Study of unusually high rotational barriers about S-N bonds in nonafluorobutane-1-sulfonamides: The electronic nature of the torsional effect

Article abstract of DOI:10.1002/hlca.200290006

Slow rotation about the S-N bond in N,N-disubstituted nonafluorobutane-1-sulfonamides 1 can easily be detected by NMR measurements at room temperature. This effect causes magnetic nonequivalence of otherwise identical geminal substituents in symmetrical s

Full text of DOI:10.1002/hlca.200290006

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Helvetica Chimica Acta Vol. 85 (2002)
Study of Unusually High Rotational Barriers about SÀN Bonds in
Nonafluorobutane-1-sulfonamides: The Electronic Nature of the Torsional
Effect
by Ilya M. Lyapkalo*, Hans-Ulrich Reissig, Andreas Sch‰fer, and Armin Wagner
Freie Universit‰t Berlin, Institut f¸r Chemie, Takustr. 3, D-14195 Berlin
Dedicated to Professor Dieter Seebach on the occasion of his 65th birthday
Slow rotation about the SÀN bond in N,N-disubstituted nonafluorobutane-1-sulfonamides 1 can easily be
detected by NMR measurements at room temperature. This effect causes magnetic nonequivalence of otherwise
identical geminal substituents in symmetrical staggered ground-state conformation A. The torsional barriers
determined (62 71 kJ ¥ molÀ1) proved to be the highest ever observed for sulfonamide moieties. They are
comparable to the values routinely measured for carboxylic acid amides or carbamates. The restricted rotation is
*
interpreted as result (nNÀdS)-p and of nNÀsS;C interactions, which develop substantial S,N double-bond
character in sulfonamides 1. The S,N binding interaction is increased by the highly electron-withdrawing effect
of the perfluorobutyl group. The anticipated symmetry of the ground-state conformation A and the considerable
shortening of the SÀN bond (1.59 ä) compared to the mean value in sulfonamides (1.63 ä) are confirmed by
single-crystal X-ray study of N,N-dibenzylnonafluorobutane-1-sulfonamide (1c).
Restricted rotation [1] is a well-known phenomenon for compounds I with single
bonds YÀA that adopt considerable double-bond character due to the binding
interactions of the electron-withdrawing p-system XˆY with the lone pair at A, as
expressed by the dipolar mesomeric formula II (Scheme 1). This has been described for
Y and A elements of the second row of the periodic table. Not surprisingly, the highest
values of barriers to rotation are normally observed for compounds containing an
amino group (A ˆ N), due to the very strong p-donating character of the N-atom.
Hindered rotation of this type is well-documented, and the barriers to rotation have
been measured for many classes of compounds [1][2], including esters, nitrites,
enamines, hydrazones, thio- and selenoamides, nitrosoamines, and triazenes [3].
Undoubtedly, carbamates and amides proved to be the most frequently occurring
substances exhibiting atropisomerism about their CÀN bonds. Reviews on dynamic
effects in amides and related compounds [2][4] reflect the fundamental character and
significance of this topic. Elements of the third (e.g., Si, P, S) and higher periods exhibit
much lower tendencies to p-bond. As a consequence, the barriers to rotation in the
Scheme 1

Helvetica Chimica Acta Vol. 85 (2002)
4207
respective acid amides, e.g., in sulfonamides1) are expected to be much lower than
those of carboxylic acid amides. In this publication, we describe for the first time
representatives of sulfonamides2) with surprisingly high barriers to rotation about the
SÀN bonds, similar to those reported for carboxylic acid amides [1][2] or carbamates
[7][8].
Because of our interest in the synthesis and application of alkenyl nonafluoro-
(i.e., perfluoro-) butane-1-sulfonates (nonaflates) in Pd-catalyzed C,C cross-coup-
ling reactions [9], we prepared several alkenyl nonaflates from ketones with a small
excess of lithium diisopropylamine as a base to ensure complete deproto-
nation. The subsequent treatment of the mixtures with nonafluorobutane-1-sulfonyl
fluoride (NfF) resulted in formation of the desired alkenyl nonaflates along with a side
product, which was identified by MS, IR, and microanalysis data as N,N-diisopro-
pylnonafluorobutane-1-sulfonamide (1a). The structure of 1a was further confirmed
by independent synthesis from lithium diisopropylamine and NfF, as shown in
Scheme 2.
Scheme 2. Synthesis of N,N-Disubstituted Nonafluorobutane-1-sulfonamides 1
1H- and 13C-NMR spectra of N,N-diisopropylnonafluorobutane-1-sulfonamide (1a)
show two magnetically nonequivalent Me groups at ambient temperature (Fig. 1). At
elevated temperature, the signals collapse to one. However, the two i-Pr groups exhibit
a single CH-signal, which remains almost intact over this temperature interval. This
1
)
)
The 1H-NMR spectra of PhSO2NEt2, MeSO2NEt2, (Et2N)2SO2 remained unchanged as a function of
temperature down to À 908 [5], hence the barriers to rotation are not higher than 35 kJ ¥ molÀ1
.
