Carbon vs. sulfur addition of nucleophiles to sulfines. Part I. The case of sulfinates

Article abstract of DOI:10.1007/s00706-004-0245-z

The nucleophilic substitution of chlorine in chlorosulfines with arylsulfinates leads to sulfonylsulfines with complete inversion of configuration within the starting surfines. A mechanism for this displacement reaction is proposed. The sulfonylsulfines s

Full text of DOI:10.1007/s00706-004-0245-z

Monatshefte f€ur Chemie 136, 543–551 (2005)
DOI 10.1007/s00706-004-0245-z
Carbon vs. Sulfur Addition
of Nucleophiles to Sulfines. Part I.
The Case of Sulfinates
ꢀ; #
Ibrahim El-Sayed
Chemistry Department, Faculty of Science, El-Menoufeia University, Shebin El-Kom, Egypt
Received June 8, 2004; accepted (revised) July 22, 2004
Published online November 24, 2004 # Springer-Verlag 2004
Summary. The nucleophilic substitution of chlorine in chlorosulfines with arylsulfinates leads to
sulfonylsulfines with complete inversion of configuration within the starting sulfines. A mechanism
for this displacement reaction is proposed. The sulfonylsulfines show good reactivity as heterodieno-
philes and the reaction with acyclic 1,3-dienes is surprisingly regio- and diastereoselective. The
stereochemical details were established by X-ray crystallography and the competitive dienophilic
properties were examined.
Keywords. Sulfines; Ab initio calculations; Hetero-Diels-Alder; 1,3-Dienes; Thiopyran-S-oxides.
Introduction
Sulfines with the general formula 1 are attractive heterocumulenes that participate
in the thioepoxidation of alkenes [1], in nucleophilic additions [2], and in cycload-
dition reactions [3]. Several routes have been developed for the synthesis of
sulfines. The most important routes to these sulfur-centered heterocumulenes are
oxidation of thiocarbonyl compounds with peracids [3], ozone [4], or singlet oxy-
gen [5]. The reactions of sulfines with nucleophiles have attracted considerable
interest because the attack of the nucleophiles can either occur in a thiophilic or
carbophilic fashion (path a or b, cf. Scheme 1), depending on the structures of both
sulfines and nucleophiles [2]. Nucleophilic reactions at the sulfine carbon atom
(path b) occur only when the sulfine carbon atom bears a potential leaving group
[6]. Therefore, chlorosulfines are expected to be the substrates of choice for car-
bophilic reactions. Displacement of chlorine in these sulfines would provide a new
synthetic route to substituted sulfines with either retention or inversion of
ꢀ
E-mail: ibrahim.el-sayed@ua.ac.be
#
Present address: University of Antwerp, Campus Drie Eiken, Faculty of Pharmacy, Department of
Medicinal Chemistry, B-2610, Wilrijk-Antwerp, Belgium.

544
I. El-Sayed
Scheme 1
Scheme 2
configuration at the sulfine moiety. In a previous paper [7] we have shown that the
oxidation of aryl chlorodithioformates by meta-chloroperbenzoic acid (m-CPBA)
leads to a stereoselective synthesis of the corresponding chlorosulfines with (Z)-
geometry (cf. Scheme 2). As part of our ongoing studies of the synthesis and reac-
tivity of sulfines [7–9], we were interested in the stereochemical pathway in which
the nucleophiles attack chlorosulfines 3 (path a or b).
We have chosen the arylsulfinates as nucleophiles for the present study because
the dienophilicity of sulfines strongly depends on the nature of the substituents at
the sulfine carbon atom [10], and the introduction of the sulfonyl group adjacent
to the sulfine moiety would enhance the reactivity of the resulting sulfines towards
the cycloaddition reactions. Moreover, sulfonyl sulfines have scarcely been men-
tioned in literature despite their potential synthetic applications [9, 11]. In addition,
we wished to examine the cycloaddition and regiochemistry of the reactions of the
new sulfonylsulfines 5 with unsymmetrical 1,3-dienes as well as the competitive
dieneophilicity of sulfines 5 compared to that of sulfines 3.
Results and Discussion
The required chlorosulfine 3 used in this study was readily obtained in 92% yield
by oxidation of the corresponding pentachlorophenyl chlorodithioformate 2 with
m-CPBA [7] according to Scheme 2.
The displacement reaction was performed in acetonitrile by using crown ether
(18-Crown-6) as solubilizing agent [12] for the sodium sulfinates 4, the reaction
with 3 could be accomplished at room temperature in a homogeneous reaction
mixture after 12 hours to afford the sulfonylsulfines 5 in fairly good yields accord-
ing to Scheme 3. To our delight the NMR and TLC analysis of the crude 5
showed that sulfines 5 were formed as a single stereoisomer and we have seen
no evidence for two isomers. Moreover, the new sulfonylsulfines 5 are stable
compounds under reaction conditions of the displacement. They could be isolated

