Tandem base-free synthesis of β-hydroxy sulphides under ultrasound irradiation

Article abstract of DOI:10.1007/s12039-012-0305-6

Rongalite promotes cleavage of diaryl disulphides generating the corresponding thiolate species in situ which then undergo facile ring-opening of epoxides in a regioselective manner under ultrasound irradiation, affording β-hydroxy sulphides in good to ex

Full text of DOI:10.1007/s12039-012-0305-6

c
J. Chem. Sci. Vol. 124, No. 5, September 2012, pp. 1057–1062. ꢀ Indian Academy of Sciences.
Tandem base-free synthesis of β-hydroxy sulphides under ultrasound
irradiation
GUANG-SHU LVa, FU-JUN DUANa, JIN-CHANG DINGa,b, TIAN-XING CHENGa,
WEN-XIA GAOa, JIU-XI CHENa,∗ and HUA-YUE WUa
aCollege of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, P. R. China
bWenzhou Vocational and Technical College, Wenzhou, 325035, P. R. China
e-mail: jiuxichen@gmail.com
MS received 8 April 2011; revised 11 July 2011; accepted 23 August 2011
R
Abstract. Rongaliteꢀ promotes cleavage of diaryl disulphides generating the corresponding thiolate species
in situ which then undergo facile ring-opening of epoxides in a regioselective manner under ultrasound irradi-
ation, affording β-hydroxy sulphides in good to excellent yields. The important features of this methodology
are base-free, odourless, high yield, reasonably rapid reaction rate, simple workup, high regioselectivity, cost-
effective and no requirement of transition metal catalysts. It is noteworthy that ring-opening reaction of 1,2-
diphenyldiselane with 2-(phenoxymethyl)oxirane are also conducted smoothly to afford β-hydroxy selenide in
excellent yield under the standard conditions.
R
Keywords. Ultrasound irradiation; Rongaliteꢀ; β-hydroxy sulphides; epoxides; ring-opening reaction.
1. Introduction
recent years for the synthesis of β-hydroxy sulfides by
the reaction of epoxides with disulphides using differ-
ent promoting agents. These promoting agents include
tetrathiomolybdate,9 sulfite/base in DMF,10 NaBH4/
amberlite IRA 400,11 ytterbium(III) chalcogeno-
late complexes12 InI–InCl3,13 Zn–Bi(OTf)3 or Zn–
Bi(TFA)3.14 However, these methods usually suffer
from one or more limitations such as the use of unpleas-
ant odour substrates,3–7 expensive, toxic or metallic
catalysts,10,12–14 long reaction times,10–13 unsatisfactory
yields12,13 as well as elevated temperature.11,13,14 There-
fore, developing versatile approaches to synthesize
β-hydroxy sulphides selectively still remains a highly
desired goal in organic synthesis.
β-Hydroxy sulphides possess unique physical properties,
which have become increasingly important in med-
icinal chemistry and organic synthesis for the prepara-
tion of building blocks and target molecules.1 On the
other hand, β-hydroxy sulphides are excellent ligands
for transition-metal-based asymmetric catalysis.2 As a
consequence, development of new methods for the syn-
thesis of β-hydroxy selenides has received much atten-
tion. Classical methods for the synthesis of β-hydroxy
sulphides involve the ring opening of an epoxide by
an excess of thiols, which inevitably gives unpleasant
odour, either catalysed by Lewis acid,3 PBu3 or under
4
microwave irradiation conditions.5 Recently, we have
studied the ring-opening reaction of epoxides in ionic
liquids without any catalyst6 or with gallium(III) triflate
as a catalyst.7
Ultrasound has increasingly been used in organic
synthesis in the last three decades. A large number of
organic reactions can be carried out in higher yields,
shorter reaction time and milder conditions under ultra-
sound irradiation.15
Recent findings concerning the ring-open reaction of
epoxides with in situ-generated thiolate species provide
an alternative to the century-old reaction of epoxides
with odour thiols. Disulphide bond cleavage could lead
to interesting products by the reaction of the resulting
nucleophilic sulphur8 species to a variety of organic
substrates. Thus, the method has been developed in
R
Rongaliteꢀ (sodium hydroxymethanesulfinate or
sodium formaldehyde sulfoxylate) is commercially
available material used in the textile industry as a decol-
ourizing agent, and it has also been used in organic syn-
R
thesis.16 Very recently, we have reported that Rongaliteꢀ
promoted cleavage of diaryl disulphides generating
the thiolate species in situ which then undergo facile
ring-opening of epoxides,17 thia-Michael addition,18
and acylation.19 As a continuation of our research in
this area, we report here a tandem base-free synthesis
∗For correspondence
1057

1058
Guang-Shu Lv et al.
