Expeditious synthesis of fluorinated styrylbenzenes and polyaromatic hydrocarbons

Article abstract of DOI:10.1016/j.tetlet.2012.11.022

A series of fluorinated styrylbenzene derivatives were synthesized by the Mizoroki-Heck reaction using phosphine-free catalytic conditions or by adopting the one-pot Wittig-Heck reaction sequence. The fluorinated styrylbenzenes were converted into polyaromatic hydrocarbons such as phenanthrenes, [4]helicenes, and benzo[ghi]perylene by a modified photocyclization procedure involving I ₂-THF condition.

Full text of DOI:10.1016/j.tetlet.2012.11.022

Tetrahedron Letters 54 (2013) 392–396
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Expeditious synthesis of fluorinated styrylbenzenes and polyaromatic
hydrocarbons
Ashutosh V. Bedekar a, , Anju R. Chaudhary a, M. Shyam Sundar a, Murali Rajappa b
⇑
a Department of Chemistry, Faculty of Science, M.S. University of Baroda, Vadodara, Gujarat 390 002, India
b Navin Fluorine International Limited, Udhna-Navsari Road, Bhestan, Surat, Gujarat 395 023, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of fluorinated styrylbenzene derivatives were synthesized by the Mizoroki–Heck reaction using
phosphine-free catalytic conditions or by adopting the one-pot Wittig–Heck reaction sequence. The
fluorinated styrylbenzenes were converted into polyaromatic hydrocarbons such as phenanthrenes,
Received 8 October 2012
Revised 4 November 2012
Accepted 5 November 2012
Available online 21 November 2012
[4]helicenes, and benzo[ghi]perylene by
a
modified photocyclization procedure involving I2-THF
condition.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Mizoroki–Heck
One-pot Reactions
Photocyclization
Fluorinated styrylbenzenes
Fluorinated polyaromatic hydrocarbons
Fluorinated polyaromatic hydrocarbons (F-PHCs) play an
important role in understanding the action and the mechanism
of carcinogenesis of this class of compounds. Presence of fluorine
at different positions of the PHC helps to narrow the possible active
sites to bind with DNA1 or in modulating the carcinogenicity from
the remote sites2 or understanding other conformational parame-
ters.3 The study has established that certain F-PHCs have lower
biological activity due to the presence of fluorine at the crucial sec-
tion of the molecular framework and hence are less tumorigenic
than the parent PHCs.1b,4 The derivatives of F-PHCs also have a sig-
nificant role in the study of reactions of standard nucleophiles with
radical cations.5 Recently polyaromatic compounds such as hexa-
benzocoronenes with the presence of a number of fluorine substit-
uents have shown novel metastable molecular conformations.6
Besides these the F-PHCs have a wide range of applications in
molecular recognition, Host–Guest interactions, material chemis-
try, biologically important compounds,7 medicinal chemistry,8 li-
quid crystals,9 and crystal engineering.10
build the structure of F-PHC and has been successfully demon-
strated in some cases.17–21
Recently we have developed phosphine-free catalyst systems
for efficient Mizoroki–Heck reaction22 as well as
a one-pot
Wittig–Heck reaction sequence.23 One of the useful methods of
synthesis of phenanthrenes, benzo[c]phenanthrenes, and helicenes
is photocyclization of the corresponding stilbene derivatives.24 In
our earlier studies we have also developed an efficient modifica-
tion of this photocyclization procedure by replacing the conven-
tionally preferred propylene oxide as the acid scavenger with
readily available tetrahydrofuran.25 In this communication we
present a combination of these two methods to synthesize fluori-
nated polyaromatic hydrocarbons.
The Path A of Scheme 1 describes the basic Mizoroki–Heck
reaction to construct styrylbenzene derivative. The phosphine free
catalyst system [comprising of the in situ mixture of ligand
1-(a-aminobenzyl)-2-naphthols L and Pd(OAc)2] was screened
for standard Mizoroki–Heck reaction with fluorinated aromatic
bromo compounds 1, 7, or 10 with good conversions, Scheme 2.
The stilbenes obtained are isolated in excellent yield under the
experimental conditions.
