Sulfonyl chloride formation from thiol derivatives by N-chlorosuccinimide mediated oxidation

Article abstract of DOI:10.1055/s-2006-950353

Oxidation of several thiol derivatives by a combination of N-chlorosuccinimide and dilute hydrochloric acid proceeded smoothly, affording the corresponding sulfonyl chlorides in good yield. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-950353

PAPER
4131
Sulfonyl Chloride Formation from Thiol Derivatives by N-Chlorosuccinimide
Mediated Oxidation
S
ulfonyl Chloride
s
t
Forma
s
tion by
N
-
C
hlorosucci
k
nimide
O
xid
o
ation Nishiguchi,* Kazuhiro Maeda, Shokyo Miki
Chemical Development Laboratories, Takeda Pharmaceutical Company Limited, 2-17-85 Jusohonmachi, Yodogawa-ku, Osaka 532-8686,
Japan
Fax +81(6)63006251; E-mail: Nishiguchi_Atsuko@takeda.co.jp
Received 14 June 2006; revised 4 August 2006
vert thioesters, especially thioacetates, into sulfonyl chlo-
Abstract: Oxidation of several thiol derivatives by a combination
rides, we examined the oxidation of thioacetates under
Kim’s conditions (NCS in aq AcOH). To the best of our
of N-chlorosuccinimide and dilute hydrochloric acid proceeded
smoothly, affording the corresponding sulfonyl chlorides in good
knowledge, there have been no reports employing NCS as
an oxidizing agent for thioacetates. We found that, though
the desired product was obtained, the rate of the reaction,
after an initial lag phase, increased exponentially and, in
some cases, violently. We therefore attempted to develop
a convenient and more controllable method for thioacetate
oxidation by NCS. For the optimization of the reaction
conditions, we chose S-phenylthioacetate as the oxidation
substrate (Table 1).
yield.
Key words: thiol derivatives, oxidation, solvent effects, NCS,
chlorosulfonation
Sulfonyl chlorides are useful reagents for the synthesis of
a range of organic compounds. The most typical method
of preparation is the oxidative chlorination of sulfur com-
pounds; thiols, sulfides, thioacetates and thiocarbamates,
with aqueous chlorine, to give the sulfonyl chlorides di-
rectly.1 Although many reactions are high yielding, chlo-
rine is hazardous and requires careful handling. Though
other oxidizing agents such as H2O2–SOCl26,2 Oxone–
Under the reaction conditions described by Kim, the reac-
tion did not occur at the same temperature (5–10 °C), but
started suddenly when the temperature was allowed to
reach 25 °C. Although sulfonyl chloride 2a was obtained,
the process could not be controlled. Indeed the reaction
became so vigorous that the mixture was expelled from
the reaction vessel after the temperature reached 40 °C. A
similar situation occurred when the reaction was conduct-
ed in either aqueous acetonitrile or a mixture of aqueous
acetic acid and acetonitrile. In these cases, the reaction
proceeded very slowly at 10–15 °C for about one hour be-
fore it suddenly accelerated out of control (entries 2 and
5
SOCl2,3 Br2–Cl3PO,4 SO2Cl2–KNO3 or KClO3 have also
been used, many are not satisfactory due to the stepwise
process of oxidation followed by chlorination, the use of
hazardous reagents, or occasionally low yields.
Recently, Kim et al.7 mentioned that the oxidation of O,S-
hemithioacetals by N-chlorosuccinimide (NCS) afforded
the corresponding sulfonyl chlorides efficiently. Since we
have been looking for mild conditions with which to con-
Table 1 NCS Oxidation of S-Phenylthioacetate 1a
NCS
PhSO2Cl
PhSAc
1a
2a
Entry Solvent
(v/v)
Temperature Results
(°C)
5–10
15
1
2
3
4
5
6
AcOH–H2O, 3:1
Reacted very slowly below 20 °C, then rapidly became uncontrollable upon reaching 25 °C.
Uncontrollable reaction.a
H2O–MeCN, 1:5
2 M AcOH–MeCN, 1:5
2 M H2SO4–MeCN, 1:5
15
Uncontrollable reaction.a
15
Uncontrollable reaction.b
2 M MeSO3H–MeCN, 1:5 15
2 M HCl–MeCN, 1:5 15
Uncontrollable reaction.b
Smooth reaction occurred on addition of reactant; 2a was obtained in 96% yield.
a Reaction proceeded very slowly for 1 h then suddenly accelerated uncontrollably.
b Reaction proceeded very slowly for 5 min then suddenly accelerated uncontrollably.
