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R. Ghorbani-Vaghei et al. / C. R. Chimie xxx (2014) xxx–xxx
Table 3
Comparison of reduction of dibenzyl sulfoxide to dibenzyl sulfide (Table 2 entry3) by the Ph3P/TBBDA system with some of those reported in the literature.
Reagent (oxidant/substrate)
Time
Yield (%)
Reference
Ph3P/Br2/CuBr/CH3CN/reflux
NiCI2/NaBH4/THF/0 8C (3:9)
PhSiH3/MoO2Cl2/PhCH3/reflux
2,6-Dihydroxypyridine/CH3CN/reflux
Ph3P/TiCl4/THF/rt
45 min
2 h
94
81
95
98
96
85
98
91
92
83
95
[1l]
[1a]
[9g]
[2c]
[3b]
[1m]
[1j]
[1k]
[1n]
[1o]
—
20 h
4 h
2 h
TiI4/CH3CN/0 8C
10 min
20 min
40 min
90 min
30 min
1 min
BF3ÁEt2O/NaI/CH3CN/rt
BBr3/CH2Cl2/–23–0 8C
PhSiH3/HReO4 (5 mol%)/THF/rt
PhSiH3/ReIO2 (PPh3)(1 mol%)/THF/rt
Ph3P/TBBDA/CH2Cl2/rt
are attached to nitrogen atoms, it is possible that they act
in the same way as Br2. Therefore, it would be expected
that the interaction of PPh3 with TBBDA generates
phosphonium halides as reactive phosphonium species
in our reactions.
reduction of dibenzyl sulfoxide (as a typical example) to
dibenzyl sulfide (Table 2, entry 3) with those of other
methods. The results show that this method is comparable
to the previously reported ones in terms of yields, reaction
times, and reaction conditions (Table 3).
To evaluate the solvent’s effect, the reduction of
diphenyl sulfoxide was carried out under similar reaction
conditions using different organic solvents, such as
toluene, dichloromethane, methanol, and acetonitrile.
The best results with respect to yields and times were
achieved using dichloromethane.
The mechanism proposed for this transformation
proceeds via the activation of the triphenylphosphine by
reaction with the N-halo compounds, which leads to
intermediate 1. Then, the nucleophilic attack of sulfoxide 2
on intermediate 1 gives intermediate 3. Finally, the
nucleophilic attack of triphenylphosphine on intermediate
In order to optimize the reaction conditions, we first
examined the effect of different molar ratios of TBBDA/
PPh3 in CH2Cl2 at room temperature for the reduction of
benzyl phenyl sulfoxide to benzyl phenyl sulfide as a
model reaction. We found that the optimized molar ratio
for the reduction of benzyl phenyl sulfoxide to benzyl
phenyl sulfide was 1/0.4/2.5 (sulfoxide/TBBDA/PPh3)
(Table 1).
3 gives the sulfide, that of triphenylphosphine on
intermediate 1 and gives the oxide (Scheme 2).
Several attempts for the reduction of sulfoxides by
poly(N-bromobenzene-1,3-disulfonylamide) (PBBS) with
PPh3 have failed (Scheme 3).
4. Conclusions
The reduction of various sulfoxides was carried
out under optimized conditions. The results are shown
in Table 2.
This method is general and can be easily applied to the
reduction of a variety of aryl alkyl, diaryl, dialkyl, and cyclic
sulfoxides to the corresponding sulfides in excellent yields
(Table 2). Sulfoxides, carrying either electron-withdrawing
(entry 5 and 6) or electron-donating (entries 7 and 9)
substituents, gave the corresponding sulfides in excellent
yields, with high purity.
In conclusion, TBBDA/PPh3 is a mild and efficient
reagent system for the reduction of sulfoxides into sulfides.
This procedure has interesting advantages, such as simple
work-up, high yields, short reaction times, and the fact that
the reactions can be carried out at room temperature.
Acknowledgements
We are thankful to Bu-Ali Sina University, Center of
Excellence and Development of Chemical Methods
(CEDCM) for financial support.
To demonstrate the efficiency of the described method
in comparison with formerly reported procedures in the
literature, we compared the results we obtained in the
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N
CH2
CH2
(
)
n
S
S
O
O
O
O
PBBS
Scheme 3.
Please cite this article in press as: Ghorbani-Vaghei R, et al. A novel method for the reduction of sulfoxides with the
j.crci.2013.11.006