHz, CD2Cl2): d 3.0
(6H, s, CH3), 4.47 (1H, br s, NH), 6.64 (2H, m, ArH), 6.84 (4H,
1
[6] bp 272 8C, H, 19F, 13C, mass spectral data agreed with
m, ArH), 7.39 (2H, s, ArH), 7.54 (2H, d, J = 8.6, Hz, ArH); 19
F
literature data).
NMR (188.14 MHz, CD2Cl2): d À70.6 (6F, s, CF3), À125.2
(1F, m); 13C {1H} NMR (50.32 MHz, CD2Cl2): d 40.2 (CH3),
2
70.4 (1C, sept, JCF = 26.8 Hz, C(CF3)2), 112.0 (2C), 115.4
4.2.3.2. (3-Fluorophenyl)-(2,2,2-trifluoro-1-phenyl-ethyl)a-
mine (3b). Yield: 83%; yellow liquid; bp 81–82 8C/0.03 Torr.
1H NMR (500 MHz, CD2Cl2): d 4.57 (1H, br d, J = 7.2 Hz,
NH), 4.93 (1H, qd, J = 7.4, 7.2 Hz, CH), 6.34 (1H, dt, J = 11.5,
2
(2C, d, JCF = 22.5 Hz), 119.3 (2C, d, JCF = 7.5 Hz), 124.4
3
1
(2C, q, JCF = 289 Hz, CF3), 128.7 (2C), 130.3, 139.2 (1C, d,
1
4JCF = 2.7 Hz), 151.7, 157.7 (1C, d, JCF = 238.4 Hz); EIMS:

N.V. Kirij et al. / Journal of Fluorine Chemistry 129 (2008) 14–21
19
m/z (%) = 380 [M]+ (25), 311 [M-CF3]+ (7), 270 [M-
NHC6H4F]+ (100). Anal. Calcd for C17H15F7N2: C, 53.7; H,
4.0; F, 34.9. Found: C, 54.1; H, 4.2; F, 34.8.
CDCl3): d 0.6 (Si(CH3)3), 64.0 (q, 2JCF = 29 Hz, CCF3), 125.6
(q, 1JCF = 285 Hz, CF3), (Ph bond to N) 143.1 (C-1), 127.9 (C-
2,6), 129.7 (C-3,5), 124.9 (C-4), (Ph bond to C) 134.8 (C-1),
4
128.1 (q, JCF = 2Hz, C-2,6), 133.2 (C-3,5), 128.2 (C-4); 29Si
4.2.4. Alkylation of the salts (2a,c)
{1H} NMR (59.6 MHz, CDCl3): d 9.6 (Si(CH3)3). EIMS: m/z
(%) = 323 [M]+ (92), 254 [M-CF3]+ (100). Anal. Calcd for
C17H20F3NSi: C, 63.1; H, 6.2; F, 17.6; N, 4.3. Found: C, 63.5;
H, 6.4; F, 17.9; N, 4.1.
To a solution of the corresponding salt (2a,c) (5.1 mmol) at
À45 Æ 5 8C, CH3I (1.1 g, 5.7 mmol) was added and the
reaction mixture was allowed to warm to room temperature.
The solvent and all volatile compounds were evaporated. The
products were extracted with pentane and purified by vacuum
distillation.
4.2.5.2. (4-Fluorophenyl)-(2,2,2-trifluoro-1-p-tolylethyl)-tri-
methylsilylamine (6c). Yield: 84%; yellow solid; bp 95 8C/
1
0.03 Torr, mp 58–59 8C. H NMR (300 MHz, CDCl3): d 0.15
4.2.4.1. Methyl-phenyl-(2,2,2-trifluoro-1-phenylethyl)amine
1
(9H, s, Si(CH3)3), 2.36 (3H, s, CH3), 4.81 (1H, q, J = 8.8, Hz,
CH), 6.63 (2H, m, H-2,6 (4-FC6H4)), 6.82 (2H, m, H-2,6 (4-
FC6H4)), 6.94 (2H, m, H-2,6 (4-CH3C6H4)), 7.08 (2H, m, H-3,5
(4-CH3C6H4)); 19F NMR (282.3 MHz, CDCl3): d À68.2 (d,
3JFH = 9 Hz, CF3), À117.0 (1F, m); 13C {1H} NMR (75.5 MHz,
(5a). Yield: 91%; yellow liquid; bp 89–90 8C/0.03 Torr. H
NMR (300 MHz, acetone-d6): d 2.75 (3H, s, CH3), 5.86 (1H, q,
J = 8.7 Hz, CH), 6.85 (1H, t, J = 7.2 Hz, ArH), 7.08 (2H, d,
J = 7.2 Hz, ArH), 7.29 (2H, m, ArH), 7.45 (5H, m, ArH); 19F
3
2
NMR (188.14 MHz, acetone-d6): d À67.2 (d, JFH = 8.7 Hz).
