320
S. Sobhani et al.
LETTER
O
S
O
2
duced diphenyl disulfide as the sole product. These results
showed the unique behavior of ZnCr2O7·3H2O over these
oxidants for the one-pot synthesis of thiosulfonates from
thiols.
ZnCr2O7⋅3H2O
r.t., solvent
PhS–SPh
Ph
SPh
PhSH
+
1
In conclusion, ZnCr2O7·3H2O has been developed as a
readily available and efficient reagent for the one-pot syn-
thesis of a variety of thiosulfonates by chemoselective ox-
idation of aryl, heteroaryl, alkyl, and cyclic thiols.
Simplicity of operation, high yields of the products, and
short reaction times are the advantages of this method.
Scheme 1
O
S
ZnCr2O7⋅3H2O
ZnCr2O7⋅3H2O
(1 equiv)
PhS–SPh
Ph
SPh
SPh
PhSH
(1 equiv)
1
O
S
Ph
General Procedure for the Synthesis of Thiosulfonates
ZnCr2O7·3H2O (2 mmol) was added to a stirred solution of thiol (1
mmol) in MeCN (10 mL). The resulting mixture was stirred at r.t.
for the appropriate time (Table 2). The pure product was isolated
from the resulting mixture by column chromatography in 90–98%
yields.
O
2
Scheme 2
In order to have more evidence in support of the interme-
diacy of disulfide in this reaction, we performed a reaction
between diphenyl disulfide and ZnCr2O7·3H2O in MeCN
at room temperature. The reaction furnished S-phenyl
benzenthiosulfonate (2) in 98% yield after 15 minutes.
S-Phenyl Benzene Thiosulfonate (1)
1
IR (KBr): 1134, 1313 (SO2) cm–1. H NMR (400 MHz, CDCl3,
TMS): d = 7.35 (t, 2 H, 3JHH = 6.8 Hz), 7.37 (t, 2 H, 3JHH = 6.8 Hz),
3
7.42–7.46 (m, 2 H), 7.49 (t, 1 H, JHH = 6.4 Hz), 7.58 (d, 2 H,
3JHH = 8.4 Hz), 7.48 (d, 1 H, 3JHH = 8.8 Hz). 13C NMR (100 MHz,
CDCl3, TMS): d = 127.5, 127.8, 128.8, 129.4, 131.4, 133.6, 136.6,
142.9. MS (EI, 70 eV): m/z (%) = 250 (28.8) [M+], 141 (33.1), 125
(80.4), 109 (47.3), 77 (100).
Next, the applicability of this method for the chemoselec-
tive oxidation of a variety of thiols to thiosulfonates by
ZnCr2O7·3H2O in MeCN at room temperature was inves-
tigated (Scheme 3). The results of these studies are sum-
marized in Table 2.
S-4-Fluorophenyl 4-Fluorobenzene Thiosulfonate (2)
1
IR (KBr): 1227, 1325 (SO2) cm–1. H NMR (400 MHz, CDCl3,
TMS): d = 7.08 (t, 2 H, 3JHH = 8.4 Hz), 7.14 (t, 2 H, 3JHH = 8.4 Hz),
7.38 (dd, 2 H, 3JHH = 5.2, 3JHF = 9.0 Hz), 7.61 (dd, 2 H, 3JHH = 4.8,
3JHF = 9.6 Hz). 13C NMR (100 MHz, CDCl3, TMS): d = 116.2 (d,
O
ZnCr2O7⋅3H2O
r.t., MeCN
RSH
R
S
SR
2
2JCF = 22.7 Hz), 116.9 (d, JCF = 22.0 Hz), 123.2, 123.3, 130.4 (d,
O
4
1
4JCF = 9.7 Hz), 138.8 (d, JCF = 8.9 Hz), 163.9 (d, JCF = 70.7 Hz),
R = Ar, Hetar, Alk
1–12
1
166.5 (d, JCF = 73.6 Hz). MS (EI,70 eV): m/z (%) = 286 (31.1)
[M+], 159 (58.5), 143 (86.2), 127 (77.3), 95 (100).
Scheme 3
S-4-Chlorophenyl 4-Chlorobenzene Thiosulfonate (3)
1
IR (KBr): 1141, 1327 (SO2) cm–1. H NMR (400 MHz, CDCl3,
As indicated in Table 2, the oxidation reaction of thiophe-
nols substituted with electron-donating and electron-with-
drawing groups proceeded well and the corresponding
thiosulfonates were obtained in high yields (entries 1–6).
These results showed that existing groups on the aromatic
ring had no obvious effect on the yield of the reaction
products. 2-Mercaptopyridine and 2-mercaptobenzox-
TMS): d = 7.33 (d, 2 H, 3JHH = 8.4 Hz), 7.37 (d, 2 H, 3JHH = 8.8 Hz),
7.44 (d, 2 H, 3JHH = 9.2 Hz), 7.54 (d, 2 H, 3JHH = 8.8Hz). 13C NMR
(100 MHz, CDCl3, TMS): d = 128.9, 129.2, 129.9, 130.3, 137.7,
138.6, 140.5, 141.3. MS (EI, 70 eV): m/z (%) = 322 [M+ + 4], 320
[M+ + 2], 318 [M+], 175 (72.2), 177 (30.3), 159 (93.9), 161 (37.9),
143 (56.2), 145 (24.6), 111 (100), 113 (45.8).
azole as heteroaromatic thiols underwent the oxidation re- S-4-Bromophenyl 4-Bromobenzene Thiosulfonate (4)
1
IR (KBr): 1058, 1320 (SO2) cm–1. H NMR (400 MHz, CDCl3,
action by ZnCr2O7·3H2O and produced the corresponding
TMS): d = 7.26 (d, 2 H, 3JHH = 8.4 Hz), 7.46 (d, 2 H, 3JHH = 8.8 Hz),
thiosulfonates (7 and 8) in high yields (entries 7 and 8).
7.53 (d, 2 H, 3JHH = 8.4 Hz), 7.62 (d, 2 H, 3JHH = 8.4 Hz). 13C NMR
This method was also applicable for the selective oxida-
(100 MHz, CDCl3, TMS): d = 126.6, 127.0, 128.9, 129.2, 132.3,
tion of aliphatic and cyclic thiols to thiosulfonates (entries
9–12).
132.9, 137.8, 141.8. MS (EI, 70 eV): m/z (%) = 410 (1.7) [M+ + 4],
408 (3.8) [M+ + 2], 406 (2.1) [M+], 219 (18.6), 221 (20.4), 203
(26.8), 205 (28.1), 187 (22.7), 189 (22.7), 155 (37.4), 157 (36.5),
107 (100).
We have also examined the oxidation reaction of thiophe-
nol by some other chromium-based oxidants such as pyri-
dinium dichromate (PDC), pyridinium chlorochromate
(PCC), nicotinium dichromate (NDC), and isonicotinium
dichromate (INDC) under the present reaction conditions.
Oxidation reaction in the presence of these reagents pro-
Acknowledgment
We are grateful to Birjand University Research Council for their
support of this work.
Synlett 2011, No. 3, 319–322 © Thieme Stuttgart · New York