Alkyl derivatives of bis(perfluoroalkylsulfonylimino) trifluoromethanesulfonic acid

Article abstract of DOI:10.1021/jo900195k

(Chemical Equation Presented) N-Methyl and N-ethyl derivatives of N-(trifluoromethylsulfonyl)-[N′-(trifluoromethylsufonyl) -trifluoromethylsulfoximidoyl] imides 2a,b were prepared by alkylation of bis(trifluoromethylsulfonylimino) trifluoromethanesulfonic

Full text of DOI:10.1021/jo900195k

substantial increase of their electron-withdrawing properties3
and considerable extension of the anionic charge delocalization
in such a substituent. This also suggests that the strength of
new bis(trifluoromethylsulfonylimino)trifluoromethanesulfonic
acid 1 must be considerably above the TfOH and HN(Tf)2,
which are the strongest organic acids with the exception of the
carborane acids.4 Moreover, several reactive centers in the
molecule are presented; therefore, our interest was an in-depth
study of its properties to be compared with the above-mentioned
acids.
Alkyl Derivatives of
Bis(perfluoroalkylsulfonylimino)
trifluoromethanesulfonic Acid
Anna G. Posternak, Romute Yu. Garlyauskayte,* and
Lev M. Yagupolskii
Institute of Organic Chemistry, National Academy of
Sciences of Ukraine, 5 Murmanskaya Str., UA-02094 KieV,
Ukraine
Powerful methylating agents, such as trimethyloxonium salts,5
methyl fluorosulfonate,6 methyl trifluoromethane sulfonate,7 and
methyl nonafluoro-n-butanesulfonate,8 are widely applicable.
Methyl esters of very strong acids are commercially available,
and other esters of these acids are easily prepared and have
found uses in solvolytic studies of otherwise unreactive sub-
strates.9 Due to the excellent leaving group properties, alkyl
perfluoroalkanesulfonates are one of the most powerful alky-
lating agents known, with the exception of the oxonium salts,
capable of alkylating carbon, oxygen, and nitrogen centers.
However, Meervein salts have low solubilities, whereas methyl
triflate as well as the somewhat less reactive but also less
expensive methyl fluorosulfonate may well be the reagent of
choice for methylation.10 It has been reported on the basis of
conductometric studies that acidities of currently used super-
acids, which determined the alkylating ability of their esters,
are approximately equal but vary in different solvents:
CF3SO2OH > HClO4 > FSO2OH > H2SO4 in acetic acid11 and
FSO2OH > ClSO2OH ∼ CF3SO2OH . HClO4 in sulfuric acid.12
We now wish to report results of acid 1 alkylation, the
synthesis of N-methyl and N-ethyl derivatives 2a,b, and their
alkylating ability toward different nucleophiles, as well as
alkylation reactions by alkyl halides in the presence of silver
salt of acid 1.
It is well-known that alkyl perfluoroalkanesulfonates are
readily available via the reaction of alkyl halides with silver
salts of the perfluoroalkanesulfonic acids. In order to
prepare alkyl esters of bis(trifluoromethylsulfonylimino)trifluo-
romethanesulfonic acid 1, we carried out similar reactions of
the silver salt of acid 1 with alkyl halides (MeI, EtI, n-BuI,
i-BuI, t-BuI, n-PrBr, i-PrBr, n-AmI) at room temperature in
different solvents (Et2O, benzene, CH2Cl2). Precipitation of silver
halide was observed in all experiments, but only N-methyl and
N-ethyl derivatives of N-(trifluoromethylsulfonyl)-[N′-(trifluo-
romethylsufonyl)trifluoromethylsulfoximidoyl]imides 2a,b have
roma@ioch.kieV.ua
ReceiVed February 2, 2009
N-Methyl and N-ethyl derivatives of N-(trifluoromethylsul-
fonyl)-[N′-(trifluoromethylsufonyl)-trifluoromethylsulfoximi-
doyl] imides 2a,b were prepared by alkylation of bis(triflu-
oromethylsulfonylimino)trifluoromethanesulfonic acid 1 or
its silver salt 1a. It turns out that these imides are strong
alkylating agents in spite of the fact that Me (Et) groups are
attached to nitrogen atom. The alkylating activity of n-PrI,
i-PrI, n-BuI, and n-AmI in the presence of silver salt of
bis(trifluoromethylsulfonylimino)trifluoromethanesulfonic acid
1a was investigated.
