Use of 1,3-dipolar reactions for the preparation of SF5- substituted five-membered ring heterocycles. Pyrroles and thiophenes

Article abstract of DOI:10.1016/j.jfluchem.2011.03.017

In situ-generated unsubstituted, "parent" azomethine and thiocarbonyl ylides are used to prepare a large variety of 3-aryl- and alkyl-substituted, 4-pentafluorosulfanylpyrroles and 3-aryl-substituted, 4-pentafluorosulfanylthiophenes, the latter of which a

Full text of DOI:10.1016/j.jfluchem.2011.03.017

Journal of Fluorine Chemistry 132 (2011) 389–393
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Use of 1,3-dipolar reactions for the preparation of SF5-substituted
five-membered ring heterocycles. Pyrroles and thiophenes
*
William R. Dolbier Jr. , Zhaoyun Zheng
Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, United States
A R T I C L E I N F O
A B S T R A C T
Article history:
In situ-generated unsubstituted, ‘‘parent’’ azomethine and thiocarbonyl ylides are used to prepare a large
variety of 3-aryl- and alkyl-substituted, 4-pentafluorosulfanylpyrroles and 3-aryl-substituted, 4-
pentafluorosulfanylthiophenes, the latter of which are to our knowledge the first reported SF5-
substituted thiophenes. The 1,3-cycloadditions of these ylides with aryl and alkyl, SF5-alkynes produce
dihydro-pyrroles and thiophenes, which without isolation can then be oxidatively aromatized to the
respective pentafluorosulfanylpyrroles and thiophenes in good yield.
Received 25 January 2011
Received in revised form 7 March 2011
Accepted 10 March 2011
Available online 4 April 2011
Keywords:
ß 2011 Elsevier B.V. All rights reserved.
Pentafluorosulfanyl group
SF5
Pyrrole synthesis
Thiophene synthesis
1,3-Dipolar cycloadditions
1. Introduction
synthesis of their SF5-substituted analogues, at least not in our
hands. Thus far, the only methodology that has been useful in such
It is now well recognized that the physicochemical and
pharmacological properties of organic compounds can be signifi-
cantly and often efficaciously affected simply by the incorporation
of a fluorine substituent or by fluorine containing substituents
such as the trifluoromethyl group [1–6]. In this respect, the
pentafluorosulfanyl (SF5) group has only recently attracted
attention as a potential replacement for trifluoromethyl groups
in molecules of pharmaceutical, agrochemical and materials
interest. Indeed, in those cases where direct comparisons can be
made, compounds where a CF3 group has been replaced with an
SF5 substituent show at least similar, but often enhanced
selectivity and biological activity [7–10].
syntheses has involved cycloaddition chemistry. Utilization of a
combination of Diels–Alder and retro-Diels–Alder reactions has
allowed the synthesis of SF5-furans (Scheme 1) [16], whereas the
use of a 1,3-dipolar reaction allowed the first preparation of SF5-
pyrroles (Scheme 2), in this case pyrrolecarboxylic esters [17].
At this time we would like to report an extension of this latter
report, the results of which have allowed us to prepare a larger
variety of SF5-pyrroles as well as the first SF5-substituted
thiophenes.
2. Results and discussion
Heterocycles comprise an important component of many
pharmaceutical and agrochemical compounds, but there have
been few reports of heterocycles that directly bear an SF5 group.
The synthesis of a quinoline was recently reported [10], and
pyrazoles [11,12], triazoles [13], and thienothiophenes [14] have
also been prepared. Triazoles tethered to an SF5 group have also
recently been reported [15]. The synthesis of basic SF5-substituted
five-membered ring heterocycles has been a particular challenge
because most of the methods that have been used to prepare CF3-
substituted furans, pyrroles and thiophenes, for the most part
involving condensation reactions, have not proved useful for the
Building upon our earlier 1,3-dipolar cycloaddition work, which
demonstrated that SF5-alkynes acted as reactive dipolarophiles in
their reactions with stabilized azomethine ylide 1, two non-
stabilized ylides were examined to determine whether they too
would undergo efficient cycloaddition with the SF5-alkynes. If
successful, azomethine ylide 2 would allow the synthesis of a wide
variety of 3-substituted, 4-pentafluorosulfanylpyrroles, whereas
thiocarbonyl ylide 3 would allow synthesis of the first SF5-
substituted thiophenes (Scheme 3).
