How trimethyl(trifluoromethyl)silane reacts with itself in the presence of naked fluoride - A one-pot synthesis of bis([15]crown-5)cesium 1,1,1,3,5,5,5,-heptafluoro-2,4-bis(trifluoromethyl)pentenide

Article abstract of DOI:10.1002/chem.200500799

Reactions of trimethyl(trifluoromethyl)silane in the presence of "naked" fluoride proceed up to a temperature of +5°C mainly with formation of [Me₃Si(CF₃)₂]. A further rise of temperature up to about 20°C gives evidence for the formation of a salt with the 1,1,1,2,3,6,6,6-octafluoro2,4,4,5,5-pentakis(trifluoromethyl)hexan-3-ide anion. This intermediate decomposes at room temperature into the 1,1,1,3,5,5,5-heptafluoro-2,4-bis(trifluoromethyl)pentenide anion. The bis([15]crown-5)cesium salt, [Cs([15]crown-5)₂] [(CF ₃)₂CCFC(CF₃)₂] has been characterized unambiguously as the stable final product of this reaction sequence. Thermal decomposition of this salt opens a convenient nontoxic route to obtain 1,1,3,3-tetrakis(trifluoromethyl)allene, (F₃C) ₂C=C=C(CF₃)₂.

Full text of DOI:10.1002/chem.200500799

DOI: 10.1002/chem.200500799
How Trimethyl(trifluoromethyl)silane Reacts with Itself in the Presence of
Naked Fluoride—A One-Pot Synthesis of Bis([15]crown-5)cesium
1,1,1,3,5,5,5-Heptafluoro-2,4-bis(trifluoromethyl)pentenide
Wieland Tyrra,*[a] Mikhail M. Kremlev,[b] Dieter Naumann,*[a] Harald Scherer,[a]
Harald Schmidt,[a] Berthold Hoge,[a] Ingo Pantenburg,[a] and Yurii L. Yagupolskii[b]
Dedicated to Professor Herbert Jacobs on the occasion of his 70th birthday
Abstract: Reactions of trimethyl(tri-
fluoromethyl)silane in the presence of
“naked” fluoride proceed up to a tem-
perature of +58C mainly with forma-
tion of [Me3Si(CF3)2]À. A further rise
of temperature up to about 208C gives
evidence for the formation of a salt
an-3-ide anion. This intermediate de-
composes at room temperature into
the 1,1,1,3,5,5,5-heptafluoro-2,4-bis(tri-
fluoromethyl)pentenide anion. The
bis([15]crown-5)cesium salt, [Cs([15]-
crown-5)2][(CF3)2CCFC(CF3)2] has
been characterized unambiguously as
the stable final product of this reaction
sequence. Thermal decomposition of
this salt opens a convenient nontoxic
route to obtain 1,1,3,3-tetrakis(trifluo-
romethyl)allene, (F3C)2C=C=C(CF3)2.
Keywords: allenes
· allylic com-
À
pounds · C C coupling · fluoride ·
silicates
with
the
1,1,1,2,3,6,6,6-octafluoro-
2,4,4,5,5-pentakis(trifluoromethyl)hex-
Introduction
In the course of our investigations mainly on halide sub-
stitutions with less-activated halides or in reactions with ele-
mental chalcogens,[5] we observed numerous signals, in most
cases of low intensity, in the 19F NMR spectra of the reac-
tion mixtures covering the region mainly between d=À45
and À80 ppm. These signals did not attract our attention so
far and were interpreted in terms of “not further identified
by-products”.
It is known that Me3SiCF3 reacts with MeCN in the pres-
ence of fluoride ions with formation of Me3SiCH2CN and
CF3H[4] and even formally adds to the “C=O” double bond
of DMF[6] in the presence of cyanide ions, while ethers such
as THF and DME (glyme, 1,2-dimethoxyethane) remain un-
affected by this reagent combination.[1] As a consequence,
THF and DME became solvents of choice in fluoride-medi-
ated reactions. But the question remained open what hap-
pens if Me3SiCF3 and small amounts of a fluoride source are
combined in these solvents in absence of any further re-
agent.
Trimethyl(trifluoromethyl)silane is widely used in different
reactions in organic and organometallic synthesis.[1] The di-
versity of these reactions spreads from additions to hetero-
multiple bonds to nucleophilic substitutions. Also the poten-
tial of trifluoromethylsilicates[2] intermediately formed in so-
lution as reagents of high nucleophilicity has been utilized
to abstract protons, for example, from alkynes[3] or acetoni-
trile[4] with formation of fluoroform and the corresponding
alkynylsilanes and cyanomethylsilane, respectively.