OH
O
HO
SO Na
2
+
SR
RSSR
1
1
2
α
R
R
β R
DMSO, U.S.
2
1
2
R
(R >R )
Scheme 1. Synthesis of β-hydroxy sulphides.
of β-hydroxy sulphides from the reaction of epoxides (CDCl3, 300 MHz) δ ppm 7.42–7.39 (m, 1H), 7.27–
with diaryl disulphides under ultrasound irradiation in 7.22 (m, 2H), 7.11 (t, J = 0.8 Hz, 1H), 6.94–6.84 (m, 3
R
the presence of Rongaliteꢀ (scheme 1).
H), 6.71–6.69 (m, 2H), 3.99–3.93(s, 4H), 3.07–3.01 (m,
1H), 2.94–2.87 (m, 1H), 13C NMR (125 MHz, CDCl3)δ
ppm 158.4, 148.2, 136.2, 130.1, 129.4, 121.1, 119.0,
117.1, 115.3, 114.5, 70.3, 68.8, 38.7; MS (EI, 70 eV)
m/z (%): 275 (M+, 40), 125 (100). Anal. Calcd. for
C15H17NO2S: C, 65.43; H, 6.22; Found: C, 65.49; H,
6.29.
2. Experimental
All reagents were purchased and used without further
purification. Melting points were recorded on Digital
Melting Point Apparatus WRS-1B and uncorrected. IR
spectra were recorded on an AVATAR 370 FI-Infrared
Spectrophotometer. NMR spectroscopy was performed
on a Bruker-300 spectrometer or Bruker-500 spectrom-
eter using CDCl3 as the solvent with tetramethylsilane
(TMS) as an internal standard at room temperature.
Mass spectrometric analysis was performed on GC–MS
analysis (SHIMADZU GCMS-QP2010). Elemental
analysis was determined on a Carlo-Erba 1108 instru-
ment. Ultrasonication was performed in a KQ-300VDE
ultrasound cleaner with a frequency of 45, 80 and
100 kHz and an output power 300 W. The reaction flask
was located in the water bath of the ultrasonic cleaner,
where the surface of reactants is slightly lower than the
level of the water. The reaction temperature was con-
trolled at 22–25◦C by addition or removal of water from
ultrasonic bath.
2.1b 1-Phenoxy-3-(thiophen-2-ylthio)propan-2-ol (3f):
1
Oil, H NMR (500 MHz, CDCl3)δ ppm 7.37–7.17 (m,
4H), 6.98–6.88 (m, 4H), 4.11–4.00 (m, 3H), 3 .09
(dd, J = 13.5 and 5.0 Hz, 1H), 3 .01 (dd, J = 13.5
and 7.5 Hz, 1H), 2.76 (s, 1H); 13C NMR (125 MHz,
CDCl3)δ ppm 158.4, 134.2,133.3, 129.8, 129.5, 127.7,
121.3, 114.6, 70.1, 68.6, 42.3; MS (ESI) m/z (%): 267
([M+1]+, 100). Anal. Calcd. for C13H14O2S2: C, 58.62;
H, 5.30; Found: C,58.77, H, 5.42.