Recently, the synthesis of bis(trifluoromethylsulfonylimi-
no)trifluoromethanesulfonic acid 1 through the condensation of
N-(trifluoromethylsulfonyl)trifluoromethanesulfoximidoyl fluo-
ride with trifluoromethanesulfonamide was described by us.1
Before this synthetic success, the calculations of deprotonation
enthalpies predicted that the gas phase acidity of acid 1 is in
excess of TfOH by 30 kcal/mol (i.e., more than 21 pKa units)
and is approximately equal to HF-SbF5, which is known as
“magic acid”.2
Acid 1 can be represented as an analogue of trifluo-
romethanesulfonic acid in which both oxygen atoms are
substituted by fragment dNTf. It was shown earlier that such
replacement contiguous to C, P, S, and I centered groups caused
(3) Garlyauskajte, R. Yu.; Sereda, S. V.; Yagupolskii, L. M. Tetrahedron
1994, 50, 6891–6906.
(4) Juhasz, M.; Hoffmann, S.; Stoyanov, E.; Kim, K.-Ch.; Reed, Ch. A.
Angew. Chem., Int. Ed. 2004, 43, 5352–5355.
(5) Perst H. Oxonium Ions in Organic Chemistry; Verlag Chemie: Weinheim,
Germany, 1971; Vol. 70, p 77.
(6) (a) Engelbrecht, A. Angew. Chem. 1965, 77, 695–699. (b) Ahmed, M. G.;
Alder, R. W.; James, G. H.; Sinnott, M. L.; Whittig, M. C. Chem. Commun.
1968, 1533.
* To whom correspondence should be addressed. Phone: +380 44 559 0349.
Fax: +380 44 573 2643.
(7) Haszeldine, R. N.; Gramstad, T. J. Chem. Soc. 1957, 4069–4079.
(8) Gramstad, T.; Haszeldine, R. N. J. Chem. Soc. 1957, 2640–2645.
(9) Su, T. M.; Sliwinski, W. F.; Schleyer, P. v. R J. Am. Chem. Soc., 1969,
91, 5386–5388.
(10) Kevill, D. N.; Lin, G. M. L. Tetrahedron Lett. 1978, 949–453.
(11) Engelbrecht, A.; Rode, B. M. Monatsh. Chem. 1972, 103, 1315–1319.
(12) Russel, D. G.; Senior, J. B. Can. J. Chem. 1974, 52, 2975–2977.
(1) Garlyauskayte, R.; Yu., Chernega, A. N.; Michot, Ch.; Armand, M.;
Yagupolskii, Yu. L.; Yagupolskii, L. M. Org. Biomol. Chem. 2005, 3, 2239–
2243.
(2) Burk, P.; Koppel, I. A.; Koppel, I.; Yagupolskii, L. M.; Taft, R. W.
J. Comput. Chem. 1996, 17, 30–41, and references therein.
10.1021/jo900195k CCC: $40.75
Published on Web 04/30/2009
2009 American Chemical Society
J. Org. Chem. 2009, 74, 4387–4389 4387

SCHEME 1. Synthesis of N-Methyl and N-Ethyl Derivatives
of N-(Trifluoromethylsulfonyl)-[N′-(trifluoromethylsufonyl)-
trifluoromethylsulfoximidoyl]imides 2a,b
product after workup. Probably, under these conditions, the
competitive elimination reaction to olefins via carbocation
formation becomes predominant.
