Episulfidation of trans-Cyclooctene with an 1,2,4-Oxadithiolane

Article abstract of DOI:10.1002/ejoc.200300124

The dipolar cycloaddition of thiobenzophenone S-oxide (1) and 2,2,4,4-tetramethyl-3-thioxocyclobutanone (2) generates the labile 1,2,4-oxadithiolane I, which in the presence of trans-cyclooctene (3) affords trans-episulfide (9). In this direct sulfur tran

Full text of DOI:10.1002/ejoc.200300124

FULL PAPER
Episulfidation of trans-Cyclooctene with an 1,2,4-Oxadithiolane
[a]
[a]
[b]
Waldemar Adam, Rainer M. Bargon,* and Grzegorz Mloston
Keywords: Sulfur heterocycles / Sulfur-atom transfer / Sulfine / Thiirane / Episulfidation
The dipolar cycloaddition of thiobenzophenone S-oxide (1)
and 2,2,4,4-tetramethyl-3-thioxocyclobutanone (2) generates
the labile 1,2,4-oxadithiolane I, which in the presence of
trans-cyclooctene (3) affords trans-episulfide (9). In this dir-
ect sulfur transfer, the oxathiirane II and/or the dithiirane IV,
both derived from the 1,2,4-oxadithiolane I, are proposed as
elusive episulfidating agents.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
persistent 1,2,4-trithiolanes are ineffective for sulfur trans-
fer, we report herein that the in-situ-generated, similarly
[
5]
Recently we have reported that the 9H-fluorenyl-9-thione substituted 1,2,4-oxadithiolane I episulfidates the strained
S-oxide engages readily in 1,3-dipolar cycloaddition with 3 trans-cyclooctene (3) to afford its episulfide 9. Several per-
to give a cyclic 1,2-oxathiolane (sulfenate, sultene) as per- sistent 1,2,4-oxadithiolanes, that have been reported in
[
1Ϫ3]
[4Ϫ6]
sistent product.
The latter was shown to transfer ef- literature,
were also tested, but they were inactive for
ficiently a sulfur atom to strained cycloalkenes under acid sulfur transfer to the strained 3 under thermal conditions.
catalysis, e.g., trans-cyclooctene, to afford the correspond-
ing episulfide in high yield. In the light of these promising
results obtained with the sultene as episulfidation agent, we
Results and Discussion
anticipated that similarly, such direct sulfur-transfer meth-
The thermally labile 1,2,4-oxadithiolane I was generated
odology should be extendable to other sulfur heterocycles.
[
6]
in situ, by heating a solution of 1 and 2 in CDCl . In
3
In particular, we focused our attention on the related 1,2,4-
oxadithiolane I as a promising candidate for the direct epi-
sulfidation of alkenes, since it also contains the reactive
sulfenate functionality.
[
4Ϫ6]
agreement with the literature data,
besides benzo-
phenone (the main thermal decomposition product of the
[
7]
sulfine 1 ), thiobenzophenone, the 2,2,4,4-tetrameth-
ylcyclobutandione (4), as well as the 1,2,4-trithiolane 5,[
were observed by NMR spectroscopy. When, however, the
same reaction was carried out in the presence of the reactive
cycloalkene 3, only traces of the cycloadduct 5 were ob-
tained. In addition to the above-mentioned sulfine 1 and
thioketone 2 products, the 13C NMR spectrum of the crude
7]
[8]
reaction mixture revealed that the DielsϪAlder adduct 6,
[
10]
its aromatized tautomer 7 , cis-cyclooctene (8), and trans-
episulfide 9 had also been formed in variable amounts,
which depended on the reaction conditions (Table 1).
Interestingly, norbornene was inert under comparable re-
action conditions. After heating for 3.5 days in the presence
of 3, approximately equal amounts of both substrates had
been consumed (entry 1). The monothione 2 was cleanly
converted into dione 4, whereas 1 gave expectedly thioben-
zophenone as main product and minor amounts of benzo-
phenone. The thiopyrans 6 and 7, detected in the crude
mixture are DielsϪAlder products of the [4ϩ2]-cycload-
dition of thiobenzophenone with 3. Although most of the
The synthesis of a series of differently substituted 1,2,4-
oxadithiolanes have been reported a few years ago in [2ϩ3]
cycloadditions of aliphatic thioketones with dialkyl or di-
aryl sulfines; some of them were shown to convert into
4]
1
,2,4-trithiolanes on thermal decomposition.[ While the
[
[
a]
Institut für Organische Chemie, Universität Würzburg,
Am Hubland, 97074 Würzburg, Germany
Fax: (internat.) ϩ49-(0)931-8884756
E-mail: adam@chemie.uni-wuerzburg.de
Internet: http://www-organik.chemie.uni-wuerzburg.de
b]
Department of Organic and Applied Chemistry, University of
Lodz,
Narutowicza 68, 90-136 Lodz, Poland, Poland
Fax: (internat.) ϩ48-(0)42-6781609
3
(76 mol %) was isomerized to 8 and appreciable quantities
of the epi- sulfide 9 (about 24 mol %) were formed. As
shown in an independent control experiment, elemental sul-
E-mail: gmloston@krysia.uni.lodz.pl
Internet: http://www.chemia.uni.lodz.pl/katchois/
4012
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200300124
Eur. J. Org. Chem. 2003, 4012Ϫ4015

