Synthesis and Diels-Alder cycloaddition reactions of [(2,2-dichloro-1- fluoroethenyl)sulfinyl] benzene and [(2-chloro-1,2-difluoro ethenyl)sulfinyl] benzene

Article abstract of DOI:10.1016/S0040-4020(00)00242-8

Synthesis of [(2,2-dichloro-1-fluoroethenyl)sulfinyl] benzene and [(2- chloro-1,2-difluoro ethenyl)sulfinyl] benzene and their Dieis-Alder cycloadditions with cyclopentadiene, furan and 1,3-diphenylisobenzofuran under thermal and microwave irradiation conditions are described. 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00242-8

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 3539±3545
Synthesis and Diels±Alder Cycloaddition Reactions of
[(2,2-Dichloro-1-¯uoroethenyl)sul®nyl] Benzene and
[(2-Chloro-1,2-di¯uoro ethenyl)sul®nyl] Benzeneq
*
Madabhushi Sridhar, K. Leela Krishna and Jampani Madhusudana Rao
Organic Chemistry Division-II, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 3 December 1999; revised 29 February 2000; accepted 16 March 2000
AbstractÐSynthesis of [(2,2-dichloro-1-¯uoroethenyl)sul®nyl] benzene and [(2-chloro-1,2-di¯uoro ethenyl)sul®nyl] benzene and their
Diels±Alder cycloadditions with cyclopentadiene, furan and 1,3-diphenylisobenzofuran under thermal and microwave irradiation conditions
are described. q 2000 Elsevier Science Ltd. All rights reserved.
Though ¯uorine substituted vinyl compounds are not very
reactive species, they are considered to be important build-
ing blocks in construction of ¯uorine substituted carbo-
cycles.1,2 This has prompted extensive studies in recent
years in developing novel and reactive ¯uorovinyl
compounds.3
under conventional heating and microwave irradiation
conditions.
The dienophiles 5a and 5b are prepared starting from
1,1,1,2-tetrachloro-2,2-di¯uoroethane and 1,1,2-trichloro-
1,2,2-tri¯uoroethane respectively using the reported pro-
cedure9 as shown in Scheme 1.
Vinyl sulfoxides are valuable dienophiles4 and widely in use
in asymmetric Diels±Alder reaction studies.5 Reactions of
these dienophiles are also highly sluggish but their reactivity
could improve considerably when they are activated further
with a functionality such as ±COOR,6 ±NO2,7 ±SO2Ph8 etc.
In the literature no reports are known on Diels±Alder
cycloaddition reactions of ¯uorine substituted vinyl-
sulfoxides and hence, the cumulative effect of sulfoxide
functionality and ¯uorine functionality on the reactivity of
these dienophiles has remained unknown. Here we report
the results of our study with the novel ¯uorovinyl sulfoxides
viz., [(2,2-dichloro-1-¯uoroethenyl)sul®nyl] benzene, 5a
and [(2-chloro-1,2-di¯uoro ethenyl)sul®nyl] benzene, 5b
in Diels±Alder cycloadditions with typical dienes such as
cyclopentadiene, furan and 1,3-diphenylisobenzofuran
In the present study, vinyl sulfoxides, 5a and 5b10 have
shown good reactivity as dienophiles forming [412]
adducts with cyclopentadiene and 1,3-diphenylisobenzo-
furan under conventional heating as well as under micro-
wave irradiation (BPL BMO 700T domestic microwave
oven, 600 W) giving the corresponding cycloadducts in
.70% yield. Furan resisted cycloaddition with 5a and 5b
when subjected to conventional heating (sealed tube at
1308C for 24 h). It did, however, undergo cycloaddition
with .35% conversion (Yield .70% based on recovered
5) in relatively short reaction times (25 min) when treated
with microwave radiation11 (Scheme 2).
Cycloaddition of cyclopentadiene with 5a gave mixtures of
Scheme 1. (i) 2a: Zn/EtOH, 608C, 3h, 80%; 2b: Zn/EtOH, 508C, 3 h, 75%; (ii) 3a: PhSH, NaOH, autoclave, 1208C, 8 h, 90%; 3b: PhSH, NaOH, autoclave,
1208C, 6 h, 85%; (iii) 4a: KOH, autoclave, 1208C, 10 h, 85%; 4b: KOH, autoclave, 1208C, 8 h, 80%; (iv) 5a and 5b: m-CPBA, DCM, RT, 24 h, 90%.
q
IICT Communication No. 4306.