Addition of Nucleophiles to Sulfines
545
Scheme 3
by chromatography as compared with the structurally related sulfenes reported by
Opitz et al. [13].
However, when we tried the same reaction with a less bulky chlorosulfine,
such as chloro(phenylthio)sulfine [PhS(C¼S¼O)Cl], we were unable to isolate
the corresponding sulfine, most likely due to the rapid reaction of the initially
formed sulfine with sulfinate resulting in a reduction of the sulfine group. This
observation is consistent with what had been observed earlier in analogous cases
[3e]. Therefore, we believe that the presence of a bulky substituent at the sulfine
moiety contributes significantly to the enhancement of the stability of 5. Special
attention was paid to the 13C NMR spectroscopic characterization of 5 compared
to 3. A comparison of ꢀC¼S¼O of 5 (182.13 ppm for 5a and 181.93 for 5b) and
3 (171.22 ppm) shows the effect of the strongly electron-withdrawing sulfonyl
group of 5 on one hand and the shielding influence of the chlorine atom of 3
on the other hand. Furthermore, the IR spectra show strong bands at ꢁꢀ¼ 1080,
1145 cmꢁ1 for 5a and 1079, 1147 cmꢁ1 for 5b in the region for sulfines symmetric
and asymmetric stretching. We were able to obtain pale yellow single crystals of
sulfine 5b and its structure and the non-linearity of the >C¼S¼O system were
finally established by X-ray crystallographic analysis. It also confirmed that sul-
fine 5b is the (E)-diastereomer, thus avoiding the steric and electronic repulsions
expected for the (Z)-diastereomer (Fig. 1). The lengths of the >C¼S and S¼O
Fig. 1. Crystal structure of sulfine 5b with 50% probability ellipsoids

546
I. El-Sayed
˚
bonds were found to be 1.64 and 1.47 A, they fall within the usual range for the
analogues groups in sulfines [14]. In order to rationalize the observed (E)-selec-
tivity we performed ab initio calculations with the G98W suite of programs [15].
The geometry of the (Z) and (E) diastereomers were optimized at the HF=
3-21G(d) level. Single point energy calculations were performed at the HF=
6-31 þ G(d)=HF=3-21G(d) level. Indeed, the results obtained indicate that the
(E)-diastereomer is thermodynamically more stable than the (Z)-diastereomer by
33.8 kJ molꢁ1.
From X-ray and the ab initio calculations of the sulfine 5b, it was concluded
that the configuration of the starting sulfines is completely inverted in the pro-
ducts. Accordingly, given a displacement of chlorine with complete inversion of
configuration we assume that an addition-elimination mechanism is operating.
The generally accepted mechanism for this nucleophilic displacement reaction
resembles that of the nucleophilic substitution of halogen at activated vinylic
carbon [3e, 16]. The incoming sulfinate anion first approaches perpendicularly
to the plane of the >C¼S double bond of the sulfine group and the chloride
anion departs in the same manner. The difference in energy barriers for the com-
petitive rotations in the adduct anions (A to B vs. A to C, cf. Scheme 4), which are
needed to move the chlorine into the desired leaving position are small, but
apparently large enough to lead to a preference of one route over the other.
However, we can not exclude the initial formation of (Z)-5 followed by diastereo-
merization into the thermodynamically more stable (E)-5 during the reaction
and=or work-up. The stereo-chemical course may vary from one involving the for-
mation of one or more anionic intermediates, such as that indicated in Scheme 4,
to a concerted mechanism.
The hetero-Diels-Alder reaction between 5 and an excess (5 equiv.) of acy-
clic 1,3-dienes was carried out at room temperature in chloroform forming the
Scheme 4

