Bahrami et al.
JOCArticle
reports are available where a given oxidant is suitable for the
controlled synthesis of sulfoxides and sulfones.13
SCHEME 2. Proposed Mechanism for the Oxidation of Sulfides
It is often noticed that sulfide oxidation is accompanied by
several disadvantages such as long reaction times, low yields,
inconvenient reaction conditions, expensive oxidants, unde-
sired side reactions at other functionalities, and the use of
organic solvents.
Hydrogen peroxide, in contrast to other oxidizing agents,
is the most attractive from an environmental viewpoint. It is
an ideal waste-avoiding oxidant since water is the only theo-
retical byproduct and is very attractive as an oxidant for
liquid-phase reactions because of its solubility in water and
many organic solvents.14,15 Moreover, aqueous hydrogen
peroxide solution shows safety in storage, operation, and
transportation, is easily available on the market, and is rela-
tively cheap.16,17
1,3,5-Triazo-2,4,6-triphosphorine-2,2,4,4,6,6-tetrachloride,
commonly called hexaclorocyclo(triphos-phazene) or trimeric
phosphonitrilic chloride, has been widely used in organic reac-
tions;18 however, it has not been studied as a promoter in
the oxidation of sulfides and the deoxygenation of sulfoxides
until now.
sulfides to their sulfoxides in excellent yields and short reac-
tion times (Scheme 1).
Results and Discussion
Recently, we reported several new synthetic methods for
environmentally benign reactions using aqueous 30% hydro-
gen peroxide.19,5f-i Herein, we wish to report an efficient proto-
col in which H2O2 has been used as the oxidizing agent in
the presence of TAPC for the chemoselective oxidation of
In the first step, we carried out a set of initial experiments
on benzyl phenyl sulfide (1 mmol) as a model substrate using
30% H2O2 (1 mmol) in the presence of 0.05, 0.075, and
0.1 mmol of TAPC under solvent-free conditions at room
temperature. The best result (99% yield) was obtained by
carrying out the reaction with 1:1:0.1 mol ratios of sulfide,
H2O2, and TAPC for 5 min.
It is noteworthy that in a blank experiment, no significant
oxidation was observed under similar reaction conditions in
the absence of TAPC, and only a low yield (35%) was obta-
ined in the presence of 1 mmol of H2O2 after 6 h.
(11) (a) Sharpless, K. B.; Verhoeven, T. R. Aldrichimica Acta 1979, 12, 63.
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In order to study the generality of this procedure, a series
of sulfides having varied R and R0 groups containing aro-
matic, allylic, and aliphatic groups attached to the sulfur
atom was reacted according to optimized reaction condi-
tions, and the results are presented in Table 1. As shown,
dialkyl, diallyl, diaryl, and aryl-allyl sulfides were oxyge-
nated, and most of the reactions proceeded nearly quantita-
tively. All of the reactions occurred with complete selectivity
for sulfoxide formation in excellent yield without any notice-
able overoxidation to sulfones. These substrates selectively
underwent oxidation at the sulfur atom without undergoing
further structural changes in their functional groups as sug-
gested by NMR analyses of the products. For example, in
the case of allylic sulfides, no over oxidation to the sulfones
or hydrochlorination of the double bond was observed, and
only the corresponding sulfoxides were obtained in excellent
yields (Table 1, entries 12 and 14). Acid sensitive sulfides
such as 2-[(benzylthio)methyl] furan worked well without the
formation of any side products, which are normally observed
either in the presence of protic or Lewis acids (Table 1, entry
8). Interestingly, the presence of ester and carboxyl groups
did not interfere with the oxidation process of the sulfide,
and desired sulfoxides were obtained in excellent yields
(Table 1, entries 10 and 11). The protocol worked efficiently
in oxidizing 2-(benzylthio)benzimidazole to afford the cor-
responding sulfoxide (Table 1, entry 9). This procedure can
also be applied to the oxidation of cyclic sulfides (Table 1,
entry 13).
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6210 J. Org. Chem. Vol. 75, No. 18, 2010