3,3-Dimethyl-1-(trifluoromethylsulfonyl)-1,3-azasilolidine

Full text of DOI:10.1134/S1070363211080287

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 8, pp. 1735–1737. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © E.N. Suslova, B.A. Shainyan, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 8, pp. 1392–1395.
LETTERS
TO THE EDITOR
3,3-Dimethyl-1-(trifluoromethylsulfonyl)-1,3-azasilolidine
E. N. Suslova and B. A. Shainyan
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: svk@irioch.irk.ru
Received March 17, 2011
DOI: 10.1134/S1070363211080287
Recently, we prepared the first representatives of
N-trifluoromethylsulfonyl-substituted Si,N-heterocycles,
namely, 4,4-dimethyl-1-(trifluoromethylsulfonyl)-1,4-
azasilinane (I) [1] and 2,2,6,6-tetramethyl-4-(tri-
fluoromethylsulfonyl)-1,4,2,6-oxaazadisilinane (II) [2].
which they play a decisive role in the so-called
“reverse–turn formation” of these compounds [6, 7].
Due to high lipophilicity of the silyl groups, the
introduction of silaprolines facilitates the solubility of
aminoacids and peptides [8, 9]. Both racemates and
optically pure isomers of silaprolines with various
substituents at the nitrogen atom and in the five-
membered ring are synthesized [10, 11]. The most
complete information on the five-membered Si,N-
heterocycles is summarized in the recent review [12].
Si
O
N
SO2CF3
N
SO2CF3
Si
Si
I
II
In the present work, we report on the synthesis of
the first representative of the N-trifluoromethylsulfon-
yl-substituted five-membered Si,N-heterocycles, 3,3-
dimethyl-1-(trifluoromethyl-sulfonyl)-1,3-azasilolidine
(IV) by the reaction of 2-bromoethyl(chloromethyl)
dimethylsilane (III) (we failed to find any information
in the literature on the latter product) with trifluoro-
methanesulfonamide in tetrahydrofuran in the presence
of triethylamine in 42–47% yield. Silane III was
prepared by hydrobromination of (chloromethyl)di-
methyl(vinyl)silane in 92% yield using the procedure
similar to that we had described earlier [13].
Their
analogs,
N-trifluoromethylsulfonyl-
substituted five-membered Si,N-heterocycles, are not
described in the literature. The first reports on the five-
membered Si,N-heterocycles refer to the synthesis of
3,3-dimethyl-1-phenyl-1,3-azasilolidine and its 5-
methyl-substituted analog prepared using the method
of electrophilic intramolecular cyclization by the
reaction of aminomercuration [3–5]. Later on, the
investigations were carried out on silaprolines (the
derivatives of 1,3-azasilolidine-5-carboxylic acid)
incorporated in the peptide and protein structures in
CH2Cl
CH2Cl
(C6H5COO)2
Me2Si
+
HBr
Me2Si
hexane, argon
CH
CH2
CH2CH2Br
III
Δ
.
NSO2CF3 + Et3N HHlg
III + NH2SO2CF3 + Et3N
Me2Si
THF
IV
At room temperature or in the absence of triethyl-
amine the reaction does not proceed. Product IV is
stable both thermally (200°С) and hydrolitically
(survives after water treatment). The conversion of the
starting silane III amounts to ~90% and practically
does not depend on the ratio silane III–triflamide.
1735