[a] Dr. W. Tyrra, Prof. Dr. D. Naumann, Dr. H. Scherer,
Dipl.-Chem. H. Schmidt, Priv.-Doz. Dr. B. Hoge, Dr. I. Pantenburg
Institut für Anorganische Chemie, Universität zu Kçln
Greinstr. 6, 50939 Kçln (Germany)
Fax : (+49)221-470-3276
Fax : (+49)221-470-5196
E-mail: tyrra@uni-koeln.de
d.naumann@uni-koeln.de
[b] Dr. M. M. Kremlev, Prof. Dr. Yu. L. Yagupolskii
Institute of Organic Chemistry
Results and Discussion
National Academy of Sciences of Ukraine
Murmanskaya St. 5, UA-02094 Kiev (Ukraine)
On the basis of our previous work,[2] we found that inde-
pendently from the solvent (THF, DME) and the fluoride
source ([NMe4]F, [Cs([15]crown-5)2]F), the silicate [Me3Si-
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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FULL PAPER
(CF3)2]À is selectively formed if the molar ratio of FÀ/
Me3SiCF3 is kept between 1:2 and 1:14. This anion can be
detected in addition to excessive silane in 19F NMR spectra
up to +58C (Scheme 1, Figure 1).
The onset of decomposition is best monitored by record-
ing a series of 19F NMR spectra as the temperature in the
NMR spectrometer is increased from 08C to +208C
(Figure 1 traces I to VI, region À40 to À90 ppm; ratio FÀ/
Me3SiCF3 =1:12). In experiments with a stoichiometric ratio
of 1:40, all compounds mentioned can be detected in the
19F NMR spectra in addition to significant quantities of un-
reacted Me3SiCF3. Prolonged reaction times of more than
96 h at ambient temperature cause a decrease of the amount
of the silane, mainly under formation of CF3H.
While at +48C mainly the significantly broadened signals
of [Me3Si(CF3)2]À and Me3SiCF3 can be detected (Figure 1,
trace II), further signals at d=À63, À71, and À73 ppm in-
tensify upon warming to +168C (Figure 1, traces III to V)
and finally to ambient temperature (Figure 1, trace VI). In
this temperature range, a complex reaction sequence occurs
yielding an intermediate that was identified on the basis of
2D 19F and 13C NMR spectra by using different programs
and pulse sequences to be most probably 1,1,1,2,3,6,6,6-
octafluoro-2,4,4,5,5-pentakis(trifluoromethyl)hexan-3-ide
(Figure 2). The 19F-COSY experiment allows the identifica-
tion of all fluorinated groups in the intermediate. Unfortu-
nately, in some cases it is not possible to determine unam-
biguously which coupling constant is cause of a special
cross-peak. Nevertheless, the proposed structure is in good
agreement with the spectrum and additionally supported by
the results of 19F NOE experiments. It has to be noted that
Scheme 1. Formation of the 1,1,1,2,3,6,6,6-octafluoro-2,4,4,5,5-pentakis-
(trifluoromethyl)hexan-3-ide.
Figure 1. Series of 19F NMR spectra recorded during the process of warm-
ing a sample of a mixture of Me3SiCF3 and [Cs([15]crown-5)2]F from 08C
to 208C (temperature of the probehead 218C at 188.3 MHz), for labelling
scheme see Figure 2.
Figure 2. 19
F COSY spectrum of the intermediate 1,1,1,2,3,6,6,6-octa-
fluoro-2,4,4,5,5-pentakis(trifluoromethyl)hexan-3-ide in [D8]THF record-
ed at À58C.
