Direct Thioepoxidation of Strained Cyclic Alkenes by the Photolytic Sulfur-Atom Transfer from Thiocarbonyl S-Oxides (Sulfines)

Full text of DOI:10.1021/jo971133e

7084
J . Org. Chem. 1997, 62, 7084-7085
4, 5) to transfer sulfur atoms to olefins was postulated
in the thermolysis of thiophene endoperoxides,8,13 but has
not been studied systematically. Therefore, we have
investigated the photolysis of the series of diaryl sulfines
1a -e in the presence of strained cyclic olefins as sulfur-
atom acceptors, in the interest of developing a useful
method for the direct thioepoxidation.14
Dir ect Th ioep oxid a tion of Str a in ed Cyclic
Alk en es by th e P h otolytic Su lfu r -Atom
Tr a n sfer fr om Th ioca r bon yl S-Oxid es
(Su lfin es)
Waldemar Adam,* Oliver Deeg,† and
Stephan Weinko¨tz
As expected, all sulfines 1a -e were converted quan-
titatively to the ketones 2a -e by irradiation. In the
absence of olefin, all available sulfur was extruded as
elemental sulfur. In the presence of excess norbornene
(6a ), 12% of the sulfur was trapped in the form of thiirane
7a (Table 1, entry 1). Additionally, traces of trithiolane
8a and pentathiepane 9a were detected, which are known
to be products of the reaction of 6a with sulfur allo-
tropes.15 The sulfur balance (>90%) was determined by
converting the extruded elemental sulfur to phosphine
sulfides with triarylphosphines.
When an equimolar amount of trans-cyclooctene (trans-
6b) was used, a more efficient, highly diastereoselective
sulfur transfer (57%, entry 3) was observed to afford the
thiirane trans-7b. The structural evidence for trans-7b
rests on its elemental analysis, the chemical shifts of the
thiirane hydrogen (δH 2.66) and carbon atoms [δC 43.4
(d)],8 and the symmetry of the molecule implied by only
four 13C NMR resonances. The change of the tempera-
ture to -30 °C had no significant effect on the reaction
time and thiirane yield (entries 2 and 4). On photolysis
of the sulfine 1a with visible light, sulfur-atom transfer
also took place, but with the advantage that under such
milder conditions less of trans-6b was isomerized to cis-
6b (entries 5 and 6).
The results of the irradiations of the para-substituted
benzothiophenone S-oxides 1b,c (entries 7-10) do not
differ significantly from those of the parent sulfine 1a .
The competition between sulfur transfer and extrusion
is, thus, not sensitive to electronic effects.
cis-Cyclooctene (cis-6b) could not be thioepoxidized by
the sulfines 1a -c. It is known for the analogous epoxi-
dation that cis-6b reacts slower than trans-6b by a factor
of 112 (mCPBA)16 or 100 (dimethyldioxirane).17 While
the less reactive cis-6b is quantitatively epoxidized, for
its thioepoxidation by sulfines 1 competitive extrusion
of elemental sulfur prevails. Nevertheless, for the sulfines
1d ,e some thiirane cis-7b was observed (entries 12 and
17) and the sulfur-transfer efficiency to norbornene (6a )
was slightly increased (entries 11 and 16).
Institut fu¨r Organische Chemie der Universita¨t,
Am Hubland, D-97074 Wu¨rzburg, Germany
Received J une 23, 1997
The syntheses and reactions of thiocarbonyl S-oxides
1 (sulfines) have been extensively studied and reviewed
in the last 25 years.1-4 A characteristic behavior of these
reactive heterocumulenes is the extrusion of elemental
sulfur under thermal or photolytic conditions to produce
the corresponding carbonyl compounds 2.1,3 The cycliza-
tion to oxathiiranes 3 is postulated as initiating step,
which theory predicts to be a thermally and photochemi-
cally allowed process.5 Although there are literature
reports in which oxathiiranes 3 have been invoked as
reactive intermediates,1,3,6-8 no persistent derivatives
have been isolated, contrary to dithiiranes9 and dioxi-
ranes.6,10
Experimental evidence for the existence of oxathiiranes
3 was provided by Carlsen et al.11,12 during the photolysis
of diphenyl sulfine (1a ) in an organic glass matrix at 85
K. The resulting diphenyl oxathiirane (3a ) was charac-
terized by low-temperature electronic absorption spec-
troscopy. This labile intermediate decomposed quanti-
tatively to benzophenone (2a ) and elemental sulfur when
the glass matrix was heated to its melting point. At-
tempts to trap the oxathiirane 3a (or its isomers 4a , 5a )
with 2,3-dimethyl-2-butene, methyl methacrylate, or
ethyl trifluoroacetate were unsuccessful.