Episulfidation of trans-Cyclooctene with an 1,2,4-Oxadithiolane
Table 1. Product distribution in the thermolysis of sulfine 1 and thione 2 in the presence of trans-cyclooctene (3)
FULL PAPER
[a]
Time
Entry (d)
2
Conversion (%)
Material balance (%)
Products (mmol)
[b]
(equiv.)
1
2
3
1
2
3
Ph
2
CO
4
Ph
2
CS
5
6
7
8
9
1
2
3
4
5
3.5 1.0
4.0 2.0
5.0 2.0
13.0 2.0
7.5 1.0
36
64
76
84
60
40
33
45
59
70
Ͼ84
Ͼ69
Ͼ95
Ͼ95
Ͼ95
92
95
Ͼ95
Ͼ95
Ͼ95
Ͼ95[
Ͼ95
Ͼ96
Ͼ95
91
0.072
0.051
0.390 0.130
0.535 0.199
0.765 0.199
0.968 0.307
0.710 0.144
Ϫ
0.081 traces 3.51 0.240
b]
b]
b]
94
traces 0.273 0.066 2.15 0.513
traces 0.365 0.070 3.54 0.647
traces 0.321 0.171 3.01 0.684
[
93
0.072
89[
[c]
[
d]
Ͼ95
83
0.080
Ϫ
0.280 0.102 6.26 0.470
[
a]
1
Normalized to 1.0 mmol sulfine 1, but 0.187 mmol were used; determined from the H NMR spectra of the crude product mixture
[
b]
with the sum of all aryl protons as internal standard (error Ϯ5% of the stated values). The trithiolane 5 was detected but not quantified
by H NMR spectroscopy due to signal overlap. Not quantified by H NMR spectroscopy due to signal overlap. 8.6 equiv. of trans-
cyclooctene (3) were used instead of 4.6 equiv.
1
[c]
1
[d]
fur (detected in the reaction mixture) was not responsible
for the episulfidation of 3 leading to 9, but only for the
isomerization of 3 to 8.
When two equivalents of 2 were employed (entry 2), the
consumption of the sulfine 1 was essentially doubled within
about the same time period. More significantly, the yield of
Scheme 1. Hetero-DielsϪAlder reaction between thiobenzo-
phenone and trans-cyclooctene (3)
the episulfide 9 increased more than twice (compare entries
1
3
and 2), and substantially less trans-to-cis isomerization of
to 8 was observed. Even after longer reaction times (com-
pare entries 2Ϫ4), the conversion of 1 was incomplete and
the yield of thiirane 9 remained nearly constant. It is note- ane 9 after heating with the cycloalkene 3. Whereas merely
worthy that under the presented conditions (entries 3 and 8% of sulfine 1 were converted into benzophenone, thione
4), the cycloalkene 3 was completely consumed, but most 2 and the authentic trithiolane 5 persisted completely under
of it was isomerized to 8. On prolonged heating consider- these conditions; only 20% of trans-cyclooctene 3 was isom-
ably more thiobenzophenone was formed, which may be erised to cis-cyclooctene 8 (see Exp. Sect.). The addition of
explained by the fact that the cycloalkene 3 was completely trans-isomer 3 to the thermolysate and subsequent heating
consumed and not available to trap more of the generated under identical conditions did not yield any episulfide 9.
thiobenzophenone. Furthermore, additional heating con-
As for the mechanism, it is relevant to mention that
[
4Ϫ6]
verted the thiopyran 6 to its aromatized tautomer 7 (com- Huisgen
had studied the stoichiometric reaction be-
[
7]
pare entries 3 and 4). Only traces of the trithiolane 5 were tween sulfine 1 and monothione 2 in the absence of an olef-
1
3
observed in the C NMR spectrum of the reaction mixture inic sulfur acceptor. Under these conditions, the intermedi-
entries 2Ϫ4). ary 1,2,4-oxadithiolane I was proposed as an elusive precur-
On doubling the amount of cycloalkene 3 (compare en- sor to the thiobenzophenone and dione 4 products
tries 1 and 5), the conversion of the sulfine 1 and mono- (Scheme 2).
(
thione 2 was approximately doubled. Expectedly, the yield
The oxathiirane II and the carbonyl O-sulfide III were
of episulfide 9 was about twice; also more of DielsϪAlder postulated to desulfurize to 4, whereas the dithiirane IV
products 6 and 7 were observed in the mixture. The initially and the thiocarbonyl S-sulfide V were suggested to generate
formed thiopyran 6 rearranges by stepwise[ hydrogen mi- thiobenzophenone. Thus, the oxadithiolane I directly, or
gration to the aromatized thiopyran 7 (Scheme 1), a re- any of its sulfur-containing species IIϪV, may be postulated
arrangement that usually requires base catalysis.[ In ab- as active sulfur-transferring agents in the episulfidation pro-
sence of a base catalyst, the thiopyran 6 was observed as cess. The oxadithiolane I is probably sterically too hindered
9]
10]
the major product even after 13 days.
to engage in sulfur transfer and, therefore, presumably the
In order to explore the nature of the sulfur-transferring short-lived and highly reactive intermediates IIϪV function
species, the following control experiments were conducted: as possible sulfurating entities. If the analogous oxygen do-
Under the same reaction conditions the sulfine 1 (or mono- nors may be taken as reactivity criterion, the oxathiirane
[
10Ϫ11]
[12Ϫ13]
thione 2), as well as the 1,2,4-trithiolane 5 (the side product II
derived from heating of 1 and 2) alone did not afford thiir- ranes,
and dithiirane IV,
which are akin to the dioxi-
[
14,15]
should possess a higher sulfur-donating ability
Eur. J. Org. Chem. 2003, 4012Ϫ4015
www.eurjoc.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4013

