Reaction of N-sulfinyltrifluoromethanesulfonamide with carbodiimides: Formation of N-trifluoromethanesulfonyl-2,4-dialkyl-1,2,4-thiadiazetidin-3-imine 1-oxides

Article abstract of DOI:10.1016/j.jfluchem.2012.04.016

N-sulfinyltrifluoromethanesulfonamide was found to react with diisopropyl- and dicyclohexylcarbodiimides with the formation of N-trifluoromethanesulfonyl- 2,4-dialkyl-1,2,4-thiadiazetidin-3-imine 1-oxides. The mechanism includes the [2π + 2π] cycloadditio

Full text of DOI:10.1016/j.jfluchem.2012.04.016

Journal of Fluorine Chemistry 140 (2012) 59–61
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Reaction of N-sulfinyltrifluoromethanesulfonamide with carbodiimides:
Formation of N-trifluoromethanesulfonyl-2,4-dialkyl-1,2,4-thiadiazetidin-3-
imine 1-oxides
*
Bagrat A. Shainyan , Ljudmila L. Tolstikova
A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of Russian Academy of Sciences, 1 Favorsky Street 664033, Irkutsk, Russia
A R T I C L E I N F O
A B S T R A C T
Article history:
N-sulfinyltrifluoromethanesulfonamide was found to react with diisopropyl- and dicyclohexylcarbo-
diimides with the formation of N-trifluoromethanesulfonyl-2,4-dialkyl-1,2,4-thiadiazetidin-3-imine
Received 3 April 2012
Received in revised form 27 April 2012
Accepted 30 April 2012
Available online 17 May 2012
1-oxides. The mechanism includes the [2
p + 2p] cycloaddition resulting in 2-trifluoromethanesulfonyl-
3-alkylimino-4-alkyl-1,2,4-thiadiazetidine 1-oxides, the ring opening of the latter, rotation about the
C–N bond and the ring closure to the final products.
ß 2012 Elsevier B.V. All rights reserved.
Keywords:
N-sulfinyltrifluoromethanesulfonamide
Carbodiimides
1,2,4-Thiadiazetidin-3-imine 1-oxides
Synthesis
Structure
Mechanism
1. Introduction
Recently we have developed two new synthetic approaches to
N-triflyl guanidines TfN55C(NHR)2 (Tf = CF3SO2) by the reaction of
N-sulfinyltrifluoromethanesulfonamide CF3SO2N55S55O (1), with
urea or by the addition of trifluoromethanesulfonamide to
carbodiimides RN55C55NR (2) [1]. It was interesting to investigate
the reaction between the two heterocumulenes, 1 and 2, in order to
examine the effect, if any, of the CF3 group on the known reaction
of N-sulfinylarenesulfonamides with carbodiimides [2,3].
NBu-t
Me
O
N
S
N
Ts
was only postulated on the basis of similarity with the reactions of
carbodiimides with other heterocumulenes like isocyanates and
isothiocyanates. More interesting are the results of Minami et al.
who have isolated the products of the reaction of MeSO2NSO and
TsNSO with symmetrical carbodiimides RN55C55NR and assigned
2. Results and discussion
them the structure of the [2
p
+ 2p
] cycloadducts [3].
The principal question arising in the analysis of the literature
data on the reactions of N-sulfinylsulfonamides with carbodii-
mides is the structure of the cycloadducts formed. In the first work
of Ulrich et al., the isolated and proved products of the reaction of
MeN55C55NBu-t with TsNSO were the products of exchange,
MeNSO and TsN55C55NBu-t [2]. The intermediacy of the four-
membered product of cycloaddition
O
R'SO2
S
N
R'SO2 N=S=O
+
RN=C=NR
N
R
RN
3
Upon heating, compounds 3 were converted into the products
of exchange RNSO and R0SO2N55C55NR, and upon hydrolysis they
gave the substituted guanidines R0SO2N55C(NHR)2 [3]. However, as
to the structure of the above cycloadducts, it was not proved,
* Corresponding author. Fax: +7 3952 419346.