However, this approach is limited to the availability of the cor-
responding styrene derivatives. To overcome this limitation we
had developed the one-pot approach of in situ synthesis of styrene
from the aldehydes by the Wittig reaction and utilized it for the
subsequent Mizoroki–Heck reaction.23 The advantage of this reac-
tion is the availability of a range of aldehydes with varied func-
tional groups and the elimination of the need of purification of
The area of chemistry of fluorinated organic molecules has been
a subject of immense research and several monograms and books
are now available for reference.11 Generally the fluorine atom is
introduced by various special fluorinating methods on the sub-
strate molecules.12 This approach of accessing F-PHCs often has a
drawback of formation of unwanted isomers.12c,13–16 The other op-
tion is to select an appropriately fluorinated starting molecule and
⇑
Corresponding author. Tel.: +91 0265 2795552.
E-mail address: avbedekar@yahoo.co.in (A.V. Bedekar).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.11.022

A. V. Bedekar et al. / Tetrahedron Letters 54 (2013) 392–396
393
Path A
Path B
+
-
F
F
i.
CH3PPh3I
Br
CHO
Wittig Conditions
Pd/L
Heck Conditions
ii. 1, Heck Condition
F
1
2
F
F
3
[67 %]
[89 %]
5
F
Path B
+
-
+
-
CHO
CH3PPh3I
i.
CH3PPh3I
CHO
Wittig Conditions
Wittig Conditions
F
F
3
4
ii. 1, Heck Condition
Cl
13
F
14
Cl
Pd/L
Heck Conditions
+
-
F
F
Ph
N
Br
1
i.
CH3PPh3I
F
CHO
O
Wittig Conditions
OH
O
O
ii. 1, Heck Condition
O
15
[52 %]
16
L
5
F
+
-
i.
CH3PPh3I
Scheme 1. Synthesis of fluorinated stilbenes.
CHO
Wittig Conditions
ii. 1, Heck Condition
Path A
17
[61 %]
18
+
-
F
Br
i.
CH3PPh3I
Wittig Conditions
17
17
Pd/L
Heck Conditions
F
1
2
6
[92 %]
[82 %]
ii. 7, Heck Condition
F
[41 %]
19
CH3
CH3
+
-
i.
CH3PPh3I
1
Wittig Conditions
Pd/L
Heck Conditions
CF3
ii. 10, Heck Condition
F
[77 %]
20
Scheme 3. Synthesis of stilbene derivatives by Path B. One-pot Wittig–Heck
conditions: Ar-CHO (1.5 equiv), CH3PPh3I (1.5 equiv), Ar-Br (1.0 equiv), Pd(OAc)2
(0.5 mol %), L (0.6 mol %), K2CO3 (4.0 equiv), TBAB (0.2 equiv), DMA, N2 atm, 140 °C,
40 h.
Br
F
Pd/L
Heck Conditions
7
8
9
[70 %]
F
F
CH3
hυ,
THF-I2
PhCH3
CH3
7
24 h
F
Pd/L
Heck Conditions
98 %
2
21
[86 %]
[84 %]
F
Scheme 4. Photodehydrocyclization of fluorinated stilbenes.
F3C
Br
F3C
A series of fluorine containing styrylbenzenes were synthesized
from corresponding aromatic aldehydes 3, 13, 15, and 17 via their
in situ conversion to styrenes and the subsequent Mizoroki–Heck
reaction with suitable aryl halide as outlined in Scheme 3. As an
example the reaction of 4-fluorobenzaldehyde 3 with one carbon
phosphonium salt (Ph3PCH3I) and base will produce 4-fluorosty-
rene 4, which will undergo in situ Mizoroki–Heck reaction with
1-bromo-4-fluorobenzene 1 to form 4,40-difluoro stilbene 5 in
moderate yield. Although the overall yields of such approach are
slightly lower as the conditions are not currently fully optimized,
this path offers wider scope for easy access to a variety of fluori-
nated stilbenes.
Pd/L
Heck Conditions
10
11
CH3
F3C
CH3
10
Pd/L
Heck Conditions
12
[98 %]
Scheme 2. Synthesis of stilbene derivatives by Path A. Heck conditions: Ar-Br
(1.0 equiv), styrene (1.5 equiv), Pd(OAc)2 (0.5 mol %),
(2.5 equiv), TBAB (0.2 equiv), DMA, N2 atm, 140 °C, 40 h.
L (0.6 mol %), K2CO3
The standard method of photodehydrocyclization of stilbene in
the presence of iodine as the oxidant produces phenanthrene and
hydriodic acid, HI. Since this acid needs to be neutralized usually
propylene oxide is used as an acid scavenger. However, the use
of propylene oxide requires slight care as it has low boiling point
the styrene for the coupling reactions. This strategy utilizes two
aromatic moieties (Ar1CHO and Ar2X), to construct the stilbene
unit and offers a variety of two different fluorine or fluorine con-
taining substitutions as shown in Path B of Scheme 1.