Keywords: Diels±Alder cycloaddition reaction; vinylphenyl sulfoxides; ¯uorovinyl.
* Corresponding author. Tel.: 191-40-717-3933; fax: 191-40-717-3387; e-mail: sridharm@iict.ap.nic.in
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00242-8

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M. Sridhar et al. / Tetrahedron 56 (2000) 3539±3545
Scheme 2.
diastereomers 6 and 7, and with 5b it gave 11 and 12, which
were easily puri®ed by normal column chromatography. In
the case of furan also we have obtained mixtures of adducts
upon its cycloaddition with 5a and 5b. Here, with the excep-
tion of 13, the other components of the mixtures were found
to be dif®cult to resolve by column chromatography.12 Each
of these components were, however, clearly characterisable
compound 6, we have assigned endo position to ¯uorine
4
3
as it gave JH7a±Fˆ7 Hz and JH1±Fˆ3 Hz. Similarly, for
3
furan adduct 9 also we observed JH1±Fˆ3 Hz. When
3
¯uorine is in exo position, the JH1±F coupling is usually
.3 Hz. In the case of adduct 7, it is found to be 5 Hz and
for 8 it is 6.4 Hz (Scheme 3).
1
from the H NMR and 19F NMR spectra of their adduct
In our study we have noticed an unusual reversal of stereo-
chemistry in cycloadditions of vinyl sulfoxide 5a and 5b
and the corresponding sulfones 6a14 and 6b11 with cyclo-
pentadiene. The cycloaddition of 5b proceeded disposing
the phenylsulfoxide group exclusively in the endo orienta-
tion, while 6b formed adducts with the phenyl sulfone group
only in exo position (Scheme 4).
mixtures.
The stereochemistry of the adducts, 6±13 was assigned
based on literature reports2,11,13 on vicinal and long range
couplings of ¯uorine with bridgehead and apical protons
respectively in each of these adducts. For example, for

M. Sridhar et al. / Tetrahedron 56 (2000) 3539±3545
3541
Scheme 3.
Scheme 4.
In conclusion, this work is the ®rst study on the Diels±Alder
cycloaddition reaction using ¯uorine substituted vinyl-
phenyl sulfoxides as dienophiles. Under microwave irradia-
tion these dienophiles showed remarkable reactivity even
with unreactive dienes like furan-forming cycloadducts.
sealed tube (Aldrich, Ace pressure tube with a te¯on plug,
10.2 cm, 15 mL).
1,1,-Dichloro-2,2-di¯uoroethene, 2a
Alkene 2a was prepared15 by the dehalogenation of 2,2-
di¯uoro-1,1,1,2-tetrachloroethane 1a in a reactive cryo-
genic distillation set up which consisted of a two-necked 1
litre round bottom ¯ask. One neck was equipped with a
fractionating column and a condenser and the other with a
dropping funnel. A coolant at 2408C was circulated through
the condenser. Activated zinc dust (163.47 g, 2.5 mol) was
suspended in ethanol (200 mL) in the round bottom ¯ask
then 1,1,1,2-tetrachloro-2,2-di¯uoroethane, 1a (101.91 g,
0.5 mol) in 100 mL ethanol was added dropwise over a
period of 30 min. The mixture was treated with 10 mL of
a 10% ethanolic solution of zinc chloride and warmed to
40±508C with continuous stirring until a spontaneous reac-
tion set in, after which the temperature was maintained at
708C. The gaseous product liberated over a period of 3 h
was collected in a trap cooled with a dry ice±acetone bath.
The crude product was puri®ed by cryogenic fractional
distillation over P2O5 and the fraction boiling at 19±208C
(lit.16 boiling point 198C) was collected as a colourless
liquid. Yield: 53.20 g (80%).