E-mail address: bagrat@irioch.irk.ru (B.A. Shainyan).
0022-1139/$ – see front matter ß 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2012.04.016

60
B.A. Shainyan, L.L. Tolstikova / Journal of Fluorine Chemistry 140 (2012) 59–61
either. Moreover, the 1H NMR spectra of compounds 3 do not
support the indicated unsymmetrical structure but rather evidence
against it [3]. Indeed, compounds 3 have two different NR groups
but the proton spectra contain only one NCH (R = i-Pr) or NCH2
(R = n-Bu) signal. The 13C NMR spectra were not recorded.
We have performed the reaction of N-sulfinyltrifluorometha-
nesulfonamide 1 with diisopropylcarbodiimide 2a and dicyclo-
hexylcarbodiimide 2b and showed the products to be N-
trifluoromethanesulfonyl-2,4-dialkyl-1,2,4-thiadiazetidin-3-im-
ine 1-oxides 4.
transitions responsible for the two bands. However, unlike
guanidine 6b, the addition of 0.1 N HCl to the acetonitrile solution
of 4b led to appearing of a long-wave absorption band with lmax
283 nm corresponding to the transition in its S55O-protonated
form 5.
3. Conclusion
As opposed to the literature data, the reaction of N-sulfinyltri-
fluoromethanesulfonamide with N,N0-dialkylcarbodiimides gives
N-trifluoromethanesulfonyl-2,4-dialkyl-1,2,4-thiadiazetidin-3-
imine 1-oxides by the rearrangement of the intermediate
O
R
[2
p + 2p] cycloadducts via the ring opening – ring closure
S
N
sequence of reactions.
CF3SO2 N=S=O
+
RN=C=NR
2
N
1
4. Experimental
R
CF3SO2N
R = i-C3H7 (a); c-C6H11 (b).
4a,b
4.1. General
The molecular formulae of compounds 4a,b were established by
high-resolution mass spectrometry (HRMS). The symmetrical
structure of 4a,b was proved by the absence of different signals of
the CH groups attached to the amine and imine nitrogen atoms both
in the 1H and 13C NMR spectra. The presence of two slightly different
signals of the CH protons in 4a (see Section 4) is, most probably, due
to different location of the two NR groups with respect to the
configurationally rigid structure of imine moiety (more close to and
more distant from the triflyl group). To exclude accidental
coincidence of the signals of R in the alternative structure 3 (highly
improbable, especially for 13C NMR, but still possible) we have
measured the 15N NMR spectrum of 4a and found the presence of
only one signal at ꢀ203.2 ppm, unequivocally indicating the
presence of two equivalent NR groups in the molecule (the use of
the hmbcgp technique does not allow to detect the 15N signal of the
CF3SO2N group due to the absence of nearby protons).
The measured dipole moment of 4b was 5.65 D, which is in
qualitative agreement with the calculated for the symmetrical
structure 4b (4.81 D) but substantially lower than that calculated
for the isomeric structure of the type 3 (7.59 D), which, besides, is
19.3 kcal/mol less stable than structure 4b.
An additional and independent support came from chemical
transformations and UV spectroscopic study of 4b. The acidic
hydrolysis of 4b in aqueous ethanol with 5–10% triflic acid gave
Melting points are uncorrected. IR spectra were taken on a Bruker
Vertex 70 spectrophotometer in KBr. UV spectra were recorded on a
Specord UV Vis spectrometer in acetonitrile. 1H, 13C, and 19F NMR
spectra were recorded on a Bruker DPX 400 spectrometer at working
frequencies 400 (1=), 100 (13E), 40 (15N) and 376 (19F) MHz in
chloroform; 1H and 13C NMR chemical shifts are reported in parts per
milliondownfieldtoTMS, and19FNMRin partspermilliondownfield
to CFCl3. 15N NMR chemical shifts were obtained from 2D{1H–15N}
spectra recorded by the use of a gradient probe working in the
hmbcgp mode optimized to the long-range coupling constant JNH of
9 Hz, and are reported in parts per million downfield to CH3NO2.
Electron impact mass spectra were obtained on a GC–MS TRACE DSQ
II mass spectrometer (Thermo Fisher Scientific GmbH) at 70 eV.