W. Adam, R. M. Bargon, G. Mloston
FULL PAPER
Experimental Section
General Remarks: All solvents were dried and distilled prior to use.
For flash chromatography, Woelm silica gel (0.032Ϫ0.063 mm) was
used. For TLC detection was performed on Polygram SIL/UV 254
plates from MacheryϪNagel. The episulfide was visualized by me-
ans of elemental iodine, alkene spots by means of potassium per-
manganate. Chemical shifts are expressed in δ values relative to
tetramethylsilane. For quantitative NMR analysis, a relaxation de-
1
lay time for T of 23 s was applied and dimethyl isophthalate was
used as internal standard. The oxadithiolane I was prepared in
situ.[
4Ϫ6]
trans-Cyclooctene (3) was synthesized from the corre-
[
21]
sponding cis-isomer 8 according to a literature procedure.
General Procedure for the Reaction of Sulfine 1 with Monothione
and Cyclooctene (3). Analytical Scale: To a solution of 40.0 mg
0.187 mmol) of 1 and 29.2Ϫ58.4 mg (0.187Ϫ0.374 mmol) of 2 in
2
(
3
0.5 mL of CDCl were added under an argon atmosphere 117 or
2
34 µL (0.860 or 1.72 mmol) of 3. The NMR tube was sealed by

