Synthesis and reactivity of (1-fluorovinyl) phenyl sulfoxide as a dienophile

Article abstract of DOI:10.1016/S0022-1139(02)00198-7

(1-Fluorovinyl) phenyl sulfoxide 2 was prepared in two steps from (1-fluorovinyl)methyldiphenylsilane. Although the sulfoxide 2 underwent Diels-Alder reaction with very reactive diene, 1,3-diphenylisobenzofuran, to give the corresponding fluorinated-napht

Full text of DOI:10.1016/S0022-1139(02)00198-7

Journal of Fluorine Chemistry 118 (2002) 99–101
Synthesis and reactivity of (1-fluorovinyl) phenyl
sulfoxide as a dienophile
Takeshi Hanamoto*, Kaoru Korekoda, Kenya Nakata, Kumiko Handa,
Yukinori Koga, Michio Kondo
Department of Chemistry and Applied Chemistry, Saga University, Honjyo-machi 1, Saga 840-8502, Japan
Received 7 January 2002; received in revised form 24 June 2002; accepted 8 August 2002
Abstract
(1-Fluorovinyl) phenyl sulfoxide 2 was prepared in two steps from (1-fluorovinyl)methyldiphenylsilane. Although the sulfoxide 2
underwent Diels-Alder reaction with very reactive diene, 1,3-diphenylisobenzofuran, to give the corresponding fluorinated-naphthalene
derivative in one step, it did not afford cycloadducts with other dienes employed.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: (1-Fluorovinyl) phenyl sulfoxide; Diels-Alder reaction; Mono-fluorinated building block; 1,3-Diphenylisobenzofuran
1. Introduction
preparation of (1-fluorovinyl)methyldiphenylsilane as a use-
ful reagent for the introduction of a 1-fluorovinyl group into
organic compounds [16,18], this method was applied to the
synthesis of the (1-fluorovinyl) phenyl sulfide 1 as a pre-
cursor for 2. The cesium fluoride-initiated cross-coupling
reaction of (1-fluorovinyl)methyldiphenylsilane with S-phe-
nyl benzenethiosulfonate in DMF at 80 8C afforded the
corresponding sulfide 1 in 93% yield. The sulfide 1 is
volatile and easily susceptible to oxidation reactions. The
second step for the preparation of 2 required the selective
oxidation of the sulfide 1. Inspection of literature sources
revealed the system of aqueous 30% H2O2 in hexafluoro-2-
propanol (HFIP) for the selective oxidation of sulfide to
sulfoxide [20]. Although we applied this method to the
sulfide 1, we obtained the mixture of 1, the desired sulfoxide
2, and the overoxidized sulfone 3 [9,21]. The difficulty of the
separation of these three compounds impelled us to examine
other selective oxidation methods. After many attempts we
obtained the sulfoxide 2 using mCPBA at 0 8C in 80% yield.
We have examined the use of 2 as a potential reagent for a
mono-fluorinated dienophile. Haufe and co-workers
described the successful Diels-Alder reaction of 1,3-diphe-
nylisobenzofuran 4 and fluorostyrenes [3,6]. This prompted
us to use 4 as a promising diene for this Diels-Alder reaction.
We examined some reaction conditions for the Diels-Alder
reaction, and the results are shown in Table 1. We obtained
not the corresponding endo-and exo-cycloadducts 6, but 2-
fluoro-1,4-diphenylnaphthalene 5 as the aromatized product
The Diels-Alder cycloaddition is a fundamental tool for the
construction of a six-membered ring. The application of this
reaction using suitable fluorinated dienophiles would selec-
tively provide fluorinated cyclohexenes that serve as versatile
synthetic intermediates for the construction of complex-fluori-
nated compounds [1]. Despite their importance, the successful
[4 þ 2] cycloaddition reactions of fluorinated dienophiles are
scarce [2]. Accordingly, the development of mono-fluorinated
dienophiles [3–9] as well as di- or tri-fluorinated dienophiles
is limited [10–15]. The reason seemed to be the difficulty with
introduction of fluorine(s) to olefins. We have been interested
in new methodologies for the incorporation of the mono-
fluorovinylic moiety and have recently reported useful mono-
fluorinated building blocks [16–19]. We have expected the
title compound as a convenient equivalent of fluoroacetylene
that is not easy to handle for the [4 þ 2] cycloaddition
reactions. This report describes the first preparation and
reactions of (1-fluorovinyl) phenyl sulfoxide.
2. Results and discussion
Our synthetic route for the preparation of the sulfoxide
2 is depicted in Scheme 1. Since we have reported the
* Corresponding author. Tel.: þ81-952-28-8704; fax: þ81-952-28-8548.
E-mail address: hanamoto@cc.saga-u.ac.jp (T. Hanamoto).
1
in moderate yield (Table 1). Its H NMR spectrum and its
0022-1139/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 0 2 ) 0 0 1 9 8 - 7