It is highly probable that the reaction runs via generation of
O-alkyl esters of bis(perfluoroalkylsulfonylimino)trifluorome-
thanesulfonic acid, which are alkylating agents so powerful that
they alkylate “themselves” through SdN double bond. The
resulting N-methyl and N-ethyl derivatives 2a,b are reasonably
stable liquids at room temperature.
N-Methyl-N-(trifluoromethylsulfonyl)-[N′-(trifluoromethylsul-
fonyl)trifluoromethylsulfoximidoyl]imide 2a can be prepared by
reaction of acid 1 with methanol in the presence of thionyl
chloride13 with excellent yield (Scheme 1).
SCHEME 2. Reactions of N-Methyl (2a) and N-Ethyl (2b)
Derivatives of N-(Trifluoromethylsulfonyl)-[N′-(trifluoro-
methylsulfonyl)trifluoromethylsulfoximidoyl]imides with Nu-
cleophiles
The imides 2a,b have been tested as methylating agents
toward S-, N-, and P-nucleophiles. It turned out that they have
been sufficiently powerful alkylating agents, in spite of the fact
that the alkyl group is connected with the nitrogen atom.
Nucleophilic substitution reactions of N-alkyldi(trifluoromethane-
sulfonyl)amides with sodium, potassium salts,14 methylation of
N-methyl, N-ethyl imidazoles or pyridine,15 as well as benzy-
lation of alcohols16 were reported. We found that imides 2a,b
react with diphenylsulfide, triphenylphosphine, and triph-
enylphosphate with good yields on warming. The imides 2a,b
react exothermically with N-methyl imidazole in methylene
chloride at 0 °C, giving the products of imidazole ring splitting,
while interaction with N-tetrafluoroethyl imidazole proceeds
easily at room temperature with quantitative yield. The data are
presented in Scheme 2 and Table 1.
It should be noted that imidazolium (6), sulfoxonium (3), and
phosphonium (5) salts are stable liquids, kept at -20 °C for a
few days without glass transition, and may be of interest as
room temperature ionic liquids with a novel anion.
We investigated a possibility of propyl, butyl, amyl in situ
carbocation generation for the reactions of acid 1 silver salt with
corresponding alkyl halides and diphenylsulfide as a model
substrate. It was found that direct alkylation of Ph2S using n-Pr,
i-Pr, n-Bu, and n-Am halides in the presence of the silver salt
1a affords high yields of the corresponding sulfonium salts
3c-e,g, respectively (Scheme 3 and Table 2).
SCHEME 3. Reactions of Alkyl Halogenides with
Nucleophiles in the Presence of Silver Salt 1a of
Bis(trifluoromethylsulfonylimino)trifluoromethanesulfonic
Acid
In the case of i-BuI and t-BuI, alkylation did not occur. If
1-tetrafluoroethylimidazole was used as a model substrate, n-BuI
produced 1-(n-butyl)-3-(1,1,2,2,tetrafluoroethyl)imidazolium bis-
(trifluoromethylsulfonylimino)trifluoromethanesulfonate 6e in
good yield while 1-(H)-3-(1,1,2,2,tetrafluoroethyl)imidazolium
bis(trifluoromethylimino)trifluoromethanesulfonate 7 was the
product of the reaction with i-BuI and t-BuI (Scheme 3).
Recently, we have prepared the unsymmetrical analogue of
acid 1, N-(trifluoromethylsulfonylimino)-N′-(nonafluoro-n-bu-
tylsulfonylimino)trifluoromethanesulfonic acid 8.17 It turned out
that the reaction of acid 8 with methanol showed methylation
on both NTf and NNf nitrogen atoms about pari passu formation
of 9 (52%) and 10 (42%) with the traces of methylation through
the SdO bond of triflic group 11 (6%), which was detected by
NMR spectroscopy (Scheme 4).