means of a rubber stopper and Parafilm , and heated in the dark
in an oil bath at 60 °C for 13 days. At the beginning of the reaction
1
a H NMR spectrum was registered as reference point and at reg-
ular time intervals, aliquots of the crude reaction mixture were sub-
mitted to C NMR and H NMR analyses.
Scheme 4. Episulfidation of trans-cyclooctene (3) in the thermolysis
of in-situ-generated 1,2,4-oxadithiolane I
1
3
1
Preparative Scale: In a Schlenk tube were placed under an argon
atmosphere 214 mg (1.00 mmol) of 1 and 312 mg (2.00 mmol) of 2
than the carbonyl O-sulfide III and the thione S-sulfide V; in 0.5 mL of CHCl , followed by 650 µL (5.00 mmol) of 3. The
3
the latter are structurally similar to the for oxidation pur- tube was sealed and heated in an oil bath at 60 °C for 3 days in
poses inactive carbonyl oxides.[
16,17Ϫ18]
In the oxathiirane II
the dark. After evaporation of the solvent (40 °C/200 mbar), the
known products 4, 5, 7, 9 were isolated as pure compounds by
the sulfur atom is positively polarized, whereas in the car-
bonyl O-sulfide III it is negatively charged. Thus, II should
be more electrophilic than III and serve more likely as the
sulfur-donating entity to a nucleophilic substrate such as
trans-cyclooctene (3). In contrast to some isolable dithiir-
anes (appropriately substituted) analogous to IV, persistent
derivatives of thiocarbonyl S-sulfides like V have not as yet
been reported; presumably the open-ring form V is not suf-
ficiently stablilized compared to the cyclic tautomer IV to
allow direct detection.[ Nonetheless, besides diphenyldi-
silica-gel chromatography. Additionally, a mixture (67.6 mg) of 6
and 8 was isolated, of which the known cycloadduct 6[
22,23]
was
identified by its characteristic NMR signals. Benzophenone and
thiobenzophenone were identified in the crude reaction mixture,
the former by comparison with a commercial sample, the latter by
comparison with a sample obtained from an independent syn-
[24]
thesis.
2
,2,4,4-Tetramethylcyclobutan-1,3-dione (4):[25] Yield 62.3 mg
(
44%).
19]
thiirane (IV), also its open-ring isomer thiobenzophenone Spiro Compound 5:[7] Yield 153 mg (40%).
S-sulfide (V) has been invoked in the thermal fragmentation
of tetraphenyl-1,2,4-trithiolane into thiobenzophenone and
6
a,7,8,9,10,11,12,12a-Octahydro-5-phenyl-5H-cycloocta[c][2]benzo-
[31]
thiopyran (7): Yield 117 mg (38%).
[
20]
elemental sulfur.
On the basis of the afore-mentioned,
we speculate that the intermediates II and IV act as sulfur- trans-9-Thiabicyclo[6.1.0]nonane (trans-9):[26] Yield 82.6 mg (58%).
transfer agents in this episulfidation of the strained cycloal-
kene 3.
Determination of the Sulfur Balance in the Reaction of Sulfine 1
with Monothione 2 and Cyclooctene (3): After complete reaction,
the tube was cooled to room temperature (ca. 20 °C) and 262 mg
(
1.00 mmol) of triphenylphosphane was added. After 2 h the sol-
Conclusion
vent was evaporated (40 °C/200 mbar), and the products were puri-
fied by silica-gel chromatography. In a control experiment, no reac-
We have shown that heating of a mixture of the sulfine 1 tion between thiirane 9 and the triphenylphosphane was observed
even after 3 days at ca. 20 °C.
with monothione 2 in the presence of the strained trans-
cyclooctene (3) results in the corresponding episulfide 9 by
direct sulfur transfer. The oxadithiolane I is proposed as
the initial intermediate, which readily converts under the
reaction conditions to the transient oxathiirane II and di-
thiirane IV. Presumably, the latter two serve as the sulfur-
transfering agents to the trans-cyclooctene (3), we favor the
trans-9-Thiabicyclo[6.1.0]nonane (trans-9):[35] Yield 110 mg (77%).
Triphenylphosphane Sulfide:[36] Yield 26.0 mg (10%).
Treatment of the Thermolysate from the Reaction between Sulfine 1
and Monothione 2 with Cyclooctene (3): In a NMR tube was placed
a solution of 40.0 mg (0.187 mmol) of 1 and 29.2 mg (0.187 mmol)
more electrophilic oxathiirane II as the more active episulfi- of 2 in 0.5 mL of CDCl under an argon atmosphere. The NMR
3

dating agent.
tube was sealed by means of a rubber stopper and Parafilm , and
4014
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2003, 4012Ϫ4015