2
To the best of our knowledge, chlorosulfonyl amides ClSO2NR2 (R ˆ Et, i-PrCH2, PhCH2) are the only
representatives of sulfonamides whose restricted amide rotation has been described at low temperature
[5], and the barriers have been found to be in the range of 46 48 kJ ¥ molÀ1, considerably lower than the
respective values for nonafluorobutane-1-sulfonamides reported herein. A sulfonamide torsional barrier
of 43.5 Æ 0.5 kJ ¥ molÀ1 has also been reported for N,N'-bis(toluene-4-sulfonyl)-5,6,7,12,13,14-hexahydro-
6,13-diazadibenzo[a,f]cyclodecene. However, the authors suggested steric hindrance at the transition state
to be the most-important contribution to the rotation barrier [6].

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Helvetica Chimica Acta Vol. 85 (2002)
observation could be interpreted as hindered rotation about the SÀN bond3), the
ground-state conformation A being as depicted in Fig. 1. This conformation is generally
favored for sulfonamides [5] as evidenced from extensive X-ray data in the literature
(e.g., [6][11]).
Fig. 1. Dynamic 1H- and 13C-NMR spectra of N,N-diisopropylnonafluorobutane-1-sulfonamide (1a). High-
temperature process, corresponding to slow rotation about SÀN bond; ground-state staggered conformation A.
At low temperature (down to À 938), we observed a second dynamic process that
resulted in the appearance of six different signals (four Me and two CH) corresponding
to two i-Pr groups in 1H- and 13C-NMR and splitting of all CF2 groups to AB systems in
19F-NMR (Fig. 2). The free energy (DG) of activation was 40 kJ ¥ molÀ1. This process
can be attributed to hindered rotation of i-Pr groups about CHÀN bonds. Torsional
effects in various geminal diisopropyl systems have been studied in detail by
experiment and theory [12].
We decided to study hindered rotation about the SÀN bond in N,N-disubstituted
perfluorobutane-1-sulfonamides 1 in more detail to verify the generality of this process
and to determine the energy parameters of the torsional barriers. By analogy to
synthesis of 1a, 1b, and 1c were prepared from the corresponding amines via lithiation
followed by sulfonylation with NfF. Unsymmetrical sulfonamide 1d was synthesized in
1
two steps starting from benzylamine (Scheme 2). As expected, H-NMR spectra of
compounds 1b d at room temperature show nonequivalence of diastereotopic CH2
protons (AB system) with the typical geminal coupling values JAB (Table). The barriers
to rotation about the SÀN bond for 1a d determined by total line shape analyses of the
NMR signals [13] are collected in the Table.
3
)
Alternatively, the observed dynamic effect could result from slow inversion of the pyramidal N-atom in 1a,
typically known for amines possessing electronegative substituents (RO, F, Cl) at N and particularly for
aziridines. However, we can safely rule out the slow inversion effect in sulfonamides because sulfonyl
substituents are known to flatten pyramidal N-atoms, resulting in a decrease of the inversion barrier in N-
sulfonylaziridines [10]; furthermore, single-crystal X-ray data ([6][11], Fig. 3) clearly indicate an almost
planar trigonal N-atom in sulfonamides.

Helvetica Chimica Acta Vol. 85 (2002)
4209
Fig. 2. Low-temperature process, most likely corresponding to slow rotation of the sterically interacting i-Pr
groups in 1a
Table. Geminal-Coupling-Constant Values and Barriers to Rotation about SÀN Bond for Nonafluorobutane-1-
sulfonamides 1a
JAB [Hz]a)
d
ˆ
Sulfonamide
DG298 [kJ ¥ molÀ1]a)
1a
70.0 Æ 2.3
70.5 Æ 2.0 (in C6D6)
42.4 Æ 3.6b)
64.4 Æ 2.8
1b
1c
1d
14.6
15.2
62.4 Æ 3.6
14.9 (PhCH2)
18.5 (CH2CO2Et)
12.0 (MeCH2O)
64.4 Æ 6.6
a) In CDCl3 (500 MHz) unless otherwise noted. b) Presumably, hindered isopropyl rotation (see text).
Evidently, the values obtained are comparable to those routinely determined for
carboxylic acid amides (e.g., MeC(O)NMe2 72 kJ ¥ molÀ1 4); MeC(O)N(i-Pr)2 [1]
68 kJ ¥ molÀ1; PhCH2OC(O)NMe2 [8] 66 kJ ¥ molÀ1). These amides are known to
possess planar or almost planar structures with the CÀN bond adopting a considerable
double-bond character. We expected a similar effect for the sulfonamides 1 and,
therefore, were interested to obtain exact structural parameters by single-crystal X-ray
analysis of N,N-dibenzylnonafluorobutane-1-sulfonamide (1c) (Fig. 3).