2.1c 1-Phenoxy-3-(pyridin-2-ylthio)propan-2-ol (3g):
1
Oil, H NMR (500 MHz, CDCl3)δ ppm 8.34–8.33 (m,
1H), 7.50–7.47 (m, 1H), 7.30–7.24 (m, 4H), 7.03–7.00
(m, 1H), 6.95–6.92 (m, 3H); 4.35–4.31 (m, 1H), 4.09
(dd, J = 9.0 and 5.0 Hz, 1H), 4.02 (dd, J = 9.0 and
7.5 Hz, 1H), 3.55–3.49 (m, 1H), 3.39 (dd, J = 14.5 and
6.0 Hz, 1H); 13C NMR (125 MHz, CDCl3)δ ppm 158.9,
158.5, 148.6, 136.5, 129.3, 125.2, 122.8, 120.8, 120.0,
114.5, 70.0, 35.4; MS (ESI) m/z (%): 262 ([M+1]+,
100). Anal. Calcd. for C14H15NO2S: C, 64.34; H, 5.79;
Found: C, 64.22, H, 5.88.
2.1 General procedure for the synthesis of β-hydroxy
sulphides
A mixture of epoxides 1 (0.5 mmol), disulphides 2
R
(0.2 mmol) (0.2 mmol), Rongaliteꢀ (3 equiv, 0.6 mmol)
and DMSO (2 mL) was irradiated under ultrasound in
an open vessel at room temperature (22–25◦C) for the
appropriate time. After completion of the reaction as
indicated by TLC, ethyl acetate (10 mL) was then added
to the mixture. The mixture was washed with brine.
The organic layer was separated and dried with sodium
sulphate, filtered and concentrated. Further purification
was achieved by silica gel chromatography using ethyl
acetate/cyclohexane as eluent to afford pure product.
2.1d 1-(p-Tolylthio)octan-2-ol (3i): Oil, IR (KBr):
3287, 3023, 2983, 2884, 2835, 1725, 1560, 1472,
1
1431 cm−1; H NMR (CDCl3, 300 MHz) δ ppm 7.31–
7.26 (m, 2H), 7.10 (d, J = 7.8 Hz, 2H), 3.62 (s, 1 H),
3.10 (dd, J = 13.8 Hz and 3.1 Hz, 1H), 2.82–2.75 (m,
1H), 2.55 (s, 1H), 2.32 (s, 3H), 1.49–1.26 (m, 10H),
0.87 (s, 3H); 13C NMR (125 MHz, CDCl3)δ ppm 136.8,
131.4, 130.9, 129.8, 69.2, 43.0, 36.0, 31.7, 29.2, 25.6,
2.1a 1-(2-Aminophenylthio)-3-phenoxypropan-2-ol (3e): 22.5, 21.0, 14.0; MS (EI, 70 eV) m/z (%): 252 (M+,
White solid, m.p. 65–68 ◦C; IR (KBr): 3405, 3333, 34), 138 (100). Anal. Calcd. for C15H24OS: C, 71.37; H,
3055, 2928, 1660, 1593, 1514, 1454 cm−1; H NMR 9.58; Found: C, 71.45, H, 9.62.