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W. Tyrra, D. Naumann et al.
the process of the formation of this intermediate is signifi-
cantly slower in THF than in DME, while with respect to
the decay the half-life time of the intermediate is significant-
ly longer in DME than in THF.
ing anion[9] in the presence of Ph3P or a consecutive reaction
with the solvent to give (CF3)3CCH2OCH2CH2OCH3 and
two
diastereomers
of
(CF3)3CCH(OCH3)CH2OCH3
(Scheme 3), which were unambiguously identified by two-di-
mensional NMR methods.[10] The formation of perfluoro-
tert-butyl ethers, (CF3)3COR, can be excluded by compari-
son with literature data.[11]
All attempts to get a deeper insight into the process of
the formation of the intermediate remained poor. Variation
of temperature, the stoichiometric ratios of the reactants,
use of different sources of fluoride only showed 19F NMR
spectroscopic evidence for products containing the C2F5
group, the tC4F9 group and in few cases the perfluoro-neo-
pentyl group, R-CF2C(CF3)3 (R: not further specified).[7] In
no case, signals for derivatives with a iC3F7 moiety were de-
tected in the 19F NMR spectra making this group suspicious
to be a key substance during the formation of 1,1,1,2,3,6,6,6-
octafluoro-2,4,4,5,5-pentakis(trifluoromethyl)hexan-3-ide.
This result can only be explained by successive substitution
of fluoride bond to sp3-hybridized carbon centres by per-
fluoroalkyl groups.
This intermediate can be stored in solution for several
weeks at À788C without any significant decomposition.
Solid material obtained upon removal of all volatile compo-
nents under reduced pressure at 08C can be stored for sever-
al days at À208C. Exposure to ambient temperature either
of the solid or of solutions was accompanied by a rapid de-
composition with formation of a salt with the 1,1,1,3,5,5,5-
heptafluoro-2,4-bis(trifluoromethyl)pentenide (allyl) anion
as the stable major product (Scheme 2).
Scheme 3. 1H, 19F and 13C NMR shifts of the ethers (CF3)3CCH2OCH2-
CH2OCH3 and (CF3)3CCH(OCH3)CH2OCH3 (13C NMR shifts in ital-
ics).[10]
Bis([15]crown-5)cesium 1,1,1,3,5,5,5-heptafluoro-2,4-bis-
(trifluoromethyl)pentenide has been isolated from the reac-
tion mixture as a colorless crystalline material in average
yields of 60% with a visible melting point of 123–1258C.
The compound, especially the anion, was characterized by
13C, 19F HMBC spectra (Figure 3). Cross-peaks from
1J(13C,19F) couplings were identified by characteristic dou-
blets splitting on the F axis (horizontal). They allow an as-
signment of the 13C signal at d=125.9 ppm to the CF3 (F)
and of the 13C resonance at d=167.6 ppm to the CF group
(G) of the anion. The fluorine signals of both the CF3 and
the CF group show additional cross-peaks to the resonance
of a quaternary carbon atom at d=70.6 ppm. The experi-
mental parameters chosen prove that these cross-peaks
2
result from J(13C,19F) couplings supporting the connectivity
of the molecule.
Negative ESI mass spectrometry (m/z (%): 330.91 (100)
[MÀ]) in solution, a single-crystal structure analysis as well
as vibrational spectra of the solid prove the composition of
the anion. The results of these last methods were supported
by DFT calculation (B3PW91/6–311G+(2d,p)).[12]
The salt crystallizes in the triclinic space group with
a=881.0(1), b=1433.7(1), c=1440.8(1) pm, a=88.78(1),
b=82.25(1), g=79.47(1)8, and Z=2. The structure of the
anion is depicted in Figure 4 and it shows only small devia-
tions from C2 symmetry, which was assumed for DFT calcu-
lations, exhibiting a very good agreement between experi-
Scheme 2. Proposed fragmentation of the 1,1,1,2,3,6,6,6-octafluoro-
2,4,4,5,5-pentakis(trifluoromethyl)hexan-3-ide anion.
The decomposition involves the formation of one per-
fluoro-tert-butyl radical as well as one fluorine radical. The
fluorine radical can be trapped by addition of triphenylphos-
phane, which is converted into the corresponding difluoride,
Ph3PF2 (19F, 31P NMR spectroscopy),[8] while without addi-
tion of Ph3P not further specified reactions of the fluorine
radical occur. Addition of Ph3P to the reaction mixture after
decomposition of the intermediate did not give any evidence
for oxidation products. The fate of the perfluoro-tert-butyl
radical may be understood as formation of the correspond-
À
mental and theoretical results. The C F bonds within the tri-
fluoromethyl groups vary between 133.6(2) and 136.4(2) pm,
while that to the central fluorine atom is slightly longer
À
(137.9(2) pm). The C C bonds to the CF3 groups show an
average value of approximately 147.4 pm and significantly
differ from that within the central “allyl” unit (137.8 pm).