The (PhÀCH2À)2NÀS(ˆO)2ÀC(1) fragment adopts an almost perfectly sym-
metrical staggered conformation with a trigonal planar N-atom, as was suggested for 1a
(see Fig. 1). Phenyl rings are arranged in two almost parallel planes in the direction
opposite to the perfluorinated butyl chain. This conformation creates minimum
crowding around the SÀN bond, which suggests that electronic and not steric effects
4
)
This value was determined in benzene; for the influence of the medium on the barrier to rotation in
amides, see [14].

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Helvetica Chimica Acta Vol. 85 (2002)
Fig. 3. ORTEP View of the crystal structure of N,N-dibenzylnonafluorobutane-1-sulfonamide (1c) showing the
arrangement of substituents around the SÀN bond. For details, see text and Exper. Part.
are responsible for the observed restricted rotation5). Indeed, the SÀN bond
(1.589(2) ä)6) seems to exhibit appreciable double-bond character: it is considerably
shorter than the mean value for sulfonamides (1.63(2) ä)7).
The comparison of the influence of the electron-withdrawing perfluorinated
substituent on the barrier to rotation in sulfonamides vs. carboxylic acid amides is most
interesting. While formal exchange of the Ph or Me substituent at the S-atom of
sulfonamides by perfluorobutyl results in an increase of the barrier to rotation by at
least 30 kJ ¥ molÀ1 1), the introduction of a CF3 substituent instead of Me has almost no
effect on the free energy of activation in carboxylic acid amides (e.g., CF3C(O)NMe2
76 kJ ¥ molÀ1; CF3C(O)N(i-Pr)2 68 kJ ¥ molÀ1, cf. the values for the corresponding
acetamides given above)8). The values for trifluoroacetamides apparently are the
result of two opposing effects. On the one hand, the highly electron-withdrawing effect
of the CF3 group favors the dipolar resonance formula with CˆN, in which the positive
charge is maximally transferred from the carbonyl C-atom to the N-atom. On the other
hand, steric demands destabilize the planar dipolar ground state, in which steric
repulsion between the relatively bulky CF3 and cis-alkyl group is unavoidable8)9). This
implies that the opposing electronic and steric effects result in little or no apparent
influence on the barrier to rotation in this particular case10).
5
)
Certainly, we realize that a conformation in solution may considerably differ from that in the crystal.
Nevertheless, we regard the observed effect as due to a p-binding interaction because no torsional effects
could be deduced from 1H-NMR spectra of sterically demanding compounds such as 2-methyl-2-propane-
[15], 2,4,6-trimethyl-1-benzene- [16], or even 2,4,6-triisopropyl-1-benzenesulfonamides [17]. The steric
demand of i-Pr substituents may give a small contribution to the slightly higher free activation energy in
the sulfonamide 1a compared to 1b d.
6
7
)
)
It is slightly longer than the genuine SˆN of arylsulfonimidoyl amides (1.52 1.55 ä) [18].
The mean value has been obtained from the respective search in the Cambridge Structural Database which
gave 272 SÀN bond lengths for N,N-disubstituted sulfonamides.
8
)
In N,N-disubstituted amides, the barrier to rotation decreases upon increase of steric demand of the
carbonyl substituent [1].
9
)
)
For a detailed discussion of effects in N,N-dialkyl trifluoroacetamides, see [19].
Switching to the acetyl substituent, which is sterically less-demanding than CF3, results in substantial
increase of the barrier to rotation in MeC(O)C(O)NMe2 (86.1 kJ ¥ molÀ1) [20].
10

Helvetica Chimica Acta Vol. 85 (2002)
4211
Unlike carboxylic acid amides, both the steric demands of substituents at the N-
atom and the electron-withdrawing ability of the substituent at the S-atom should
stabilize the symmetrically staggered ground-state conformation A (Fig. 1), in which a
desirable (nNÀdS)-p overlap is most efficiently attained [5]. The dynamic NMR effects
for N,N-diisopropyl sulfonamides with other electronegative substituents at the S-atom
were expected to be similar to those described herein for sulfonamides 1. Surprisingly,
we could not deduce hindered rotation about SÀN bonds from literature NMR data of
several candidates [21], e.g., N,N-diisopropyl trichloromethanesulfonamide, N,N-
diisopropyl 4,6-dimethylpyrimidine-2-sulfonamide, or N,N-diisopropylnitromethane-
sulfonamide. Furthermore, none of numerous N,N-dialkyl trifluoromethanesulfon-
amides have been found to exhibit hindered S,N rotation at ambient temperature [22].
Notably, the 1H-NMR spectra of N-perchloryl-N,N-dialkylamines reported in the
literature [23] indicate a broadening or a multiplicity of NCH2 groups that may result
from the torsional effect related to that found for sulfonamides 1.