100
T. Hanamoto et al. / Journal of Fluorine Chemistry 118 (2002) 99–101
anthracene, 1,4-diphenyl-1,3-butadiene under various condi-
tions. Unfortunately, these dienes afforded no cycloadduct
along with the recovery of 2. Furthermore, the reaction of 2
with o-quinodimethane as a more reactive diene also failed
[29].
In order to obtain information about the lower reactivity
of 2 compared to 7, the orbital energies of 2 and phenyl vinyl
sulfoxide 7 were calculated on the ab initio level (6-31G). To
our surprise, they have nearly the same value (3.977 eV for 2
and 4.000 eV for 7) with respect to the LUMO energies. We
are afraid that it is not so easy to explain the lower reactivity
of 2.
Scheme 1.
13C NMR spectrum cleanly characterized the product 5. The
values of the chemical shifts and coupling constants of
3. Conclusion
19
13CÀ F are in good agreement with those of 2-fluoro-
We have demonstrated the first preparation of (1-fluor-
ovinyl) phenyl sulfoxide 2 from (1-fluorovinyl)methyldi-
phenylsilane in two steps in good overall yields and the
successful Diels-Alder reaction of 2 with 1,3-diphenyliso-
benzofuran 4. We have shown that the sulfoxide 2 functioned
as a fluoroacetylene synthon albeit only one example.
naphthalene as a similar compound [22]. These findings
are suggested that the sulfoxide 2 has lower reactivity than
1-fluorostyrene on the contrary of our expectation. We have
not examined the reaction mechanism in detail; however, the
reaction proceeded via in situ thermal elimination of ben-
zenesulfenic acid followed by deoxygenation.
Since phenyl vinyl sulfoxide 7 has so far been shown to
react with various dienes at high temperature [23–28], we
next examined the reaction of 2 with an excess of other
dienes such as cyclopentadiene, 2,3-dimethyl-1,3-butadiene,
4. Experimental
Melting points were measured with a Yanagimoto micro
melting point apparatus MP-S3 and are uncorrected. Infra-
red (IR) spectra were recorded on Perkin-Elmer Spectrum
2000. 1H NMR spectra were measured on JEOL JNM-
GX270. 13C NMR spectra were measured on JEOL
JNM-EX400 at the Institute for Fundamental Research of
Organic Chemistry, Kyushu University. Chemical shifts
were given by d relative to that of an internal Me4Si
(TMS). GC-mass spectra were obtained with JEOL JMS-
AMII15. Elemental analyses were accomplished at the
service center of the elementary analysis of organic com-
pounds, Kyushu University. Analytical thin layer chroma-
tography (TLC) was performed on a silica gel plate (Merck,
Kieselgel 60 F254, 20 cm  20 cm, 0.25 mm). DMF,
toluene, tetraglyme and CH2Cl2 were used as a reaction
solvent after distillation from CaH2.
Table 1
Diels-Alder reaction of (1-fluorovinyl) phenyl sulfoxide and 1,3-dipheny-
lisobenzofuran
4.1. (1-Fluorovinyl) phenyl sulfide (1)
To a solution of (1-fluorovinyl)methyldiphenylsilane
(1.00 g, 4.13 mmol) and S-phenyl benzenethiosulfonate
(1.35 g, 5.39 mmol) in DMF (30 ml) was added cesium
fluoride (0.95 g, 6.25 mmol) at room temperature under
argon. The solution was heated at 80 8C for 12 h. After
cooling to room temperature, water was added to the result-
ing solution. The mixture was twice extracted with hexane/
ether ¼ 3/1, and the combined organic layer was dried over
Na2SO4. The solution was concentrated in vacuo, and the
residue was purified by chromatography on silica gel (hex-
ane) to give the desired sulfide 1 as a colorless oil (0.59 g,
Entry
Solvent
Additive
Temperature
Yield
(%)a
(8C)
1
2
3
4
5
6
7
Toluene
Toluene
Tetraglyme
Ethylene glycol
Neat
None
ZnCl2
None
None
None
None
None
110
100
180
100
80
12
Trace
33
49
40
47
Neat
100
120
Neat
39
a Isolated yield.

T. Hanamoto et al. / Journal of Fluorine Chemistry 118 (2002) 99–101
101
93%): IR (neat) n 3063, 1629, 1584, 1479, 1442, 1162, 1086,
Acknowledgements
1024, 1000, 923, 867, 743, 689 cmÀ1; 1H NMR (270 MHz,
CDCl3) d 4.97 (1H, dd, J ¼ 42:7, 2.9 Hz), 5.12 (1H, dd,
J ¼ 10:7, 2.9 Hz), 7.24–7.47 (5H, m); GC-MS 70 eV, m/z
(rel int): 154 (Mþ, 99), 153 (60), 134 (36), 109 (86), 91
(100), 77 (44), 65 (30), 51 (67), 50 (33); Anal. Calcd. for
C8H7FS: C, 62.31; H, 4.58. Found: C, 62.07; H, 4.57.
We are grateful to professor Koikawa at Saga University
for his valuable discussions on the ab initio calculations. We
also express our appreciation to professor Inanaga’s group at
Kyushu University for 13C NMR spectroscopy. We thank
Chemetall Japan Co. Ltd. for a gift of CsF and F-Tech Co.
Ltd. for a gift of 1,1-difluoroethylene for the preparation of
(1-fluorovinyl)methyldiphenylsilane.
4.2. (1-Fluorovinyl) phenyl sulfoxide (2)
mCPBA (0.92 g, 5.33 mmol) was slowly added to a
solution of (1-fluorovinyl) phenyl sulfide (0.69 g,
4.47 mmol) in CH2Cl2 (4 ml) at 0 8C. The resulting mixture
was stirred for 5 h at 0 8C, and then the reaction was
quenched with saturated sodium hydrogen sulfite. The
organic layer was separated and the aqueous layer was
extracted with CH2Cl2. After the combined organic layer
was dried over anhydrous sodium sulfate and concentrated,
the residue was purified by column chromatography (silica
gel, hexane/ethyl acetate ¼ 20/1) to give the desired sulf-
oxide 2 as a colorless oil (0.61 g, 80%): IR (neat) n 3121,
3037, 1651, 1476, 1446, 1180, 1087, 1057, 920, 878, 751,
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