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Allylic Compounds
FULL PAPER
2308C into 1,1,1,5,5,5-hexafluoro-2,4-bis(trifluoromethyl)-
penta-2,3-diene
(1,1,3,3-tetrakis(trifluoromethyl)allene)[16]
and cesium fluoride with release of two equivalents of the
crown ether (Scheme 4).
Scheme 4. Thermal decomposition of [Cs([15]crown-5)2][(CF3)2CCFC-
(CF3)2].
This reaction sequence opens a new and convenient
access to 1,1,3,3-tetrakis(trifluoromethyl)allene avoiding the
use of highly toxic perfluoroisobutene.[17]
Experimental Section
NMR spectra: The 19F COSY and 19F NOE spectra were performed on a
Bruker Avance 400 spectrometer by using a triple-resonance 1H, 19F, BB
inverse probehead with the 19F frequency on the detection coil. The 13C,
19F HMBC spectrum of bis([15]crown-5)cesium 1,1,1,3,5,5,5-heptafluoro-
2,4-bis(trifluoromethyl)pentenide was recorded with a triple resonance
1H, 19F, BB inverse probehead with the 19F frequency on the detection
coil and the decoupling coil tuned on 13C. 1D-NMR spectra were run
either on the Bruker spectrometer AC200 or Avance 400.
Figure 3. 13C, 19F HMBC spectrum of bis([15]crown-5)cesium
1,1,1,3,5,5,5-heptafluoro-2,4-bis(trifluoromethyl)pentenide in CD3CN at
258C.
Bis([15]crown-5)cesium 1,1,1,3,5,5,5-heptafluoro-2,4-bis(trifluoromethyl)-
pentenide: A quantity of CsF (0.30 g, 2 mmol) was added in one portion
to a well-stirred mixture of Me3SiCF3 (3.40 g, 24 mmol) and [15]crown-5
(0.88 g, 4 mmol) in anhydrous dimethoxyethane (4 mL) at À208C. The
mixture was slowly warmed to ambient temperature (about 3 h) and vig-
orously stirred for another 12 h. All volatile materials were condensed in
vacuo at room temperature; the residue was washed with anhydrous ben-
zene (2”3 mL), dried in vacuo and dissolved in diethyl ether. The solu-
tion was placed in a cold bath at À508C, while a triple amount of n-
hexane was condensed onto the solution over a period of 3 d. Colorless
crystals suitable for XRD measurement were collected in 60.7% yield
(1.10 g). Elemental analysis calcd (%) for C27H40F13O10Cs (904.49): C
35.85, H 4.46; found: C 35.46, H 4.25; m.p. 123–1258C (glass capillary),
>2308C (decomp; DTA); 1H NMR (400.1 MHz, CD3CN, 218C, TMS):
d=3.56 ppm (s); 19F NMR (376.4 MHz, CD3CN, 08C, CCl3F): d=À53.4
(br, 6F; CF3), À54.1 (br, 6F; CF3), À74.5 ppm (tridecet, 4J(F,F)=19 Hz,
1F; CF); 13C NMR (100.6 MHz, CD3CN, 218C, TMS): d=167.7 (dm,
1J(F,C)=262 Hz; CF), 125.9 (qm, 1J(F,C)=266 Hz; CF3), 70.6 (m;
C(CF3)2), 68.7 ppm (tm, 1J (C,H)=141 Hz; OCH2); MS (neg. ESI,
MeCN): m/z (%): 330.91 (100) [MÀ]; MS (EI, 20 eV): m/z (%): 312 (65)
[M+ÀF], 293 (19) [M+À2F], 224 (14) [M+ÀCF4], 133 (51) [C6H13O3+]/
[Cs+], 89 (100) [C4H9O2+], 45 (75) [C2H5O+]. Fragments with intensities
less than 5% were detected for 243, 205, 155. The EI mass spectrometric
fragmentation (m/z from 312 to 155) was identical with that reported for
(CF3)2C=C=C(CF3)2.[16]
Figure 4. Molecular structure of the 1,1,1,3,5,5,5-heptafluoro-2,4-bis(tri-
fluoromethyl)pentenide anion. Interatomic distances [pm] and angles [8];
À
calculated values with assumption of C2 symmetry in italics: C31 C33
À
À
À
147.5(3) C35 C36 147.2(3), 148.0; C32 C33 147.5(3) C35 C37 147.4(3),
À
À
À
147.4; C33 C34 137.8(3) C35 C34 137.7(3), 138.3; C34 F341 137.9(2),
136.7; C F in CF3 groups 133.6(2)–136.4(2), 135.0–136.0; C31-C33-C32
116.5(2) C36-C35-C37 116.3(2), 116.3; C31-C33-C34 120.3(2) C36-C35-
C34 119.6(2), 119.1; C32-C33-C34 122.6(2) C37-C35-C34 123.8(2), 124.2;
C33-C34-C35 134.4(2), 134.5; C33-C34-F341 112.7(2) C35-C34-F341
112.9(2), 112.8.