1

Tandem base-free synthesis of β-hydroxy sulphides
1059
2.1e 2-(4-Fluorophenylthio)-1-phenylethanol (3o): (1a) with 1,2-diphenyldisulphide (2a) under ultrasound
Oil; IR (KBr): 3433, 3032, 2922, 1594, 1532, 1490, irradiation at room temperature and the results are
1
1441 cm−1; H NMR (CDCl3, 300 MHz) δ ppm 7.44– summarized in table 1. Initially, the effect of solvents
7.31 (m, 7H), 7.05–6.99 (m, 2H), 4.69 (dd, J = 9.2 was tested. Among the solvents screened (toluene, 2-
and 3.7 Hz, 1H), 3.25 (dd, J = 13.7 and 3.7 Hz, 1H), methyl-tetrahydrofuran (2-MeTHF), CH2Cl2, C2H5OH,
3.11–3.03 (m, 1H), 2.89 (s, 1H); 13C NMR (75 MHz, THF, CH3CN, DMF, and 1,4-dioxaneoluene), the corre-
CDCl3)δ ppm 163.8, 160.5, 142.0, 133.2, 133.1, 129.9, sponding β-addition product 1-phenoxy-3-(phenylthio)
129.9, 129.8, 128.5, 128.0, 125.8, 116.3, 116.1, 71.7, propan-2-ol (3a) was obtained in low yield. When the
45.1; MS (EI, 70 eV) m/z (%): 248 (M+, 12), 142 (100). reaction was performed in DMSO, 1a undergoes the
Anal. Calcd. for C14H13FOS: C, 67.72; H, 5.28; Found: cleavage with 2a to produce only β-addition product
C, 67.66; H, 5.33.
3a in 99% yield under ultrasound irradiation (table 1,
entries 1–9).
We also have observed the effect of frequency of
ultrasound irradiation on the model reaction. The reac-
tion rate was compared at 45, 80 and 100 kHz hav-
ing the same output power of 300 W. In the presence
of ultrasound the yield was 99% only after 20 min for
80 kHz (table 1, entry 9). The yield decreased dras-
tically without ultrasound irradiation (table 1, entries
12–13). Experiments performed with variable fre-
quency (45 and 100 kHz) showed the same trend. It was
indicated from table 1 that that there was remarkable
ultrasonic effect on this reaction and there was an opti-
mum frequency of 80 kHz for effective ring-opening
reaction. The reason may be the phenomenon of cavi-
tation produced by ultrasound. Because the super-high
pressure and temperature generated by the collapse of
the acoustic cavitations can never be gained in classical
heating, the thermal effects of ultrasonic waves observ-
ably accelerate the reaction rate and enhance the yield.
2.1f 1-Chloro-3-(p-tolylthio)propan-2-ol (3r): Oil;
1H NMR (300 MHz, CDCl3)δ ppm 7.28 (d, J = 8.2 Hz,
2H), 7.08 (d, J = 8.0 Hz, 2 H), 3.88–3.83 (m, 1 H),
3.66–3.60 (m, 2 H), 3.12–2.95 (m, 2 H), 2.72 (d, J =
4.9 Hz, 1 H), 2.29 (s, 3 H); 13C NMR (75 MHz, CDCl3)
δ: 137.2, 130.9, 130.7, 130.0, 69.4, 47.9, 39.0, 21.0;
IR (KBr, cm−1): 3226, 3024, 2980, 2887, 1600, 1529,
1466, 1396; MS (EI, 70 eV) m/z (%): 218 ([M+2]+,
19), 216 (M+, 55), 137(100). [α]2D0 +26.8 (c 0.99
in CHCl3), R; 98% ee [tR(S) 39.50 min and tR(R)
41.63 min].
3. Results and discussion
Initially, the efficacy of various solvents was investigated
in the model reaction using 2-(phenoxymethyl)oxirane
Table 1. The synthesis of 3a under different conditionsa.
OH
O
HO
SO2Na
PhSSPh
PhO
SPh
PhO
Ultrasound irradiation
1a
2a
3a
Entry
Solvent
toluene
2-Me-THF
CH2Cl2
C2H5OH
THF
CH3CN
DMF
1,4-dioxane
DMSO
Ultrasound (kHz)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
80
80
80
80
80
80
80
80
80
60
60
60
60
60
60
40
60
20
20
20
20
300
trace
14
10
trace
11
trace
43
15
99
98
99
9
10
11
12
13
DMSO
DMSO
DMSO
DMSO
45
100
without
without
trace
16
R
aReaction conditions: 1a (0.5 mmol), 2a (0.2 mmol), Rongaliteꢀ (0.6 mmol), under ultra-
sound irradiation at room temperature.
bIsolated yields.