CDCl3): d 0.4 (Si(CH3)3), 21.1 (CH3), 63.4 (q, JCF = 29 Hz,
13C {1H} NMR (75.5 MHz, CDCl3): d 33.6 (CH3), 64.8 (q,
2JCF = 29 Hz, CCF3), 126.2 (q, 1JCF = 287 Hz, CF3), (Ph bond
to N) 150.2 (C-1), 114.2 (C-2,6), 129.6 (C-3,5), 119.1 (C-4),
(Ph bond to C) 132.8 (C-1), 128.1 (C-2,6), 128.9 (C-3,5), 128.5
(C-4); EIMS: m/z (%) = 265 [M]+ (78), 196 [M-CF3]+ (100),
181 [M-CF3-CH3]+ (12). Anal. Calcd for C15H14F3N: C, 67.9;
H, 5.3; F, 21.5; N, 5.3. Found: C, 68.2; H, 5.6; F, 21.9; N, 5.6.
CCF3), 126.2 (q, 1JCF = 286 Hz, CF3), (4-FC6H4) 138.6 (1C, d,
4JCF = 3 Hz, C-1), 134.7 (2C, d, 3JCF = 9 Hz, C-2,6), 114.6 (2C,
d, 2JCF = 22 Hz, C-3,5), 160.8 (2C, d, 1JCF = 245 Hz, C-4), (4-
4
CH3C6H4) 131.4 (C-1), 129.5 (2C, q, JCF = 2 Hz, C-2,6),
128.8 (C-3,5), 138.1 (C-4); 29Si{1H} NMR (59.6 MHz,
CDCl3): d 9.8 (Si(CH3)3). EIMS: m/z (%) = 355 [M]+ (48),
286 [M-CF3]+ (100). Anal. Calcd for C18H21F4NSi: C, 60.8; H,
5.9; F, 21.4; N, 3.9. Found: C, 60.5; H, 6.1; F, 20.9; N, 3.7.
4.2.4.2. Methyl-(4-fluorophenyl)-2,2,2-trifluoro-1-p-tolyl-
ethyl)amine (5c). Yield: 79%; yellow liquid; bp 150–152 8C/
0.02 Torr. H NMR (200 MHz, CD2Cl2): d 2.42 (3H, s, CH3),
4.2.6. Formation of difluoromethylated imines (7a–c)
A solution of the salts (2a–c) was allowed to warm to room
temperature. The solvent and volatile compounds were
evaporated. The products were extracted with pentane. The
products (7a,b) were purified by vacuum distillation, product
(7c) by crystallization from EtOH.
1
2.74 (3H, s, CH3), 5.42 (1H, q, J = 8.6, Hz, CH), 6.97 (4H, m,
ArH), 7.28 (4H, m, ArH); 19F NMR (188.14 MHz, CD2Cl2): d
3
À70.2 (3F, d, JFH = 8.6 Hz, CF3), À128.6 (1F, s); 13C {1H}
NMR (50.32 MHz, CD2Cl2): d 21.2 (CH3), 34.3 (CH3), 66.2
2
2
(1C, q, JCF = 28.8 Hz, CCF3), 116.1 (2C, d, JCF = 22.2 Hz),
116.5 (2C, d, 3JCF = 7.6 Hz), 126.8 (1C, q, 1JCF = 286 Hz, CF3),
128.4 (2C), 129.7, 129.9 (2C), 139.1, 147.4 (d, 4JCF = 2.1 Hz),
4.2.6.1. (2,2-Difluoro-1-phenyl-ethylidene)-phenyl-amine (E/
Z-mixture) (7a). Yield: 79%; yellow liquid; bp 72–73 8C/
1
157.1 (d, JCF = 237.3 Hz); EIMS: m/z (%) = 297 [M]+ (67),
0.03 Torr.
(2,2-Difluoro-1-phenyl-eth-(E)-ylidene)-phenyl-
283 [M-CH3]+ (7), 228 [M-CF3]+ (100), 212 [M-CF3-CH3]+
(10), 173 [M-N(CH3)C6H4F]+ (14). Anal. Calcd for
C16H15F4N: C, 64.6; H, 5.1; F, 25.6; N, 4.7. Found: C, 64.2;
H, 5.4; F, 25.2; N, 4.5.