À
Together with the angle C33-C34-C35 of 134.4(2)8, these
data appear to be representative for a (CF3)2CCC(CF3)2
moiety in comparison with literature values.[13]
The process of formation of the “allyl” anion—addition of
a fluoride source to tetrakis(trifluoromethyl)allene[13–15]—ap-
pears to be reversible; [Cs([15]crown-5)2][(CF3)2CCFC-
(CF3)2] decomposes selectively at a temperature above
Single-crystal structure determination: The intensity data were collected
on an imaging-plate diffractometer (IPDS II, Stoe & Cie) with MoKa ra-
diation (l=71.073 pm, graphite monochromator) at 130 K. The structure
was solved by direct methods and refined by full-matrix least-squares
methods on F2. The hydrogen atoms were placed in idealized positions
and constrained to ride on their parent atom. The last cycles of refine-
ment included atomic positions for all the atoms, anisotropic thermal pa-
rameters for all the non-hydrogen atoms and isotropic thermal parame-
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6517

W. Tyrra, D. Naumann et al.
ters for all of the hydrogen atoms. A numerical absorption correction
was applied after optimization of the crystal shape.[18–21]
[8] a) H. J. Frohn, H. Maurer, J. Fluorine Chem. 1986, 34, 129–145;
b) P. J. Harvey, I. D. Jenkins, Tetrahedron Lett. 1994, 35, 9775–9778.
[9] a) A. E. Bayliff, M. R. Bryce, R. D. Chambers, R. S. Matthews, J.
Chem. Soc. Chem. Commun. 1985, 1018–1019; b) B. E. Smart, W. J.
Middleton, W. B. Farnham, J. Am. Chem. Soc. 1986, 108, 4905–4908.
[10] 19F and 1H NMR chemical shifts are in accordance with values re-
ported for related compounds; K. N. Makarov, T. N. Abroskina,
Yu. A. Cherburkov, I. L. Knunyants, Izv. Akad. Nauk SSSR Ser.
Khim. 1976, 940–942; N. I. Delyagina, B. L. Dyatkin, I. L. Knuny-
ants, Zh. Org. Khim. 1974, 10, 935–941.
[11] N. Takada, T. Abe, A. Sekiya, J. Fluorine Chem. 1998, 92, 167–171.
[12] A table of measured and calculated vibrational data is available as
Supporting Information. Gaussian 98, Revision A.7, M. J. Frisch,
G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr., R. E. Strat-
mann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K. N.
Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R.
Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochter-
ski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslow-
ski, J. V. Ortiz, A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong,
J. L. Andres, C. Gonzalez, M. Head-Gordon, E. S. Replogle, J. A.
Pople, Gaussian, Inc., Pittsburgh PA, 1998.
Crystal data for bis([15]crown-5)cesium 1,1,1,3,5,5,5-heptafluoro-2,4-bis-
¯
(trifluoromethyl)pentenide: C27H40F13O10Cs, triclinic space group P1, a=
881.0(1), b=1433.7(1), c=1440.8(1) pm, a=88.78(1), b=82.25(1), g=
79.47(1)8, V=1772.8(2)”106 pm3, Z=2, m=1.163 mmÀ1
,
F(000)=908,
R
int =0.0312, no. collected/unique/I0 >2s(I0) data=21951/7694/7206, R1/
wR2 (all data)=0.0285/0.0694, R1/wR2 [I0 >2s(I0)]=0.0266/0.0679, max/
min electron density=0.529/À0.915”10À6 epmÀ3. CCDC-265521 contains
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
1,1,3,3-Tetrakis(trifluoromethyl)allene:
Solid
[Cs([15]crown-5)2]-
[(CF3)2CCFC(CF3)2] (3.52 g, 3.8 mmol) was heated to 2308C under a
weak flow of nitrogen for 2.5 h. Volatile products were collected in a
cold trap at À788C. After distillation (CF3)2C=C=C(CF3)2 was obtained
(0.60 g, 51% yield). B.p. 43–458C (418C (743 mmHg)[16]); 19F NMR
(188.3 MHz, CDCl3, 218C, CCl3F): d=À61.4 ppm (s); 13C NMR
1
(50.3 MHz, CDCl3, 218C, TMS): d=204.7 (br; =C=), 118.5 (qm, J(F,C)=
2
277 Hz; CF3), 106.8 ppm (septet, J(F,C)=40 Hz; C(CF3)2).
Acknowledgements
Generous financial support of this work by the Deutsche Forschungsge-
meinschaft is gratefully acknowledged (436 UKR 113/26).
