Application of trimethylvinylsilane as a convenient synthetic precursor of (perfluoroalkyl)ethenes: An unusual fluoride-induced elimination-desilylation coupled reaction

Article abstract of DOI:10.1021/ol006105o

(equation presented) A convenient and effective method for the preparation of perfluoroalkylated ethenes is described. First, the free radical addition of perfluoroalkyl iodides to trimethylvinylsilane in the presence of AIBN gave iodoethylsilane intermediates (F(CF₂)_nCH₂CHISiMe₃, n = 4 (1), 6 (2),8 (3), 10 (4); 94-99%). Then an unusual dehydrohalogenation-desilylation reaction was effected by tetrabutylammonium fluoride, and finally the product isolation (F(CF₂)_nCH=CH₂ (5-8), 62-87%) was facilitated using a fluorous phase separation technique. This novel approach can also be applied to adjust short C₂ hydrocarbon units to functionalized fluorinated segments (e.g., HOCH₂(CF₂)₈CH=CH₂ (11), 71%). All structures were verified by state-of-the-art multinuclear one- and two-dimensional NMR experiments involving both homo-(¹⁹F-¹⁹F) and heteronuclear (¹H-¹³C, ¹⁹F-¹³C) correlations based on the GMQFCOPS and inverse ¹H and/or ¹⁹F detected GHSQC, GHMQC sequences with broad-band adiabatic ¹³C decoupling.

Full text of DOI:10.1021/ol006105o

ORGANIC
LETTERS
2000
Vol. 2, No. 15
2347-2349
Application of Trimethylvinylsilane as a
Convenient Synthetic Precursor of
(Perfluoroalkyl)ethenes: An Unusual
Fluoride-Induced
Elimination−Desilylation Coupled
Reaction
Zolta´n Szla´vik, Ga´bor Ta´rka´nyi,† AÄ gnes Go1mo1ry,‡ and Jo´zsef Ra´bai*
Department of Organic Chemistry, Eo¨tVo¨s UniVersity, P.O. Box 32,
H-1518 Budapest 112, Hungary
rabai@szerVes.chem.elte.hu
Received May 25, 2000
ABSTRACT
A convenient and effective method for the preparation of perfluoroalkylated ethenes is described. First, the free radical addition of perfluoroalkyl
iodides to trimethylvinylsilane in the presence of AIBN gave iodoethylsilane intermediates (F(CF2)nCH CHISiMe3, n ) 4 (1), 6 (2), 8 (3), 10 (4);
2
94−99%). Then an unusual dehydrohalogenation−desilylation reaction was effected by tetrabutylammonium fluoride, and finally the product
isolation (F(CF2)nCHdCH (5−8), 62−87%) was facilitated using a fluorous phase separation technique. This novel approach can also be
2
applied to adjust short C hydrocarbon units to functionalized fluorinated segments (e.g., HOCH (CF2)8CHdCH (11), 71%). All structures were
2
2
2
verified by state-of-the-art multinuclear one- and two-dimensional NMR experiments involving both homo- (19F−19F) and heteronuclear (1H−13C,
19F−13C) correlations based on the GMQFCOPS and inverse 1H and/or 19F detected GHSQC, GHMQC sequences with broad-band adiabatic 13
C
decoupling.
The recent discovery of the concept of fluorous biphase
systems (FBS)1 and fluorous synthesis2 based on the unique
properties of perfluorocarbon fluids provides attractive
alternatives for conventional organic synthesis. A more
extensive application of this novel phase separation and
immobilization concept requires designed fluorous catalysts,
reagents, and labels. In the present work, we describe a
convenient and effective laboratory-scale access to (perfluo-
roalkyl)ethenes RfnCHdCH2 (Rfn ) F(CF2)n, n ) 4 (5), 6
(6), 8 (7), 10 (8)), useful building blocks of fluorous phase
ligands having a wide range of applicability in the planning
of fluorous synthesis.3 These compounds can be prepared
industrially via the alkaline treatment of Rfn(CH2)2I,4
components of the telomerization reactions of perfluoroalkyl
iodides with ethene.5 As a synthetic equivalent of ethene,
(3) (a) Alvey, L. J.; Rutherford, D.; Juliette, J. J. J.; Gladysz, J. A. J.
Org. Chem. 1998, 63, 6302. (b) Brown, H. C.; Chen, G.; Jennings, M. P.;
Ramachandran, P. V. Angew. Chem., Int. Ed. 1999, 38, 2052. (c) Richter,
B.; de Wolf, E.; van Koten, G.; Deelman, B.-J. J. Org. Chem. 2000, 65,
3885.