Whereas the epoxidation of olefins by dioxiranes is a
well established and synthetically valuable oxidation
mode,6,10 the ability of oxathiiranes 3 (or their isomers
As already addressed above in connection with the
wavelength dependence, besides sulfur transfer and
extrusion, as additional reaction mode, the isomerization
(6-39%) to cis-6b was observed for olefin trans-6b with
all sulfines 1a -e (entries 3, 8, 10, 13, 18). The ratio of
isomerization and thiirane formation decreased with
increasing starting concentration of trans-6b, as dis-
played by sulfine 1d (entries 13-15). This trend indi-
cates that the isomerization of trans-6b is not connected
† Undergraduate Research Participant (Spring 1997).
(1) Zwanenburg, B. Phosphorus Sulfur 1989, 43, 1-24.
(2) Still, I. W. J . Phosphorus Sulfur 1991, 58, 129-149.
(3) Metzner, P. Phosphorus Sulfur 1991, 59, 1-16.
(4) Block, E. Angew. Chem. 1992, 104, 1158-1203.
(5) Snyder, J . P. J . Am. Chem. Soc. 1974, 96, 5005-5007.
(6) Murray, R. W.; Singh, M. In Comprehensive Heterocyclic Chem-
istry II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds.;
Pergamon: Oxford, 1996; Vol. 1A, pp 429-456.
(7) Huisgen, R.; Mloston, G.; Polborn, K.; Palacios-Gambra, F.
Liebigs Ann./ Recueil 1997, 187-192.
(13) Matturro, M. G.; Reynolds, R. P.; Kastrup, R. V.; Pictroski, C.
F. J . Am. Chem. Soc. 1986, 108, 2775-2776.
(14) For other methods of thiirane syntheses see: Dittmer, D. C. In
Comprehensive Heterocyclic Chemistry; Katritzky, A. R., Rees, C. W.,
Eds.; Pergamon: Oxford, 1984; Vol. 7, pp 131-184. Nakayama, J .; Ito,
Y.; Mizumura, A. Sulfur Lett. 1992, 14, 247-250. Abu-Yousef, I. A.;
Harpp, D. N. Tetrahedron Lett. 1995, 36, 301-204.
(15) Bartlett, P. D.; Ghosh, T. J . Org. Chem. 1987, 52, 4937-4943.
(16) Shea, K. J .; Kim, J .-S. J . Am. Chem. Soc. 1992, 114, 3044-
3051.
(17) Adam, W.; Curci, R.; D′Accolti, L.; Dinoi, A.; Fusco, C.; Gas-
parrini, F.; Kluge, R.; Paredes, R.; Schulz, M.; Smerz, A. K.; Veloza,
L. A.; Weinko¨tz, S.; Winde, R. Chem. Eur. J . 1997, 3, 105-109.
(8) Adam, W.; Weinko¨tz, S. J . Chem. Soc., Chem. Commun. 1996,
177-178.
(9) Ishii, A.; Hoshino, M.; Nakayama, J . Pure Appl. Chem. 1996,
68, 869-874.
(10) (a) Adam, W.; Smerz, A. K. Bull. Soc. Chim. Belg. 1996, 105,
581-599. (b) Kirschfeld, A.; Muthusamy, S.; Sander, W. Angew. Chem.
1994, 106, 2261-2263.
(11) Sander, W.; Kirschfeld, A. In Advances in Strain in Organic
Chemistry; J AI Press Inc.: Greenwich, CT, 1995; Vol. 4, pp 1-80.
(12) Karlstro¨m, G.; Roos, B. O.; Carlsen, L. J . Am. Chem. Soc. 1984,
106, 1557-1561.