[13] W. B. Farnham, W. J. Middleton, W. C. Fultz, B. E. Smart, J. Am.
Chem. Soc. 1986, 108, 3125–3127.
[14] a) L. L. Gervits, L. A. Rozov, N. S. Mirzabekyants, K. N. Makarov,
Yu. V. Zeifman, Yu. A. Cherburkov, I. L. Knunyants, Izv. Akad.
Nauk SSSR Ser. Khim. 1976, 1676; b) N. S. Mirzabekyants, L. L.
Gervits, Yu. A. Cherburkov, I. L. Knunyants, Izv. Akad. Nauk SSSR
Ser. Khim. 1977, 2772–2775.
[15] A. Yu. Volonsky, E. M. Rokhlin, J. Fluorine Chem. 1984, 26, 183–
210.
[16] Yu. E. Aronov, Yu. A. Cherburkov, I. L. Knunyants, Izv. Akad.
Nauk SSSR Ser. Khim. 1967, 1758–1768.
[17] C. M. Timperley, J. Fluorine Chem. 2004, 125, 685–693 and referen-
ces therein.
[18] SIR-92: A program for crystal structure solution: A. Altomare, G.
Cascarano, C. Giacovazzo, J. Appl. Crystallogr. 1993, 26, 343–350.
[19] G. M. Sheldrick, SHELX-97; Programs for Crystal Structure Analy-
sis, University of Gçttingen, 1997.
[1] a) G. K. S. Prakash, A. K. Yudin, Chem. Rev. 1997, 97, 757–786;
b) G. G. Furin, Russ. J. Org. Chem. 1997, 33, 1209–1242; c) R. P.
Singh, J. M. Shreeve, Tetrahedron 2000, 56, 7613–7632; d) E. Abele,
E. Lukevics, Main Group Met. Chem. 2001, 24, 315–350.
[2] N. Maggiarosa, W. Tyrra, D. Naumann, N. V. Kirij, Yu. L. Yagupol-
skii, Angew. Chem. 1999, 111, 2392–2393; Angew. Chem. Int. Ed.
1999, 38, 2252–2253.
[3] a) M. Ishizahi, O. Hoshino, Tetrahedron 2000, 56, 8813–8819; b) M.
Yoshimatsu, M. Kuribayashi, J. Chem. Soc. Perkin Trans. 1 2001,
1256–1257; c) M. Ishizaki, H. Satoh, O. Hoshino, K. Nishitani, H.
Hara, Heterocycles 2004, 63, 827–844.
[4] D. J. Adams, J. H. Clark, L. B. Hansen, V. C. Sanders, S. J. Taverner,
J. Fluorine Chem. 1998, 92, 123–125.
[5] a) W. Tyrra, D. Naumann, B. Hoge, Yu. L. Yagupolskii, J. Fluorine
Chem. 2003, 119, 101–107; b) W. Tyrra, D. Naumann, Yu. L. Yagu-
polskii, J. Fluorine Chem. 2003, 123, 183–187; c) W. Tyrra, N. V.
Kirij, D. Naumann, Yu. L. Yagupolskii, J. Fluorine Chem. 2004, 125,
1435–1438.
[20] X-RED 1.22, Stoe Data Reduction Program (C), Stoe
& Cie
GmbH, Darmstadt, 2001 .
[21] X-Shape 1.06, Crystal Optimisation for Numerical Absorption Cor-
rection (C), STOE & Cie GmbH, Darmstadt, 1999 .
[6] P. Panne, D. Naumann, B. Hoge, J. Fluorine Chem. 2001, 112, 283–
286.
Received: July 12, 2005
[7] W. Tyrra, M. M. Kremlev, D. Naumann, unpublished results.
Published online: August 25, 2005
6518
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Chem. Eur. J. 2005, 11, 6514 – 6518