HRMS measurements were performed on a Micromass Q-TOFmicro
instrument (Waters, Manchester, UK) in the positive electrospray
mode. The elemental composition was determined using H3PO4 as a
standard with deviation < 3 ppm. The dipole moment of 4b was
measured on a Sh2-5 instrument (Angarsk, AO OKBA) at 1 MHz.
Quantum chemical calculations were performed with full
geometry optimization using the Gaussian09 package [6] and
employing the B3LYP exchange correlation potential in connection
with the 6-311G(d,p) basis set.
All solvents were dried and purified before use according to
standard procedures. Commercial diisopropylcarbodiimide 2a of
99% purity (Aldrich) and dicyclohexylcarbodiimide 2b of 99%
1,3-dicyclohexyl-2-(trifluoromethylsulfonyl)guanidine
Hex), which is identical to the authentic sample [1].
6
(R = c-
Tf
N
C
S
Tf
N
C
S
R
N
C
S
O
O
O
1 + 2
RN
RN
TfN
NR
NR
NR
R
N
S
R
N
S
OH
O
R
H+
H2O
-SO2, -H+
TfN=C(NHR)2
TfN
TfN
C
N
C
NR
6
4
5
Note, that a similar symmetrization of the originally formed
[2 + 2] cycloadduct via the sequence of the ring opening – ring
closurereactionswas observed inthe reaction ofcarbodiimideswith
(dimethylamino)bis(trifluoromethyl)borane, (CF3)2BNMe2 [4].
In the UV spectrum of 4b an absorption band was observed with
lmax 216 nm, which practically coincides with the band at lmax
214 nm in the spectrum of the corresponding N-triflylguanidine
purity (Alfa Aesar) were used. N-sulfinyltrifluoromethanesulfona-
mide [5] was synthesized by the known procedure.
4.2. Synthesis
N-trifluoromethanesulfonyl-2,4-diisopropyl-1,2,4-thiadia-
zetidin-3-imine 1-oxide 4a. N-sulfinyltrifluoromethanesulfona-
(6b, R = c-Hex). This is suggestive of the similarity of the
p
–p
*
mide 1 (0.23 g, 1.2 mmol) was added to the solution of

B.A. Shainyan, L.L. Tolstikova / Journal of Fluorine Chemistry 140 (2012) 59–61
61
diisopropylcarbodiimide 2a (0.15 g, 1.2 mmol) in 1 ml of benzene
(or chloroform, methylene chloride, or cyclohexane) at vigorous
stirring at room temperature, stirred for 4 h, kept overnight,
evaporated in vacuum to give 4a (0.38 g, 98%) as solid with m.p.
(lit. 160 8C [1]). The IR and NMR spectra coincided with those
previously reported [1].
Acknowledgements
60 8E. IR,
746, 621. 1= NMR,
6.5 Hz), 1.35 d and 1.34 d (12H, CH3, J 6.5 Hz). 13E NMR,
153.06 (E55NTf), 118.88 q (CF3, J 318.6 Hz), 50.08 (CH0), 21.05
(CH3). 19F NMR,
, ppm: ꢀ79.73. Mass spectrum, m/z (Irel., %) ion:
n
, cmꢀ1: 2986, 2940, 1619, 1465, 1346, 1207, 1129, 795,
, ppm: 4.17 sept and 4.18 sept (1H, NEH,
, ppm:
d
The financial support of this work by the Russian Foundation for
Basic Research and Deutsche Forschungsgemeinschaft (Grants
RFBR 10-03-00110 and RFBR-DFG 11-03-91334) is greatly
acknowledged. We thank Dr. I.A. Ushakov and Dr. T.N. Aksamen-
tova (Irkutsk) for measuring the 15N NMR spectra and dipole
moment, and Dr. I. Starke (Potsdam University) for mass
spectrometry measurements.