1060
Guang-Shu Lv et al.
Table 2. Ultrasound-assisted synthesis of β-hydroxy sulphidesa.
OH
R1
SR
O
SR
OH
HO
SO2Na
+
+
R1
RSSR
R1
R2
R2
R2
(C- )
DMSO, U.S.
(R1>R2)
(C- )
1
2
3
4
Entry
R1
R2
R
Product Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
PhOCH2
PhOCH2
PhOCH2
PhOCH2
PhOCH2
PhOCH2
PhOCH2
n-CH3(CH2)5
n-CH3(CH2)5
n-CH3(CH2)5
-(CH2)4-
-(CH2)4-
Ph
H
H
H
H
H
H
H
H
H
H
Ph
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
20
20
15
20
25
20
20
20
20
20
20
20
20
25
20
25
99
96
98
95
71
81
94
89
88
86
92
94
97
82
86
70
p-(Cl)C6H4
p-(CH3)C6H4
p-(F)C6H4
o-(NH2)C6H4
2-thienyl
2-pyridyl
Ph
p-(CH3)C6H4
p-(Cl)C6H4
Ph
p-(CH3)C6H4
Ph
9
10
11
12
13
14
15
16
H
H
H
H
Ph
Ph
Ph
p-(CH3)C6H4
p-(F)C6H4
o-(NH2)C6H4
R
aAll reactions were run with epoxide 1 (0.5 mmol), disulfide 2 (0.2 mmol), and Rongaliteꢀ
(0.6 mmol), in 2 mL of DMSO for the appropriate time under ultrasound irradiation at room
temperature.
bIsolated yield.
The critical size and life time of the cavitation bub- possible regio-isomers (3 and 4) as a result of the exclu-
bles depend on the liquid and the frequency of ultra- sive attack of the sulphide anions on the less hindered
sound. On account of longer ultrasonic periods, the carbon of the epoxide.
implosion time and the size of the cavitation bubbles
A series of various epoxides and disulphides bear-
and the mechanical mixing effects in the liquid increase ing either electron-donating or electron-withdrawing
with decreasing frequencies. Lower frequencies are pre- groups were investigated. The substitution groups on
ferred for the ring-opening reaction due to the more the aromatic ring had no obvious effect on the yield.
intense mechanical effects. Furthermore, the character- When less nucleophilic disulphides (R = p-FC6H4)
istics of the liquid (such as viscosity, temperature and (table 2, entries 4 and 15) was used, the reactions could
vapour pressure) can affect cavitation as well, but the also work efficiently compared to electron-rich disul-
mechanisms are complicated.
phides (R = p-MeC6H4) (table 2, entries 3, 9, 12 and
With the optimal reaction conditions in hand, the 14) under the same conditions. On the other hand, the
scope of epoxides was explored and the results are sum- chemoselective reaction in the presence of unprotected
marized in table 2. As shown in table 2, in the case of reactive functional groups such as -NH2 also proved to
alkyl-substituted unsymmetrical epoxides, the reaction be successful. The corresponding products of 3e and
proceeds with a remarkable region-selectivity to give 3p were obtained in moderate yields (table 2, entries
only one β-hydroxy sulphides isomer (3a–j) of the two 5 and 16). Furthermore, we examined the reactivity
OH
HO
SO Na
2
O
PhSeSePh
PhO
SePh
PhO
DMSO, U.S., 25 min
1a
3q
Scheme 2. Synthesis of 1-phenoxy-3-(phenylselanyl)propan-2-ol (3q).

Tandem base-free synthesis of β-hydroxy sulphides
OH
1061
O
Cl
S
.
.