We assume that the SÀN double-bond character is a result of (nNÀdS)-p overlap11)
*
along with considerable contribution of the nNÀsS;C binding interaction, which
accounts for the observed exceptionally high rotational barriers in perfluorobutane-1-
sulfonamides. This negative hyperconjugative effect is well-known to assist the
stabilization of S- and Se-substituted carbanions, the effect being subject to stereo-
electronic control [24]. Furthermore, it is evident that the symmetrically staggered
conformation A (see Fig. 1) is optimal for this kind of interaction, since the lone pair at
the N-atom is disposed in the same plane as the SÀC bond. Finally, the energy of the
*
sS;C orbital is strongly reduced by the highly electron-withdrawing perfluorinated
substituent in sulfonamides 1a d, thereby facilitating the nNÀsS;C overlap12
)
13). We
*
believe that appropriate calculations will allow estimation of the electronic contribu-
tion to the observed slow rotation.
The notable difference in spectral appearances between the sulfonamides 1a d and
trifluoromethanesulfonamides [22] remains to be rationalized. Since the electronic
effects described above would also operate in the trifluoromethyl derivative, the
difference might be a consequence of the stronger electron-withdrawing effect of the
perfluorobutyl substituent compared to trifluoromethyl. This results in better leaving-
group ability of a nonaflate compared to a triflate [26], although the difference is
usually moderate to low.
*
*
Alternatively, an extended negative hyperconjugative effect with nNÀsS;CÀsS;CꢀF†
overlap (Fig. 4) could account for the observed differences between the perfluorinated
substituents14). As evidenced from the X-ray structure of 1c (see Fig. 3), the dihedral
11
)
)
A stabilization of the negative charge of a-deprotonated sulfones, which are isoelectronic to sulfonamides,
is achieved by overlap with d-orbitals of the SO2 S-atom [24].
12
13
14
Obviously, the geometry of the planar ground-state conformation of carboxylic acid amides, in which the
lone pair of the N-atom and the CÀC bond adjacent to the carbonyl group are arranged in the
*
perpendicular planes, a priori excludes simultaneous (nNÀpCˆO)-p and nNÀsC;C overlap.
)
)
A remarkably fast intermolecular halogen exchange in N,N-dialkyl halogeno-sulfinylamides could be
*
rationalized in terms of strong nNÀsS;X interaction leading to the equilibrium by dissociation:
‡
R2NS(O)X > [R2NˆSˆO] XÀ [25].
To our surprise, no slow rotation about the SÀN bond could be concluded from the NMR data available of
a few other poly- and perfluorinated sulfonamides described in the literature [27], e.g., Cl(CF2)2O(CF2)2-
SO2N(CH2Ph)2 or N,N-diethylperfluorooctane-1-sulfonamide.

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Helvetica Chimica Acta Vol. 85 (2002)
*
*
Fig. 4. Schematic representation of the extended nN ÀsS;C ÀsC;CꢀF† overlap in nonafluorobutane-1-sulfonamides 1
angle SÀC(1)ÀC(2)ÀC(3) has a value of 1618, which is rather close to the optimal 1808
for this kind of interaction15). On the other hand, the effect should be rather subtle
since it does not affect CÀC bond lengths in the perfluorinated butyl chain of 1c.
Conclusion. We described herein unusually slow rotation about the SÀN bond in
sulfonamides, easily detectable at ambient temperature by NMR. The determined
barriers to rotation in nonafluorobutane-1-sulfonamides 1 proved to be comparable to
those well-known for carboxylic acid amides. The effect is rationalized as a result of the
appreciable double-bond character adopted by the SÀN bond due to (nNÀdS)-p and
*
nCÀsS;C interactions that are amplified by the highly electron-withdrawing nature of
the perfluorobutyl substituent. We did not try to determine the specific contribution of
either of the electronic interactions to the observed atropisomerism and defer this
problem to calculations remaining to be performed. Since sulfonamides are isoelec-
tronic to a-sulfonyl carbanions, we believe that the dynamic effects described herein
may improve insight into the origin of negative-charge delocalization in a-sulfur
carbanions [24][29] and into the nature of p-binding of third- and higher-period
elements.
Generous support by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie and the
Alexander von Humboldt Foundation (research fellowship for I. M. L.) is most gratefully acknowledged. We
thank Schering AG, Berlin for general support, Bayer AG, Leverkusen for generous donations of nona-
fluorobutane-1-sulfonyl fluoride, Mr. B. F¸ger for the synthesis of the compound 1b and Dr. R. Zimmer for help
during preparation of this manuscript.
Experimental Part
1. General. NMR Spectra: Bruker WH-270 at 208. Dynamic NMR measurements Bruker AMX-500 under
cooling and Jeol Eclipse-500 under heating conditions; chemical shifts (d) in ppm down-field from Me4Si (d ˆ 0)
as an internal standard; coupling constant J in Hz. An assignment of 19F signals of the CF3(CF2)3 group is given
according to [30] in ppm up-field from CFCl3 (d ˆ 0) as an internal standard; 13C-NMR signals of the CF3(CF2)3
group are not given since, due to strong splitting by coupling with the 19F nuclei, unambiguous assignment is not
possible. MS: Varian MAT-711; m/z (%). IR: Nicolet 5 SXC; n in cmÀ1. TLC: Merck 60 F254 silica gel plates.