(4) (a) Brace, N. O.; Marshall, L. W.; Pinson, C. J.; Wingerden, G. J.
Org. Chem. 1984, 49, 2361. (b) Ame´duri, B.; Boutevin, B.; Nouiri, M.;
Talbi, M. J. Fluorine Chem. 1995, 74, 191.
† Spectroscopic Research Division, Chemical Works of Gedeon Richter,
Budapest, Hungary.
‡ Institute of Chemistry, Chemical Research Center, Hungarian Academy
of Sciences, Budapest, Hungary.
(1) (a) Horva´th, I. T.; Ra´bai, J. Science 1994, 266, 72. (b) Horva´th, I. T.
Acc. Chem. Res. 1998, 31, 641.
(2) Curran, D. P. Angew. Chem., Int. Ed. Engl. 1998, 37, 1175.
(5) (a) Brace, N. O. U.S. Patent 3016406, 1962; Chem. Abstr. 1962, 57,
2078a. (b) Brace, N. O. U.S. Patent 3145222, 1964; Chem. Abstr. 1964,
61, 10589.
10.1021/ol006105o CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/28/2000

trimethylvinylsilane (TMVS) was used to react with a
homologous series of F-alkyl iodides in the presence of
azoisobutyronitrile (AIBN) to produce RfnCH2CHISiMe3
a shorter fluorinated chain (5 and 6) can be separated with
a satisfactory result only from a more polar solvent with a
higher boiling point, such as DMSO (Table 1). This way in
6
(n ) 4 (1), 6 (2), 8 (3), 10 (4)) with excellent yields.7 The
tetrabutylammonium fluoride8 (TBAF) treatment of these
adducts unexpectedly resulted in products 5-8 in one step,9
indicating that both dehydrohalogenation and cleavage of the
C-Si bond occurred (Scheme 1). The applied polar aprotic
Table 1. Radical Addition to TMVS and Cleavage with
TBAF, Yields of Isolated products and gas chromatographic
purities
RfnCH2CHI-SiMe3
RfnCHdCH2
n
yield (%)
GC (%)
yield (%)
GC (%)
Scheme 1
4
6
8
1
2
3
4
99
97
97
94
99.3
98.9
100
96.1
5
6
7
8
62
74
76
87
91.1
95.3
96.5
97.1
10
the latter case one can avoid the addition of any fluorous
solvents, which could cause complications during the final
purification using atmospheric distillation.
An analogue to this reaction was found in the literature,
the fluoride-promoted alkyne-forming reaction of chloro-
vinyltrimethylsilanes,10 suggesting that the first step of the
complex mechanism is dehydrohalogenation (i.e., nucleo-
solvents (THF, DMSO) are readily miscible with water;
therefore, the strongly hydrophobic products separate spon-
taneously from the diluted reaction mixture. In the case of
the longer chain olefins 7 and 8 the less polar THF was used
as solvent to provide homogeneous reaction conditions, and
perfluorinated methylcyclohexane was applied as solvent
during the workup procedure to increase the efficiency of
fluorous phase separation. On the other hand, analogues with
115.5 [C-3], 118.1 [C-12], 125.7 (2JC,F ) 23.6 Hz) [C-2], 127.3 (3JC,F
)
9.6 Hz) [C-1]; 19F NMR: -81.0 (3F) [F-12], -113.3 (2F) [F-3], -121.1
(2F) [F-5], -121.4 (4F) [F-7 and F-8], -121.5 (4F) [F-6 and F-9], -122.4
(2F) [F-10], -123.3 (2F) [F-4], -125.9 (2F) [F-11]. The asterisk (*) denotes
interchangeable assignments. 19F NMR (ppm; in CDCl3): -81.8 (3F) (3JF,F
4
) 3.3 Hz, JF,F ) 9.9 Hz) [F-6], -114.6 (2F) [F-3], -125.0 (2F) [F-4],
-126.3 (2F) [F-5]. MS (EI, 70 eV; m/z, I (relative intensity), M• - X):
546, <0.1, M•; 527, 12, M• - F.; 481, 1.6, M• - F - (FCHdCH2); 457,
2.0, M - F - (HCF3); 181, 3.9, C4F7; 169, 5.5, C3F7; 131, 16, C3F5; 119,
11, C2F5; 100, 7.3, CF2dCF2; 77, 100, CF2CHdCH2; 69, 25, CF3; 51, 23,
HCF2; 31, 2.2, CF. FT-IR (liquid film; ν, cm-1): 2964.7 (CHas); 1245.2,
1202.7 (CF).
