N-benzyl-n-[(E)-2-phenylethenyl]trifluoromethanesulfonamide

Article abstract of DOI:10.1134/S1070428014080041

In the search for an approach to N-vinyltriflamides with a free NH group TfNHCH=CHR (Tf = CF₃SO₂) N-(benzyl)-N-(2-bromo-2-phenylethenyl)triflamide TfN(Bn)CH=CHPh was synthesized through bromination-dehydrobromination of N-(benzyl)-N-

Full text of DOI:10.1134/S1070428014080041

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2014, Vol. 50, No. 8, pp. 1093–1096. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © B.А. Shainyan, I.V. Ushakova, 2014, published in Zhurnal Organicheskoi Khimii, 2014, Vol. 50, No. 8, pp. 1112–1115.
N-Benzyl-N-[(E)-2-phenylethenyl]trifluoromethanesulfonamide
B. А. Shainyan and I. V. Ushakova
Favorsky Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
е-mail: bagrat@irioch.irk.ru
Received December 4, 2013
Abstract—In the search for an approach to N-vinyltriflamides with a free NH group TfNHCH=CHR (Tf =
CF SO ) N-(benzyl)-N-(2-bromo-2-phenylethenyl)triflamide TfN(Bn)CH=CHPh was synthesized through
3 2
bromination-dehydrobromination of N-(benzyl)-N-(2-phenylethyl)triflamide. At removing the benzyl protect-
tion by the action of trifluoromethanesulfonic acid benzyl alcohol separated; however instead of the target N-
styryltriflamide unexpectedly the product of its hydrogenation was obtained, N-(2-phenylethyl)triflamide. Obviously,
the benzyl alcohol was the hydrogen donor, and the easy hydrogenation was facilitated by the high electrophilicity
of the double bond in N-styryltriflamide because of strong electron-acceptor effect of the triflyl group.
DOI: 10.1134/S1070428014080041
The unsaturated derivatives of trifluoromethane-
sulfonamide (triflamide) are the smallest class of its
derivatives [1]. At the same time the compounds,
where the triflamide group and the multiple carbon-
carbon bond are separated by two or more atoms and,
as a result, do not affect each other, may be easily obtained
by aminolysis of anhydride or halides of trifluoro-
methanesulfonic acid with the corresponding amines.
Triflamide derivatives of CF SO NH–CH CH=CHR
compounds with a free NH group are yet unknown.
Meanwhile, the triflamides, containing in their structure
a free NH group conjugated with vinyl fragment, are
interesting from the viewpoint of possible enamine-
imine tautomerism [9] and also as strong NH acids and
substrates for further transformations involving the
C=C double bond. We failed to synthesize the
vinyltriflamides of CF SO NHCH=CHR type by the
3
2
elimination of the molecule of hydrogen halide from
their saturated precursors CF SO NHCH CH(Hlg)R,
3
2
2
type (N-allyltriflamide) were obtained by the reaction of
oxidative triflamidation of dienes [2] or by the
interaction of trifluoromethanesulfonyl fluoride with
allylamine [3], and their properties were studied [4, 5].
A different situation arises with triflamides, containing
double C=C bond directly linked to the nitrogen atom,
CF SO N(R)–CН=CН–. Recently we synthesized the
3
2
2
because in alkaline media the protonation of NH group
occurs first, and then the heterocyclization proceeds
with the formation of substituted piperazine [10]. We
succeeded to avoid it and to obtain first N-
alkenylsubstitued triflamide by preliminary methylation
of the NH group [6], however to obtain the target
vinyltriflamide with the free NH group it was necessary
to introduce a protective group to the nitrogen atom that
would be retained in conditions of alkaline
3
2
first representatives of N-alkenyl triflamide derivatives
of CF SO N(CH )CH=CR–Ph type [6, 7] and studied
3
2
3
their structure and basicity [8]. The analogs of these
Scheme 1.
Br2
BnBr
_HBr
TfNHCH CHBrPh
_HBr
BnBr
_HBr
2
II
TfNHCH CH Ph
TfN(Bn)CH CHBrPh
2
2
2
Br2
_HBr
I
TfN(Bn)CH CH Ph
IV
2
2
III
+
[
H ], H O
2
TfN(Bn)CH=CHPh
TfNHCH=CHPh
VI
_HBr
_BnOH
V
1
093