(13) Brenner, M.; Huber, W. HelV. Chim. Acta 1953, 2334–2335.
(14) Glass, R. S.; Swedo, R. J. J. Org. Chem. 1978, 43,11, 2291–2293, and
references therein.
(15) Zhang, J. Z.; Martin, G. R.; DesMarteau, D. D. Chem. Commun. 2003,
2334–2335.
(16) Toulgoat, F.; Langlois, B. R.; Medebielle, M.; Sanchez, J.-Y. J. Org.
Chem. 2008, 73, 5613–5616.
(17) Posternak, A. G.; Garlyauskayte, R. Yu.; Polovinko, V. V.; Yagupolskii,
L. M.; Yagupolskii, Yu. L J. Org. Biomol. Chem. 2009, 7, 1642–1645.
been obtained with good yields in the cases of methyl and ethyl
halides (Scheme 1).
We failed to obtain esters of acid 1 or N-alkyl imides 2 with
propyl, butyl, or amyl halides or to detect them by NMR method,
and the acid 1 was isolated in 70-80% yield as the major
4388 J. Org. Chem. Vol. 74, No. 11, 2009

SCHEME 4. Synthesis of N-Methyl Derivatives of N-(Trifluoromethylsulfonylimino)-N′-(nonafluoro-n-butylsulfonylimino)tri-
fluoromethanesulfonic Acid 8
TABLE 1. Reactions of N-Methyl (2a) and N-Ethyl (2b) Deriva-
tives of N-(Trifluoromethylsulfonyl)-[N′-(trifluoromethylsulfonyl)tri-
fluoromethylsulfoximidoyl]imides with Nucleophiles via Scheme 2
Preparation of Silver Salt of Bis(trifluoromethylsulfonylimi-
no)trifluoromethanesulfonic Acid (1a). Silver carbonate (0.36 g,
1.3 mmol) was gradually added to aquatic solution of acid 1 (0.41
g, 1 mmol). The mixture was stirred for 15 h at rt and filtered, and
water was removed in vacuo. The residue was dried for 25 h at 50
°C/0.04 mmHg: Yield 0.43 g (85%); mp 105-108 °C; decomposi-
tion started at 180 °C; 19F NMR (200 MHz, Et2O) δ -79.2 (6F, s,
6F, CF3), -79.35 (3F, s, CF3). Anal. Calcd for C3F9AgN2O5S3: C,
6.94; F, 32.95; N, 5.39; S, 18.49. Found: C, 6.94; F, 32.94; N,
5.42; S, 18.9.
alkylating
agent
isolated
N
nucleophiles
τ (h) T (°C) product yield (%)
1
2
3
4
5
6
7
2a
2a
2b
2b
2a
2a
2a
Ph2S
Ph2S
Ph2S
Ph2S
Ph3PdO
Ph3P
12
24
12
24
15
17
rt
38
rt
38
80
80
rt
3a
3a
3b
3b
4a
5a
6a
(10)a
(97)a 89
(0)a
(95)a 56
(100)a 92
(100)a 89
(97)a 90
Preparation of N-Methyl (2a) and N-Ethyl (2b) Derivatives
of N-(Trifluoromethylsulfonyl)-[N′-(trifluoromethylsulfonylimi-
no)trifluoromethylsulfoximidoyl]imides.
1-CF2CF2H-imidazole 24
a The yield calculated on the basis of 19F and H NMR spectra data.
1
Method A: Methyl or ethyl iodide (0.71 and 0.78 g, 5 mmol)
was gradually added to a solution of silver salt 1a (2 g, 4 mmol)
in 5 mL of CH2Cl2 with effective stirring and protection from
moisture and light. The mixture was stirred for 12 h at room
temperature, and AgI was filtered off. The solvent was removed in
vacuo, and the residue was distilled: yields 1.07 g (65%) (2a) and
1.28 g (76%) (2b).