S0022-3263(97)01133-X CCC: $14.00 © 1997 American Chemical Society

Communications
J . Org. Chem., Vol. 62, No. 21, 1997 7085
Ta ble 1. P r od u ct Stu d ies of th e P h otolytic Su lfu r -Atom Tr a n sfer fr om Su lfin es 1 to Cycloa lk en es 7
products (%)b
entry
sulfine 1a
olefin
6a
equiv of olefin
T (°C)
λ (nm)
t (h)
thiirane 7c,d
cis-6be
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1a
1a
1a
1a
1a
1a
1b
1b
1c
1c
1d
1d
1d
1d
1d
1e
1e
1e
6.3
5.3
1.0
1.0
3.3
2.0
6.2
2.2
5.8
2.2
4.1
4.9
1.1
1.7
2.7
4.2
5.1
1.0
5
350
350
350
350
350
>400
350
>400
350
>400
350
350
350
350
350
350
1.3
1.3
1.3
1.3
1.3
6.5
1.3
4.0
3.0
6.5
4.5
3.5
3.5
3.5
4.8
1.5
3.0
3.0
12f
6a
-30
9f
trans-6b
trans-6b
trans-6b
trans-6b
6a
trans-6b
6a
trans-6b
6a
cis-6b
trans-6b
trans-6b
trans-6b
6a
5
57
54
94
92
12f
91
13f
89
18f
13
51
88
94
17f
11
64
32
31
16
3
-30
5
5
5
5
5
5
5
5
5
5
5
5
5
5
20
6
39
22
7
cis-6b
trans-6b
>400
>400
33
a
b
Concentration 0.15 M. Yields were determined by 1H NMR analysis of the crude reaction mixture (error (5%), olefin mass balances
were >90%. c Based on sulfine 1. By converting the extruded elemental sulfur with triarylphosphine to the phosphine sulfide, the sulfur
d
mass balance was determined to be >90%. e Based on olefin trans-6b. f Traces of trithiolane 8a and pentathiepane 9a (ref 21b) were
detected.
with the sulfur-transfer step. Although it is known that
the olefin isomerization may be photosensitized by aro-
matic ketones18 or catalyzed by traces of acid, these
isomerization modes are independent of starting olefin
concentration and, therefore, should not be responsible.
The suspicion that isomerization is mainly induced by
the extruded elemental sulfur, since the extent of isomer-
ization is lowest when most of the sulfur is trapped by
trans-6b (entry 15), was confirmed when trans-6b was
irradiated in the presence of elemental sulfur. Indeed,
isomerization to cis-6b occurred, but under these condi-
tions thiirane trans-7b was also formed.15,19 The ratio
trans-7b:cis-6b (17:83, 19:81, and 14:86) was within the
error limits regardless of the amount (0.3, 1.0, and 3.1
equiv) of olefin trans-6b used. In contrast, in the
photolytic sulfur transfer from sulfine 1d , the trans-7b:
cis-6b ratio (55:45, 70:30, and 84:16) increases with
increasing number of equivalents of trans-6b (1.1, 1.7,
and 2.7 equiv, entries 13-15). Consequently, different
sulfur-transfering species operate in the photolysis of
sulfines versus that of elemental sulfur.
The high diastereoselectivity of the sulfur transfer
implies a concerted mechanism. If a stepwise diradical
or dipolar mechanism had operated, the formation of the
less strained, thermodynamically more stable thiirane
cis-7b should have been observed in the sulfur transfer
from sulfines 1 to trans-6b, but not even traces were
detected.17 Such high diastereoselectivities are known
for oxygen-atom (dioxiranes6,10,17 or N-substituted ox-
aziridines20) or NH-group (oxaziridines21) transfer reac-
tions of three-membered heterocycles. In analogy, the
F igu r e 1. Steric interaction between oxathiiranes 3a -c and
the attacking olefin.
oxathiiranes 3, which are initially generated as labile
intermediates in the sulfine photolysis,11,12 qualify as
highly stereoselective sulfur-transfering species. Con-
sequently, the enhanced sulfur-transfer efficiency in the
photolysis of the planar fluorene- and xanthene-derived
sulfines 1d ,e may be rationalized in terms of decreased
steric interactions between the sulfur-transfering inter-
mediate and the olefin (Figure 1).22 These novel results
on the direct diastereoselective thioepoxidation of olefins
allow hope that still more effective sulfines may be
developed for preparative purposes.
Ack n ow led gm en t. We thank the Deutsche For-
schungsgemeinschaft and the Fonds der Chemischen
Industrie for financial support. S.W. is grateful to the
Hermann-Schlosser-Stiftung for a doctoral fellowship.
Su p p or tin g In for m a tion Ava ila ble: Experimental sec-
tion (3 pages).
J O971133E
(20) Davis, F. A.; Reddy, R. T. In Comprehensive Heterocyclic
Chemistry II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds.;
Pergamon: Oxford, 1996; Vol. 1A, pp 365-413.
(18) Wayne, R. P. Principles and applications of photochemistry;
Oxford University Press: Oxford, 1988.
(19) Inoue, S.; Tezuka, T.; Oae, S. Phosphorus Sulfur 1978, 4, 219-
221.
(21) Andreae, S; Schmitz, E. Synthesis 1991, 327-341.
(22) These steric effects provide circumstantial evidence against the
carbonyl O-sulfides 5 (formed thermally or photochemically from the
oxathiiranes 3) as sulfur-transfer intermediates.