2.1. SF5-pyrrole synthesis
Azomethine ylide 2 was first generated by Padwa from
its precursor, N-benzyl-N-(methoxymethyl)-N-[(trimethylsilyl)-
methyl]amine (4), via the treatment of 4 with either LiF or CsF
in acetonitrile [18]. This ylide has been widely used for the
* Corresponding author at: University of Florida, Department of Chemistry, PO
Box 117200, Gainesville, FL 32611-7200, United States.
E-mail address: wrd@chem.ufl.edu (W.R. Dolbier Jr.).
0022-1139/$ – see front matter ß 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2011.03.017

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W.R. Dolbier Jr., Z. Zheng / Journal of Fluorine Chemistry 132 (2011) 389–393
Scheme 1. Preparation of SF5-substituted furans by Diels–Alder Chemistry.
Scheme 2. Preparation of SF5-substituted pyrrolecarboxylic esters via 1,3-dipolar cycloaddition.
Scheme 3. Generation of azomethine ylide 2 and thiocarbonyl ylide 3.
synthesis of pyrrolidines and dihydropyrroles, of particular
relevance to our work are its reactions with trifluoromethylalkenes
[19,20].
The TIPS, SF5-acetylene 5e produced pyrrole 7e, which could be
readily desilated to give N-benzyl-3-pentafluorosulfanylpyrrole, 7f
(Scheme 6).
In our hands, as shown in Table 1 (Scheme 4), the use of these
fluoride catalysts proved not to be effective in carrying out the
desired cycloadditions with typical SF5-alkyne 5a. Instead, the
reaction proceeded smoothly when 4 was treated with catalytic
(0.2 eq) trifluoroacetic acid (TFA) in refluxing methylene chloride
in the presence of alkyne substrate [21].
Lastly, it was desirous to demonstrate the ability to remove the
protective benzyl group from the pyrrole products. However,
catalytic hydrogenolysis of the N-benzylpyrroles using either Pd/C
or Pd(OH)2/C catalysis proved unsuccessful. Instead it was found
necessary to carry out the debenzylation at the dihydropyrrole
stage by a method developed by Olofson and Senet to dealkylate
In practice the dihydropyrroles (6a–e) were not isolated, but
were converted, in situ, to the respective pyrroles (7) by treatment
with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) (Scheme 5).
The results of this two step, one pot process are given in Table 2.
tertiary amines using the reagent a-chloroethyl chloroformate
(Scheme 7) [22]. Debenzylated dihydropyrrole 8 could then be
aromatized in the usual manner by treatment with DDQ to form
pyrrole 9.
Table 1
Conditions for generation of azomethine ylide 2 from precursor 4, and its cycloaddition with SF5-alkyne 5a to form dihydropyrrole 6a.
Entry
4 (eq)
Catalyst
Solvent
T (8C)
Conversion (%)
1
2
3
4
5
6
7
8
2
CsF (2 eq)
CsF (2 eq)
LiF (2 eq)
CH3CN
CH3CN
CH3CN
CH3CN
THF
rt
NR
2
Reflux
rt
NR
2
NR
2
LiF (2 eq)
Reflux
rt
NR
2
TBAF (2 eq)
TFA (0.2 eq)
TFA (0.2 eq)
TFA (0.2 eq)
100a
65
2
CH2Cl2
CH2Cl2
CH2Cl2
rt
4
rt
100
100b
2.5
Reflux
a
No desired product obtained.
b
Isolated yield is 96%.

W.R. Dolbier Jr., Z. Zheng / Journal of Fluorine Chemistry 132 (2011) 389–393
391
Scheme 4. Use of precursor 4 to generate azomethine ylide 2 for use in 1,3-dipolar cycloadditions with SF5-alkyne 5a.
Scheme 5. Two step, one pot synthesis of SF5-pyrroles.
Table 2
Synthesis of N-benzylpyrroles (7).
Entry
1
Substrate
Product yield (%)
7a, 96
S
SF5
5a
2
7b, 79
SF5
5b
5c
5d
3
4
5
7c, 80
7d, 88
7e, 78
SF5
SF5
TIPS
SF5
5e
2.2. SF5-thiophene synthesis
Chloromethyl trimethylsilylmethyl sulfide was first devised
and used as a parent thiocarbonyl ylide synthon by Sakurai in 1986
[23,24], being utilized to prepare di- and tetrahydrothiophenes via
1,3-dipolar cycloadditions by treatment with CsF in acetonitrile in
the presence of appropriate dipolarophiles [25]. Indeed, when
various SF5-aryl-substituted alkynes were used as substrates, the
cycloadditions proceeded smoothly to form the respective
dihydrothiophenes, 10a, c and d (Scheme 8). Alkynes substituted
with alkyl groups proved to be unsatisfactory substrates.