Column chromatography (CC): silica gel 60 (40 63 mm, Fluka). Lithiation and −nonaflation× reactions were
carried out under Ar in heat-gun dried reaction flasks by adding the components via syringe. Solvents for
reactions were dried by standard procedures. Nonafluorobutane-1-sulfonyl fluoride was obtained from Bayer
AG ; it can also be purchased from Aldrich. Commercially available 2.5m BuLi (Aldrich) was titrated by the
[1,10]phenanthroline method [31].
15
)
A perfectly staggered conformation of perfluorinated chains in sodium bis(perfluorobutane-1-sulfonyl)-
imide with 1758 SÀC(1)ÀC(2)ÀC(3) dihedral angle detected by single-crystal X-ray analysis might gain in
stabilization from such an extended hyperconjugative effect [28].

Helvetica Chimica Acta Vol. 85 (2002)
4213
2. Synthesis of Perfluorobutane-1-sulfonamides 1a c. General Procedure (GP). A soln. (2.45m) of BuLi in
hexane (5.6 ml, 13.7 mmol) was added to a soln. of R2NH (15.0 mmol) in THF (40 ml) at À 788. The cooling
bath was removed, and the resulting mixture was allowed to warm to r.t., before recooling to À 788. To the thus-
generated soln. of R2NLi (13.7 mmol), neat NfF (6.06 g, 20.0 mmol) was added via syringe at À 908. The
mixture was gradually warmed to 188 and stirred overnight. After aq. workup (150 ml hexane, 60 ml sat. aq.
NaHCO3, and 60 g ice), the aq. phase was extracted with hexane (3 Â 30 ml), and the combined org. phases
were dried (Na2SO4). Filtration, removal of volatile components in vacuo followed by distillation or CC gave
the expected pure sulfonamides 1a c.
N,N-Diisopropylperfluorobutane-1-sulfonamide (1a). According to the GP, diisopropylamine (1.52 g,
15.0 mmol) furnished sulfonamide 1a after bulb-to-bulb distillation at 1058 (1 mbar) as a pale yellowish liquid
(4.29 g, 75% yield), essentially pure according to 1H- and 13C-NMR. For analytical purposes, a sample of 1a was
further purified by CC (hexane) and isolated as a colorless microcrystalline material after re-condensation in
high vacuum (258/ < 5 ¥ 10À4 mbar) in a cold (À 308) Schlenk flask. It melts below r.t. to give a clear colorless
liquid. IR (film): 2985 2885 (CÀH), 1380 (SO2), 1240 (CÀF), 1205 (CÀF), 1140 (CÀF). 1H-NMR (270 MHz,
CDCl3): 1.37 (br. d, 3J ˆ 6.8, Me2CHN); 1.38 (d, 3J ˆ 6.8, Me2CHN); 3.93 (hept., 3J ˆ 6.8, 2 Me2CH). 13C-NMR
(67.5 MHz, CDCl3): 22.1 (q, Me); 22.6 (q, Me); 51.5 (d, CH). 19F-NMR (470.6 MHz, CDCl3, 348): À 126.4
(t*, J ˆ 13.9, CF2(3)); À 121.6 (mc, CF2(2)); À 112.8 (br. t, J ˆ 13.8, CF2(1)); À 81.3 (tt, J1 ˆ 10.0, CF3); *
indicates further splitting due to multiple 19F,19F couplings. 19F-NMR (470.6 MHz, 12CD2Cl2, À 938): À 127.9 (br.
d, 2J ˆ 292, FÀC(3)); À 126.2 (br. d, 2J ˆ 292, FÀC(3)); À 122.6 (br. d, 2J ˆ 303, FÀC(2)); À 121.9 (br. d, 2J ˆ
303, FÀC(2)); À 115.2 (br. d, 2J ˆ 261, FÀC(2)); À 113.3 (br. d, 2J ˆ 261, FÀC(2)); À 81.0 (br. s, CF3). MS (EI,
‡
‡
‡
‡
80 eV): 383 (1, M ), 368 (10, [M À Me] ), 326 (50, [M À i-PrN] ), 262 (10, [M À i-PrN À SO2] ), 242 (4, [M À i-
‡
‡
‡
‡
PrN À SO2 À HF] ), 219 (9, [CF3(CF2)3] ), 164(10, [ M À CF3(CF2)3] ), 131 (3, [CF2ˆCFCF2] ), 122 (15,
‡
‡
[M À CF3(CF2)3 À CH3CHˆCH2]), 69 (13, CF3 ), 43 (100, Me2CH ). Anal. calc. for C10H14F9NO2S (383.3): C
31.34, H 3.68, N 3.65, S 8.37; found: C 31.37, H 3.59, N 3.58, S 8.16.