(6) Other methods for the preparation of (Rf)nCH2CHISiMe3 (n ) 6, 8):
(a) Chen, Q. Y.; Yang, Z. Y.; Zhao, C. X.; Qiu, Z. M. J. Chem. Soc., Perkin
Trans. 1 1988, 563. (b) Fuchikami, T.; Ojima, I. Tetrahedron Lett. 1984,
25, 303. (c) Beyou, E.; Babin, P.; Bennetau, B.; Dunogues, J.; Teyssie, D.;
Boileau, S. Tetrahedron Lett. 1995, 11, 1843.
(10) (a) Clark, J. H. Chem. ReV. 1980, 80, 429. (b) Cunico, R. F.;
Dexheimer, E. M. J. Am. Chem. Soc. 1972, 94, 2868.
(11) Experimental conditions: 0.1 g of TBAF (0.4 mmol) and acetic
acid 0.05 g (0.8 mmol) were dissolved in 2 mL of THF. The temperature
was set to 65 °C and 0.1 g of 3 was added to the mixture. The reaction was
quenched after 30 min, adding 10 mL of 2 M HCl solution to the mixture,
which was extracted with diethyl ether (10 mL). The etherous phase was
washed twice with distilled water and dried over Na2SO4 and 1 mL of the
sample was analyzed with gas chromatography (Hewlett-Packard 5890
Series II; Pona 50 m × 0.2 mm × 0.5 mm column, H2 carrier gas; FID;
temperature program initial temp 60 °C (5 min), rate 10 °C/min, final temp
250 °C). Experimental values (rt, purity): 5.71 min, 26.2%, 5; 13.10 min,
12.8% and 13.78 min, 11.1%, cis and trans isomers of Rf 8CHdCHSiMe3;
14.39 min, 3.61%, Rf 8CH2CH2I; 19.29 min, 38.5%, 3.
(12) The intermediate Rf 8CHdCHSiMe3 was identified through prepara-
tion from the reaction of 3 with KOH: Chen, Q. Y.; Yang, Z. Y.; Rong, D.
Q. J. Fluorine Chem. 1985, 29, 147.
(13) Szla´vik, Z.; Csa´mpai, A.; Krafft, M. P.; Riess, J. G.; Ra´bai, J.
Tetrahedron Lett. 1997, 38, 8757.
(7) Typical procedure and analytical data for 4: a predried 25 mL glass
tube was filled with F-decyl iodide (9.0 mmol), trimethylvinylsilane (10.0
mmol), and AIBN (0.2 mmol), sealed under a nitrogen atmosphere, and
heated to 75 °C for 8 h. The crude product was purified by distillation
(140-150 °C bath temperature, 0.1 mmHg). NMR (ppm; in acetone): 1H
NMR, 0.24 s (9H) [SiMe3], 2.68-2.83 m (1H) and 2.90-3.03 m (1H) [H-2x
and H-2y], 3.42 dd (1H) (3JH,H ) 10.5 Hz, 3JH,H ) 2.5 Hz) [H-1]; 13C NMR,
-2.4 [SiMe3], 1.9 [C-1], 36.0 (2JC,F ) 21.9 Hz) [C-2], 109.5 [C-11], 111.3
[C-10], 111.8 and 111.9 [C-6 and C-9]*, 112.0 [C-7 and C-8], 112.2 [C-4],
112.4 [C-5], 118.2 [C-12], 119.4 [C-3]; 19F NMR, -80.5 (3F) [F-12],
-112.7 d (1F) (2JF,F ) 267.4 Hz) and -114.6 d (1F) (2JF,F ) 267.4 Hz)
[F-3x and F-3y], -120.8 (2F) [F-5], -120.9 (4F) [F-7 and F8], -121.1 (4F)
[F-6 and F-9], -121.9 (2F) [F-10], -122.8 (2F) [F-4], -125.4 (2F) [F-11].
The asterisk (*) denotes interchangeable assignments. MS (EI, 70 eV; m/z,
I (relative intensity), M• - X): 746, <0.1, M•; 654, 22, M• - FSi(CH3)3;
635, 18, M• - F2Si(CH3)3; 527, 55, M• - IFSi(CH3)3; 507, 10, M• - IF2-
Si(CH3)3; 189, 20; 185, 20; 139, 32; 77, 78, CF2CHdCH2; 73, 100, Si-
(CH3)3. FT-IR (KBr; ν, cm-1): 2957.1 (CHas); 2900.4 (CHs); 1240.2, 1207.2
(CF).