1
094
SHAINYAN, USHAKOVA
dehydrohalogenation, but would be easily removed in
the other conditions.
Compound IV was successfully obtained by the
alternative method shown on Scheme 1, namely, I →
III → IV. The interaction of compound I with benzyl
bromide in DMF solution at heating for 3 h results in
benzylation product III in aquantitative yield. Its
In this connection in this research an attempt of
synthesis of unsaturated triflamide VI from N-
phenylethyltriflamide (I) along Scheme 1 was made
with the removal of the benzyl protective group after
dehydrobromination of the intermediate substrate IV.
bromination with elemental bromine in CCl under UV
4
irradiation proceeds selectively at the С-benzyl group
without affecting the N-benzyl group and results in
product IV in a 60% yield. Finally the dehydrobro-
mination of compound IV with alcohol solution of
alkali affords the new unsaturated triflamide V in
approximately the same yield.
The latter may be obtained either by alkylation of the
previously described triflamide II, or by bromination of
preliminary alkylated compound III. To avoid possible
complications connected with the presence of two
benzyl fragments in compound III we carried out the
bromination of substrate II with benzyl bromide in
DMF in the presence of K CO . Unexpectedly the only
The removal of the benzyl protection occurred by
boiling the solution of compound V in acetonitrile in
the presence of trifluoromethanesulfonic acid. After
separating the mixture of compounds by column
chromatography the unreacted substrate V, benzyl
alcohol and initial N-substitued triflamide I were
isolated. The isolation of benzyl alcohol evidences the
removal of the benzyl protection; however the unex-
pected generation of compound I, lacking in the initial
triflamide V shows that the hydrogenation was
performed of the intermediately formed target N-
styryltriflamide VI. Evidently the hydrogen donor is
benzyl alcohol, as it is described in [11–13], and the
ease of hydrogenation is due to the high electro-philicity
of the double bong in the molecule VI because of strong
electron-acceptor effect of triflyl group. The oxidation
products of benzyl alcohol (benzaldehyde, benzoic acid)
2
3
isolated product of the reaction was dimethyldibenzyl-
ammonium bromide (VII) (Scheme 2).
Scheme 2.
TfN(Bn)CH CHBrPh
2
_
BnBr K CO , Δ
2
3
IV
TfNHCH CHBrPh
2
DMF
II
Me Bn NBr
2
2
VII
Without K CO the reaction does not proceed. The
2
3
reaction performed in DMSO did not give any
isolable products. In a blank experiment without
compound II salt VII is formed in a yield of as low as
6
.5%.
As far as the only compound in the reaction
Scheme 2) containing dimethylamino group is DMF it
1
(
were not isolated, however in the Н NMR spectra the
is obvious that salt VII forms by the reaction of DMF
with benzyl bromide catalyzed by bromide II. The
mechanism of generation of salt VII considering the
catalytic role of compound II may presumably be
described in the following way (Scheme 3).
signals in the downfield region (8–12 ppm) are present
typical of aldehyde and acid protons.
The structure of all compounds was established
1
13
19
from Н, С and F NMR spectra, the composition
was confirmed by the elemental analysis. The assign-
ment of the methylene groups signals in the benzyl
fragments NCH CHBr and NCH Ph in compound IV
A similar mechanism obviously operates in the
formation of salt VII as a side product of benzylation
of N-(2,3-dibromopropyl)triflamide [4] (Scheme 4,
R = CH CHBrCH Br).
2
2
1
1
1
13
was accomplished by 2D H– H COSY, H– C
HMBC and HSQC NMR spectra. The trans-
2
2
Scheme 3.
Ph
Ph
CH Br
2
H C
Br
O
2
TfNR
H
Me
Me
H
Me NBn + HBr
+
C
O
N
H
2
Me N
C
O
H
2
CH
TfNR
_CO
BnBr
Tf
NR
VII
II
R = CH
2
CHBrPh.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 8 2014