N,N-Diethylperfluorobutane-1-sulfonamide (1b). According to the GP, diethylamine (1.10 g, 15.0 mmol)
furnished pure sulfonamide 1b as a yellowish liquid after fractional distillation (3.62 g, 68% yield). B.p. 918
(8 mbar). IR (film): 2985 2905 (CÀH), 1390 (SO2), 1240 (CÀF), 1215 (CÀF), 1140 (SO2). 1H-NMR
(500 MHz, CDCl3, À 108): 1.28 (t, 3J ˆ 7.2, 2 Me); 3.47 (dq, 2J ˆ 14.6, 3J ˆ 7.2, 2 CHAHB); 3.59 (dq, 2J ˆ 14.6, 3J ˆ
7.2, 2 CHAHB). 13C-NMR (67.5 MHz, CDCl3): 14.0 (q, Me), 42.9 (t, CH2). 19F-NMR (470.6 MHz, CDCl3, 208):
À 126.4( t*, J ˆ 14.1, CF2(3)); À 121.8 (mc, CF2(2)); À 113.4( t*, J ˆ 14.1, CF2(1)); À 81.2 (tt, J ˆ 10.1, 2.4,
‡
CF3); * indicates further splitting due to multiple 19F,19F couplings. MS (EI, 80 eV): 355 (19, M ), 340 (90, [M À
‡
‡
‡
‡
Me] ), 312 (5, [M À NEt] ), 248 (24, [M À NEt À SO2] ), 228 (3, [M À NEt À SO2 À HF] ), 219 (22,
‡
‡
‡
‡
[CF3(CF2)3] ), 169 (1, [CF3(CF2)2] ), 136 (100, [M À CF3(CF2)3] ), 131 (19, [CF2ˆCFCF2] ), 120 (21,
‡
‡
‡
‡
‡
[Et2NSˆO] ), 119 (5, C2F5 ), 108 (32, [M À CF3(CF2)3 À CH2ˆCH2] ), 100 (5, C2F4 ), 92 (9, [EtNHSˆO] ),
‡
‡
‡
‡
‡
80 (10, [H2NSO2] ), 72 (15, C4H10N ), 71 (9, C4H9N ), 70 (5, [MeCHˆNˆCHMe] ), 69 (75, CF3 ), 64(10,
‡
‡
2
‡
‡
‡
‡
[H2NSO] or SO ), 57 (73, [EtNˆCH2] ), 56 (67, [MeCHˆNˆCH2] ), 50 (2, CF ), 44 (87, CH6N ), 42 (68,
2
2
‡
‡
‡
‡
‡
C2H4N ), 29 (69, C2H5 ), 28 (34, C2H4 ), 27 (16, C2H3 ). HR-MS: 355.02911 (M , C8H10F9NO2S; calc.
‡
355.028855), 136.04621 (Et2NSO2 , C4H10NO2S; calc. 136.043225).
N,N-Dibenzylperfluoro-1-butanesulfonamide (1c). According to the GP, dibenzylamine (2.96 g,
15.0 mmol) furnished pure sulfonamide 1c after CC (gradient elution: hexane ! hexane/Et2O 30 :1 ! hex-
ane/Et2O 20 :1 ! hexane/Et2O 8 :1) as colorless crystals (5.97 g, 83% yield). M.p. 82 848. IR (KBr): 3090
1
3035 (HÀCˆ), 1495 1450 (CˆC), 1380 (SO2), 1250 (CÀF), 1215 (CÀF), 1135 (SO2). H-NMR (500 MHz,
CDCl3, 108): 4.39 (d, 2J ˆ 15.2, 2 CHAHB); 4.55 (d, 2J ˆ 15.2, 2 CHAHB); 7.17 7.20 (m, 4arom. H), 7.32 7.36
(m, 6 arom. H). 13C-NMR (125.8 MHz, CDCl3, 108): 51.3 (t, CH2); 128.5 (d, Cp); 128.7, 128.8 (br. d, d, Co, Cm);
133.5 (s, Cipso). 19F-NMR (470.6 MHz, CDCl3, 208): À 126.2 (t*, J ˆ 13.9, CF2(3)); À 121.4( mc, CF2(2)); À
111.8 (t*, J ˆ 13.9, CF2(2)); À 81.3 (tt, J ˆ 9.9, 2.4, CF3); * indicates further splitting due to multiple 19F,19F
‡
‡
‡
‡
couplings. MS (EI, 80 eV): 480 (3, [M ‡ 1] ), 479 (13, M ), 388 (4, [M À PhCH2] ), 260 (1, [M À CF3(CF2)3] ),
‡
‡
‡
219 (1, [CF3(CF2)3] ), 196 (6, [M À CF3(CF2)3SO2] ), 195 (6, [PhCH2NˆCHPh] ), 194(6,
‡
‡
‡
‡
[PhCHˆNˆCHPh] ), 182 (1, [M À CF3(CF2)3SO2 À CH2] ), 167 (1, Ph2CH ), 131 (1, [CF2ˆCFCF2] ), 118
‡
‡
‡
‡
‡
(4, [CH2ˆNˆCHPh] ), 104(3, PhC ꢁNH ), 92 (85, [PhMe] ), 91 (100, [PhCH2] ), 69 (4, CF3 ). Anal. calc. for
C18H14F9NO2S (479.4): C 45.10, H 2.94, N 2.92; found C 45.14, H 2.81, N 2.78.