(14) Takahashi, M.; Nagasaki, Y.; Fujii, S. Jpn. Patent 02169528, 1990;
Chem. Abstr. 1993, 113, 190741q.
(15) Analytical data for 11: NMR (in ppm; acetone): 1H NMR, 4.15 dt
3
(8) Tetrabutylammonium fluoride hydrate ((C4H9)4NF‚xH2O; 98%, Al-
drich) was used as received.
(2H) (3JH,F ) 14.0 Hz, JH,H ) 6.5 Hz) [H-11], 5.12 t (1H) (3JH,H ) 6.5
Hz) [OH], 6.00 d (1H) (3JH,H ) 11.0 Hz) [H-1C], 6.07 dt (1H) (3JH,H
)
)
4
3
(9) Typical procedure and analytical data for 8: TBAF (11.5 mmol) and
4 (4.0 mmol) were dissolved in 30 mL of THF and heated to 65 °C for 5
min. The mixture was diluted with water (150 mL) and extracted with
F-methylcyclohexane (10 mL). The fluorous phase was washed with water
and separated. F-Methylcyclohexane was recovered by atmospheric distil-
lation (95% GC purity), while crude 8 was distilled at reduced pressure
(90-95 °C bath temperature, 16 mmHg). NMR (ppm; in acetone): 1H
NMR, 5.99 d (3JH,H ) 11.0 Hz) (1H) [H-1C], 6.05 dt (3JH,H ) 17.0 Hz,
4JH,F ) 2.5 Hz) (1H) [H-1B], 6.19 dq (3JH,H ) 17.0 Hz,3JH,H ) 11.0 Hz,
4JH,F ) 11.5 Hz) (1H) [H-2A]; 13C NMR, 109.4 [C-11], 111.2 [C-10], 111.7
[C-6]*, 111.8 [C-8]*, 111.9 [C-9]*, 111.9 [C-7]*, 111.9 [C-4], 112.2 [C-5],
17.0 Hz, JH,F ) 2.0 Hz) [H-1B], 6.22 dq (1H) (3JH,H ) 17.0 Hz, JH,H
11.0 Hz, 3JH,F ) 11.5 Hz) [H-2A]; 13C NMR, 60.9 (2JC,F ) 25.2 Hz) [C-11],
112.2 [C-4, C-6 and C-7], 112.3 [C-8], 112.4 [C-5], 112.7 [C-9], 115.7
[C-3], 117.4 [C-10], 125.9 (2JC,F ) 23.6 Hz) [C-2], 127.4 (3JC,F ) 21.9
Hz) [C-1]; 19F NMR, -113.1 (2F) [F-3], -120.9 (2F) [F-5], -121.3 (2F)
[F-10], -121.4 (4F) [F-6 and F-7], -121.5 (2F) [F-8], -123.0 (2F) [F-9],
-123.2 (2F) [F-4]. MS (EI, 70 eV; m/z, I (relative intensity), M• - X):
458, <0.1, M•; 439, 3.5, M• - F.; 438, 1.8, M• - HF; 419, 1.4, M• - HF2;
408, 4.8, M• - CF4; 207, 1.0; 181, 1.4; 157, 3.6; 139, 3.2; 131, 15, C3F5;
77, 100, CF2CHdCH2, 51, 16, CF2H; 31, 72, CF. FT-IR (KBr; ν, cm-1):
3384.4 (OH); 2958.9 (CHas); 2891.9 (CHs); 1209.9, 1149.9 (CF).
2348
Org. Lett., Vol. 2, No. 15, 2000

philic attack of the fluoride ion at hydrogen). In our
experiments we attempted to identify the intermediates of
the reaction (in the case of the transformation of 3 to 5) using
gas chromatography. Since the reaction is relatively fast
(complete reaction was observed after 5 min), the reactivity
of the fluoride ion was reduced by acidifying the initial
reaction mixture slightly with acetic acid.11 (Strong acids,
such as CF3COOH, inhibit the reaction completely.) In this
buffered reaction media elimination products were proved
to be intermediates, as cis and trans isomers of Rf 8CHd
Table 2. Radical Addition and Cleavage with TBAF in the
Case of Functionalized Perfluorinated Derivatives
compound
yield (%)
GC (%)
9
10
11
MeOOC(CF2)8CH2CHISiMe3
HOCH2(CF2)8CH2CHISiMe3
HOCH2(CF2)8CHdCH2
98
90
71
95.2
96.9
94.9
together with homologous longer chain alkyl derivatives will
soon be published elsewhere.