SYNTHESIS 2006, No. 24, pp 4131–4134
x
x.
x
x
.
2
0
0
6
Advanced online publication: 02.11.2006
DOI: 10.1055/s-2006-950353; Art ID: F09206SS
© Georg Thieme Verlag Stuttgart · New York

4132
A. Nishiguchi et al.
PAPER
3). Changing the solvent system to a mixture of aqueous Table 2 Oxidation of Thioacetates 1
sulfuric acid and acetonitrile or aqueous methane sulfonic
NCS
RSO2Cl
RSAc
acid and acetonitrile did not improve this unpredictable
behavior (entries 4 and 5). In contrast, when the reaction
was conducted in a mixture of aqueous hydrochloric acid
and acetonitrile (entry 6), the reaction occurred concur-
rently with thioacetate (1a) addition to the reaction mix-
ture. The expected product 2a was obtained in 96% yield.
2 M HCl–MeCN
1
2
Entrya
R
Yield (%)b
1
2
1a; Ph
2a; 96.3
2b; 96.8
2c; 95.6
2d; 97.7
2e; 97.5
2f; 64.0
1b; 4-Cl-C6H4
A plausible reason for why the reaction proceeded
smoothly with hydrochloric acid could be that molecular
chlorine, a highly reactive species, was generated quickly,
either by the process depicted in Equation 18 or in
Equation 2. Our assumption that chlorine is the reactive
species is consistent with the fact that the other acids em-
ployed did not lead to a smooth reaction, but rather, after
the whole amount of reactant was added to the reaction
mixture, a rapid acceleration in rate occurred when a
threshold amount of HCl was generated from the gradual
formation of the sulfonyl chlorides (Equation 3). The
present reaction with NCS–HCl, on the other hand, was
practical since there was no time lag between the addition
of the reactant and the beginning of the reaction.
3
1c; 4-NO2-C6H4
1d; 4-MeO-C6H4
1e; Bn
4
5
6
1f; 4-Cl-C6H4-CH2
1g; 4-NO2-C6H4-CH2
1h; 4-MeO-C6H4-CH2
1i; Et
7
2g; 95.7
2h; 0c
8
9
2i; 68.6 [71]d
2j; 98.3 [72]d
2k; 6.1
10
12
1j; C6H11-CH2
1k; CH2=CH-CH2
a Reagents and conditions: A solution of 1 in MeCN was added to a
mixture of NCS (4 equiv) and 2 M HCl–MeCN (1:5) at 10 °C.
b Isolated yield.
+
+
H2O
HCl
+
HOCl
O
O
O
O
N
N
H
c 4-Methoxybenzyl chloride was obtained in 74% yield.
d Yields using aqueous chlorine.11
Cl
Cl2
+
H2O
HOCl
Table 3 Oxidation of Thiocarbamates 3a
Equation 1
NCS
RSO2Cl
RSCONHMe
2 M HCl–MeCN
+
Cl2
+
HCl
2
3
O
O
O
O
N
N
H
Cl
Entry
R
Yield (%)b
2a; 96.6
2b; 96.1
2d; 98.1
2e; 98.8
2f; 98.7
2g; 90.9
2h; 0c
Equation 2
1
2
3
4
5
6
7
8
9
3a; Ph
3b; 4-Cl-C6H4
3d; 4-MeO-C6H4
3e; Bn
3 H O
RSO2Cl
RSAc
3 NCS
2 HCl AcOH
+ +
+
+
+
3
2
O
O
N
H
Equation 3
3f; 4-Cl-C6H4-CH2
3g; 4-NO2-C6H4-CH2
3h; 4-MeO-C6H4-CH2
3i; Et
In order to evaluate the generality of this technique, vari-
ous thioacetates 19 were submitted to the optimized reac-
tion conditions, in order to obtain the corresponding
sulfonyl chlorides 210 (Table 2).