394
A. V. Bedekar et al. / Tetrahedron Letters 54 (2013) 392–396
Table 1
Table 1 (continued)
Photocyclization of fluorinated stilbenes
No.
11
Stilbene
Derivative
Cyclized product
No.
Stilbene
Derivative
Cyclized product
20
ƒƒƒƒƒ!
82%
F
1
6
ƒƒƒƒƒ!
96%
CF3
22
32
Conditions for photocyclization: iodine (1.1 equiv), THF (100 equiv), toluene, 125 W
HPMV lamp, 24 h.
CH3
F
2
3
8
9
ƒƒƒƒƒ!
97%
and proper cooling is necessary to prevent its loss during reaction.
We have developed a modified method of similar photodehydro-
cyclization utilizing commonly available tetrahydrofuran as a
readily available, less toxic acid scavenger with higher boiling
point for practical applications.25 The modified method is applied
for the photodehydrocyclization of fluorinated stilbenes for the
synthesis of corresponding fluorine containing phenanthrene
derivatives, Scheme 4.
23
F
ƒƒƒƒƒ!
95%
24
The photolysis is performed with iodine and excess of THF in
degassed toluene under the irradiation of high pressure mercury
vapor lamp till the cyclization is complete. The cyclization in most
cases was complete in 24 h with excellent conversions as can be
seen from the examples listed in Table 1. The 1,3-dioxolane con-
taining derivative of stilbene 16 prepared from piperonal 15, on
photodehydrocyclization gave a linear product 29 instead of the
angular product due to the steric constraints.26 The fluorinated
helical PHCs are also important compounds and a set of fluorinated
[4]helicenes 30, 31, and 32 were prepared from the corresponding
styrylnaphthalenes 18, 19, and 20, respectively, in good chemical
yields. In all the three cases the angular cyclization occurred and
no linear products were detected.
CH3
F3C
4
5
11
12
ƒƒƒƒƒ!
98%
25
F3C
ƒƒƒƒƒ!
84%
26
CH3
Having established the conditions for the improved procedure of
photodehydrocyclization of fluorinated stilbenes it was envisaged
to apply this strategy for the construction of larger F-PHCs by
selecting fluorinated bis(stilbenes) or tris(stilbenes) as substrates.
With this aim a number of such conjugated compounds were syn-
thesized. The method of one-pot Wittig–Heck reaction developed
in our laboratory23 was extended for the synthesis of 1,4-bis(4-flu-
orostyryl)benzene 35.27 The process involved in situ synthesis of
divinylbenzene starting from terephthalaldehyde 33 and the Wittig
salt (Ph3PCH3I), which was trapped by the Mizoroki–Heck reaction
with p-bromofluorobenzene 1 (Scheme 5). The reaction furnished a
mixture of mono-Heck reaction product 34 and the expected dou-
ble Heck reaction product 35, the former was separated and further
subjected to Mizoroki–Heck conditions22 with iodobenzene to pre-
pare 1-(4-fluorostyryl)-4-styrylbenzene 36 in excellent yield. The
sample of 36 was subjected to the standard photocyclization condi-
tion, however the expected 2-fluoro[5]helicene 37 was not detected
but 5-fluorobenzo[ghi]perylene 38 was isolated in small amount.
Such type of further cyclization of [5]helicene is a common occur-
rence under photochemical conditions.19a,28
F
6
7
8
5
ƒƒƒƒƒ!
98%
27
F
Cl
14
16
ƒƒƒƒƒ!
96%
28
F
O
O
ƒƒƒƒƒ!
28%
29
F
Synthesis of 35 by the above approach was less effective prob-
ably due to the polymerization and cross-linking of in situ formed
divinylstyrene. Another approach for its synthesis was investigated
where 4-fluorostyrene was in situ synthesized and subjected to a
double Mizoroki–Heck reaction with 1,4-dibromobenzene 39
(Scheme 6). This approach was a better option for accessing the de-
sired 1,4-bis(4-fluorostyryl)benzene 35.
9
18
19
ƒƒƒƒƒ!
71%
30
F
F
10
ƒƒƒƒƒ!
81%
Another route for the preparation of 2-fluoro[5]helicene was
investigated where 3-bromophenanthrene 43 was prepared from
31

A. V. Bedekar et al. / Tetrahedron Letters 54 (2013) 392–396
395
+
-
+
-
i.
i.