amine: 1H NMR (400 MHz, CDCl3): d 6.42 (1H, t,
2JHF = 55.3 Hz, CHF2), (Ph bond to N) 6.79 (2H, m, H-2,6),
7.06 (1H, m, H-4), 7.22 (2H, m, H-3,5), (Ph bond to C) 7.29
(4H, m, H-2,6; H-3,5), 7.30 (1H, m, H-4); 19F NMR
2
(282.4 MHz, CDCl3): d À117.0 (2F, d, JFH = 55.3 Hz), 13C
4.2.5. Silylation of salts (2a,c)
{1H} NMR (100.6 MHz, CDCl3):
d
115.5 (1C, t,
2
To a solution of the corresponding salt (2a,c) (5.1 mmol) at
À45 Æ 5 8C, Me3SiCl (0.62 g, 5.7 mmol) was added and the
reaction mixture was allowed to warm to room temperature.
The precipitate formed was filtered off, the solvent and all
volatile compounds were evaporated. The products were
extracted with pentane and purified by vacuum distillation or
crystallization from pentane.
1JCF = 245 Hz, CHF2), 162.1 (1C, t, JCF = 28 Hz, CCHF2),
(Ph bond to N) 148.1 (1C, C-1), 120.5 (2C, C-2,6), 124.9 (1C,
C-4), 128.9 (2C, C-3,5); (Ph bond to C) 130.4 (1C, C-1), 128.5
(2C, t, 4JCF = 2 Hz, C-2,6), 129.9 (1C, C-4), 128.7 (2C, C-3,5).
(2,2-Difluoro-1-phenyl-eth-(Z)-ylidene)-phenyl-amine:
1H
2
NMR (400 MHz, CDCl3): d 6.44 (1H, t, JHF = 52.4 Hz,
CHF2), (Ph bond to N) 6.94 (2H, m, H-2,6), 7.21 (1H, m, H-4),
7.42 (2H, m, H-3,5), (Ph bond to C) 7.51 (2H, m, H-3,5), 7.54
(1H, m, H-4), 8.15 (2H, m, H-2,6); 19F NMR (282.4 MHz,
4.2.5.1. Phenyl-(2,2,2-trifluoro-1-phenyl-ethyl)-trimethylsila-
nylamine (6a). Yield: 76%; yellow solid; bp 75 8C/0.03 Torr,
2
CDCl3): d À115.6 (2F, d, JFH = 52.3 Hz), 13C {1H} NMR
1
1
mp 37–38 8C. H NMR (300 MHz, CDCl3): d 0.21 (9H, s,
(100.6 MHz, CDCl3): d 107.9 (1C, t, JCF = 247 Hz, CHF2),
Si(CH3)3), 4.95 (1H, q, J = 9 Hz, CH), 6.75 (2H, m, ArH), 7.17
(5H, m, ArH), 7.31 (3H, m, ArH); 19F NMR (188.14 MHz,
CDCl3): d À67.9 (d, 3JFH = 9 Hz). 13C {1H} NMR (75.5 MHz,
158.7 (1C, t, 2JCF = 23 Hz, CCHF2), (Ph bond to N) 147.9 (1C,
C-1), 119.2 (2C, C-2,6), 124.9 (1C, C-4), 129.4 (2C, C-3,5); (Ph
bond to C) 133.1 (1C, C-1), 128.8 (2C, t, 4JCF = 2 Hz, C-2,6),

20
N.V. Kirij et al. / Journal of Fluorine Chemistry 129 (2008) 14–21
131.3 (1C, C-4), 128.6 (2C, C-3,5); EIMS: m/z (%) = 231 [M]+
(38), 180 [M-CF2H]+ (100). Anal. Calcd for C14H11F2N: C,
72.7; H, 4.8; F, 16.4; N, 6.1. Found: C, 72.9; H, 4.6; F, 16.1; N,
5.7.