N-BENZYL-N-[(E)-2-PHENYLETHENYL]TRIFLUOROMETHANESULPHONAMIDE
1095
Scheme 4.
i; ii; iii
TfNHCH CH Ph
TfN(Bn)CH=CHPh
2
2
+
[
H ]
BnOH + TfNHCH=CHPh
TfNHCH CH Ph + PhCHO, PhCOOH
2
2
i = BnBr; ii = Br ; iii = KOH; Tf = CF SO .
2
3
2
configuration of N-benzyl-N-styryltriflamide (V) is
identical to the configuration of N-methyl-N-
added dropwise 1.15 mL (0.01 mol) of Br during 7 h
2
while stirring and irradiating with UV. The solution
was evaporated at reduced pressure, the residue was
distillated in a vacuum, bp 158°С (1 mmHg). Yield
styryltriflamide [6] that is confirmed by high value of
3
the coupling constant J ~15 Hz.
HH
–
1
2
.78 g (60%). IR spectrum, ν, cm : 3087, 3068, 2941,
1
EXPERIMENTAL
1495, 1391, 1228, 1141, 938, 580, 499, 454. Н NMR
spectrum, δ, ppm: 3.68 br.s (1H, CH CHBr), 3.88 m
(2H, CH CHBr + NCH Ph), 4.58 br.s (1Н, NCH Ph),
4.92 m (1H, CHBr), 7.32–7.11 m (10Н, Ph). At 50°C
the signals are well resolved multiplets: 3.74 d.d
B
A
B
A
The IR spectra were registered on Bruker Vertex 70
spectrophotometer from pellets with KBr. NMR
spectra were obtained in CDCl on a Bruker DPX 400
3
1
B
A
spectrometer at working frequencies 400 ( Н), 100
С), and 386 МHz ( F), chemical shifts reported
with respect to TMS ( Н, С) and CCl F ( F).
(CH CHBr, J 15.2, 7.8 Hz), 3.93 d.d (CH CHBr,
1
3
19
B
(
J 15.2, 7.3 Hz), 4.04 d (1H, NCH Ph, J 15.2 Hz), 4.63
1
13
19
A
3
d (1Н, NCH Ph, J 15.2 Hz), 4.98 t (1H, CHBr, J 7.5 Hz).
С NMR spectrum, δ, ppm: 50.23 (CHBr), 53.41
PhCH N), 54.24 (CH CHBr), 119.99 q (CF , J
1
3
N-(2-Phenylethyl)trifluoromethanesulfonamide
(
3
2
2
о
3
CF
(I) and N-(2-bromo-2-phenylethyl)trifluoromethane-
m
23.1 Hz), 128.01 (C in CHBrPh), 128.62 (C in
sulfonamide (II) were synthesized by the method [10].
p
о
CHBrPh), 128.91 (С in NCH Ph), 129.04 (С in
2
p
NCH Ph), 129.19 (Cm in NCH Ph), 129.38 (C in
N-(Benzyl)-N-(2-phenylethyl)trifluoromethane-
sulfonamide (III). To a solution of 2.53 g (0.01 mol)
of compound I in 10 mL of anhydrous DMF was
added 6.9 g (0.05 mol) of potassium carbonate, to the
obtained mixture was added dropwise 1.83 mL of
benzyl bromide, and the mixture was stirred for 4 h at
2
2
i
i
19
CHBrPh), 133.61 (CH С ), 138.11 (CHBrС ). F NMR
2
spectrum, δ, ppm: –75.30. Compound IV was used for
dehydrobromination without additional purification.
N-Benzyl-N-[(E)-2-phenylethenyl]trifluoromet-
hanesulfonamide (V). To the solution of 0.56 g
1
00°С. The precipitate was filtered off, washed with
(
0.01 mol) of KOH in 10 mL of anhydrous methanol
was added dropwise at stirring during 1 h 2.32 g
5 mmol) of compound IV, and the reaction mixture
chloroform, the chloroform extract was combined with
the filtrate and dried with anhydrous MgSO . The
4
(
solvents were removed at 10 mmHg, the residue was
was heated for 4 h at 100°С. Then the mixture was
cooled, filtered, the precipitate was washed with CCl4,
the filtrate was evaporated at low pressure, the residue
was distillated in a vacuum, bp 128°С (0.5 mmHg). To
obtain analytically pure compound it was purified by
chromatography on a column with silica gel (Меrck,
Geduran, 0.063–0.200 mm), eluent hexane–
dichloromethane, 6 : 1. Yield 1.1 g (58%). IR spectrum,
distillted in a vacuum, bp 136–138°С (0.5 mmHg, mp
2
0
3
3
5°С, d4 1.60 g/cm . Yield 3.38 g (88%). IR
–
1
spectrum, ν, cm : 3090, 3033, 2949, 1498, 1385,
228, 1121, 930, 786, 699. Н NMR spectrum, δ, ppm:
.75 br.s (2Н, NCH CH Ph), 3.48 (2Н,
1
1
2
t
2
2
NCH CH Ph), 4.42 br.s (2Н, NCH Ph), 7.03–7.40
2
2
2
1
3
(
10Н, C Н ). С NMR spectrum, δ, ppm: 34.5
6 5
(
NCH CH Ph), 48.9 (NCH CH Ph), 52.0 (NCH Ph),
–1
2
2
2
2
2
ν, cm : 3087, 3065, 2930, 1951, 1876, 1649, 1401,
1
1
19.5 q (СF , J 323.3 Hz), 126.2, 128.0, 128.1,
28.1, 128.4, 133.6, 136.6. F NMR spectrum, δ,
1
3
СF
1
5
7
228, 1141, 939, 737, 694. Н NMR spectrum, δ, ppm:
1
9
.00 br.s (2Н, NCH Ph), 6.07 d (1Н, =CHPh, J 14.5 Hz),
.14 d (1Н, NCH=, J 14.5 Hz), 7.21–7.45 m (10Н,
C Н ). С NMR spectrum, δ, ppm: 51.2 (NCH Ph),
2
ppm: –74.79. Found, %: C 55.82; H 4.83; F 16.09; N
.30; S 9.44. C H F NO S. Calculated, %: C 55.97;
4
13
1
6
16
3
2
6
5
2
H 4.70; F 16.60; N 4.08; S 9.34.
1
17.3 (=CHPh), 120.1 q (СF , J 324.6 Hz), 129.1
3 СF
(
1
NCH=), 124.2, 124.9, 125.7, 126.0, 127.0, 127.6,
28.3, 128.8, 134.1, 134.8. F NMR spectrum, δ,
N-(Benzyl)-N-(2-bromo-2-phenylethyl)trifluoro-
methanesulfonamide (IV). To the solution of 3.85 g
1
9
ppm: –73.86. Found, %: C 55.79; H 4.04; F 16.59; N
(
0.01 mol) of compound III in 15 mL of ССl was
4
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 8 2014