CH3PPh3I
CH3PPh3I
Wittig Conditions
Wittig Conditions
OHC
CHO
33
F
CHO
ii. Heck Condition
Br
ii. Heck Condition
Br
3
1
39
F
F
Br
F
Br
+
+
34 (26 %)
F
35 (11 %)
40 (21 %)
F
35 (32 %)
F
F
Ph I
Scheme 6. Improved Synthesis of 1,4-bis(4-fluorostyryl)benzene 35. One-pot
Wittig–Heck conditions: Ar(Br)2 39 (1.0 equiv), 3 (2.5 equiv), CH3PPh3I (2.5 equiv),
Pd(OAc)2 (2.0 mol %), L (2.4 mol %), K2CO3 (8.0 equiv), TBAB (0.4 equiv), DMA, N2
atm, 140 °C, 40 h.
Heck Condition
36 (84 %)
hυ,
Wittig Conditions
PPh3Br
F
Br
PhCHO
Br
24 h
41
THF-I2
PhCH3
42 (95%)
hυ,
24 h THF-I2
PhCH3
+
-
F
F
CH3PPh3I
Wittig Conditions
CHO
Br
3
37 (Expected)
38 (15 %)
F
43 (76 %)
Heck Condition
Scheme 5. Attempted synthesis of 2-fluoro[5]helicene. Conditions for Wittig–Heck
step: Ar(CHO)2 33 (1.0 equiv), CH3PPh3I (2.5 equiv), ArBr 1 (2.5 equiv), Pd(OAc)2
(1.0 mol %), L (1.2 mol %), K2CO3 (8.0 equiv), TBAB (0.4 equiv), DMA, N2 atm, 140 °C,
40 h. Conditions for Mizoroki–Heck step: 34 (1.2 equiv), PhI (1.0 equiv), Pd(OAc)2
(0.5 mol %), L (0.6 mol %), K2CO3 (2.5 equiv), DMA, N2 atm, 140 °C, 40 h.
F
44 (70 %)
hυ,
THF-I2
PhCH3
18 h
.
.
F
the phosphonium salt 41 via an intermediate 4-bromostilbene 42.
This bromophenanthrene 43 was subjected to another one-pot
Wittig–Heck reaction sequence to introduce fluorinated stilbene
derivative 44. However the photolysis of 44 also resulted in the for-
mation of 5-fluorobenzo[ghi]perylene 38 as a major product
(Scheme 7). It is noteworthy that photocyclization of distyrylben-
zene 36 as well as styrylphenanthrene 44 gave the same product
38 but the latter case was more efficient possibly due to the forma-
tion of a more stable diradical intermediate 44a.
F
38 (43 %)
44a
Scheme 7. Attempted synthesis fluoro[5[helicene. Conditions for Wittig step: PhCHO
(1.0 equiv), 41 (1.1 equiv), Na (1.1 equiv), MeOH, rt, N2 atm, 24 h. Conditions for
3 (1.5 equiv), CH3PPh3I (1.5 equiv), Pd(OAc)2
(0.5 mol %), L (0.6 mol %), K2CO3 (2.5 equiv), TBAB (0.4 equiv), DMA, N2 atm, 140 °C,
Wittig–Heck step: 43 (1.0 equiv),
40 h.
In continuation with our efforts to construct highly conjugated
fluorinated molecules a combination of Wittig–Heck reaction was
performed on 4-fluorobenzaldehyde 3 to make in situ 4-fluorosty-
rene which was trapped by the triple Heck reaction with 1,3,5-trib-
romobenzene 45 (Scheme 8). The fluorinated tri-styrylbenzene 46
was isolated in all E form, but efforts to subject it to the photolysis
to construct trifluoro benzo[c]naphtha[2,1-p]chrysene29 were not
successful. Under the present conditions several unidentifiable
products were detected during the photochemical reaction of 46.
In this Letter we present our initial results for the synthesis of
fluorine containing styrylbenzene derivatives by the Mizoroki–
Heck reaction and the one-pot Wittig–Heck reaction sequence.
The fluorinated stilbene derivatives were then subjected to modi-
fied photodehydrocyclization reaction to efficiently prepare several
fluorinated polyaromatic hydrocarbons.30
F
F
+
-
i.
CH3PPh3I
CHO
Wittig Conditions
ii. Heck Condition
F
3
Br
Br
46 (35%)
45
Br
F
Scheme 8. Synthesis of tri-styrylbenzene derivative. One-pot Wittig–Heck condi-
tions: Ar(Br)3 45 (1.0 equiv), (3.6 equiv), CH3PPh3I (3.6 equiv), Pd(OAc)2
(3.6 mol %), K2CO3 (12.0 equiv), TBAB (0.6 equiv), DMA, N2 atm,
3
(3.0 mol %),
140 °C, 40 h.