Episulfidation of trans-Cyclooctene with an 1,2,4-Oxadithiolane
heated in the dark at 60 °C for 4 days by means of an oil bath.
FULL PAPER
Mloston, K. Polborn, J. Rapp, W. Sicking, R. Sustmann,
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Subsequently, to this thermolysate were added 117 µL
[
1
L. Carlsen, A. Holm, E. Koch, B. Stilkerieg, Acta Chem.
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10]
(
0.860 mmol) of 3, immediately a H NMR spectrum was taken as
reference point and a sample of the crude reaction mixture was
[
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1
submitted to H NMR analysis; no episulfide 9 was observed.
[11]
1
969, 8, 781Ϫ853.
Reaction of Sulfine 1 with Cyclooctene (3): In a NMR tube were
placed 40.7 mg (190 µmol) of 1 and 130 µL (940 µmol) of 3 in
[
[
12]
13]
J. P. Snyder, J. Am. Chem. Soc. 1974, 96, 5005Ϫ5007.
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0
.5 mL of CDCl
3
. The NMR tube was sealed by means of a rubber

stopper and Parafilm , and heated in the dark in an oil bath at 60
[14]
L. Carlsen, J. P. Snyder, A. Holm, E. Pedersen, Tetrahedron
981, 37, 1257Ϫ1261.
1
°C for 4 days. Immediately a H NMR spectrum was taken as refer-
1
[
[
[
[
[
[
15]
16]
17]
18]
19]
20]
ence point and a sample of the crude reaction mixture was submit-
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1
ted to H NMR analysis, which revealed that 179 µmol of its cis-
isomer 8 and 15.0 µmol of benzophenone had been formed.
A. Ishii, R. Yamashita, M. Saito, J. Nakayama, J. Org. Chem.
2
003, 68, 1555Ϫ1558.
Reaction of Monothione 2 with Cyclooctene (3): In a NMR tube
were placed 40.0 mg (256 µmol) of 2 and 154 µL (1.18 mmol) of 3
G. Mloston, A. Majchrzak, A. Senning, I. Sotofte, J. Org.
Chem. 2002, 67, 5690Ϫ5695.
in 0.6 mL of CDCl
rubber stopper and Parafilm , and heated in the dark at 60 °C for
3
. The NMR tube was sealed by means of a
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221Ϫ284.

1
K. Shimada, K. Kodaki, S. Aoyagi, Y. Takikawa, C. Kabuto,
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days by means of an oil bath. Immediately a H NMR spectrum
was taken as reference point and a sample of the crude reaction
1
mixture was submitted to H NMR analysis, which revealed that
the trans-isomer 3 had been completely (Ͼ 95%) converted into its
cis-isomer 8, but no episulfide 9 was detected.
5
09Ϫ523.
[
21]
W. Adam, A. K. Smerz, Bull. Soc. Chim. Belg. 1996, 105,
5
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placed 37.0 mg (95.7 µmol) of 5 and 61.2 µL (440 µmol) of 3 in
81Ϫ599.
[22]
[23]
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mediates III and V may also function as sulfur transfering
species but we suspect that catenated sulfur entities should not
be sufficiently electrophilic for this purpose.
0
.6 mL of CDCl
3
. The NMR tube was sealed by means of a rubber

stopper and Parafilm , and heated in the dark in an oil bath at 60
1
°C for 4 days. Immediately, a H NMR spectrum was registered as
[
24]
reference point and a sample of the crude reaction mixture was
submitted to 1H NMR analysis, which revealed that 5 persisted
under the reaction conditions, whereas the 3 was completely
(Ͼ 95%) converted into 8; no 9 was detected.
[
25]
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This work was generously financed by the Deutsche Forschungsge-
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Received February 27, 2003
Eur. J. Org. Chem. 2003, 4012Ϫ4015
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4015