2i; 89.6
In the cases of arylthioacetates, the corresponding sulfo-
nyl chlorides were afforded in excellent yields, regardless
of the substituents on the aromatic ring (entries 1–4). Ben-
zyl- and 4-nitrobenzylthioacetates also gave the desired
products in excellent yields. However, 4-chlorobenzyl-
thioacetate gave sulfonyl chloride in comparatively
moderate yield (entry 5–7). In contrast, 4-methoxy-
benzylthioacetate (1h) provided 4-methoxybenzylchlo-
ride in 74% yield, instead of the sulfonyl chloride. With
alkylthioacetates, sulfonyl chlorides were obtained in
good to excellent yield. The yield of 2j was higher than
the reported yield obtained with aqueous chlorine (entry
3j; C6H11
2j; 96.8
a Reagents and conditions: A solution of 3 in MeCN was added to a
mixture of NCS (4 equiv) and 2 M HCl–MeCN (1:5) at 10 °C.
b Isolated yield.
c 4-Methoxybenzyl chloride was obtained in 98% yield.
10), and the yield of 2i was comparable to the reported
yield (entry 9).11 The reaction with allylthioacetate (1k),
produced many impurities and the desired sulfonyl chlo-
ride (2k) was obtained in only 6% yield.
Synthesis 2006, No. 24, 4131–4134 © Thieme Stuttgart · New York

PAPER
Sulfonyl Chloride Formation by N-Chlorosuccinimide Oxidation
4133
This method was then applied to thiocarbamates 3,12 and
the results are presented in Table 3.
The abbreviation IPE denotes (i-Pr)2O. The notation ‘v/w to NCS’
indicates the number of volume equivalents (in mL) with respect to
the mass of NCS used (in g).
Most aryl- and alkylthiocarbamates provided the corre-
sponding sulfonyl chlorides in excellent yield, except for
4-methoxybenzylthiocarbamate (3h), which produced 4-
methoxybenzylchloride in 98% yield. The yields of sulfo-
nyl chlorides 2f and 2i, from thiocarbamates 1f and 1i,
were higher than those obtained from the corresponding
thioacetates 3f and 3i (compare Table 2, entries 6 and 9,
to Table 3, entries 5 and 8), though the reason for this is
unclear.
S-(4-Chlorobenzyl)methylthiocarbamate (3f)
To a solution of (4-chlorophenyl)methylthiol (10.0 g, 63.0 mmol) in
MeCN (50 mL) was added phenyl methylcarbamate (9.53 g, 63.0
mmol), n-Bu3P (1.55 mL, 6.3 mmol) and K2CO3 (4.36 g, 31.5
mmol). The resulting mixture was stirred at r.t. for 4 h, and then
EtOAc (50 mL), citric acid monohydrate (13.2 g, 63.0 mmol), H2O
(50 mL) and sat. NaCl (50 mL) were added to the mixture. The
aqueous layer was extracted with EtOAc (50 mL), and then the
combined organic layer was washed with NaCl soln (7%, 2 × 50
mL), and concentrated in vacuo. The residue was crystallized from
IPE (25 mL) and hexane (25 mL) to obtain pure 3f.
The reactions of thiols and disulfides 4 afforded the corre-
sponding sulfonyl chlorides in moderate to good yield
(Table 4). In the case of 4a, the sulfonyl chloride 2a was
obtained in higher yield than that reported for oxidative
chlorination, however, both the alkyl thiol and the disul-
fide provided 2i in lower yields.
Yield: 8.20 g (60.3%); white crystals; mp 92–93 °C.
IR (ATR): 3276, 1643, 1530, 1488, 1410, 1223, 1099 cm–1.
1H NMR (300 MHz, CDCl3): d = 2.88 (d, J = 4.9 Hz, 3 H), 4.11 (s,
2 H), 5.29 (br s, 1 H), 7.23–7.29 (m, 4 H).
13C NMR (75 MHz, CDCl3): d = 28.1, 33.5, 128.7, 130.2, 132.9,
137.2, 167.1.
Table 4 Oxidation of Thiols and Disulfides 4
NCS
Anal. Calcd for C9H10NOClS: C, 50.11; H, 4.67; N, 6.49; Cl, 16.44;
S, 14.87. Found: C, 50.05; H, 4.64; N, 6.51; Cl, 16.28; S, 14.94.
