7470
C. C. Silveira, S. R. Mendes / Tetrahedron Letters 48 (2007) 7469–7471
Table 2. Oxidative coupling of thiophenol supported in graphite under
different solvent
Acknowledgments
a
Entry Solvent
Time
I
2
CeCl
3
Æ7H
2
O
Conversion
(%, GC)
The authors thank FAPERGS, MCT/CNPq and
CAPES for financial support.
(
h)
(equiv) (equiv)
1
2
3
4
5
6
7
8
9
MeCN
MeOH
EtOH
AcOEt
AcOEt
AcOEt
AcOEt
AcOEt
AcOEt
1
1
1
1
1
0.08
—
0.08
0.05
0.05
1
1
1
1
0.5
0.5
—
0.1
0.1
100
57
44
100
100
39
14
14
1
1
1
1
1
14
References and notes
1
2
. (a) Capozzi, G.; Modena, G. In The Chemistry of the Thiol
Group, Part 2; Patai, S., Ed.; Wiley: New York, 1974; (b)
Jocelyn, D. C. Biochemistry of the Thiol Group; Academic
Press: New York, 1992.
. (a) Dhar, D. N.; Bag, A. K. Indian J. Chem. 1984, 23B,
974; (b) Firouzbadi, H.; Iranpoor, N.; Parham, H. A.
Synth. Commun. 1984, 14, 717.
75
100
b
33
a
Solvent (1 mL/mmol), PhSH (1 mmol), graphite (0.3 g/mmol).
Reaction performed without graphite.
b
3
4
5
. Wallace, T. J. J. Org. Chem. 1966, 31, 1217.
. Liu, K. T.; Tong, Y. C. Synthesis 1978, 669.
. Pryor, W. A.; Church, D. F.; Govindan, C. K.; Crank, G.
J. Org. Chem. 1982, 47, 156.
I2 (5 mol%),CeCl ·7H O (10 mol%)
3
2
R
SH
R
S
S R
AcOEt / Graphite
6. (a) Schaeffer, J. R.; Goodhue, C. D.; Risle, H. A.; Stevens,
R. E. J. Org. Chem. 1967, 32, 392; (b) Drabowicz, J.;
Mikolajczyk, M. Synthesis 1980, 32; (c) Ali, M. H.;
McDermott, M. Tetrahedron Lett. 2002, 43, 6271; (d)
Aida, T.; Akasaka, T.; Furukawa, N.; Oae, S. Bull. Chem.
Soc. Jpn. 1976, 49, 1441.
1
a-h
2 a-h
Scheme 1.
being entries 7 and 8, Table 3, mostly related to difficulty
of isolation of the corresponding disulfide, since the
reactions demanded the use of water as a co-solvent
and adjust of pH. The oxidation reaction can be easily
scaled-up with similar results.
7. McKillop, A.; Koyuncu, D. Tetrahedron Lett. 1990, 31,
5007.
8. Evans, B. J.; Doi, J. T.; Musker, W. K. J. Org. Chem.
1
5
1
990, 55, 2337.
9
. Shaabani, A.; Lee, D. G. Tetrahedron Lett. 2001, 42, 5833.
1
1
0. Tajbakhsh, M.; Hosseinzadeh, R.; Shakoori, A. Tetrahe-
dron Lett. 2004, 45, 1889.
1. Khazaei, A.; Zolfigol, M. A.; Rostami, A. Synthesis 2004,
In conclusion, the method described is very simple and
efficient for coupling of thiols, using catalytic amounts
of iodine and CeCl3 in the inexpensive graphite as
solid support. The method is applicable to a wide variety
of thiols, being a useful alternative of the existing
methodologies.
2
959.
12. (a) Akdag, A.; Webb, T.; Worley, S. D. Tetrahedron Lett.
006, 47, 3509; (b) Hajipour, A. R.; Mallakpour, S. E.;
2
Adibi, H. J. Org. Chem. 2002, 67, 8666; (c) Shaabani, A.;
Teimouri, F.; Lee, D. G. Synth. Commun. 2003, 33, 1057;
Table 3. Catalytic oxidation of thiols to disulfides
a
Entry
1
Thiol
Time (h)
1.5
Product
Yield (%)
Mp/bp °C (Lit.)
b
16
2a
97
195 (194/760 mmHg)
SH
SH
SH
b
17
2
3
4
5
0.8
1.0
1.0
0.9
2b
98
99
97
98
30–32 (32)
1
0
b
18
2c
57–58 (59–60)
SH
b
6b
2d
69–70 (70–71)
b
19
MeO
Cl
SH
2e
42–43 (43–44)
b
20
6
7
SH
1.0
2.5
2f
96
74
72–73 (73–74)
N
c
21
SH
2g
167–169 (168–170)
N
O
OH
SH
c
22
8
3.5
2h
77
243–245 dec (>240 dec)
2
H N
a
b
c
Isolated yield.
Reaction in AcOEt (Method A).
Reaction in AcOEt/H O (Method B).
2