Scheme 6. Removal of TIPS group from pyrrole 7e.
Scheme 7. Removal of benzyl group from dihydropyrrole 6a.

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W.R. Dolbier Jr., Z. Zheng / Journal of Fluorine Chemistry 132 (2011) 389–393
Scheme 8. Synthesis of SF5-dihydrothiophenes and thiophenes.
Conversion of the dihydrothiophenes to the respective thio-
13CNMR
d 60.1, 61.8 (m), 64.8, 125.5 (m), 125.7, 127.6 (m), 127.7,
phenes proved more difficult than was the case for the pyrroles.
DDQ was ineffective, and the method which was finally successful
was treatment of the dihydrothiophenes with SO2Cl2 in methylene
chloride. Although this two step procedure is not as general as we
had hoped, nevertheless the synthesis depicted in Scheme 8
comprises, to our knowledge, the first reported preparation of SF5-
substituted thiophenes [26].
128.8, 128.9, 132.5, 137.0 (m), 138.1, 144.4 (m); 19F NMR
d 83.9 (p,
J = 164 Hz, 1F), 66.4 (d, J = 166 Hz, 4F).
4.3.2. N-benzyl-3-pentafluorosulfanyl-4-(3-thienyl)pyrrole (7a)
(96%); mp 69–71 8C; 1H NMR
5.00 (s, 2H), 6.57 (s, 1H), 7.13–
7.15 (m, 2H), 7.19–7.23 (m, 3H), 7.25–7.28 (m, 1H), 7.35–7.42 (m,
3H); 13C NMR
54.3, 117.5 (m), 120.3 (m), 122.1 (m), 123.1, 124.6,
127.9, 128.7, 129.30, 129.5 (m), 134.3, 135.9; 19F NMR
88.4 (p,
d
d
d
J = 168 Hz, 1F), 75.7 (d, J = 163 Hz, 4F); HRMS calcd for C15H12F5NS2
365.0331, found 365.0319; anal. calcd for C15H12F5NS2: C, 49.31; H,
3.31; N, 3.76. Found: C, 49.58; H, 3.25; N, 3.76.
3. Conclusion
In conclusion, by means of the 1,3-dipolar cycloadditions of in
situ-generated unsubstituted, ‘‘parent’’ azomethine and thiocar-
bonyl ylides 2 and 3 it has been possible to synthesize a variety of
3-aryl- and alkyl-substituted, 4-pentafluorosulfanylpyrroles and
3-aryl-substituted, 4-pentafluorosulfanylthiophenes, the latter to
our knowledge being the first reported SF5-substituted thiophenes.
4.3.3. N-benzyl-3-pentafluorosulfanyl-4-(2-phenylethyl)pyrrole (7b)
(79%); 1H NMR
d
2.93 (m, 4H), 4.95 (s, 2H), 6.33 (s, 1H), 7.06–
7.07 (d, J = 2.4 Hz, 1H), 7.13–7.16 (m, 2H), 7.22–7.25 (m, 3H), 7.30–
7.37 (m, 2H), 7.38–7.44 (m, 3H); 13C NMR
28.6, 36.8, 54.1, 118.9
(m), 120.7 (m), 121.6 (m), 126.2, 127.6, 128.50, 128.6, 128.7, 129.2,
136.4, 142.0; 19F NMR
89.6 (p, J = 164 Hz, 1F), 74.6 (d, J = 161 Hz,
d
d
4. Experimental
4F). HRMS calcd for C17H18F5NS 387.1080; found 388.1153 (M+H);
anal. calcd for C17H18F5NS: C, 58.90; H, 4.68; N, 3.62. Found: C,
58.74; H, 4.29; N, 3.78.
NMR spectra were obtained in CDCl3 using TMS as the internal
standard for 1H (300 MHz) and 13C NMR (75 MHz) and CFCl3 for 19
F
NMR (282 MHz). Melting points were uncorrected. Starting
material SF5-alkynes 5a–e were prepared according to the
previous literature [17,27].