bond to N = ) 6.45 (1H, dm, 3JHF = 8.8 Hz, H-2), 6.50 (1H, dm,
5JHF = 3 Hz, H-6), 6.77 (1H, dm, 3JHF = 9.4 Hz, H-4), 7.18 (1H,
4
dm, JHF = 6.2 Hz, H-5) (Ph bond to C = N) 7.00 (2H, m, H-
2,6), 7.33 (1H, m, H-4), 7.25 (2H, m, H-3,5), (3-FC6H4 bond to
3
NH) 6.1 (1H, dm, JHF = 8.3 Hz, H-2), 6.27 (1H, dm,
3
4.2.6.2. (2,2-Difluoro-1-phenyl-ethylidene)-(3-fluoro-phenyl)-
amine (E/Z-mixture) (7b). Yield: 47%; yellow liquid; bp 73–
74 8C/0.03 Torr. 1H NMR (200 MHz, CD2Cl2): d 6.35 (t,
5JHF = 3 Hz, H-6), 6.43 (1H, dm, JHF = 11.5 Hz, H-4), 7.0
(1H, dm, 4JHF = 6.9 Hz, H-5) (Ph bond to C-NH) 7.49 (3H, m,
H-3,4,5), 7.73 (2H, m, H-2,6); 19F NMR (282.4 MHz, CDCl3):
(CF2-group) d À97.6 (1F, d, 2JFa-Fb = 269 Hz, FA), À100.5 (1F,
2
2JFH = 52.8 Hz, CHF2), 6.36 (t, JFH = 56.2 Hz, CHF2), 6.47
2
4
(m, ArH), 6.64 (m, ArH), 6.71 (m, ArH), 6.87 (m, ArH), 7.11
(m, ArH), 7.23 (m, ArH), 7.28 (m, ArH), 7.34 (m, ArH), 7.46
(m, ArH), 7.52 (m, ArH), 8.02 (d, J = 7.5 Hz, ArH); 19F NMR
(188.14 MHz, CDCl3): d À111.5 (1F, br s), À112.3 (1F, br s),
ddd, JFb-Fa = 269 Hz, JFb-H = 19.1 Hz, JFb-CHF = 6.7 Hz,
2
3
FB), (3-FC6H4 bond to N = ) À111.9 (1F, ddd, JFH = 9.4 Hz,
3JFH = 8.8 Hz, JFH = 6.2 Hz, 3-FC6H4), (3-FC6H4 bond to
4
3
3
NH) À112.5 (1F, ddd, JFH = 11.5 Hz, JFH = 8.3 Hz,
4JFH = 6.9 Hz, 3-FC6’H4), (CHF2-group) À119.5 (1F, ddt,
2JFa-Fb = 288 Hz, 2JFa-H = 54 Hz, 4JFa-CF2 = 5.6 Hz, FA),
2
À115.7 (2F, d, JFH = 52.8 Hz, CHF2), À117.4 (2F, d,
2JFH = 56.2 Hz, CHF2); 13C {1H} NMR (125.77 MHz,
2
2
CD2Cl2):
d
106.6 (d, 2JCF = 23.5 Hz), 107.6 (d,
À124.1 (1F, dddd, JFb-Fa = 288 Hz, JFb-H = 54 Hz, JFb-
1
2JCF = 25.5 Hz), 108.2 (t, JCF = 247.2 Hz, CHF2), 111.4 (d,
H = 19.1 Hz, 4JFb-CF = 7.9 Hz, FB); 13C {1H} NMR
(100.6 MHz, CDCl3): d 70.4 (1C, m, C(CF2)CHF2), 114.7
2
2JCF = 20.2 Hz), 111.5 (d, JCF = 21.9 Hz), 114.8 (br s), 115.1
2
1
(t, JCF = 245.5 Hz, CHF2), 116.0 (d, JCF = 2.8 Hz), 128.4,
4
1
(1C, t, JCF = 259 Hz, CF2), 115.8 (1C, t, JCF = 251 Hz,
1
3
128.5, 128.7, 130.1, 130.2 (d, JCF = 9.4 Hz), 130.7 (d,
CF2H), 166.7 (C = N), (3-FC6H4 bond to N = ) 148.8 (1C, d,
2
3JCF = 9.4 Hz), 131.6, 132.9, 133.7, 146.9 (d, JCF = 9.2 Hz),
3JCF = 9.9 Hz, C-1), 107.9 (1C, d, JCF = 23.8 Hz, C-2), 116.2
3
3
1
4
2
149.9 (d, JCF = 9.2 Hz), 162.9 (d, JCF = 246 Hz), 163.1 (t,
2JCF = 27.8 Hz, CCHF2), 163.3 (1C, d, 1JCF = 248 Hz); EIMS:
m/z (%) = 249 [M]+ (34), 198 [M-CF2H]+ (100). Anal. Calcd for
C14H10F3N: C, 67.5; H, 4.04; F, 22.9; N, 5.6. Found: C, 67.3; H,
4.2; F, 23.4; N, 5.9.