d
d
321 (13) [M], 264 (16) [MꢀNPr], 217 (19) [TfNHCHPr], 201 (48)
[TfNCNCH2CH2], 188 (8) [M–Tf], 175 (15) [TfNHCNH], 147 (47)
[TfN], 146 (100) [MꢀNTfꢀC3H6], 137 (33) [201ꢀSO2], 105 (41)
[PrNSO], 90 (22) [CH2CH2NSO], 83 (12) [PrNCN], 69 (40) [CF3], 58
(19) [PrNH], 43 (17) [Pr]. HRMS: found m/z for [M]+ 321.0438; calcd
for C8H14F3N3O3S2: 321.0429. Anal. calcd. for C8H14F3N3O3S2: C
29.90; H 4.39; N 13.08; found: C, 30.51; H, 4.96; N, 13.32.
N-trifluoromethanesulfonyl-2,4-di(cyclohexyl)-1,2,4-thia-
diazetidin-3-imine 1-oxide 4b was prepared in a similar fashion.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jfluchem.
2012.04.016.
Yield 0.47 g (97%), solid with m.p. 56 8C. IR,
1612, 1451, 1348, 1190, 1141, 898, 797, 617. 1H NMR,
t.t (2H, CH, J 11.1, 3.7 Hz), 2.18 d (4H, Heq2,6, J 11.1 Hz), 1.83 (4H,
Hax2,6, J 12.4, 2.0 Hz), 1.75–1.10 m (12H, H3,4,5). 13C NMR,
, ppm:
152.76 (C55NTf), 119.06 q (CF3, J 318.8 Hz), 57.05 (CH), 32.20 and
32.11 (C2,6 and C2’,6’), 24.82 (C3,5), 24.64 (C4). 19F NMR,
, ppm:
n
, cmꢀ1: 2941, 2863,
, ppm: 3.92
d
References
d
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(1972) 3484–3487.
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2156–2159.
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[6] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li,
H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M.
Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J.
Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K.
Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega,
J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W.
Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J.
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d
ꢀ79.25. Mass spectrum, m/z (Irel., %) ion: 401 (20) [M], 352 (9) [M–
HSO], 320 (67) [M–C6H9], 268 (17) [MꢀTf], 238 (64) [MꢀTfꢀC2H6],
220 (22) [MꢀTfꢀSO], 219 (17) [MꢀHSOꢀTf], 186 (100)
[MꢀTfꢀC6H10], 145 (59) [C6H11NSO], 138 (33) [C6H11NC(N)NH],
98 (39) [C6H11NH], 83 (100) [C6H11], 81 (82) [C3H5NCN], 69 (28)
[CF3], 55 (64) [C4H7], 41 (29) [C2H2NH]. HRMS: found m/z for [M]+
401.1064; calcd for C14H22F3N3O3S2: 401.1055. Anal. calcd. for
C
14H22F3N3O3S2: C 41.88; H 5.52; N 10.47; found: C, 41.86; H, 5.49;
N, 10.42.
Hydrolysis of N-trifluoromethanesulfonyl-2,4-di(cyclo-
hexyl)-1,2,4-thiadiazetidin-3-imine 1-oxide 4b. To the solution
of 4b (0.24 g, 0.6 mmol) in 36% ethanol (8 ml) two drops of TfOH
was added, stirred for 2 h at room temperature and kept overnight.
The product was collected by filtration, washed with water and
dried to yield 1,3-dicyclohexyl-2-(trifluoromethylsulfonyl)guani-
dine 6 (R = c-Hex) (0.14 g, 66.7%) as white crystals with m.p. 152 8C