R1SO2Cl
R1SR2
2 M HCl–MeCN
4
2
Chlorosulfonation; General Procedure
Entry
1a
R1, R2
Yield (%)c
NCS (4 equiv) was added to a mixture of 2 M HCl–MeCN (1:5; 3
v/w to NCS) and then cooled to 10 °C. A solution of the substrate
(1 equiv) in MeCN (0.5 v/w to NCS) was added dropwise to the
mixture, which was kept below 20 °C. The resulting solution was
stirred at <20 °C for 10–30 min, and then diluted with IPE (3.5 v/w
to NCS). The organic layer was washed with aq NaCl (12%; 3 × 1.5
v/w to NCS), and concentrated in vacuo. The residue was purified
by column chromatography to obtain 2.
4a; R1 = Ph, R2 = H
4b; R1 = Ph, R2 = S-Ph
4c; R1 = Et, R2 = H
4d; R1 = Et, R2 = S-Et
2a; 80.6 [55]d
2a; 86.7
2b
3a
2i; 55.6 [73]d
2i; 53.1 [90]d
4b
a Reagents and conditions: A solution of thiol in MeCN was added to
a mixture of NCS (4 equiv) and 2 M HCl–MeCN (1:5) at 10 °C.
b Reagents and conditions: A solution of disulfide in MeCN was add-
ed to a mixture of NCS (6 equiv) and 2 M HCl–MeCN (1:5) at 10 °C.
c Isolated yield.
The reaction conditions mentioned below were used when the sub-
strate would not dissolve in acetonitrile.
To a mixture of substrate (1 equiv) in 2M HCl–MeCN (1:5; 3 v/w
to NCS) was added NCS (4 equiv) in portions at 0 °C.9 The mixture
was stirred at <20 °C for 10–30 min, then diluted with IPE (3 v/w
to NCS). The organic layer was washed with aq NaCl (12%; 3 × 1.5
v/w to NCS), and concentrated in vacuo. The residue was purified
by column chromatography to obtain 2.
d Yields using aqueous chlorine.11
In this series of reactions, chlorinating agents such as 1,3-
dichloro-5,5-dimethylhydantoin (5) or trichloroisocyanu-
ric acid (6), could also be used instead of NCS: in fact, the
oxidation of 3e with 5 and 6 afforded 2e in 97% and 99%
yield, respectively.13,14 Though the reactivity of these N-
chloro derivatives were similar, we consider NCS to be fa-
vorable from the viewpoints of handling, toxicity and be-
cause the byproduct (succinimide) could be easily
removed.
Benzenesulfonyl Chloride (2a)
NCS (35.1 g, 0.26 mol) was added to a mixture of 2M HCl (17.5
mL) and MeCN (87.7 mL) and then cooled to 10 °C. A solution of
1a (10.0 g, 65.7 mmol) in MeCN (17.5 mL) was added dropwise to
the mixture, which was kept below 20 °C. The resulting solution
was stirred at below 20 °C for 10 min, and then diluted with IPE
(340 mL). The organic layer was washed with aq NaCl (12%; 3 ×
170 mL), and concentrated in vacuo. The residue was purified by
column chromatography (n-hexane–EtOAc, 4:1) to obtain 2a.
In conclusion, we have developed a safe, convenient and
controlled oxidation method with which to convert thiol
derivatives to give the corresponding sulfonyl chlorides in
good yield.15
Yield: 11.2 g (96.3%); colorless liquid.
1H NMR (300 MHz, CDCl3): d = 7.63 (t-like, 2 H), 7.73–7.78 (m,
1 H), 8.05 (dd, J = 1.3, 8.2 Hz, 2 H).
HRMS (EI): m/z [M]+ calcd for C6H5ClO2S: 175.9699; found:
175.9682.
Melting points were recorded on a Büchi melting point B-540 and
were uncorrected. IR spectra were recorded on a FT-IR Thermo
Electron Nicolet 4700. 1H NMR and 13C NMR spectra were record-
ed on a Bruker DPX-300 spectrometer using TMS as an internal
standard. Elemental analyses and mass spectra were recorded by
Takeda Analytical Research Laboratories Limited. The preparation
of the following compounds are described elsewhere: thioacetates
1b–e,9a 1f,9b 1g,9c 1h,9d 1j,9e 1k,9f thiocarbamates 3a–e,12a and 3i.12b
4-Chlorobenzenesulfonyl Chloride (2b)
White crystals; mp 47–48 °C.
1H NMR (300 MHz, CDCl3): d = 7.60 (d, J = 8.8 Hz, 2 H), 7.99 (d,
J = 8.8 Hz, 2 H).
Anal. Calcd for C6H4Cl2O2S: C, 34.14; H, 1.91; Cl, 33.59; S, 15.19.