4.3.4. N-benzyl-3-pentafluorosulfanyl-4-phenylpyrrole (7c)
(80%); 1H NMR
d
5.05 (s, 2H), 6.56 (s, 1H), 7.19 (s, 1H), 7.26–7.28
(d, J = 7.5 Hz, 2H), 7.37–7.44 (m, 8H); 13C NMR
54.3, 120.3, 121.8,
122.9, 127.3, 127.8, 127.9, 128.7, 129.3, 130.1, 134.9, 135.9; 19F NMR
d
4.1. Preparation of 1-pentafluorosulfanyl-2-(3-thienyl)-acetylene
(5a)
d
88.6 (p, J = 169 Hz, 1F), 76.2 (d, J = 163 Hz, 4F); HRMS calcd for
C17H14F5NS 359.0767, found 359.0786; anal. calcd for C17H14F5NS:
This new alkyne was prepared according to the literature [17]:
C, 56.82; H, 3.93; N, 3.90. Found: C, 56.47; H, 3.82; N, 4.01.
(60%) 1H NMR
d
7.18–7.20 (dd, J = 1.2, 3.6 Hz, 1H), 7.32–7.34 (dd,
J = 3.0, 2.1 Hz, 1H), 7.73–7.34 (m, 1H); 13C NMR
126.7, 129.8 (m),
134.0 (m); 19F NMR
83.6 (m, 4F), 76.9 (m, 1F).
d
4.3.5. N-benzyl-3-pentafluorosulfanyl-4-tolylpyrrole (7d)
d
(88%); 1H NMR
d
2.43 (s, 3H), 5.05 (s, 2H), 6.54 (s, 1H), 7.18–7.23
(m, 3H), 7.25–7.28 (m, 2H), 7.32–7.35 (m, 2H), 7.40–7.45 (m, 3H);
13C NMR
21.4, 54.2, 120.1, 121.6, 122.8, 127.8, 128.6, 129.2, 129.9,
131.9, 135.9, 136.9; 19F NMR
88.6 (p, J = 160 Hz, 1F), 76.1 (d,
4.2. General procedure for preparation of pyrroles 7a–f
d
d
Trifluoroacetic acid solution (0.9 mL, 0.2 eq, 1 M in CH2Cl2) was
slowly added to a mixture of 5 (4.27 mmol, 1 eq) and N-
J = 150 Hz, 4F); HRMS calcd for C18H16F5NS 373.0923, found
373.0921; anal. calcd for C18H16F5NS: C, 57.90; H, 4.32; N, 3.75.
Found: C, 57.65; H, 4.35; N, 3.80.
(methoxymethyl)-N-(trimethylsilylmethyl)-N-benzylamine
4
(10 mmol, 2.5 eq) in 10 mL CH2Cl2. After addition, the reaction
mixture was refluxed for 24 h, and then cooled with an ice-water
bath. DDQ (4.7 mmol, 1.1 eq) was then carefully added to the light-
yellow solution. After stirring for another 2 h, the dark-red mixture
was diluted with 10 mL CH2Cl2 and poured into saturated NaHCO3
solution (20 mL), the organic phase separated and solvent
evaporated. Column chromatography allowed isolation of the
product as either a white solid or a colorless liquid.
4.3.6. N-benzyl-3-pentafluorosulfanyl-4-triisopropylsilylpyrrole (7e)
(78%); mp 37–39 8C; 1H NMR
d
1.07–1.09 (d, J = 7.2 Hz, 18H),
1.31–1.41 (m, 3H), 5.05 (s, 2H), 6.67 (s, 1H), 7.08–7.11 (m, 2H),
7.18–7.19 (m, 1H), 7.31–7.39 (m, 3H); 13C NMR
12.6, 19.3, 53.8,
110.9 (m), 123.6 (m), 127.2, 128.4, 129.2, 129.4, 136.5, 142.5 (m);
19F NMR
89.4 (p, J = 164 Hz, 1F), 72.6 (d, J = 156 Hz, 4F); HRMS
d
d
calcd for C20H30F5NSSi 439.1788, found 440.1859 (M+H); anal.
calcd for C20H30F5NSSi: C, 54.64; H, 6.88; N, 3.19. Found: C, 54.67;
H, 6.62; N, 3.19.
The intermediate 6a was separated and characterized by NMR
analysis prior to its oxidative conversion to pyrrole 7a.