Experimental
Infrared spectra were scanned on a Shimadzu Perkin±Elmer
1310 spectrometer. Proton magnetic resonance spectra were
recorded on Varian FT-200 (Gemini) and Unity 400 spec-
trometers in CDCl3 using tetramethylsilane (TMS) as an
internal standard. Chemical shifts are expressed in ppm
units down®eld from TMS. Fluorine NMR was recorded
on a Unity 400 spectrometer at an operating frequency of
376.3 MHz in CDCl3 using trichloro¯uoromethane (CFCl3)
as an internal standard. Chemical shifts are expressed in
ppm units down®eld from CFCl3. Electron Impact (EI)
and gas chromatographic mass spectra (GCMS) were
recorded on VG 7070 H instrument at 70 eV. Chemical
ionization mass spectra (CIMS) were recorded on VG
7070 H at 70 eV using acetone as CI reagent. Liquid second-
ary ion mass spectrometry (LSIMS) was carried out on VG
Autospec M using Cs1 ion gun. High-resolution mass spec-
tra (HRMS) were recorded on VG Autospec M at 5000
resolution and per¯uoro kerosine was used as an internal
standard. Gas chromatography was carried out on HP-5890
Series II gas chromatograph with helium as a carrier gas
(30 mL/min). Microwave irradiations were carried out on
BPL BMO-700T (600 W) domestic microwave oven in a
2,2-Dichloro-1,1-di¯uoro-1-(phenyl thio) ethane,17 3a
Alkene 2a (33.23 g, 250 mmol), thiophenol (30.30 g,
275 mmol) and powdered NaOH (1.2 g, 30 mmol) were
taken in an autoclave and heated at 1208C for 8 h under a

3542
M. Sridhar et al. / Tetrahedron 56 (2000) 3539±3545
nitrogen atmosphere. The reaction mixture was cooled to
room temperature, discharged and extracted with diethyl
ether (2£100 mL). The ether layer was washed successively
with 10% aqueous sodium hydroxide solution (2£50 mL),
water (2£100 mL) and brine solution (50 mL). The organic
layer was dried over anhydrous sodium sulfate and concen-
trated under reduced pressure. The crude product was
distilled under vacuum (80±858C/0.6 mmHg) to obtain 3a
(54.70 g, 90%) as a colourless liquid. IR (Neat) nmax: 1480,
crude product was further puri®ed by cryogenic fractional
distillation over P2O5 and 2b is collected as a fraction
boiling at 224±2268C as a colourless liquid. Yield:
135.40 g (75%).
2-Chloro-1,1,2-tri¯uoro-1-(phenyl thio) ethane,19 3b
Alkene 2b (29.12 g, 250 mmol), thiophenol (30.30 g,
275 mmol) and powdered NaOH, (1.2 g, 30 mmol) were
taken in an autoclave and heated at 1208C for 6 h under
nitrogen atmosphere. The reaction mixture was cooled, the
reactor was discharged and extracted with diethyl ether
(2£100 mL). The ether layer was washed successively
with 10% aq. NaOH solution (2£50 mL), water
(2£100 mL) and brine solution (50 mL). The organic layer
was dried over anhydrous sodium sulfate and ether was
removed under reduced pressure. Distillation of the crude
furnished pure 3b (48.16 g, 85%; bp: 708C/0.6 mmHg) as a
colourless liquid. IR (neat) nmax: 1480, 1430, 1160 and
1080 cm21; MS (EI): m/z 226 (M1, 45), 159 (100), 109
(60), 77 (40); 1H NMR (200 MHz): d 5.9±6.3 (dm,
Jˆ50 Hz, 1H); 7.4±7.7 (m, 5H, Ar-H); HRMS: Calculated
for C8H6ClF3S 225.9830, found: 225.9830.
1
1430, 1160, 1070 cm21; H NMR (200 MHz): d 5.7 (t,
Jˆ7 Hz, 1H), 7.4±7.6 (m, 5H, Ar-H); 19F NMR: d 282.5
(d, Jˆ7 Hz); MS (EI): m/z 242 (M1,15), 159 (80), 109
(100), 83 (15); HRMS: Calculated for C8H6Cl2F2S
241.9535, found: 241.9525.
2,2-Dichloro-1-¯uoro-1-(phenyl thio) ethylene,17 4a
Thioether 3a (24.31 g, 100 mmol) and powdered KOH
(11.2 g 200 mmol) were placed in an autoclave and heated
at 1208C for 10 h under nitrogen atmosphere. The mixture
was cooled to room temperature, discharged and extracted
with diethyl ether (2£100 mL). The ether layer was washed
successively with water (2£100 mL) and brine (50 mL).