(1C, d, JCF = 2 Hz, C-6), 112.0 (1C, d, JCF = 21.5 Hz, C-4),
162.8 (1C, d, 1JCF = 247 Hz, C-3), 130.2 (1C, d, 3JCF = 9.5 Hz,
C-5), (Ph bond to C = N) 131.1 (1C, C-1), 128.6 (2C, C-2,6),
128.2 (2C, C3,5), 130.0 (1C, C-4), (3-FC6H4 bond to NH) 145.4
3
2
(1C, d, JCF = 11.5 Hz, C-1), 103.4 (1C, d, JCF = 26.6 Hz, C-
4
2),112.2 (1C, d, JCF = 2 Hz, C-6), 105.4 (1C, d,
1
4.2.6.3. (2,2-Difluoro-1-p-tolyl-ethylidene)-(4-fluoro-phenyl)-
amine (E/Z-mixture) (7c). Yield: 66%; yellow solid; mp 58–
2JCF = 20.8 Hz, C-4), 163.2 (1C, d, JCF = 243 Hz, C-3),
3
129.8 (1C, d, JCF = 10.1 Hz, C-5), (Ph bond to C-NH)
1
59 8C. H NMR (200 MHz, CD2Cl2): d 2.36 (s, CH3), 2.48 (s,
131.0 (1C, C-1), 129.7 (2C, C-2,6), 129.4 (1C, C-4), 128.6 (2C,
C-3,5); EIMS: m/z (%) = 498 [M]+ (52), 388 [M-NHC6H4F]+
2
2
CH3), 6.44 (t, JFH = 55.4 Hz, CHF2), 6.48 (t, JFH = 53 Hz,
CHF2), 6.70–7.45 (m, ArH), 8.06 (d, J = 8 Hz, ArH); 19F NMR
(188.14 MHz, CD2Cl2): d À116.0 (2F, d, 2JFH = 53 Hz, CHF2),
À117.8 (2F, d, 2JFH = 55.4 Hz, CHF2), À119.1 (1F, m), À119.6
(1F, m); 13C {1H} NMR (50.32 MHz, CD2Cl2): d 21.5 (CH3),
(100),
250
[C6H5C(CHF2)NHC6H4F]+
(56),
198
[C6H5C = NC6H4F]+ (37). Anal. Calcd for C28H20F6N2: C,
67.5; H, 4.0; F, 22.9. Found: C, 67.9; H, 4.2; F, 22.8.
1
26.6 (CH3), 108.6 (t, JCF = 247.6 Hz, CF2H), 116.0 (d,
1
4.2.7.2. (1-Difluoromethyl-2,2,2-trifluoro-1-p-tolylethyl)-(4-
fluorophenyl)amine (11). To a solution of ketimine (7c)
(0.62 g, 2.4 mmol) and Me3SiCF3 (0.44 g, 3.1 mmol) in THF
(20 mL) at À55 Æ 5 8C [Me4N]F (0.28 g, 3.1 mmol) was added
in portions over 60 min. The mixture was stirred for 2 h at
À50 Æ 5 8C. H2O (5 mL) was added and the product was
extracted with Et2O (2Â 10 mL). The extract was washed with
H2O (5 mL), dried (MgSO4) and purified by silica gel column
2JCF = 22.5 Hz), 116.1 (t, JCF = 244.7 Hz, CF2H), 116.4 (d,
2JCF = 22.2 Hz), 121.3 (d, 3JCF = 7.5 Hz), 122.8 (d,
3JCF = 7.9 Hz), 127.9, 129.2, 129.6, 130.8, 140.9, 141.5,
4
4
142.6, 144.6 (d, JCF = 2.8 Hz), 144.9 (m, JCF = 2.1 Hz),
2
154.9 (t, JCF = 22 Hz, CCHF2), 160.6 (d, JCF = 243.4 Hz),
1
1
163.2 (d, JCF = 251.1 Hz); EIMS: m/z (%) = 263 [M]+ (32),
212 [M-CF2H]+ (100). Anal. Calcd for C15H12F3N: C, 68.4; H,
4.6; F, 21.6; N, 5.3. Found: C, 68.1; H, 4.7; F, 21.8; N, 4.9.