Method B: SOCl2 (5 g, 42 mmol) was gradually added to the
solution of acid 1 or 8 (0.8 or 1.12 g, 2 mmol) in methanol (1.12
g, 35 mmol) with stirring and protection from moisture. The mixture
was refluxed until hydrogen chloride evolution ceased (0.5 h), and
the product was isolated by distillation: yields 0.63 g (76%) (2a)
and 1.02 g (89%) (9-11).
Preparation of Bis(perfluoroalkylsulfonylimino)trifluorome-
thanesulfonates (3a,b, 4a, 5a, 6a). The mixture of 2a or 2b (0.43
or 0.44 g, 1 mmol) and corresponding nucleophile (1 mmol) was
heated with stirring and then was been reprecipitated from CH2Cl2
by hexane. The temperature, time, and yields of salts are listed in
Table 1.
Preparation of Bis(perfluoroalkylsulfonylimino)trifluorome-
thanesulfonates (3c-h, 6e, 7). The mixture of corresponding alkyl
iodide (1 mmol) and diphenylsulfide or 1-(1,1,2,2,tetrafluoroeth-
yl)imidazole (1 mmol) was gradually added to solution silver salt
of acid 1 (0.52 g, 1 mmol) in CH2Cl2 (6 mL). The mixture was
refluxed, and the product was precipitated from CH2Cl2 by hexane
addition. The temperature, time, and yields of salts are listed in
Table 2.
TABLE 2. Reactions of Alkyl Halides with Nucleophiles in the
Presence of Silver Salt of Bis(trifluoromethylsulfonylimino)-
trifluoromethanesulfonic Acid 1a via Scheme 3
alkylating
agent
isolated
τ (h) T (°C) product yield (%)
N
nuc
1
2
1a + n-PrI Ph2S
1a + n-PrI Ph2S
48
19
rt
38
3c
3c
(0)a
(72)a
45
3d
3d
(3.6)a
(94)a
50
3
4
1a + i-PrBr Ph2S
1a + n-BuI Ph2S
48
17
38
38
3e
(80)a
68
3f
3f
(5)a
0
5
6
7
8
1a + i-BuI Ph2S
1a + t-BuI Ph2S
1a + t-BuI Ph2S
1a + n-AmI Ph2S
24
14
14
19
38
38
140
38
0
0
3g
(85)a
83
3h
6e
(14)a
(91)a
84
9
1a + n-BuI 1-CF2CF2H imidazole 15
rt
rt
10 1a + i-BuI 1-CF2CF2H imidazole 18
7
(91)a
84
a The yield calculated on the basis of 19F and1H NMR spectra data
In conclusion, N-methyl and N-ethyl derivatives of
N-(trifluoromethylsulfonyl)-[N′-(trifluoromethylsulfonyl)trifluo-
romethylsulfoximidoyl]imides 2a,b are formed upon alkyl-
ation of bis(trifluoromethylsulfonylimino)trifluorometh-
anesulfonic acid 1 or its silver salt 1a, and they turned out
to be strong alkylating agents, in spite of the fact that the
alkyl group is attached to the nitrogen atom. Alkylation of
nucleophiles by n-PrI, n-BuI, and n-AmI in the presence of silver
salt 1a runs more selectively than probably arises from the
formation of transitional complex with a voluminous anion.
Acknowledgment. We thank Dr. T. M. Sokolenko (Institute
of Organic Chemistry, National Academy of Sciences of
Ukraine) for amiable supply of N-tetrafluoroethylimidazole, and
V.V. Polovinko (Enamine Ltd., Kiev) for recording 13C NMR
spectra.
Supporting Information Available: Compound character-
1
ization, analytical data, and H, 13C, and 19F NMR spectra of
Experimental Section
all new compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
All reactions were carried out in oven-dried glassware under
nitrogen atmosphere, unless otherwise noted. All solvents and
reagents were distilled immediately before use.
JO900195K
J. Org. Chem. Vol. 74, No. 11, 2009 4389