N-Benzylperfluorobutane-1-sulfonamide. Neat NfF (6.65 g, 22 mmol) was carefully added dropwise to a
vigorously stirred soln. of benzylamine (2.36 g, 22 mmol) and Et3N (4.76 g, 47 mmol) in CH2Cl2 (15 ml) at 08.
After 1 h, the temp. was allowed to rise to 208, and the mixture was stirred for further 96 h. It was then subjected
to aq. workup (150 ml Et2O, 100 ml H2O, 50 g ice, and 4ml 85% H 3PO4); the aq. phase was extracted with Et2O
(3 Â 20 ml), the combined org. phase was washed successively with H2O (70 ml) and brine (50 ml) and dried

4214
Helvetica Chimica Acta Vol. 85 (2002)
(MgSO4). Filtration, removal of the volatile components in vacuum, and thorough drying of the residue in high
vacuum at ambient temperature (0.005 mbar) for 12 h gave pure N-benzylperfluoro-1-butanesulfonamide
(7.62 g, 89% yield) as slightly yellowish crystals, which was used in the next step without further purification.
M.p. 57 608. IR (KBr): 3310 (NÀH), 3040 (HÀCˆ), 1495 1440 (CˆC), 1360 (SO2), 1235 (CÀF), 1210
(CÀF), 1140 (SO2). 1H-NMR (270 MHz, CDCl3): 4.47 (br. s, CH2); 5.30 (br. s, NH); 7.30 7.45 (m, 5 arom. H).
13C-NMR (67.5 MHz, CDCl3): 48.6 (t, CH2), 127.9, 129.1 (2d, Co, Cm), 128.7 (d, Cp), 135.1 (s, Cipso). MS (EI,
‡
‡
‡
‡
80 eV): 390 (2, [M ‡ 1] ), 389 (12, M ), 219 (<1, [CF3(CF2)3] ), 170 (6, [M À CF3(CF2)3] ), 131 (2,
‡
‡
‡
‡
‡
‡
[CF2ˆCFCF2] ), 119 (2, C2F5 ), 107 (3, C7H9N ), 106 (36, C7H8N ), 105 (25, C7H7N ), 104(16, PhC ꢁNH ),
‡
‡
‡
‡
‡
‡
‡
103 (1, PhCN ), 100 (2, C2F4 ), 92 (8, PhMe ), 91 (100, PhCH2 ), 79 (12, C6H7 , 78 (6, C6H6 ), 77 ( 12, C6H5 ), 69
‡
‡
‡
‡
‡
‡
‡
‡
(15, CF3 ), 65 (5, HSO2 ), 51 (8, HCF2 ), 50 (2, CF2 ), 39 (3, HC2N or F2 ), 28 (20, HCꢁNH ), 27 (2, HCN ).
Anal. calc. for C11H8F9NO2S (389.2): C 33.94, H 2.07, N 3.60; found C 33.96, H 1.85, N 3.67.
Ethyl N-Benzyl-N-[(perfluorobut-1-yl)sulfonyl]aminoacetate (1d). Na Metal (0.219 g, 9.53 mmol) was
dissolved in abs. EtOH (10 ml), and the resulting clear, colorless soln. was cooled to 08. To the prepared EtONa
soln., N-benzylperfluorobutane-1-sulfonamide (3.71 g, 9.52 mmol) was added in one lot at 08, and the mixture
was gradually warmed to ambient temp. for 1 h with stirring. After all volatile components had been removed in
vacuo, toluene was added to the residue, and the resulting suspension was vigorously stirred for 10 15 min
followed by removal of toluene in vacuo and drying of the resulting Na salt at ambient temp. (0.005 mbar) for
2 h. The prepared sodium N-benzylperfluorobutane-1-sulfonamide (3.03 g, 7.37 mmol) was dissolved in DMF
(7 ml), and neat ethyl 2-bromoacetate (1.35 g, 8.10 mmol) was added dropwise at 08. After 2 h, the temp. was
allowed to rise to 208, and the mixture was stirred for a further 17 h. It was then subjected to aq. workup (100 ml
hexane and 100 ml H2O), the aq. phase was extracted with hexane (20 ml), and the combined org. phases were
washed successively with H2O (50 ml) and brine (30 ml) and dried (Na2SO4). Filtration, removal of volatile
components in vacuo followed by CC of the residue (gradient elution: hexane ! hexane/Et2O 20 :1) furnished