Addition of Nucleophiles to Sulfines
547
Scheme 5
corresponding cycloadducts 6, 7, and 8 in quantitative yield after 2 hours
(cf. Scheme 5). The NMR and TLC analysis of the crude materials showed that
single diastereomers were obtained. As expected for Diels-Alder reactions, the
sulfonyl group at the sulfine carbon atom of 5 enhanced the reactivity towards
cycloaddition considerably. In addition to 2,3-dimethyl-1,3-butadiene, the unsym-
metrical 1,3-dienes, such as 2-methyl-1,3-butadiene and (E)-1,3-pentadiene, were
studied.
Formation of the single cycloadducts shows that the reaction is regioselective
by more than 90%. Such a high degree of regioselectivity in hetero-Diels-Alder
reactions of sulfines is surprising. It should be noted that, contrary to what was
observed earlier in dihydrothiopyrane [17], adducts 6, 7, and 8 do not, at least
during the work-up, eliminate sulfinic acid R2SO2H to any significant extent, nor
do they isomerize by elimination-addition of sulfinic acid. In order to gain an
insight into the steric course of the cycloaddition reaction, the structure of the
crystalline cycloadduct 8b was determined by X-ray analysis (Fig. 2). It showed
that the sulfonyl group and sulfoxide oxygen are in a trans position to each other
(i.e. the electrostatic interaction of the sulfone oxygen atoms and the sulfoxide
oxygen will be minimized when these functions are placed in an anti position).
This implies that during the cycloaddition reaction the stereochemistry present in
the sulfine ((E)-geometry) is retained in the adduct.
In addition, the competitive dieneophilicity of sulfine 5a was compared to that
of 3 by preparing a mixture of one equivalent of sulfines 3 and 5a in chloroform
and letting them compete for 2,3-dimethyl-1,3-butadiene (one equivalent) at room
temperature. The reaction, as monitored by NMR, revealed that the >C¼S group
of the resulting sulfine 5a reacts selectively with the diene in the presence of the
starting sulfine 3. No evidence, however, was found for the cycloadduct from the

548
I. El-Sayed
Fig. 2. Crystal structure of the cycloadduct 8b with 50% probability ellipsoids
reaction between the sulfine 3 and 2,3-dimethyl-1,3-butadiene. This experiment
confirms the higher dienophilic reactivity of the sulfonylsulfines 5 in [4 þ 2] cy-
cloaddition reactions as compared to the starting sulfines 3.
In conclusion, the reaction of chlorosulfines with sulfinates provides easy
access to new substituted sulfonylsulfines. Kinetic stabilization by sterically demand-
ing groups is clearly a prerequisite. These results indicate that the displacement
at the sp2 carbon atom in the chlorosulfine occurs with complete inversion of con-
figuration. Such substitution reactions at sp2 centers are not frequently encountered.
Sulfines react as dienophiles with 1,3-dienes in a [4 þ 2] type cycloaddition reac-
tion to give six-membered ring sulfoxides with high regio- and diastereoselectiv-
ity. The study also confirmed the higher reactivity of 5 as a dienophile compared
to 3 in [4 þ 2] cycloaddition reactions. Further work is underway to investigate
the reactivity of sulfines 3 towards other nucleophiles and investigate sulfines 5 in
1,3-dipolar cycloadditions as well as to explore their synthetic utility especially
in stereoselective synthesis.
Experimental
All 1H and 13C NMR experiments (CDCl3) were carried out with a Varian Unity 400 MHz spectrom-
1
eter (400 MHz for H, 100 MHz for 13C). Chemical shifts are reported in ppm relative to TMS using
appropriate solvent signals as internal standard. Mass spectra analysis was performed with a Kratos
50tc spectrometer. The elemental analysis results agreed with the calculated values within experi-
mental error. Melting points were recorded on a B€uchi melting point apparatus and are uncorrected.
TLC was done on Merck Kieselgel F254 precoated plates (Merck). Column chromatography was
performed with silica gel 60 Fluka, particle size 0.035–0.070 mm (220–440 mesh ASTM) and the
eluent is shown in parentheses. Solvents were dried=purified according to literature procedures. Single
crystals suitable for X-ray studies from sulfine 5b and the cycloadduct 8b were grown in a mixture of
CH2Cl2 and n-hexane (1=3), intensity data were measured at room temperature on a Siemens SMART