The organic layer was dried over anhydrous sodium sulfate
and the solvent was removed under reduced pressure. The
crude product was distilled under vacuum to yield 4a as a
colourless liquid (18.96 g, 85%, bp: 60±658C/1 mmHg). IR
2-Chloro-1,2-di¯uoro-1-(phenyl thio) ethylene,19 4b
1
(neat) nmax: 1600, 1500, 1420, 1120, 980 cm21; H NMR
(200 MHz): d 7.3±7.5 (m, Ar-H); 19F NMR: d 285.0 (s);
MS (EI): m/z 222 (M1, 10), 152 (100), 109 (20), 77 (80);
HRMS: Calculated for C8H5Cl2FS 221.9473, found:
221.9474
Thioether 3b (22.66 g, 100 mmol) and powdered KOH
(11.2 g, 200 mmol) were taken in an autoclave and heated
at 1208C for 8 h under nitrogen atmosphere. The mixture
was cooled to room temperature, discharged and extracted
with diethyl ether (2£100 mL). The organic layer was
washed successively with water (2£50 mL), brine solution
(50 mL), and dried over anhydrous sodium sulphate and
solvent was removed under reduced pressure. The crude
product upon distillation gave 4b as a colourless liquid
(16.53 g, 80%; bp: 206±2088C, lit. bp:19 2088C). IR (neat)
nmax: 3050, 1700, 1125 cm21; MS (EI): m/z 206 (M1, 40),
[(2,2-Dichloro-1-¯uoroethenyl)sul®nyl] benzene 5a
A mixture consisting of alkene 4a (4.46 g, 20 mmol) and
m-CPBA (60%: 5.75 g, 20 mmol) was stirred in dry
dichloromethane (100 mL) for 24 h at room temperature.
The ether layer was washed successively with saturated
sodium bicarbonate solution (2£50 mL), water (2£
100 mL), brine (50 mL) and then dried over anhydrous
sodium sulfate. The crude product obtained after the
removal of the solvent was puri®ed by column chromatog-
raphy (silica gel, 60±120 mesh, 10% EtOAc in petroleum
ether) to obtain 5a (4.30 g, 90%) in the form of an oil. IR
1
171 (50), 143 (26), 127 (100), 109 (15); H NMR (200
MHz): d 7.2±7.5 (m, Ar-H). GC-mass analysis of 4b indi-
cated it to be a mixture of its geometrical isomers in 2:3
ratio. HRMS: Calculated for C8H5ClF2S 205.9768, found:
205.9775.
1
(neat) nmax: 3150, 1650, 1060 (SvO) and 950 cm21; H
NMR (200 MHz): d 7.5±7.8 (m, Ar-H); 19F NMR: d
2121.66 (s); MS (EI): m/z 238 [M1, 0.7] 222 (29), 190
(75), 125 (47), 109 (97), 77 (100); HRMS: Calculated for
C8H5Cl2FOS 237.9422, found 237.9416.
[(2-Chloro-1,2-di¯uoro ethenyl)sul®nyl]benzene, 5b
A mixture consisting of alkene 4b (4.13 g, 20 mmol) and
m-CPBA (60%, 5.75 g, 20 mmol) was stirred in dry
dichloromethane (100 mL) for 24 h at room temperature.
The organic layer was washed successively with saturated
NaHCO3 solution (2£50 mL), water (2£50 mL) and satu-
rated brine solution (50 mL) and then dried over anhydrous
sodium sulphate. The crude product obtained after removal
of solvent was puri®ed by column chromatography (silica
gel, 60±120 mesh, 10% EtOAc in petroleum ether) to obtain
5b (4.01 g, 90%) in the form of colourless oil. IR (neat)
1-Chloro-1,2,2-tri¯uoroethene,18 2b
Activated zinc dust (143.86 g, 2.2 mol) was suspended in
230 mL of ethanol in the round bottom ¯ask then 1,1,2-
trichloro-1,2,2-tri¯uoroethane, 1b (290.44 g, 1.55 mol)
was added dropwise at room temperature. After addition
was complete, the mixture was treated with 10 mL of 10%
alcoholic solution of zinc chloride and warmed to 40±508C
with continuous stirring until a spontaneous reaction sets in,
after which the temperature was maintained at 508C. The
gaseous product liberated over a period of 3 h was collected
in a cold trap at 2788C using a dry ice±acetone bath. The
;
nmax: 3075, 1680, 1200, and 1080 cm21 1H NMR
(200 MHz): d 7.5±7.8 (m, Ar-H); Mass (EI): m/z 222
(M1, 3.6), 206 (25), 174 (100), 125 (53), 109 (75), 77
(97). HRMS: Calculated for C8H5ClF2OS 221.9723,
found: 221.9717.