NaHSO2 CH2O 2H2O
+
Me
S
Cl
2
DMSO, U.S., 25 min
Me
(R), 89% yield, 98% ee 3r
(R)
Scheme 3. Synthesis of (R)-2-(chloromethyl)oxirane (3r).
HOCH SO
HSO
2
A
HCHO +
(1)
(2)
2
2
RSSR +
HSO
+
RY
2
RY
+ HSO
2
2
A
B
C
D
+
HSO
RY
+ SO +
RY
H
(3)
2
2
B
D
C
O
OH
O
H
+
YR
YR (4)
RY
1
1
2
1
R
R
R
R
2
1
C
2
R
R
Scheme 4. A proposed mechanism.
of epoxides with heterocyclic disulphides such as proposed in scheme 4. According to the previous pro-
R
1,2-di(thiophen-2-yl)disulphide and 1,2-di(pyridin-2- posed mechanism,20 Rongaliteꢀ can be readily decom-
yl)disulphide. Similarly, the corresponding products posed into HCHO and HSO−2 anion (A). Intermediate
3f and 3g were obtained with 89% and 94% yields, (A) then reacts with RYYR (2, Y = Se or S) to gen-
respectively. On the other hand, the ring-opening of erate two radical intermediates (B and D) and an anion
symmetrical epoxide, such as cyclohexene oxide with (C). The radical (B) can also be converted into the
1,2-diphenyldisulphide and 1,2-dip-tolyldisulphides to anion (C) by reacting with intermediate (D). Finally,
afford trans-2-(phenylthio)cyclohexanol and trans-2- the nucleophilic attack of the anion (C) to the less
(p-tolylthio)cyclohexanol with high stereoselectivity in hindered position of the epoxide (1) affords the target
92% and 94% yields, respectively (table 2, entries product.
1
11–12). The H NMR spectra indicated that only the
trans-isomer was formed.
As listed in scheme 2, ring-opening reaction of 2-
(phenoxymethyl)oxirane with 1,2-diphenyl diselenide
smoothly to afford 1-phenoxy-3-(phenylselanyl)propan-
2-ol (3q) in 98% yields under ultrasound irradiation.
Finally, to extend the scope of this reaction, the
thiolysis of chiral epoxide, such as (R)-2-(chloromethyl)
oxirane (99% ee) was also examined under the opti-
mized conditions. It was found that optically pure epox-
ide was converted into the corresponding β-hydroxy
sulphide 3q in good yield without any racemization or
inversion (scheme 3).
4. Conclusions
In conclusion, an efficient and simple method for the
odourless tandem synthesis of β-hydroxy sulphides
with high regioselectivity under ultrasound irradia-
tion has been developed. Compared with the previ-
ously reported methods, the present method is bestowed
with several advantages, such as odourless, high yield,
reasonably rapid reaction rate, simple workup, high
regioselectivity, cost-effective and no need for transi-
tion metal catalysts. This procedure would be a valuable
addition to the current methodologies.
A tentative mechanism for the formation of
β-hydroxy selenides and β-hydroxy sulphides was

1062
Guang-Shu Lv et al.
7. Su, W K, Chen J X, Wu H Y and Jin C 2007 J. Org.
Acknowledgements
Chem. 72 4524
We thank the Science and Technology Department
of Zhejiang Province (No. 2010C33061) and the
Wenzhou Science & Technology Bureau Program (No.
S20100004) for financial support.
8. Kondo T, Uenoyama S, Fujita K and Mitsudo T 1999 J.
Am. Chem. Soc. 121 482
9. Devan N, Sridhar P R, Prabhu K R and Chandrasekaran
S 2002 J. Org. Chem. 67 9417
10. Ganesh V and Chandrasekaran S 2009 Synthesis 3267
11. Yoon N M, Choi J and Ahn J H 1994 J. Org. Chem. 59
3490
12. Jennifer D, Fiona M and David J P 2000 Tetrahedron
Lett. 41 4923
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