Addition of Nucleophiles to Sulfines
549
CCD diffractometer with a graphite-monochromator. Crystal data for sulfine 5b; Mo Kꢂ radiation,
˚
ꢃ ¼ 0.71073A, cell measurement temperature: 120 K, crystal color: light yellow, crystal system:
˚
triclinic, unit cell parameters: a ¼ 18.772(1), b ¼ 11.6329(8), c ¼ 20.470(1) A, ꢂ ¼ 71.718(1), ꢄ ¼
3
ꢂ
˚
81.993(1), ꢅ ¼ 86.943(1) , space group P-1, cell volume: 882.16(9) A , Rall: 0.025, cell formula units
Z: 2, absorption coefficient: 1.339 mmꢁ1, F(000): 512. Crystal data for the cycloadduct 8b; Mo Kꢂ
˚
radiation, ꢃ ¼ 0.71073A, cell measurement temperature: 120K, crystal color: colourless, crystal shape:
˚
orthorhombic, unit cell parameters: a ¼ 18.772(1), b ¼ 11.6329(8), c ¼ 20.470(1) A, ꢂ ¼ 90, ꢄ ¼ 90,
3
ꢂ
˚
ꢅ ¼ 90 , space group Pbca, cell volume: 4470(1) A , Rall: 0.027, cell formula units Z: 2, absorption co-
efficient: 1.068 mmꢁ1, F(000): 2344. Complete X-ray data for compounds 5b and 8b were deposited at
the Cambridge Crystallographic Data Center under the reference numbers CCDC 226257 and CCDC
226256, copies of the data can be obtained free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 IEZ, UK [Fax: int. code þ44-1223-336033 or E-mail: deposit@ccdc.cam.ac.uk]. The
starting pentachlorophenyl chlorodithioformate (2) and the corresponding chlorosulfine 3 were pre-
pared according to Refs. [18] and [7].
Phenylsulfonyl(pentachlorophenylthio)sulfine (5a, C13H5Cl5O3S3)
Sodium benzene sulfinate (4a, 153 mg, 0.93 mmol) was complexed with 18-crown-6 (246mg,
0.93mmol) by dissolving it in 25 cm3 of methanol. After evaporation of the methanol, the com-
plexed sulfinate was added to a solution of 350mg of 3 (0.93 mmol) in 30 cm3 of acetonitrile. The
resulting solution was stirred for 12 h at room temperature. After concentration of the mixture, the
product was passed through celite to remove the salts. The crude sulfine was purified by chromato-
graphy (CH2Cl2:n-hexane¼ 1:3) to give 5a as a single isomer. Yellowish white crystals (300mg,
1
67%), mp 199ꢂC; IR (KBr): ꢁꢀ¼ 1155, 1343 (vSO ), 1080, 1145 (vC¼S¼O) cmꢁ1; H NMR (CDCl3):
2
ꢀ ¼ 7.62 (m, 2H), 7.75 (m, 1H), 7.99 (d, J ¼ 8.00Hz, 2H); 13C NMR (CDCl3); ꢀ ¼ 128.52, 128.80,
129.40, 129.57, 132.33, 135.05, 136.81, 137.78, 182.13 (>C¼S¼O) ppm; MS: m=z (%) ¼ 339
(54, M–C6H5SO2).
p-Chlorophenylsulfonyl(pentachlorophenylthio)sulfine (5b, C13H4Cl6O3S3)
The procedure as given for 5a was followed starting from 350mg of 3 (0.93 mmol), 185 mg of sodium
p-chlorobenzene sulfinate (4b, 0.93mmol), and 246 mg of 18-crown-6 (0.93 mmol). The crude sulfine
was purified by chromatography (CH2Cl2:n-hexane¼ 1:3) to give 5b as a single isomer. Yellowish
white crystals (295 mg, 61%), mp 232ꢂC; IR (KBr): ꢁꢀ¼ 1157, 1345 (vSO ), 1079, 1149 (vC¼S¼O
)
2
cmꢁ1; H NMR (CDCl3): ꢀ ¼ 7.59 (d, J ¼ 8.40Hz, 2H), 7.91 (d, J ¼ 8.40 Hz, 2H) ppm; 13C NMR
(CDCl3): ꢀ ¼ 129.98, 130.19, 131.15, 132.51, 136.32, 136.69, 136.84, 142.26, 181.93 (>C¼S¼O)
ppm; MS: m=z (%) ¼ 339 (67, M–p-ClC6H5SO2).
1
3,6-Dihydro-4,5-dimethyl-2-(phenylsulfonyl)-2-(pentachlorophenylthio)-2H-
thiopyran-S-oxide (6a, C19H15Cl5O3S3)
To a solution of 250 mg of 5a (0.52 mmol) in 3 cm3 of chloroform was added an excess of 0.60 cm3
of 2,3-dimethyl-1,3-butadiene (5.30 mmol). After stirring for 2 h at room temperature, the volatiles
were evaporated in vacuo and the crude product was crystallized from CH2Cl2:diethyl ether (1:3) and
cooling overnight gave analytically pure 6a as colorless crystals (275mg, 94%), mp 161ꢂC; IR
(KBr): ꢁꢀ¼ 1150, 1313 (vSO ), 1086 (vS¼O) cmꢁ1
;
1H NMR (CDCl3): ꢀ ¼ 1.22 (s, 3H), 1.60 (s,
2
3H), 2.62 and 3.00 (ABq, J ¼ 18.60 Hz, 2H), 3.72 and 3.96 (ABq, J ¼ 15.80 Hz, 2H), 7.58 (m, 2H),
7.70 (m, 1H), 8.20 (d, J ¼ 8.40Hz, 2H) ppm; 13C NMR (CDCl3): ꢀ ¼ 19.02, 19.22, 33.92, 54.66,
96.03, 120.53, 126.02, 128.64, 128.80, 131.23, 132.26, 134.84, 135.47, 136.58, 141.26 ppm; MS: m=z
(%) ¼ 562 (44, Mþ).

