N-allenyl-N-benzyltrifl uoromethanesulfonamide

Article abstract of DOI:10.1134/S1070428013080034

First N-allenyl-substitued triflamides CF₃SO₂N(Bn)CH= C=CH₂ were synthesized from N-allyltriflamides by sucessive reactions of bromination, N-alkylation, and dehydrobromination. Isomeric N-propargyltriflamide CF₃SO₂N(Bn)CH₂C≡CH is present in the reaction products as a minor admixture.

Full text of DOI:10.1134/S1070428013080034

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 8, pp. 1112−1116. © Pleiades Publishing, Ltd., 2013.
Original English Text © B. A. Shainyan and Yu. S. Danilevich, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 8, pp. 1132−1135.
N-Allenyl-N-benzyltrifluoromethanesulfonamide
B. A. Shainyan and Yu. S. Danilevich
A.E. Faworsky Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
Irkutsk, 664033 Russia
e-mail: bagrat@irioch.irk.ru
Received February 28, 2013
Abstract—First N-allenyl-substitued triflamides CF3SO2N(Bn)CH=C=CH2 were synthesized from N-allyltriflamides
by sucessive reactions of bromination, N-alkylation, and dehydrobromination. Isomeric N-propargyltriflamide
CF3SO2N(Bn)CH2C≡CH is present in the reaction products as a minor admixture.
DOI: 10.1134/S1070428013080034
N-allenylsulfonamides are insufficiently studied rivatives of triflamides I, III [9] (Scheme 1), and some
compounds. They are generated along with the N-pro- of their properties were investigated.
pargylsulfonamides by a reaction of the lithium salts of
the substitued tosylamides with propargyl carbonate [1].
Reactions of [2+2]-cycloaddition of substitued styrenes
[2] and vinyl ethers [3] are known, catalyzed by the
gold complexes. When the alkynyl group is present in
the orto-position of the benzene ring in the N-aryl-N-
allenyltosilamide molecule the intermolecular cyclyzation
into benzazepines occurs, as well as elimination of the
allenyl group and its isomerisation into propenyl one [4].
N-propargylsulfonamides isomeric to N-allenylsulfon-
amides are obtained by interaction of propargylamines
with sulfonyl chlorides [5]; recently their synthesis with
high yield by the InCl3-catalyzed nucleophilic substi-
An attempt of further dehydrobromination of
compound III aiming to obtain an acetylene deriva-
tive (N-propargyltriflamide), or its allenyl isomere
(N-allenyltriflamidee) was not succesful. Apparently it
is due to the high NH-acidity of the substrate III that
gives triflamide salt with sodium alcoholate. That, in
its turn, makes dehydrobromination difficult because of
disadvantageous interaction of two anions: triflamidic
and alkoxylic. That does not interfere with the reaction
of dehydrobromination of dibromide II, obviously, due
to easier of elimination of HBr from the polybrominated
fragment. To overcome these difficulties, we decided to
insert a protective group to the nitrogen atom in adduct
tuation of the acetate group in propargyl acetates with II at the start and then the N-protected product, unable
to generate the amide anion, would be brought in the
dehydrobromination reaction.
tosylamide residue [6] have been described. However,
neither fluorine-containing N-allenylsulfonamides, nor
their isomeric propargylsulfonamides were known until
present time.
The alkylation of N-(2,3-dibrompropyl)triflamide (II)
with benzylbromide was carried out in dipolar aprotic sol-
vents (DMSO, DMF) at heating. The reaction in DMSO
goes well, however the process does not stop at the alkyla-
The first N-alkenyl derivatives of triflamidees [7–9]
we synthesized recently, including also the first allyl de-
Scheme 1.
Et3N
_Et3NHF
+
CF3SO2F H2NCH2CH=CH2
CF3SO2NHCH2CH=CH2
I
Br2
EtONa
_NaBr, _EtOH
CF3SO2NHCH2CBr=CH2
CF3SO2NHCH2CHBrCH2Br
CCl4
II
III
1112