M. Sridhar et al. / Tetrahedron 56 (2000) 3539±3545
3543
Diels±Alder cycloaddition reactions of [(2,2-dichloro-1-
¯uoroethenyl)sul®nyl] benzene, 5a with cyclopentadiene
Diels±Alder cycloaddition reactions of 5a with furan
Microwave assisted cycloaddition. Sulfoxide 5a (0.119 g,
0.5 mmol) and furan (2 mL, 27 mmol) were taken in a
sealed pressure tube under a nitrogen atmosphere. The
mixture was subjected to microwave irradiation for
5£5 min and then cooled. After attaining room temperature
the reaction mixture was discharged, excess furan distilled
off and the product was subjected to column chromato-
graphy (silica gel, ®ner than 200 mesh, 3±5% EtOAc in
pet ether) to obtain 60 mg. of unreacted 5a followed by
54 mg of cycloadduct in 70.7% yield based on recovered
starting material (35% conversion) as an inseparable
mixture of two diastereomers 5,5,-dichloro-6-¯uoro-endo-
6-(phenyl-sul®nyl)-7-oxabicyclo[2.2.1]hept-2-ene, 8 and
5,5,-dichloro-6-¯uoro-exo-6-(phenyl-sul®nyl)-7-oxabicyclo-
[2.2.1]-hept-2-ene, 9 in the ratio 0.9:1.1 based on relative
(a) Thermal cycloaddition. Sulfoxide 5a (0.238 g, 1 mmol)
and dry toluene (15 mL) were placed in a two-necked round
bottom ¯ask ®tted with a rubber septum and a cold water
condenser. To this freshly cracked cyclopentadiene,
(0.660 g, 10 mmol) was added and the mixture was re¯uxed
for 10 h under nitrogen atmosphere. Toluene and the
unreacted cyclopentadiene were removed under reduced
pressure and the crude product was subjected to column
chromatography (silica gel, ®ner than 200 mesh, 100 mL
of petroleum ether followed by 3±5% EtOAc in petroleum
ether) to obtain 33 mg. (10.9%) of pure 5,5-dichloro-6-
¯uoro-exo-6-(phenylsul®nyl)-bicyclo[2.2.1]hept-2-ene,
6
followed by 15 mg (4.9%) of mixture of 6 and 7 and
165 mg (54.3%) of pure 5,5-dichloro-6-¯uoro-endo-6-
(phenylsul®nyl)bicyclo[2.2.1]hept-2-ene, 7. Ratio of 6 and
7 (1:5) was determined by the relative peak intensities in the
1H NMR spectrum of the adduct mixture.
1
peak intensities in H NMR and 19F NMR of their mixture.
In these spectra the signals of 8 and 9 are clearly distinguish-
able.
(b) Microwave assisted cycloaddition. Sulfoxide 5a
(0.119 g, 0.5 mmol) and freshly cracked cyclopentadiene
(0.330 g, 5 mmol) were taken in sealed pressure tube
under nitrogen atmosphere. The reaction mixture was
subjected to microwave irradiation in a domestic microwave
oven (BPL BMO 700T, 600 W) for 7 min and then cooled.
After attaining room temperature the crude reaction product
was subjected to column chromatography (silica gel, 60±
120 mesh, 100 mL petroleum ether followed by 5±10%
EtOAc in petroleum ether) to afford cycloadduct 0.114 g
(75%) as a mixture of two diastereomers 6 and 7 in the
5,5,-Dichloro-6-¯uoro-endo-6-(phenyl sul®nyl)-7-oxabi-
cyclo[2.2.1]hept-2-ene, 8
Waxy solid (mixture); IR (KBr) nmax:1050 cm1 (SO
1
Stretch); H NMR (200 MHz): d 5.0±5.1 (dd, JH1±F6
3
ˆ
3
3
6.40 Hz, JH1±H2ˆ1.5 Hz, H-1), 5.2 (d, JH4±H3ˆ1.6 Hz,
H-4), 6.7±6.8 (m, H-2), 6.9±7.0 (m, H-3), 7.5±8.0 (m,
5H, Ar-H); 19F NMR: 2144.26 (d, JF±Hˆ6.40 Hz); MS
(LSIMS): m/z 307 (M11H, 40), 238 (30), 125 (20), 109
(100); HRMS: Calculated for (M11H) C12H10O2FSCl2
306.9762, found: 306.9766.
1
ratio of 1:5 based on relative peak intensities in H NMR
of the mixture.
5,5,-Dichloro-6-¯uoro-exo-6-(phenyl sul®nyl)-7-oxabi-
cyclo[2.2.1]hept-2-ene, 9
5,5-Dichloro-6-¯uoro-exo-6-(phenylsul®nyl)-bicyclo-
[2.2.1]hept-2-ene, 6
1H NMR (200 MHz): d 5.2±5.3 (dd, 3JH1±Fˆ3.0 Hz, 3JH1±H2
ˆ
1.5 Hz, H-1), 5.6±5.7 (d, 3JH4±H3ˆ1.7 Hz, H-4), 6.5±6.6 (m,
H-2), 6.7 (m, H-3), 7.5±8.0 (m, 5H, Ar-H); 19F NMR: d
2141.20 (s). HRMS: Calculated for (M11H)
C12H10O2FSCl2 306.9762, found: 306.9766.