4.3. Yields, spectral and analytical data for pyrrole products
4.4. Preparation of N-benzyl-3-pentafluorosulfanylpyrrole (7f) from
7e
4.3.1. N-benzyl-3-pentafluorosulfanyl-4-(3-thienyl)-2,5-
dihydropyrrole (6a)
0.9 mL TBAF (1 M in THF) was added to a round flask containing
7e (200 mg, 0.455 mmol) and 3 mL THF, and then it was heated to
reflux overnight. The mixture was poured into water (5 mL),
1H NMR
d
3.79 (s, 2H), 3.84–3,87 (m, 2H), 4.00–4.03 (t,
J = 4.2 Hz, 2H), 7.13–7.14 (d, J = 4.8 Hz, 1H), 7.26–7.36 (m, 7H);

W.R. Dolbier Jr., Z. Zheng / Journal of Fluorine Chemistry 132 (2011) 389–393
393
extracted with CH2Cl2 (5 mL ꢀ 3), the solvent removed, and the
residue purified by column chromatography. Product 7f (0.12 g)
was obtained (95%) as a colorless oil: 1H NMR
5.04 (s, 2H), 6.43–
6.45 (m, 1H), 6.60 (s, 1H), 7.05 (s, 1H), 7.15–7.18 (m, 2H), 7.32–7.42
(m, 3H); 13C NMR
54.2, 107.3 (m), 120.1 (m), 120.4, 127.6, 128.6,
129.2, 136.2; 19F NMR
87.6 (p, J = 162 Hz, 1F), 70.8 (d, J = 163 Hz,
4F); HRMS calcd for C11H10F5NS 283.0454, found 283.0458; anal.
calcd for C11H10F5NS: C, 46.64; H, 3.56; N, 4.94. Found: C, 46.82; H,
3.55; N, 5.15.
128.36, 135.51, 145.32, 148.62 (m); 19F NMR
1F), 66.11 (d, J = 163 Hz, 4F).
d
83.00 (p, J = 152 Hz,
d
4.8.3. 3-Pentafluorosulfanyl-4-p-tolyl-dihydrothiophene (10d)
1H NMR
2.36 (s, 3H), 3.99 (s, 2H), 4.31–4.34 (t, J = 5.1 Hz, 2H),
7.06–7.08 (d, J = 8.1 Hz, 2H), 7.17–7.19 (d, J = 7.8 Hz, 2H); 13C NMR
21.43, 39.68, 44.09, 126.86, 129.12, 132.40, 138.34, 145.50, 148.34
(m); 19F NMR
83.12 (p, J = 153 Hz, 1F), 67.05 (d, J = 163 Hz, 4F).
d
d
d
d
d
4.9. Spectral and analytical data for thiophenes (11)
4.5. Preparation of 3-pentafluorosulfanyl-4-(3-thienyl)-2,5-dihydro-
pyrrole (8)
4.9.1. 3-Pentafluorosulfanyl-4-(30-thienyl)thiophene (11a)
1H NMR
d
7.07–7.08 (d, J = 4.8 Hz, 1H), 7.12–7.14 (m, 1H), 7.23–
7.24 (dd, J = 1.2, 2.1 Hz, 1H), 7.28–7.31 (dd, J = 3, 1.8 Hz, 1H), 7.85–
7.87 (d, J = 3.9 Hz, 1H); 13C NMR
124.7, 125.3, 128.3, 129.3, 134.6,
135.3, 150.3; 19F NMR
84.0 (m, 1F), 72.1 (d, J = 162 Hz, 4F). HRMS
Following the procedure of Renslo et al. [28], 1-chloroethyl
chloroformate (156 mg, 1.1 mmol) was added to a solution of 6a
(200 mg, 0.55 mmol) and triethylamine (55 mg, 0.55 mmol) in
2 mL CH2Cl2 at 0 8C with stirring. The mixture was then
concentrated after 30 min, dissolved in methanol (2 mL) and
stirred overnight. The solvent was then removed, and the residue
underwent column chromatography to produce 102 mg of
d
d
calcd for C8H5F5S3 291.9474, found 291.9504.
4.9.2. 3-Pentafluorosulfanyl-4-phenylthiophene (11c)
1H NMR
d
7.10–7.12 (m, 1H), 7.31–7.34 (m, 2H), 7.38–7.40 (m,
3H), 7.89–7.90 (d, J = 3.9 Hz, 1H); 13C NMR
125.02, 127.80,
128.10, 129.81, 136.07, 139.80, 150.65 (m); 19F NMR
84.11 (p,
colorless oil product 8 (68%): 1H NMR
2H), 4.19–4.21 (t, J = 7.2 Hz, 2H), 7.10–7.11 (d, J = 4.8 Hz, 1H), 7.26–
d
2.17 (s, 2H), 4.06 (m,
d
d
7.29 (m, 1H), 7.33–7.34 (m, 1H); 13C NMR
d
56.9 (m), 59.8, 125.2
J = 161 Hz, 1F), 72.08 (d, J = 162 Hz, 4F); HRMS calcd for C10H7F5S2
285.9909, found 285.9929; anal. calcd for C10H7F5S2: C, 41.95; H,
2.46. Found: C, 42.28; H, 2.49.
(m), 125.7, 127.5, 132.2, 139.1 (m), 147.1 (m); 19FNMR
d 84.2 (p,
J = 162 Hz, 1F), 67.4 (d, J = 164 Hz, 4F).