N-ALLENYL-N-BENZYLTRIFLUOROMETHANESULFONAMIDE
1113
Scheme 2.
Bn
Bn
K2CO3, Δ
II
BnBr
+
CF3SO2NCH2CHBrCH2Br
CF3SO2NCH2CBr=CH2
_HBr
DMF or DMSO, _HBr
IV
V
tion stage, but it is followed by dehydrobromination of
the intermediate N-benzyl-N-(2-bromopropyl)-triflamide
(IV) with the formation of N-benzyl-N-(2-bromoallyl)
triflamide (V) (Scheme 2). The structure of compound V
was established by 1H, 13C, and 19F NMR spectroscopy
and was proved by the elemental analysis. The assign-
ment of the methylene groups signals in the benzyl and
allyl fragments was performed using the 1H–13C HSQC
spectrum, and the presence of the carbon atom of the ter-
minal vinyl group =CH2, with the help of the j-modulated
13C NMR spectrum.
EtO–, and the analytically pure product cannot be isolated
[9]) proves that the strategy of preliminary protection of
the triflamide NH group is adequate.
The dehydrobromination of compound V can lead
either to acetylene, or to allene product. Higher stability
of the conjugated carbanion A compared to unconjugated
terminal carbanion B allows to assume the easier forma-
tion of allene VI than of acetylene VII (Scheme 3).
However, considering the possibility of the acetylene-
allene rearrangement, the ratio of the products VI and
VII can be defined not only, and not as much by the ease
of their formation, as by their comparative stability. As a
result we have made calculations of the molecules of the
compounds VI and VII in the approximation of B3LYP/6-
311G(d,p), including the force problem, and calculated
the difference of the total energies ΔE and the difference
of the free energies ΔG0 of the isomers VI and VII. The
difference of the total energies for the acetylene-allene
isomerisation (VII) → (VI) (Fig. 1) isΔE 2.5 kcal mol−1,
the difference of free energies is ΔG0 3.2 kcal mol−1
(298 K). Hence, the formation of the allene isomer VI
must be preferential to the formation of the acetylene
isomer VII kinetically, as well as thermodynamically.
The observed regioselective dehydrobromination of
the intermediate dibromide IV is similar to the formation
of 1-(2-bromoallyl)isatin at the alkylation of isatin with
1,2,3-tribrompropane in DMF in the presence of potas-
sium carbonate [10].
The reaction in DMF goes in the similar way, but with
the lower yield, and up to 30% of side product dimeth-
ylbenzylammonium bromide Me2Bn2NBr was isolated,
identified by comparing 1H and 13C NMR spectra to the
spectra of the authentic sample. The generation mecha-
nism of such salt is not clear; the reaction corresponds
the formal scheme:
1
According to the data of the H, 13C NMR and IR
spectroscopy, the N-benzyl-N-allenyltriflamide (VI) is
actually generated. It is proved by the presence of the
doublet at ~5.4 ppm and the triplet at ~6.6 ppm in the
1H NMR spectrum, and of signals at 202, 98 and 89 ppm
in the 13C NMR spectrum, typical of the allenyl, but not
the propargyl fragment. In the IR spectrum a doublet band
Me2NCHO + 2BnBr → Me2Bn2NBr + HBr + CO
The easier dehydrobromination of the dibromide
IV (yield 65% in presence of K2CO3 in process of the
alkylation) compared to dehydrobromination of its N-
unsubstitued analog II (yield ~40% with stronger base
Scheme 3.
Bn
Bn
Bn
B_
_HB
B_
_HB
_
_
CF3SO2N CH CBr=CH2
CF3SO2NCH2CBr=CH2
CF3SO2N CH2 CBr=CH
B
A
_Br_
Bn
V
_Br_
Bn
CH2 C CH
CF3SO2N
CF3SO2N CH=C=CH2
VII
VI
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 8 2013