1
chromotography (hexane). Yield: 78 % (0.5 g); yellow oil. H
NMR (200 MHz, CDCl3): d 2.44 (3H, s, CH3), 4.46 (1H, br s,
4.2.7. Hydrolysis of difluoromethylated imines (7a–c)
To a reaction mixture containing the corresponding imine
(c.f. 4.2.6.), H2O (2 mL) was added and the reaction mixture
was stirred for 24 h. The formation of the difluoromethyl ketone
8 was confirmed by 19F NMR experiments (relative to C6H5F):
8a yield: 85%; 8c yield: 83%. The imine 7b formed the
‘‘dimer’’ 10.
D
1/2 = 10 Hz, NH), 6.17 (1H, t, 2JHF = 54 Hz, CHF2), 6.47 (2H,
m, ArH), 6.78 (2H, m, ArH), 7.29 (2H, m, ArH), 7.57 (2H, m,
ArH); 19F NMR (188.14 MHz, CDCl3): d À67.5 (3F, dd,
4
4JCF -FA = 11 Hz, JCF -FB = 8 Hz, CF3), À124.5 (1F, m),
3
3
2
CHF2-group–ABM3X spin system: À127.8 (1F, ddq, JFa-
Fb = 280 Hz, 2JFa-H = 54 Hz, 4JFa-CF = 11 Hz, FA), À129.1 (1F,
3
ddq, 2JFb-Fa = 280 Hz, 2JFb-H = 54 Hz, 4JFb-CF = 8 Hz, FB); 13
C
3
{1H} NMR (50.32 MHz, CDCl3): d 21.1 (CH3), 68.2 (1C, qt,
2
4.2.7.1. (2,2,4,4-Tetrafluoro-3-(3-fluoro-anilino)-1,3-diphe-
nyl-butylidene)-(3-fluoro-phenyl)-amine (10). Yield: 42%;
2JC-CF = 25 Hz, JC-CF H = 18 Hz, C(CF3)CHF2), 114.7 (1C,
1 3
3 2
J
tq,
J
= 255 Hz,
= 2 Hz, CHF2) 115.2 (2C, d,
CF
CF
1
3
pink solid; mp 139–141 8C. H NMR (400 MHz, CDCl3): d
2JCF = 22 Hz), 118.5 (2C, d, JCF = 8 Hz), 124.7 (1C, qt,
1JCF = 291 Hz, JCF = 2 Hz, CF3), 126.8, 128.3 (2C), 129.7
6.55 (1H, m, NH), 6.87 (1H, t, 1JHF = 54 Hz, CHF2), (3-FC6H4
3

N.V. Kirij et al. / Journal of Fluorine Chemistry 129 (2008) 14–21
21
4
[8] L.F. Lee, G.L. Stikes, J.M. Molyneaux, Y.L. Sing, J.P. Chupp, S.S.
Woodard, J. Org. Chem. 55 (1990) 2872–2877.
(2C), 139.0 (1C, d, JCF = 2 Hz), 139.8, 157.3 (1C, d,
1JCF = 240 Hz); EIMS: m/z (%) = 333 [M]+ (74), 282 [M-
CHF2]+ (100), 264 [M-CF3]+ (20). Anal. Calcd for C16H13F6N:
C, 57.7; H, 3.9; F, 34.2. Found: C, 58.1; H, 4.2; F, 34.1.
[9] H. Hata, T. Kobayashi, H. Amii, K. Uneyama, J.T. Welch, Tetrahedr. Lett.
43 (2002) 6099–6102.
[10] G.K.S. Prakash, R. Mogi, G.A. Olah, Org. Lett. 8 (2006) 3589–3592.
[11] Yu.L. Yagupolskii, V.N. Movchun, N.V. Kirij, D. Naumann, N. Magiarosa,
W. Tyrra, in: Proceedings of the 16th International Symposium of Fluorine
Chemistry, University of Durham UK July 16–21 Abstract A38, 2000.
[12] A.R. Martin, A. Svensson, R.B. Bates, R.B. Ortega, Acta Cryst. C41
(1985) 1804–1807.
Acknowledgment
The generous financial support of this work by the DFG
(grant 436 UKR 113) is gratefully acknowledged.
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