550
I. El-Sayed
3,6-Dihydro-4,5-dimethyl-2-(p-chlorophenylsulfonyl)-2-(pentachlorophenylthio)-
2H-thiopyran-S-oxide (6b, C19H14Cl6O3S3)
The procedure as given for 6a was followed starting from 250 mg of 5b (0.48 mmol) and 0.54cm3
of 2,3-dimethyl-1,3-butadiene (4.80 mmol). The cycloadduct 6b was obtained as colorless crystals
1
(265 mg, 92%), mp 174ꢂC; IR (KBr): ꢁꢀ¼ 1147, 1310 (vSO ), 1089 (vS¼O) cmꢁ1; H NMR (CDCl3):
2
ꢀ ¼ 1.19 (s, 3H), 1.60 (s, 3H), 2.63 and 3.02 (ABq, J ¼ 18.60Hz, 2H), 3.74 and 4.01 (ABq,
J ¼ 16.20 Hz, 2H), 7.55 (d, J ¼ 8.40 Hz, 2H), 8.16 (d, J ¼ 8.40 Hz, 2H) ppm; 13C NMR (CDCl3):
ꢀ ¼ 18.91, 19.19, 33.69, 54.71, 96.30, 120.77, 125.97, 128.64, 129.03, 129.42, 130.07, 132.77,
134.03, 136.79, 141.97 ppm; MS: m=z (%) ¼ 596 (62, Mþ).
3,6-Dihydro-5-methyl-2-(phenylsulfonyl)-2-(pentachlorophenylthio)-2H-
thiopyran-S-oxide (7a, C18H13Cl5O3S3)
The procedure as given for 6a was followed starting from 250 mg of 5a (0.52 mmol) and 0.52 cm3 of
2-methyl-1,3-butadiene (5.20 mmol). After stirring for 2 h at room temperature, the volatiles were
evaporated in vacuo and the crude product was crystallized from CH2Cl2:diethyl ether (1:3) and
cooling gave 7a as colorless crystals (257mg, 90%), mp 138ꢂC; IR (KBr): ꢁꢀ¼ 1156, 1315 (vSO
)
2
1083 (vS¼O) cmꢁ1; 1H NMR (CDCl3): ꢀ ¼ 1.68 (s, 3H), 2.72 (m, 1H), 3.00 (part of ABq, J ¼ 19.20 Hz,
1H), 3.80 and 3.93 (ABq, J ¼ 16.60 Hz, 2H), 5.04 (m, 1H), 7.60 (m, 2H), 7.72 (m, 1H), 8.20 (d,
J ¼ 7.60Hz, 2H) ppm; 13C NMR (CDCl3): ꢀ ¼ 23.32, 27.93, 53.75, 94.81, 118.63, 128.27, 128.70,
131.10, 131.27, 132.42, 134.93, 135.55, 136.85, 141.30ppm; MS: m=z (%) ¼ 548 (24, Mþ).
3,6-Dihydro-5-methyl-2-(p-chlorophenylsulfonyl)-2-(pentachlorophenylthio)-
2H-thiopyran-S-oxide (7b, C18H12Cl6O3S3)
The procedure as given for 6a was followed starting from 250 mg of 5b (0.48 mmol) and 0.48cm3 of 2-
methyl-1,3-butadiene (5.20 mmol). After stirring for 2 h at room temperature, the volatiles were evapo-
rated in vacuo and the crude product was crystallized from CH2Cl2:diethyl ether (1:3) and cooling gave
7b as colorless crystals (255 mg, 91%), mp 152ꢂC; IR (KBr): ꢁꢀ¼ 1155, 1313 (vSO ), 1085 (vSO) cmꢁ1; 1H
2
NMR (CDCl3): ꢀ ¼ 1.68 (s, 3H), 2.73 (m, 1H), 3.03 (d, part of ABq, J ¼ 18.80Hz, 2H), 3.80 (d, part of
ABq, J ¼ 16.40 Hz, 1H), 3.99 (d, part of ABq, J ¼ 16.40 Hz, 1H), 5.00 (m, 1H), 7.56 (d, J ¼ 8.40Hz, 1H),
8.16 (d, J ¼ 8.40Hz, 2H) ppm; 13C NMR (CDCl3): ꢀ ¼ 23.24, 27.93, 53.80, 95.28, 118.63, 128.42,
128.60, 129.01, 129.40, 130.06, 132.76, 134.05, 138.45, 142.00 ppm; MS: m=z (%) ¼ 582 (57, Mþ).
3,6-Dihydro-3-methyl-2-(phenylsulfonyl)-2-(pentachlorophenylthio)-
2H-thiopyran-S-oxide (8a, C18H13Cl5O3S3)
The procedure as given for 6a was followed starting from 300 mg of 5a (0.62 mmol) and 0.62 cm3 of
trans-piperylene (6.20 mmol). After stirring for 2 h at room temperature, the volatiles were evaporated
in vacuo and the crude product was crystallized from CH2Cl2:diethyl ether (1:3) to give 8a as colorless
1
crystals (325mg, 95%), mp 119ꢂC; IR (KBr): ꢁꢀ¼ 1155, 1311 (vSO ), 1090 (vS¼O) cmꢁ1; H NMR
2
(CDCl3): ꢀ ¼ 1.82 (d, J ¼ 7.20 Hz, 3H), 3.08 (m, 1H), 3.73 (m, 1H), 4.27 (d, part of ABq, J ¼ 16.40 Hz,
1H), 5.52 (d, J ¼ 10.40 Hz, 1H), 5.62 (m, 1H), 7.60 (m, 2H), 7.72 (m, 1H), 8.09 (d, J ¼ 7.60Hz, 2H)
ppm; 13C NMR (CDCl3): ꢀ ¼ 18.41, 38.14, 48.15, 96.47, 118.57, 124.75, 129.05, 131.18, 131.93,
133.85, 135.04, 135.61, 136.95, 142.43 ppm; MS: m=z (%) ¼ 548 (45, Mþ).
3,6-Dihydro-3-methyl-2-(p-chlorophenylsulfonyl)-2-(pentachlorophenylthio)-
2H-thiopyran-S-oxide (8b, C18H12Cl6O3S3)
The procedure as given for 6a was followed starting from 250mg of 5b (0.48 mmol) and 0.48cm3 of
trans-piperylene (4.80 mmol). After stirring for 2 h at room temperature, the volatiles were evaporated