SHAINYAN, DANILEVICH
1114
Fig. 1. Conformers obtained by preliminary optimisation of the geometry by the program Chem3D Ultra 8.0.
with maxima at 1963 and 1988 cm–1 (Fig. 2) corresponds
to the vibrations of the allenyl fragment.
the NMR spectra as well: a triplet at 2.4 ppm (≡CH)
4JHH 2.4 Hz, in the 1H NMR spectrum and the signals at
74.6 (≡CH) and 35.9 ppm (CH2C≡CH) in the 13C NMR
spectrum. Comparison of the integral intensities of the
signals of the allenyl and the acetylene isomers allows
to evaluate their ratio, (VI):(VII) ≈ 97 : 3, that agrees
qualitatively with the theoretically calculated signifi-
cant predominance of the allene isomer, (VI) : (VII) ≈
99.5 : 0.5.
However, the thorough analysis of the IR and NMR
spectra of the obtained product reveals the presence in
it of insignificant amount of the acetylene isomer, N-
benzyl-N-propargyltriflamide (VII). It is indicated by
the presence of a band in the IR spectrum at 3299 cm–1,
corresponding to the stretching vibrations ν(C–H) in the
acetylene compounds (Fig. 2), and the minor signals in
Fig. 2. IR spectrum of the N-benzyl-N-allenyltriflamide (VI).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 8 2013

N-ALLENYL-N-BENZYLTRIFLUOROMETHANESULFONAMIDE
1115
EXPERIMENTAL
solvents were evaporated at a reduced pressure, the resi-
due (yellowish liquid, 0,25 g) was distilled in a vacuum,
bp 95°C (1 mm Hg). To obtain an analytically pure
substance it was purified on a column with a silica gel
35-70 mesh, eluent hexane-chloroform, 1 : 1, and distil-
lated again. Yield 0.144 g (50%), bp 76°C (0.5 mm Hg),
d420 1.72 g/cm3. 1H NMR spectrum, δ, ppm: 4.68 m (2H,
CH2), 5.38 d (2H, =CH2, 1JHH 6.3 Hz), 6.64 t (2H, CH=,
1JHH 6.3 Hz), 7.37 m (5H, Ph). 13C NMR spectrum, δ,
ppm: 51.51 (NCH2), 89.49 (=CH2), 98.55 (CH=), 120.17
q (CF3, 1JCF 324.7 Hz), 127.94 (CO), 128.33 (Cp), 128.71
(Cm), 134.81 (Ci), 201.83 (=C=). NMR spectrum 19F, δ,
ppm: –74.22. Found, %: C 47.25; H 3.43; N 4.98; S 11.32.
C11H10F3NO2S. Calculated, %: C 47.65; H 3.64; N 5.05;
S 11.56.
The IR spectra were recorded on a Varian 3100 spec-
trometer from the microlayer of the sample. The NMR
spectra were registered on a spectrometer Bruker DPX
400 with working frequencies 400 (1H), 100 (13C) and
386 MHz (19F) in CDCl3, chemical shifts reported with
respect to ТMC (1H, 13C) and CCl3F (19F). Quantum-
chemical calculations, including the calculation of the
thermodynamic parameters, were made by using a pro-
gram package GAUSSIAN09 with a full geometrical
optimisation [11].
N-benzyl-N-(2-bromallyl)triflamide (V) 4.0 g
of N-(2,3-dibrompropyl)triflamide (II), obtained by the
method [3], 1.96 g (1.36 ml) of benzyl bromide, 20 ml of
dry DMSO were placed in a single-neck round-bottom
flask and stirred until complete dissolution. Then 6.4 g
of potassium carbonate was added and stirred for 10 h
at 110°C. The mixture was cooled, the precipitate was
filtered off, dissolved in water, extracted with chloroform.
The extract was combined with the filtrate and dried
with anhydrous MgSO4. The solvents were removed
at a reduced pressure, the residue was distilled in a
vacuum. Yield 2.67 g (65%), bp t 98°C (0.5 mm Hg.),
d420 1.60 g cm–3, mp 35°C. IR spectrum, ν, cm–1: 3068,
3035, 2936, 1630, 1497, 1391, 1227, 1195, 1142, 1085,
ACKNOWLEDGMENTS
The study was carried out under the financial support
of the Russian Foundation for Basic Research (grant
no.13-03-00055).
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1061, 928, 901, 797, 740, 700, 614, 590. H NMR
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