Found: C, 34.13; H, 1.93; Cl, 33.45; S, 15.38.
Synthesis 2006, No. 24, 4131–4134 © Thieme Stuttgart · New York

4134
A. Nishiguchi et al.
PAPER
4-Nitrobenzenesulfonyl Chloride (2c)
White crystals; mp 72–73 °C.
Acknowledgment
We would like to thank Mr. K. Yoshida, Mr. Y. Saito and Dr. K.
Tomimatsu for their encouragement throughout this work.
1H NMR (300 MHz, CDCl3): d = 8.27 (d, J = 8.8 Hz, 2 H), 8.49 (d,
J = 8.9 Hz, 2 H).
Anal. Calcd for C6H4ClNO4S: C, 32.52; H, 1.82; Cl, 16.00; N, 6.32;
S, 14.47. Found: C, 32.63; H, 1.87; Cl, 15.77; N, 6.31; S, 14.24.
References
(1) (a) Watson, R. J.; Batty, D.; Baxter, A. D.; Hannah, D. R.;
Owen, D. A.; Montana, J. G. Tetrahedron Lett. 2002, 43,
683. (b) Percec, V.; Bera, T. K.; De B, B.; Sanai, Y.; Smith,
J.; Holerca, M. N.; Barboiu, B.; Grubbs, R. B.; Fréchet, J. M.
J. J. Org. Chem. 2001, 66, 2104. (c) Chen, Z.; Demuth, T. P.
Jr.; Wireko, F. C. Bioorg. Med. Chem. Lett. 2002, 11, 2111.
(2) (a) Monnee, M. C. F.; Marijne, M. F.; Brouwer, A. J.;
Liskamp, R. M. J. Tetrahedron Lett. 2000, 41, 7991.
(b) Piatek, A.; Chapuis, C.; Jurczak, J. Helv. Chim. Acta
2002, 85, 1973. (c) Humljan, J.; Gobec, S. Tetrahedron Lett.
2005, 46, 4069.
4-Methoxybenzenesulfonyl Chloride (2d)
Colorless liquid.
1H NMR (300 MHz, CDCl3): d = 3.93 (s, 3 H), 7.05 (d, J = 9.3 Hz,
2 H), 7.98 (d, J = 9.1 Hz, 2 H).
HRMS (EI): m/z [M]+ calcd for C7H7ClO3S: 205.9805; found:
205.9817.
Phenylmethanesulfonyl Chloride (2e)
White crystals; mp 91–93 °C.
1H NMR (300 MHz, CDCl3): d = 4.87 (s, 2 H), 7.45–7.50 (m, 5 H).
(3) Kværnø, L.; Werder, M.; Hauser, H.; Carreira, E. M. Org.
Lett. 2005, 7, 1145.
(4) Meinzer, A.; Breckel, A.; Thaher, B. A.; Manicone, N.; Otto,
H.-H. Helv. Chim. Acta 2004, 87, 90.
Anal. Calcd for C7H7ClO2S: C, 44.10; H, 3.70; Cl, 18.60; S, 16.82.
Found: C, 44.18; H, 3.59; Cl, 18.43; S, 16.96.
(4-Chlorophenyl)methanesulfonyl Chloride (2f)10a
White crystals; mp 92–93 °C.
1H NMR (300 MHz, CDCl3): d = 4.83 (s, 2 H), 7.43 (s, 4 H).
(5) Park, Y. J.; Shin, H. H.; Kim, Y. H. Chem. Lett. 1992, 1483.
(6) Schindler, W. Helv. Chim. Acta 1957, 40, 2148.
(7) Kim, D. W.; Ko, Y. K.; Kim, S. H. Synthesis 1992, 1203.
(8) Higuchi, T.; Hussain, A.; Pitman, H. J. Chem. Soc. B 1969,
626.
(9) (a) Romero-Ortega, M.; Covarruvias-Zunñiga, A.; Cruz, R.;
Avila-Zarraga, J. G. Synthesis 2003, 2765. (b) Elson, K. E.;
Jenkins, I. D.; Loughlin, W. A. Org. Biomol. Chem. 2003, 1,
2958. (c) Aoyama, T.; Takido, T.; Kodomari, M. Synth.