White solid; mp: 99±1008C; IR (KBr) nmax: 1052 cm1 (SO
1
Stretch); H NMR (400 MHz): d 1.9±2.1 (m, JH7a±H7b
2
ˆ
10.9 Hz, 3JH±Hˆ1.83 Hz, 4JH7a±Fˆ7.0 Hz irradiation,
2
3
H-7a), 2.52 (dm, JH7b±H7aˆ10.9 Hz, JH±Hˆ1.80 Hz,
Diels±Alder cycloaddition reactions of 5a with 1,3-
diphenylisobenzofuran
irradiation, H-7b), 3.48 (m, H-1), 3.56 (m, H-4), 6.1±6.2
3
3
(m, JH±Hˆ5.7 Hz, irradiation, H-2), 6.4±6.5 (m, JH±H
ˆ
5.7 Hz, irradiation, H-3); 7.6±7.9 (m, 5H, Ar-H); MS
(LSIMS): m/z 305 (M11H, 100), 269 (10), 179 (30), 77
(40), 66 (30%); HRMS: Calculated for [M11H]
C13H12Cl2FOS 304.9970, found: 304.9991.
(a) Thermal cycloaddition. Sulfoxide 5a (0.238 g, 1 mmol)
and 1,3-diphenylisobenzofuran (0.270 g, 1 mmol) were
re¯uxed in dry toluene (15 mL) for 24 h under nitrogen
atmosphere. Toluene was removed under reduced pressure
and the mixture was subjected to column chromatography
(silica gel, 60±120 mesh, 10% EtOAc in petroleum ether) to
afford 0.406 g (80%) of cycloadduct 2,2-dichloro-3-¯uoro-
1,2,3,4-tetrahydro-1,4-diphenyl-3-(phenyl sul®nyl) 1,4-epoxy
napthalene, 10 as a white solid.
5,5,-Dichloro-6-¯uoro-endo-6-(phenylsul®nyl)-bicyclo-
[2.2.1]hept-2-ene, 7
White solid; mp: 163±1658C; IR (KBr) nmax:1050 cm1 (SO
2
Stretch); 1H NMR (400 MHz): d 2.1 (ddd, JH7a±H7b
ˆ
10.26 Hz, J2ˆ3.3 Hz, J3ˆ1.46 Hz, irradiation, H-7a), 2.30
(dd, 2JH7b±H7aˆ10.26 Hz, J2bˆ1.4 Hz, irradiation, H-7b), 3.4
(m, H-1), 3.5 (m, H-4), 6.4 (m, H-2), 6.6 (m, H-3), 7.6±7.8
(m, 5H, Ar-H); MS (LSIMS): m/z 305 (M11H, 100), 288
(10), 269 (20), 179 (60), 77 (60), 66 (30); HRMS (LSIMS):
Calculated for (M11H) C13H12Cl2FOS 304.9970, found:
304.9990.
(b) Microwave assisted cycloaddition. A mixture of 5a
(0.119 g, 0.5 mmol) and 1,3-diphenylisobenzofuran
(0.135 g, 0.5 mmol) were taken in a sealed tube and
subjected to microwave irradiation for 7 min and crude
product subjected to column chromatography (silica gel,
60±120 mesh, 10% EtOAc in petroleum ether) to afford
0.228 g (90%) of cycloadduct, 10.

3544
M. Sridhar et al. / Tetrahedron 56 (2000) 3539±3545
2,2-Dichloro-3-¯uoro-1,2,3,4-tetrahydro-1,4-diphenyl-3-
(phenyl sul®nyl)1,4-epoxy napthalene, 10
Diels±Alder cycloaddition reactions of sulfoxide 5b with
furan
White solid; mp: 180±1818C; IR (KBr) nmax:1050 cm21; 1H
NMR (200 MHz):d 7.3±8.0 (m, Ar-H); MS (LSIMS): m/z
509 [(M11H), 30], 270 (100), 238 (20); HRMS (LSIMS):
Calculated for (M11H) C28H20Cl2FO2S 509.0545, found:
509.0555.