L

396
A. V. Bedekar et al. / Tetrahedron Letters 54 (2013) 392–396
19. (a) Mallory, F. B.; Mallory, C. W. J. Org. Chem. 1983, 48, 526; (b) Weis, U.;
Acknowledgment
Andersson, J. T. Polycyclic Aromat. Compd. 2002, 22, 71.
20. Li, S.; Xiang, J.; Mei, X.; Xu, C. Tetrahedron Lett. 2008, 49, 1690.
21. Amsharov, K. Y.; Kabdulov, M. A.; Jansen, M. Eur. J. Org. Chem. 2009, 6328.
22. Chaudhary, A. R.; Bedekar, A. V. Synth. Commun. 2012, 42, 1778.
23. (a) Saiyed, A. S.; Bedekar, A. V. Tetrahedron Lett. 2010, 51, 6227; (b) Saiyed, A. S.;
Patel, K. N.; Kamath, B. V.; Bedekar, A. V. Tetrahedron Lett. 2012, 53, 4692.
24. (a) Harvey, F. R. Polycyclic Aromatic Hydrocarbons; Wiley-VCH: New York, 1997;
(b) Shen, Y.; Chen, C.-F. Chem. Rev. 2012, 112, 1463.
25. (a) Talele, H. R.; Gohil, M. J.; Bedekar, A. V. Bull. Chem. Soc. Jpn. 2009, 82, 1182;
(b) Talele, H. R.; Chaudhary, A. R.; Patel, P. R.; Bedekar, A. V. ARKIVOC 2011, ix,
15.
Financial support for this work by the Council of Scientific and
Industrial Research (CSIR), New Delhi [No. 01(2386)/10/EMR-II] is
gratefully acknowledged. We also thank CSIR, New Delhi for the
award of research fellowship to ARC, Navin Fluorine International
Limited for providing samples of fluorinated reagents and Profes-
sor B.V. Kamath, Head, Department of Chemistry for the infrastruc-
tural facilities and constant encouragements.
26. A similar observation was reported earlier, see Ref. 25a.
27. Renak, M. L.; Bartholomew, G. P.; Wang, S.; Ricatto, P. J.; Lachicotte, R. J.; Bazan,
G. C. J. Am. Chem. Soc. 1999, 121, 7787.
References and notes
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45, 2064; (b) Boger, E.; O’Malley, R. F.; Sardella, D. J. J. Fluorine Chem. 1976, 8,
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29. (a) Winter, W.; Langjahr, U.; Meier, H.; Merkushev, E. B.; Yur´ev, Y. G. Chem. Ber.
1984, 117, 2452; (b) Erickson, M. S.; Miliken, J. Polycyclic Aromat. Compd. 1996,
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38; (b) Black, S. D.; Sharma, P. K.; Gallucci, J. D.; Blackburn, A. C.; Downs, J. W.;
Rinderle, S. J.; Witiak, D. T. Carcinogenesis 1992, 13, 1337; (c) Harvey, R. G.;
Dunne, F. B. Science 1978, 273, 566; (d) Bernard Daniel, F.; Cazer, F. D.;
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DiGiovanni, J. Chem. Res. Toxicol. 1996, 9, 722.
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30. Representative procedure for the one pot Wittig–Heck reaction:
E-2-[2-(4-Fluorophenyl)vinyl]naphthalene (18):
In dry N2 flushed two-necked r.b. flask a mixture of p-bromofluorobenzene
(0.50 g,
triphenylmethylphosphonium iodide (1.73 g, 4.286 mmol), palladium acetate
(0.0032 g, 0.014 mmol) and (0.0055 mg, 0.017 mmol), TBAB (0.184 g,
0.571 mmol), and K2CO3 (1.591 g, 11.43 mmol) in dry N,N-
2.857 mmol),
2-naphthaldehyde
(0.67 g,
4.286 mmol),
L
dimethylacetamide (20 mL) was taken and kept under N2 atmosphere. The
reaction mixture heated to 140 °C for 40 h. The cooled mixture was then
poured into water (25 mL) and extracted with ethyl acetate (3 ꢀ 25 mL). The
combined organic layer was washed with water (2 ꢀ 20 mL), dried with
anhydrous sodium sulfate, concentrated in vacuum and purified by column
chromatography over silica gel and petroleum ether as eluent to give E-2-[2-
(4-fluorophenyl)vinyl]naphthalene 18 as white solid (0.428 g, 61%); mp 148–
150 °C (Lit.21 151–152 °C).