Addition of Nucleophiles to Sulfines
551
in vacuo and the crude product was crystallized from CH2Cl2:diethyl ether (1:3) to give 8b as colorless
1
crystals (260mg, 93%), mp 142ꢂC; IR (KBr): ꢁꢀ¼ 1153, 1312 (vSO ), 1089 (vSO) cmꢁ1; H NMR
2
(CDCl3): ꢀ ¼ 1.79 (d, J ¼ 6.80 Hz, 3H), 3.10 (m, 1H), 3.75 (m, 1H), 4.30 (d, J ¼ 15.60Hz, 1H), 5.51
(m, 1H), 5.62 (m, 1H), 7.55 (d, J ¼ 8.40 Hz, 2H), 8.03 (d, J ¼ 8.40Hz, 2H) ppm; 13C NMR (CDCl3):
ꢀ ¼ 18.37, 28.20, 48.15, 96.65, 118.50, 123.71, 128.04, 129.33, 132.02 132.50, 133.62, 134.07, 142.12,
142.40 ppm; MS: m=z (%) ¼ 582 (38, Mþ).
Acknowledgements
The author thanks Prof. R. Hazell, Aarhus University, Denmark, for the X-ray structural analysis and
Dr. A. El-Nahas, El Menoufiea University, Egypt, for performing the computation for sulfine 5.
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