12
CHSiMe3 were detected by GC (Path I in Scheme 2).
Structure Elucidation with NMR Spectroscopy. All
structures were verified by one- and two-dimensional NMR
experiments using recent assignment strategies that allowed
a so-called ab initio structure determination. Two-dimen-
sional experiments involved both homo- (19F-19F) and
heteronuclear (1H-13C, 19F-13C) correlations based on the
Scheme 2
1
GMQFCOPS and inverse H and/or 19F detected GHSQC,
GHMQC sequences employing broad-band adiabatic 13C
decoupling. The 1H, 13C, and 19F NMR measurements were
carried out at 30 °C in CDCl3 and CD3COCD3 on a Varian
1
INOVA-500 spectrometer (operating at 500 MHz for H)
1
equipped with a waveform generator, using a H{13C,15N}
PFG triple-resonance 5 mm probe tunable for 19F. Samples
were prepared and measured in ca. 40-60 mmol/L concen-
trations. 1H and 19F chemical shifts are given relative to δTMS
0.00 ppm and δCFCl ) 0.00 ppm, respectively, where TMS
3
and CFCl3 were used as internal standards. 13C chemical
shifts are reported by recording broad-band 1H or 19F
decoupled spectra and are referenced relative to the solvent
Surprisingly, the peak of Rf 8CH2CH2I could also be
assigned (Path II in Scheme 2), indicating that the activation
energies of the first steps of the basic and nucleophilic
pathway are similar. On the other hand, we have to note
that the dehalogenated derivative of 3 (Rf 8CH2CH2SiMe3)
was completely resistant to TBAF; thus, the neighboring
iodine atom has an important contribution to the nucleophilic
cleavage of the trimethylsilyl group.
This novel method can be generalized to the preparation
of functionalized F-alkylated ethenes. Methyl 9-iodoperfluo-
rononanoate13 was reacted with TMVS similarly as in the
case of nonfunctionalized derivatives to produce 9. Direct
TBAF treatment of this adduct resulted in a complex mixture
of products; therefore, ester 9 was first reduced to the
corresponding alcohol 10 with NaBH4 in 2-propanol under
mild conditions.14 The F--induced cleavage in THF followed
by fluorous extraction with F-methylcyclohexane, as in the
case of 7 and 8, produced the olefin-capped alcohol 1115
(Table 2).
13C shifts δ
77.00 ppm and δ
9.92 ppm. The
CD3COCD3
CDCl3
1
reported homonuclear 19F-19F and heteronuclear H-19F
scalar coupling constants were verified from band-selective
decoupled 19F spectra. Both broad-band 19F and 13C decou-
pling and band-selective 19F decoupling was performed by
adiabatic decoupling using the WURST17 decoupling se-
quence. We note that the previously reported 19F assignments4b
for the F-hexyl and F-octyl analogues of (perfluoroalkyl)-
ethenes are in disagreement with our results. The assignments
for compound 6 in CDCl3 are as follows: -81.5 ppm (3F)
[F-8]; -114.4 ppm (2F) [F-3]; -122.1 ppm (2F) [F-5];
-123.4 ppm (2F) [F-6]; -124.1 ppm (2F) [F-4]; -126.7
ppm (2F) [F-7].
Acknowledgment. Support from the Hungarian Scientific
Research Foundation (OTKA; Grant No. T 022169) and the
COST Action D12 “Fluorous medium: a tool for environ-
mentally compatible oxidation processes” is gratefully
acknowledged.
This method provides a convenient synthetic pathway to
new reverse fluorinated amphiphiles11 containing short C2
hydrocarbon units via catalytic hydrogenation of the double
bond16 and transformations of the hydroxyl terminus. Syn-
theses and supramolecular properties of these F-amphiphiles
Supporting Information Available: 1H, 13C, and 19F
NMR, MS (EI, 70 eV), and FT-IR data. This material is
available free of charge via the Internet at http://pubs.acs.org.
OL006105O
(16) Puy, M.; Poss, A. J.; Persichini, P. J.; Ellis, L. A. S. J. Fluorine
Chem. 1994, 67, 215.
(17) Kupcˇe, E.; Freeman, R. J. Magn. Reson. A 1995, 115, 273.
Org. Lett., Vol. 2, No. 15, 2000
2349