1H NMR (CDCl3, 400 MHz) d 7.89–7.83 (m, 4H), 7.77–7.74 (dd, J = 8.8, 1.6 Hz,
1H), 7.6–7.46 (m, 4H), 7.22 (s, 2H), 7.12–7.07 (m, 2H).
Mass (EI) 248.5 (M)+ (40), 247.8 (98), 247 (55), 246 (100), 245 (39), 229 (23).
IR (KBr) 3051, 3017, 2926, 2354, 1897, 1666, 1596, 1509, 1411, 1238, 1158,
1097, 966, 903, 855, 826, 740, 694, 641 cmꢁ1
.
General procedure for photodehydrocyclization:
2-Fluorobenzo[c] phenanthrene (30):
10. Reichenbächer, K.; Süss, H. I.; Hulliger, J. Chem. Soc. Res. 2005, 34, 22.
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Chemists; Oxford University Press: New York, 2000; (c) Hiyama, T. In
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Synthesis, Reactivity Applications; Wiley-VCH: Weinheim, 2004.
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307; (c) Lal, G. S.; Pez, G. P.; Syvret, R. G. Chem. Rev. 1996, 96, 1737; (d) Adams,
D. J.; Clark, J. H. Chem. Soc. Rev. 1999, 28, 225; (e) Singh, R. P.; Shreeve, J. M. Acc.
Chem. Res. 2004, 37, 31; (f) Ma, J. –A.; Cahard, D. Chem. Rev. 2004, 104, 6119; (g)
Wang, Y.; Burton, D. J. Tetrahedron Lett. 2006, 47, 9279. and the references cited
therein.
To
a
solution of E-2-[2-(4-fluorophenyl)vinyl]naphthalene 18 (0.20 g,
0.806 mmol) in toluene (550 mL) was added iodine (225 mg, 0.887 mmol)
and dry tetrahydrofuran (6.6 mL, 80.64 mmol) in a standerd immersion photo
reactor. The mixture is degassed (15 min.) by sonication and irradiated with
125 W high pressure mercury vapor lamp for 24 h. The reaction mixture was
washed with aquous sodium thiosulfate (3 ꢀ 150 mL), dried over anhydrous
sodium sulfate. The solvent was removed under reduced pressure. The residue
was chromatograhed on silica gel column by eluting with petroleum ether to
afford 2-fluorobenzo[c]phenanthrene 30 as white solid (0.14 g, 71%), mp 64–
66 °C (Lit.31 63.7–64.1 °C).
1H NMR (400 MHz, CDCl3)
d 9.09–9.07 (d, J = 8.4 Hz, 1H), 8.84–8.80 (dd,
J = 12.4, 2.4 Hz, 1H), 8.05–8.99 (m, 2H), 7.94–7.89 (m, 2H), 7.85–7.79 (m, 2H),
7.74–7.69 (m, 1H), 7.68–7.63 (m, 1H), 7.43–7.38 (td, J = 8.8, 2.8 Hz, 1H).
Mass (EI) 246.3 (100), 245.2 (93), 243.8 (80), 241.7 (15), 228.3 (20), 227.2 (20),
226.1(18), 225.2 (11), 121.9 (60), 113.1 (12), 112.1 (11), 110.1 (11), 98.7 (10).
13. Laali, K. K.; Tanaka, M.; Forohar, F.; Cheng, M.; Fetzer, J. C. J. Fluorine Chem.
1998, 91, 185.
14. Filler, R. Isr. J. Chem. 1978, 17, 71.
15. Rozen, S. Chem. Rev. 1996, 96, 1717.
16. Laali, K. K.; Hansen, P. E. J. Org. Chem. 1993, 58, 417.
IR (KBr)
1124, 1010, 974, 885, 837, 784, 744 cmꢁ1
31. Ittah, Y.; Jerina, D. M. J. Fluorine Chem. 1980, 16, 137.
t 3046, 1684, 1598, 1499, 1429, 1357, 1289, 1247, 1216, 1199, 1176,
.
17. Bernstein, W. J.; Calvin, M.; Buchardt, O. J. Am. Chem. Soc. 1973, 95, 527.
18. Sardella, D. J.; Ghoshal, P. K.; Boger, E. J. Fluorine Chem. 1982, 20, 459.