product 1d (3.43 g, 97% yield) as a clear, colorless oil. IR (film): 3090 2880 (HÀCˆ, HÀCÀ), 1755 (CˆO),
1495 1460 (CˆC), 1395 (SO2), 1240 (CÀF), 1215 (CÀF), 1140 (SO2). 1H-NMR (270 MHz, C6D6): 0.75
(t, Me); 3.47 (br. d, 2J ˆ 18.3, CHAHBCO2Et); 3.71 (mc, MeCH2O); 3.89 (br. d, 2J ˆ 18.2, CHAHBCO2Et); 4.34
(br. d, 2J ˆ 14.6, CHAHBPh); 4.80 (br. d, 2J ˆ 14.6, CHAHBPh); 6.96 7.05 (m, 5 arom. H). 13C-NMR (67.5 MHz,
CDCl3): 13.9 (q, Me); 4 7.1 (t, CH2CO2Et); 53.0 (t, CH2Ph); 61.8 (t, MeCH2O); 128.9 (d, Cp); 129.0, 129.1 (2d,
‡
‡
Co, Cm); 133.1 (s, Cipso); 167.3 (s, CˆO). MS (EI, 80 eV): 474 (<1, [M À H] ), 430 (<1, [M À OEt] ), 403 (1,
‡
‡
‡
‡
[M À C3H4O2] ), 402 (4, [M À CO2Et] ), 388 (3, [M À CH2CO2Et] ), 228 (2, [M À CF3(CF2)3 À C2H4] ), 219
‡
‡
‡
(1, [CF3(CF2)3] ), 192 (89, [M À CF3(CF2)3SO2] ), 164(3, [ M À CF3(CF2)3SO2 À C2H4] ), 131 (2,
‡
‡
‡
‡
‡
[CF2ˆCFCF2] ), 119 (6, [CH2ˆNCH2Ph] or C2F5 ), 118 (35, [CH2ˆNˆCHPh] ), 107 (1, C7H9N ), 106 (2,
‡
‡
‡
‡
‡
‡
‡
C7H8N ), 105 (2, C7H7N ), 104(2, PhC ꢁNH ), 100 (2, C2F4 ), 92 (22, PhMe ), 91 (100, PhCH2 ), 77 (2, C6H5 ),
‡
‡
‡
‡
‡
‡
‡
69 (11, CF3 ), 65 (14, HSO2 ), 64(2, [H 2NSO] or SO2 ), 63 (2, HNSO ), 62 (1, NSO ), 61 (2, C2H5O2 ), 60 (3,
‡
‡
‡
‡
‡
‡
‡
‡
C2H4O2 ), 59 (2, C2H3O2 ), 51 (3, HCF2 ), 50 (1, CF2 ), 39 (4, HC2N or F2 ), 31 (2, CH3O ), 29 (16, C2H5 ), 28 (4,
C2H4 or HCꢁNH ), 27 (5, C2H3 or HCN ). Anal. calc. for C15H14F9NO4S (475.3): C 37.90, H 2.97, N 2.95;
‡
‡
‡
‡
found C 37.83, H 2.76, N 2.97.
X-Ray Crystal-Structure Determination of 1c (see Fig. 3). A colorless needle of size 0.18 Â 0.22 Â 0.75 mm
was grown from CHCl3 and measured on a Bruker Smart 1000 CCD diffractometer with MoKa (l ˆ 0.71073 ä).
The structure was solved by direct methods by means of SHELXS86 [32]. Non-H-atoms were refined
anisotropically with SHELXL97 [33]; H-atoms were calculated at idealized positions and refined with isotropic
displacement parameters: C18H14F9NO2S, Mr 479.37, a ˆ 6.1579(7) ä, b ˆ 20.729(2) ä, c ˆ 30.716(4) ä, b ˆ
94.471(2)8, monoclinic, P21/n, Z ˆ 8, m ˆ 0.265 mmÀ1, F(000) ˆ 1936, 1calc. ˆ 1.629 g ¥ cmÀ3, Tˆ 133(2) K, w scans,
scan width 0.38, 2.68 < 2q < 58.08. The measurement was monitored with SMART [34], integration performed
with SAINT [34] and absorption corrected empirically with SADABS [34] ( Tmin ˆ 0.78, Tmax ˆ 1.00), 34895
measured reflections, 9552 unique, 7483 observed reflections with j Fo j> 4s(Fo), 581 parameters, final R ˆ
4.40%, wR2 ˆ 15.54%, goodness-of-fit 1.041, D1 (max, min) in final Fourier synthesis 0.88 e äÀ3, À 0.48 e äÀ3
pointing to a small portion of disorder in the perfluorobutyl chain of one of two independent molecules that
could not be resolved. Crystallographic data (excluding structure factors) for the structure reported in this paper
have been deposited with the Cambridge Crystallographic Data Centre as deposition No. CCDC-187041. Copies
of the data can be obtained, free of charge, on application to the CCDC, 12 Union Road, Cambridge
CB21EZUK (fax: ‡44(1223)336033; email: deposit@ccdc.cam.ac.uk).

Helvetica Chimica Acta Vol. 85 (2002)
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