Sulfoxide 5b (0.110 g, 0.5 mmol) and furan (2 mL,
27 mmol) were taken in an pressure tube under a nitrogen
atmosphere and subjected to microwave irradiation for
5£5 min and cooled to room temperature. Excess furan
was distilled off and the reaction mixture was subjected
to column chromatography (silica gel, ®ner than
200 mesh, 3±5% EtOAc in petroleum ether) to afford
successively 56 mg of unreacted 5b followed by 20 mg
of cycloadduct exo-5-chloro-5,6-di¯uoro-endo-6-(phenyl-
sul®nyl)-7-oxa-bicyclo[2.2.1]hept-2-ene, 13 and 37 mg of
cycloadduct 5-chloro-5,6-di¯uoro-6-(phenyl sul®nyl)-7-
oxabicyclo[2.2.1]hept-2-ene, 14 which is a mixture of
inseparable diastereomers. Yield: 80% based on recovered
starting material
Diels±Alder cycloaddition reactions of sulfoxide 5b with
cyclopentadiene
(a) Thermal cycloaddition. Sulfoxide 5b (0.222 g, 1 mmol)
and dry toluene (10 mL) were taken in a two-necked ¯ask
equipped with a rubber septum and a cold water condenser.
Freshly cracked cylopentadiene (0.660 g, 10 mmol) was
added and the mixture was re¯uxed for 10 h under nitrogen
atmosphere. Solvent was removed under reduced pressure
and the crude product was subjected to column chromato-
graphy (silica gel, 60±120 mesh, 100 mL petroleum ether
followed by 3±5% EtOAc in petroleum ether) to obtain
38 mg (13.2%) of pure exo-5-chloro-5,6-di¯uoro-endo-6-
(phenyl sul®nyl)-bicyclo[2.2.1]hept-2-ene, 11 followed by
17 mg (5.9%) of mixture of 11 and 12 and 160 mg (55.6%)
of pure endo-5-chloro-5,6-di¯uoro-endo-6-(phenyl sul®nyl)-
bicyclo[2.2.1]hept-2-ene, 12.
exo-5-Chloro-5,6-di¯uoro-endo-6-(phenyl sul®nyl)-7-
oxabicyclo[2.2.1]hept-2-ene, 13
White solid; mp: 1028C; IR (KBr) nmax:1075 cm21 (SO
3
stretch); 1H NMR (200 MHz): d 5.1±5.2 (d, JH±F
ˆ
6.10 Hz, H-1), 5.60 (brs, H-4), 6.5±6.6 (m, H-2), 6.7±6.8
(m, H-3), 7.5±8.0 (m, 5H, Ar-H); 19F NMR: d 2111 (s, 1F),
2154.75 (d, 3JF±Hˆ6.10 Hz); MS (EI) m/z 290 (M1, 5), 165
(20), 125 (100), 68 (60); HRMS: Calculated for
C12H9ClF2O2S 289.9979, Found: 289.9971.
(b) Microwave assisted cycloaddition. Sulfoxide 5b
(0.110 g, 0.5 mmol) and freshly cracked cyclopentadiene,
(0.33 g, 5 mmol) were taken in an sealed pressure tube
under a nitrogen atmosphere and subjected to microwave
irradiation for 7 min and then cooled. The crude reaction
product was puri®ed by column chromatography (silica gel,
60±120 mesh, 50 mL pet ether followed by 10% EtOAc in
petroleum ether) to obtain 115 mg. (80%) of cycloadduct as
a mixture of two diastereomers 11 and 12 in the ratio 1:4
based on relative peak intensities in 1H NMR of their
mixture.
5-Chloro-5,6-di¯uoro-6-(phenyl sul®nyl)-7-oxabicyclo-
[2.2.1]hept-2-ene, 14
IR (KBr)
n
max:1070 cm21 (SO stretch); 1H NMR
(200 MHz): d 4.9±5.0 (m, 1H), 5.2±5.3 (m, 1H), 6.6±6.9
(m, 2H), 7.5±7.9 (m, 5H, Ar-H); MS (EI) m/z 290 (M1, 10),
165 (20), 125 (100), 68 (60); HRMS: Calculated
C12H9ClF2O2S 289.9979, Found: 289.9968.