4.6. Preparation of 3-pentafluorosulfanyl-4-(3-thienyl)pyrrole (9)
4.9.3. 3-Pentafluorosulfanyl-4-p-tolylthiophene (11d)
mp 73–75 8C; 1H NMR
d
2.40 (s, 3H), 7.07 (m, 1H), 7.19 (s,, 4H),
7.87–7.88 (d, J = 3.9 Hz, 1H); 13C NMR
21.43, 124.93, 127.90,
128.50, 129.64, 133.09, 137.85, 139.77, 150.65 (m); 19F NMR
84.27 (p, J = 167 Hz, 1F), 72.55 (d, J = 162 Hz, 4F); HRMS calcd for
11H9F5S2 300.0066, found 300.0060; anal. calcd for C11H9F5S2: C,
DDQ (125 mg, 0.66 mmol) was added to a solution of 8 in CH2Cl2
at 0 8Cwithstirring,afterstandingfor2 h, themixturewassubmitted
to column directly. 95 mg of 9 as a colorless oil was obtained (95%):
d
d
1HNMR (CDCl3),
(m, 2H), 7.26–7.29 (m, 1H), 8.43 (s, 1H); 13CNMR,
(m), 123.2, 124.7, 129.6, 134.1, 136.6 (m); 19FNMR,
d
6.67 (s, 1H), 7.12–7.14(d, J = 5.1 Hz, 1H), 7.21–7.22
117.4 (m), 119.4
87.9 (p,
C
d
43.99; H, 3.02. Found: C, 43.91; H, 3.06.
d
J = 167 Hz, 1F), 75.5 (d, J = 163 Hz, 4F). HRMS calcd for C8H6F5NS2
274.9862, found 274.9864; anal. calcd for C8H6F5NS2: C, 34.91; H,
2.20; N, 5.09. Found: C, 35.29; H, 2.25; N, 4.75.
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TBAF (1.0 M in THF, 1.3–5 eq) was added to a mixture of
chloromethyl trimethylsilylmethyl sulfide (1.3–5 eq) and SF5-
alkyne (5a, c or d) (1 eq) in THF at room temperature. After stirring
for several hours (monitoring by 19F NMR), the reactions were
quenched by water and submitted to column chromatography.
Products 10a, c or d were obtained as white solids.
A solution of 10a, c or d in DCM was cooled to ꢁ30 8C, after
which sulfuryl chloride (2 eq) was added slowly during 10 min.
After stirring for another 30 min, the reaction was quenched by
water, and the organic phase was separated and dried by Na2SO4.
The solvent was evaporated, and the residue purified by column
chromatograph to give 11a, c, or d as white solids or colorless oils.
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4.8. Spectral data for dihydrothiophenes (10)
4.8.1. 3-Pentafluorosulfanyl-4-(30-thienyl)-dihydrothiophene (10a)
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1H NMR
d
3.96–4.01 (m, 2H), 4.26–4.29 (t, J = 4.8 Hz, 2H), 6.96–
6.98 (d, J = 5.1 Hz, 1H), 7.19–7.20 (d, J = 1.8 Hz, 1H), 7.28–7.31 (dd,
J = 5.1 Hz, 1H); 13C NMR
d 39.54, 43.23, 123.82, 125.94, 127.12,
134.22, 140.91, 148.72 (m); 19F NMR
d 82.97 (p, J = 161 Hz, 1F),
66.11 (d, J = 164 Hz, 4F).
4.8.2. 3-Pentafluorosulfanyl-4-phenyl-dihydrothiophene (10c)
1H NMR
3.99–4.04 (m, 2H), 4.33–4.39 (t, J = 4.8 Hz, 2H), 7.17–
7.20 (m, 2H), 7.35–7.38 (m, 3H); 13C NMR
39.74, 44.10, 127.00,
d
d