7660
K. Bahrami et al. / Tetrahedron 65 (2009) 7658–7661
Thioketones and a thioester, under similar conditions for thio-
amides, also underwent the reaction, affording the corresponding
products in excellent yields (Table 2, entries 20–24).
In order to evaluate the selectivity of this reagent system, we
studied the desulfurization of thioamides in the presence of alco-
hol, oxime and acid. The results are depicted in Scheme 3.
temperature. This methodology also overcomes the formation of
unwanted by-products, and the use of hazardous solvents, thus, we
believe that the present methodology could be an important ad-
dition to the existing methodologies.
4. Experimental
4
.1. General remark
H
N
H
N
The thiocarbonyl compounds are either commercially available
S
O
or were prepared as follows: thioamides from the reaction of the
corresponding amides with P
the reaction of the corresponding carbonyl compounds with Law-
esson’s reagent. Melting points were determined in a capillary
tube. H NMR and C NMR spectra were recorded on a Bruker-200
NMR spectrometer using TMS as internal standard.
H O /SOCl
2
2
2
95%
24
+
+
4
S
10
,
thioketones and thioester from
EtOH, 25 °C
OH
Cl
2
5
0%
1
13
S
O
N
H
N
H
9
6%
H O /SOCl
2
4.2. General procedure for deprotection of thioamides to
amides
2
2
+
+
H
OH
EtOH, 25 °C
N
N
CHO
0%
A mixture of thiocarbonyl comopund (2 mmol), H
2
O
2
(30%,
Br
Br
4 mmol, 0.4 mL) and SOCl
2
(2 mmol, 0.14 mL) was stirred in EtOH at
H
N
H
N
ꢀ
25 C for an appropriate time (Table 2). A yellow solid, (elemental
ꢀ
sulfur, mp 120 C) immediately precipitated. After completion of
S
O
0%
the reaction as indicated by TLC, the reaction mixture was filtered
to give elemental sulfur. The filtrate was poured into water (10 mL),
extracted with ethyl acetate (4ꢁ5 mL) and the extract dried with
9
O
H O /SOCl
O
0
+
2
2
2
+
EtOH, 25 °C
OH
Cl
4
anhydrous MgSO . The filtrate was evaporated under vacuum to
%
afford the analytically pure product (Table 2).
All of products are known compounds and characterized easily
by comparison with authentic samples ( H NMR, C NMR, mp).
Scheme 3. Reagents and conditions: molar ratio of substrates to H
2
O
2
to SOCl
2
ꢀ
(
1:1:2:1), EtOH, 25 C.
1
13
A comparison of the efficiency of this method with selected
previously methods is collected in Table 3. As can be seen, our
method is simpler, more efficient, and uses no toxic solvents.
Acknowledgements
Table 3
We are thankful to the Razi University Research Council for
partial support of this work.
Comparison of desulfurization of thiocarbonyls by the H
with some of those reported in the literature
2 2 2
O /SOCl reagent system
Entry
Thiocarbonyl
Conditions
Time
Yield
%)
Supplementary data
(
1
2
S
H
2
O
2
/SOCl
2
/EtOH/rt 3 min
5 h
C
98
61
Caro’s acid/SiO
/CH
2
C
N
H
Cl
ꢀ
5
3
CN/40
3
4
S
H
2
O
2
/SOCl
2
/EtOH/rt 1 min
96
78
References and notes
Oxone/MgSO
milling/rt
4
/ball 90 min
O N
C
N
H
Me
2
1
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Me
5
6
7
H
2
O
2
/SOCl
NOBF /CH
(4-MeOC
2
/EtOH/rt 1 min
95
88
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H
4
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a
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90
S
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2
14
C
NH2
reflux
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2
/SOCl /EtOH/rt 2 min
1
0
4
/CH
2
2
/rt12 8 h
76
94
60
8
1
1
H
2
O
2
S
2
3
12
Clyfen/MW
1.5 min
C
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a
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7
1
1
1
3
. Conclusion
2 2 2
In conclusion, H O /SOCl is an efficient reagent system for the
1
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Bahrami, K.; Khedri, M. Can. J. Chem. 2007, 85, 7–11; (c) Khodaei, M. M.; Bah-
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Kavianinia, I. Synthesis 2007, 547–550; (e) Bahrami, K.; Khodaei, M. M.; Naali, F.
conversion of thiocarbonyls to carbonyl compounds. The advan-
tages are high chemoselectivity, environmentally efficient, excel-
lent yields, fast reaction, low cost, and operation at room