1736
SUSLOVA, SHAINYAN
Apart from the main product IV, according to the data
of 1Н, 29Si NMR spectroscopy, bis(chloromethyl)
In contrast to triflamide, its sodium salt
CF3SO2NHNa does not react with silane III: after
several hours of reflux in THF in the presence of
triethylamine the starting silane III was isolated. This
fact, as well as the earlier demonstrated sharp decrease
in the yield of compound II in the reaction of siloxane
V with sodium salt of triflamide even under more
severe conditions than with triflamide itself [2], allows
a conclusion that the reaction of heterocyclization of
halosilanes with triflamide does not follow the me-
chanism of double nucleophilic substitution of halogen
atoms by the triflamide residue. Presumably, due to
high NH-acidity and very low basicity of triflamide
and its N-monosubstituted analogs, the determining
moment for the reaction of halogenosilanes with
triflamide is the interaction CF3SO2N–H···Br(Cl). In
this case the triflamide acts as an electrophilic reagent
in the four-center mechanism leading to the formation
of the N–C bond in the fragment CF3SO2N···CH2CH2Si–
or CF3SO2N···CH2Si–.
tetramethyldisiloxane (ClCH2SiMe2)2O
V
(16%),
heterocycle II (6%), and ca. 10% of unidentified
admixture is formed. The structure of compounds II
and V isolated as individual products was proved by
1
coincidence of their Н, 13С, 19F, 29Si NMR spectra
with those of the authentic samples [2, 14].
When the reaction is carried out in methanol, with
the same high degree of conversion of the starting
silane the yield of the target product IV is reduced and
the content of by-products increases, especially of
heterocycle II, up to 24%. Presumably, in a proton-
donor medium (methanol) the process of splitting of
the Si–C bond of the SiCH2CH2Br fragment in silane
III is more active (the β-effect). This leads to the
formation of siloxane V which further reacts with
triflamide to give heterocycle II [2]. This is proved by
the formation of siloxane V at reflux of the solution of
silane III in methanol for 5 h.
Me
CH2Cl
Cl
H
NSO2CF3
Me2Si
Si
Me
Me
CH2
_HBr
_HBr
Si
Me
CH2CH2
Br
H
NSO2CF3
IV
CH2CH2
CF3SO2 NH
At first, probably, the halogen atom in the
bromoethyl rather than the chloroethyl fragment is
replaced, as proved, for example, by the inertness of
the SiCH2Cl group in the reaction of hydrolysis of the
closest analog of silane III, (2-chloroethyl)(chloro-
methyl)dimethylsilane ClCH2SiMe2CH2CH2Cl result-
ing in β-hydroxysilane ClCH2SiMe2CH2CH2ОН and
siloxane V with retention of the Me2SiCH2Cl group
[15], which is fully consistent with the formation of
siloxane V in our case.
methyl)dimethyl(vinyl)silane and 0.05 g (0.2 mmol) of
benzoyl peroxide in 40 ml of anhydrous hexane dry
gaseous НВr was passed in argon atmosphere under
UV irradiation and stirring for 3–3.5 h. The reaction
mixture was left overnight at room temperature, then
the excess of НВr was removed by bubbling of argon
and the solvent was removed at atmospheric pressure.
After vacuum distillation of the residue 9.87 g (92%)
of silane III was isolated with bp 96–97°С (12 mm Hg),
nD22 1.4923. IR spectrum, ν, cm–1: 2960, 1394, 1251,
1
1029, 880, 844. Н NMR spectrum, δ, ppm: 0.18 s
19
29
1Н, 13С, F, and Si NMR spectra were registered
from solutions in CDCl3 on a Bruker DPX 400 spectro-
meter (400, 100, 376 and 79.5 MHz, respectively),
chemical shifts are given relative to TMS (1Н, 13С,
29Si) or CCl3F (19F). The IR spectrum was taken on a
Bruker Vertex 70 spectrometer in thin layer. Mass
spectrum of electron impact (70 eV) was obtained on a
GCMS-QP5050A Shimadzu chromatomass-spec-
trometer (quadruple mass analyzer, capillary column,
liquid phase SPB-5).
(6Н, SiМе2), 1.51 t (2Н, SiCН2, J 8.7 Hz), 2.81 s (2H,
SiCH2Cl), 3.58 t (2Н, CН2Br, J 8.7 Hz). 13С NMR
spectrum, δС, ppm: –4.62 (SiMe), 20.79 (SiCH2),
29.54(CH2Cl), 30.19 (CH2Br). 29Si NMR spectrum: δSi
2.99 ppm. Mass spectrum, m/z (Irel, %): 137 (100)
35
[Me2Si79Br], 107 (77) [Me2SiCH2 Cl], 79 (84)
35
[H2SiCH2 Cl]. Found, %: С 27.89; Н 5.35; Br 37.98;
Cl 15.77; Si 13.10. C5H12BrClSi. Calculated, %: С
27.84; Н 5.57; Br 37.12; Cl 16.47; Si 12.99.
2-Bromoethyl(chloromethyl)dimethylsilane (III).
3,3-Dimethyl-1-(trifluoromethylsulfonyl)-1,3-aza-
Into the solution of 6.69 g (0.05 mol) of (chloro-
silolidine (IV). а. Synthesis in THF. To the mixture of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 8 2011

1737
3,3-DIMETHYL-1-(TRIFLUOROMETHYLSULFONYL)-1,3-AZASILOLIDINE
scopically). Individual products were isolated by
column chromatography, as above; the target product
IV was obtained in 13% yield. mp and NMR spectra of
compound II coincide with [2].
0.772 g (3.6 mmol) of 2-bromoethyl(chloromethyl)
dimethylsilane III and 1.07 g (7.2 mmol) of trifluoro-
methanesulfonamide in 4 ml of anhydrous THF at
stirring in argon atmosphere the solution of 0.724 g
(7.2 mmol) of triethylamine in 2 ml of anhydrous THF
was added dropwise during 15 min. The reaction
mixture was stirred at room temperature for 1 h and for
another 5 h at 65°С, cooled, diluted with hexane (7 ml)
and left till separation of the layers. The organic layer
was separated from the precipitate, washed with water
(2Ч4 ml), dried over Na2SO4. After removal of
solvents and evacuation of the residue 0.593 g of liquid
1
Bis(chloromethyl)tetramethyldisiloxane (V). Н
NMR spectrum, δ, ppm: 0.33 s (12Н, SiМе2), 2.74 s
(4H, SiCH2Cl). 13С NMR spectrum, δС, ppm: –1.39
(SiMe2), 30.72 (SiCH2Cl). 29Si NMR spectrum: δSi
3.27 ppm (δН, ppm: 0.3, δС –1.4, δSi 3.3 [14]).
ACKNOWLEDGMENTS
This work was performed with the financial support
from the Russian Foundation for Basic Research (grant
no. 10-03-00110). The authors are grateful to Dr.
S.V. Kirpichenko for helpful discussion of the mechanism.
1
was obtained consisting, in keeping with Н and 29Si
NMR data, of the starting silane III (7%), product IV
(55%), 2,2,6,6-tetramethyl-4-(trifluoromethylsul-
fonyl)-1,4,2,6-oxaazadisilinane (II) (6%), and bis-
(chloromethyl)tetramethyldisiloxane V (16%). Distilla-
tion of the crude product [bp 112–115°С (22 mm Hg)]
does not free the main product of admixtures of
compounds II, III, and V. They were separated by
column chromatography on silica (ALFA); 0.375 g
(42%) of product IV was obtained. The analytically
pure sample was obtained after column chromato-
graphy on silica ICN with gradient elution by hexane–
ether from 100:1 to 1:1, Rf = 0.46. nD22 1.4279. IR
spectrum, ν, cm–1: 2962, 1475, 1383, 1141, 1256,
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1
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19
29
J 323.0 Hz). F NMR spectrum: δF –73.93 ppm. Si
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1
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 8 2011