1
4
096
SHAINYAN, USHAKOVA
.72; S 9.64. C H F NO S. Calculated, %: C 56.30;
The study was performed under the financial
support of the Russian Foundation for Basic Research
1
6
14
3
2
H 4.13; F 16.70; N 4.10; S 9.39.
(
project no. 13-03-00055).
REFERENCES
. Shainyan, B.A., and Tolstikova, L.L. Chem. Rev., 2013,
Dimethyldibenzylammonium bromide (VII). To a
solution of 4.22 g (0.01 mol) of compound IV in 15 mL
of DMF was added 2.76g (0.2 mmol) of K CO , and the
2
3
mixture was stirred for 1 h while adding dropwise
.83 mL (0.015 mol) of benzyl bromide. After stirring
1
2
3
4
1
vol. 113, p. 699.
for 3 h at 100°С, the solvent was removed in a vacuum,
the residue was mixed with diethyl ether, the formed
precipitate of salt VII was filtered and dried. Yield
. Shainyan, B.A., Moskalik, M.Yu., Starke, I., and
Schilde, U., Tetrahedron, 2010, vol. 66, p. 8383.
. Shainyan, B.A., and Danilevich, Yu.S., Russ. J. Org.
Chem., 2013, vol. 49, p. 922.
. Shainyan, B.A., and Danilevich, Yu.S., Russ. J. Org.
Chem., 2013, vol. 49, p. 1112.
5. Shainyan, B.A., Chipanina, N.N., Oznobikhina, L.P.,
and Danilevich, Yu.S., J. Phys. Org. Chem., 2013,
vol. 26, p. 653.
–
1
0
2
.68 g (30%), mp 164°С. IR spectrum, ν, cm : 3028,
1
972, 2959, 1639, 1496, 1487, 1453. Н NMR
spectrum, δ, ppm: 3.13 s (6Н, CH ), 5.18 s (4Н,
3
13
NCH ), 7.35–7.69 (10Н, Ph). С NMR spectrum, δ,
2
ppm: 48.2 (CH ), 67.5 (CH Ph), 127.5, 129.2, 130.7,
3
2
1
33.5. Found, %: C 61.81; H 6.10; Br 27.90; N 4.16.
C H BrN. Calculated, %: C 62.75; H 6.58; Br 26.09;
N 4.57.
6. Shainyan, B.A., and Ushakova, I.V., Russ. J. Org.
Chem., 2012, vol. 48, p. 141.
1
6
20
7
8
9
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Shainyan, B.A., Russ. J. Org. Chem., 2013, vol. 49, p. 999.
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ethenyl]trifluoromethanesulfonamide (V) with tri-
fluoromethanesulfonic acid. To a solution of 1.70 g
(
5 mmol) of compound V in 10 mL of acetonitrile was
added dropwise at stirring 0.63 mL (7.5 mmol) of
CF SO H, and the mixture was refluxed for 10 h,
1
979, vol. 48, p. 107.
3
3
10. Shainyan, B.A., and Sterkhova I.V., Russ. J. Org.
Chem., 2010, vol. 46, p. 1743.
cooled, treated with CCl , evaporated at reduced
4
pressure, the residue was chromatographed on a
column with silicagel (Меrck, Geduran, 0.063–0.200 mm),
eluent hexane–chloroform, 4 : 1. Benzyl alcohol and
N-(phenylethyl)triflamide (I) were isolated, identified
by coincidence of their NMR spectra with the spectra
of the authentic samples.
1
1. Vitali, R., Caccia, G., and Gardi, R., J. Org. Chem.,
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 8 2014