exo-5-Chloro-5,6-di¯uoro-endo-6-(phenyl sul®nyl)-
bicyclo[2.2.1]hept-2-ene, 11
Diels±Alder cycloaddition reaction of sulfoxide 5b with
1,3-diphenylisobenzofuran
White solid; mp: 98±998C; IR (KBr) nmax: 1075 cm21 (SO
stretch); 1H NMR (200 MHz): d 1.85 ± 2.0 (brm, 2JH7a±7b
ˆ
4
3
11 Hz, J7a±Fˆ8 Hz, JH7a±H-1ˆ3JH7a±H-4ˆ1.5 Hz, irradia-
(a) Thermal cycloaddition. A solution consisting of sul-
foxide 5b (0.222 g, 1 mmol) and diphenylisobenzofuran,
(0.270 g, 1 mmol) in dry toluene (15 mL) was re¯uxed for
24 h under nitrogen atmosphere. Toluene was removed
under reduced pressure and the reaction product was
subjected to column chromatography (silica gel, 60±
120 mesh, 10% EtOAc in petroleum ether) to obtain
0.394 g (80%) of the cycloadduct [2-chloro-2,3-di¯uoro-
1,2,3,4-tetrahydro-1,4-diphenyl-3-(phenyl sul®nyl)]-1,4-epoxy
naphthalene, 15 which is a mixture of inseparable dia-
stereomers.
tion, H-7a), 2.3±2.4 (dd, 2J7b±7aˆ11 Hz, 3JH7b±H-1ˆ3JH7b±H-4
ˆ
1.5 Hz, irradiation, H-7b), 3.3 (m, 3JH1±F6ˆ5 Hz, irradiation,
H-1), 3.4 (m, H-4), 6.1±6.2 (m, H-2), 6.3±6.4 (m, H-3),
7.6±7.9 (m, 5H, Ar-H); MS (EI): m/z 288 (M1, 30), 163
(50), 125 (100), 66 (40); HRMS: Calculated for
C13H11ClF2OS 288.0187, Found: 288.0177.
endo-5-Chloro-5,6-di¯uoro-endo-6-(phenyl sul®nyl)-
bicyclo[2.2.1]hept-2-ene, 12
White solid; mp: 1108C; IR (KBr) nmax:1075 cm21 (SO
stretch); H NMR (200 MHz): d 2.0±2.1 (m, H-7a, 7b),
1
(b) Microwave assisted cycloaddition. A mixture consisting
of sulfoxide 5b (0.111 g, 0.5 mmol), 1,3 diphenylisobenzo-
furan, (0.135 g, 0.5 mmol) were subjected to microwave
irradiation for 7 min and the reaction mixture upon column
chromatography (silica gel, 60±120 mesh, 10% EtOAc in
petroleum ether) afforded 0.225 g (90%) of the cycloadduct,
15 as a white solid.
3.2±3.3 (m, H-1), 3.4±3.5 (m, H-4), 6.4±6.5 (m, H-2),
6.6±6.7 (m, H-3), 7.4±7.8 (m, 5H, Ar-H); 19F NMR d
3
3
2108 (d, JF±Fˆ20 Hz, 1F), 2154 (d, JF±Fˆ20 Hz, 1F);
MS (EI): m/z 288 (M1, 30), 163 (70), 125 (100), 66 (30);
HRMS: Calculated for C13H11ClF2OS 288.0187, Found:
288.0203.

M. Sridhar et al. / Tetrahedron 56 (2000) 3539±3545
3545
Ikeda, A.; Taga, T.; Miwa, Y.; Node, M. J. Org. Chem. 1994, 59,
2211.
[2-Chloro-2,3-di¯uoro-1,2,3,4-tetrahydro-1,4-diphenyl-
3-(phenyl sul®nyl)] 1,4 epoxy naphthalene, 15
8. (a) Lopez, R.; Carretero, J. C. Tetrahedron: Asymmetry 1991, 2,
93. (b) De Lucchi, O.; Lucchini. V.; Marchioro, C.; Valle, G.;
Modena, G. J. Org. Chem. 1986, 51, 1457.
White solid mp: 116±1178C; IR (KBr) nmax 1060 cm21 (SO
1
stretch); H NMR (200 MHz) d 7.4±8.2 (m, Ar-H); MS
(LSIMS) m/z 493 [(M11H), 15], 287 (90), 270 (60), 149
(100); HRMS: Calculated for (M11H) C28H20ClF2O2S
493.084, Found 493.082.
9. Knunyants, I. L.; Fokin, A. V. Izvest. Akad. Nauk. SSSR 1952,
261 [CA 47: 3221c].
10. 4b is determined to be a mixture of its geometrical isomers in
the ratio 2:3. Its oxidation product 5b, however could not give good
resolution in GC analyses and hence we could not obtain the ratio
of its geometrical isomers.
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