Similar results were obtained when we repeated the
experiment with benzonitrile and 2,4-dimethoxy benzonitrile.
In these cases also, no participation of the nitrile was
observed; both nitriles were quantitatively recovered after
the reaction.
is known that CAN promotes selective oxidation of diaryl
sulfides to sulfoxides in excellent yields. The thiosulfinate
2
7 formed by the oxidation of disulfide 4 with CAN gets
further oxidized to the disulfoxide 8 which undergoes
6
rearrangement leading to the formation of 5.
The products were characterized by the usual spectroscopic
methods and by comparing the data with those of authentic
An alternative mechanism for the formation of 5 can
invoke the formation of the sulfinyl radical 11, which in turn
is derived by the trapping of the thiyl radical 6 with oxygen,
and subsequent transformations. The sulfinyl radical 11
undergoes coupling reaction to deliver thiosulfonate 5
5
samples. The IR spectrum of 4 showed absorptions at 2920,
-
1
1
1
634, 1600, 1465, 1398, and 795 cm . In the H NMR
spectrum, the signal corresponding to the methyl protons
appeared as a singlet at δ 2.32 (s, 6H, Me) and the aromatic
protons appeared as doublets at δ 7.37 (d, 4H, ArH, J ) 8.3
7
presumably through the sulfenyl sulfinate 12 (Scheme 3).
1
3
Hz) and 7.10 (d, 4H, ArH, J ) 8.3 Hz). In the C NMR
spectrum, the methyl carbons appeared as a singlet at δ 21.04.
In the IR spectrum of 5, the stretching corresponding to the
Scheme 3
-1
1
S-O bond appeared at 1330 and 1142 cm . In the H NMR
spectrum, the methyl protons appeared as singlets at δ 2.42
and 2.38 and the aromatic protons appeared as doublets at δ
7.56 (d, 2H, ArH, J ) 8.2 Hz), 7.42 (d, 2H, ArH, J ) 8.1
Hz), 7.29 (d, 2H, ArH, J ) 8.0 Hz), and 7.18 (d, 2H, ArH,
J ) 7.9 Hz). In the 13C NMR spectrum, the methyl carbons
resonated at δ 21.61 and 21.44. In the mass spectrum, the
.+
peak observed at 278 corresponds to the molecular ion [M] .
Interestingly, when we conducted the same experiment
with only 1 equiv of CAN instead of 2 equiv, the disulfide
was formed exclusively in 91% yield.
A mechanistic rationale for this reaction as shown in
Scheme 2 can be given. The initial event would be the
It may be emphasized that we have conducted the
experiment several times precisely under the reported condi-
tions and found that our results as outlined above are
consistently reproducible.
Scheme 2
Acknowledgment. A. A. thanks Council of Scientific and
Industrial Research, New Delhi, for a research fellowship,
Ms. Saumini Mathew for recording high-resolution NMR
spectra, and Mrs. S. Viji for elemental analysis and HRMS.
OL027452W
(
3 × 15 mL). After the mixture was dried over anhydrous Na2SO4, the
solvent was removed and the crude product, when subjected to column
chromatography, afforded the products 4 (60 mg, 49%) and 5 (50 mg, 36%)
as crystalline solids. Data of 4. Mp: 44-46 °C. IR (KBr) νmax: 2920, 1634,
-
1 1
1
600, 1465, 1398, 795 cm . H NMR (300 MHz; 3:1 v/v CDCl3-CCl4):
δ 7.37 (d, 4H, ArH, J ) 8.3 Hz), 7.10 (d, 4H, ArH, J ) 8.3 Hz), 2.32 (s,
6
1
1
H, Me). 13C NMR (75 MHz; 3:1 v/v CDCl3-CCl4): δ 137.33, 134.18,
29.77, 128.77, 21.04. Data of 5. Mp: 74-75 °C. IR (KBr) νmax: 2915,
-
1 1
593, 1485, 1330, 1142, 818 cm . H NMR (300 MHz; 3:1 v/v CDCl3-
CCl4): δ 7.56 (d, 2H, ArH, J ) 8.2 Hz), 7.42 (d, 2H, ArH, J ) 8.1 Hz),
7
H, Me), 2.38 (s, 3 H, Me). C NMR (75 MHz; 3:1 v/v CDCl3-CCl4): δ
1
.29 (d, 2H, ArH, J ) 8.0 Hz), 7.18 (d, 2H, ArH, J ) 7.9 Hz) 2.42 (s, 3
13
44.37, 141.85, 140.87, 136.49, 130.14, 129.31, 127.66, 124.93, 21.61,
oxidation of the thiocresol to the radical 6, which undergoes
dimerization resulting in the formation of the disulfide 4. It
21.44. HRMS: calcd for C14H14O2S2, 278.0435; found 278.0424. Anal.
Calcd for C14H14O2S2: C, 60.40; H, 5.07; S, 23.04. Found: C, 60.68; H,
5.02; S, 23.18.
(
6) (a) Freeman, F. Chem. ReV. 1984, 64, 117. (b) Folkins, P. L.; Harpp,
(
5) Typical Experimental Procedure and Data of 4 and 5. To a mixture
D. N. J. Am. Chem. Soc. 1991, 113, 8998. (c) Gu, D.; Harpp, D. N.
Tetrahedron Lett. 1993, 34, 67.
(7) Kice, J. L. In Free Radicals; Kochi, J. K., Ed.; Wiley: New York,
1973; Vol. 2, Chapter 2. (b) Mizuno, H.; Matsuda, M.; Iino, M. J. Org.
Chem. 1981, 46, 520.
of p-thiocresol (248 mg, 2 mmol) and NaHCO3 (500 mg) in anhydrous
MeCN (15 mL) was added dropwise a solution of CAN (2.192 g, 2 equiv)
in the same solvent at room temperature with stirring. After 30 min, the
reaction mixture was washed with water and extracted with chloroform
544
Org. Lett., Vol. 5, No. 4, 2003