Commun. 2003, 33, 3817. (d) Gauthier, J. Y.; Bourdon, F.;
Young, R. N. Tetrahedron Lett. 1986, 27, 15. (e) Chandra,
K. L.; Saravanan, P.; Singh, R. K.; Singh, V. K. Tetrahedron
2002, 58, 1369. (f) Morse, B. K.; Tarbell, D. S. J. Am. Chem.
Soc. 1952, 74, 416.
Anal. Calcd for C7H6Cl2O2S: C, 37.35; H, 2.69; Cl, 31.50; S, 14.25.
Found: C, 37.57; H, 2.79; Cl, 31.58; S, 14.05.
(4-Nitrophenyl)methanesulfonyl Chloride (2g)10a
White crystals; mp 92–93 °C.
1H NMR (300 MHz, CDCl3): d = 4.97 (s, 2 H), 7.71 (dd, J = 1.9, 8.7
Hz, 2 H), 8.33 (dd, J = 2.0, 9.1 Hz, 2 H).
Anal. Calcd for C7H6ClNO4S: C, 35.68; H, 2.57; Cl, 15.05; N, 5.94;
S, 13.61. Found: C, 35.81; H, 2.64; Cl, 15.05; N, 5.94; S, 13.63.
(10) (a) Lee, I.; Kana, H. K.; Lee, H. W. J. Am. Chem. Soc. 1987,
109, 7472. (b) Bougeard, P.; Johnson, M. D.; Lampman, G.
M. J. Chem. Soc., Perkin Trans. 1 1982, 3, 849. (c) Truce,
W. E.; Norell, J. R. J. Am. Chem. Soc. 1963, 85, 3231.
(11) (a) The yields of 2i, 2a from 1i, 4a and 4c (Tables 2 and 4):
Douglass, I. B.; Johnson, T. B. J. Am. Chem. Soc. 1938, 60,
1486. (b) The yield of 2j from 1j (Table 2): Bordwell, F. G.;
Hewett, W. A. J. Org. Chem. 1957, 22, 980. (c) The yield
of 2i from 4d (Table 4): Lee, S. W.; Dougherty, G. J. Org.
Chem. 1940, 5, 81.
(12) (a) Diaz, D.; Finn, M. G. Org. Lett. 2004, 6, 43. (b) Tandel,
S. K.; Rajappa, S.; Pansare, S. V. Tetrahedron 1993, 49,
7479.
(13) Oxidation of 3e with 5; the procedure was the same as the
general procedure for NCS. This reaction required 2 equiv of
5.
(14) Oxidation of 3e with 6; the procedure was the same as the
general procedure for NCS. This reaction required 1.3 equiv
of 6. The resulting solid was filtered off and washed with
IPE (3.5 v/w to NCS) before work-up.
(15) Depending on the substrate properties, e.g. solubility,
reactivity may somewhat differ from these results.
Especially for large-scale synthesis, appropriate hazardous
safety evaluations should be undertaken.
Ethanesulfonyl Chloride (2i)
Colorless liquid.
1H NMR (300 MHz, CDCl3): d = 1.63 (t, J = 7.3 Hz, 3 H), 3.69 (q,
J = 7.3 Hz, 2 H).
HRMS (EI): m/z [M + H]+ calcd for C2H6ClO2S: 128.9777; found:
128.9798.
Cyclohexanesulfonyl Chloride (2j)10b
Colorless liquid.
1H NMR (300 MHz, CDCl3): d = 1.22–1.45 (m, 3 H), 1.66–1.98 (m,
3 H), 1.99–2.04 (m, 2 H), 2.40–2.45 (m, 2 H), 3.52 (tt, J = 3.5, 11.9
Hz, 1 H).
HRMS (EI): m/z [M + H]+ calcd for C6H12ClO2S: 183.0247; found:
183.0223.
Prop-2-ene-1-sulfonyl Chloride (2k)10c
Colorless liquid.
1H NMR (300 MHz, CDCl3): d = 4.33 (d, J = 7.2 Hz, 2 H), 5.65 (dd,
J = 0.7, 18.0 Hz, 1 H), 5.70 (dd, J = 0.6, 10.2 Hz, 1 H), 6.01 (ddt,
J = 7.2, 10.1, 17.1 Hz, 1 H).
HRMS (EI): m/z [M – H]+ calcd for C3H4ClO2S: 138.9587; found:
138.9617.
Synthesis 2006, No. 24, 4131–4134 © Thieme Stuttgart · New York