148 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 148±149$
A Novel Synthesis of Allyl Sul®des by
Organosamarium Reagents$
Zhuangping Zhan and Yongmin Zhang*
Department of Chemistry, Hangzhou University, Hangzhou 310028, P.R. China
Organosamarium reagents react with sodium alkyl thiosulfates to afford allyl sul®des; a reaction mechanism involving
organosamarium(II) and organosamarium (III) intermediates is suggested.
Intensive studies have been carried out on the role of SmI2
in organic synthesis.1±3 In general, the reactivity of
samarium(II) iodide is characterized by the single electron
transfer (SET) from samarium(II) to a suitable substrate.
Recently, the use of samarium metal in organic synthesis
has stimulated great interest.4±7 Curran ®rst reported the
Grignard reaction of alkylsamarium(III) reagents.8 S. H. Wu
et al. reported the Barbier-type allylation of ketones9 and
carboxylic esters10 with samarium metal and allyl bromide
and an allylsamarium(II) intermediate reaction mechanism
has been suggested. Our group have studied the reaction
(no allyl sul®des) were obtained. However, allyl sul®des
were obtained when the reaction was carried out at 60 8C.
Considering the experimental facts mentioned above and
according to our previous work that samarium diiodide
reductively cleaves the S0S bond of sodium alkyl thio-
sulfates to give the corresponding disul®des,15 we suggest
that the reaction may occur via single electron transfer
from the allylsamarium(II) intermediate to the sodium alkyl
thiosulfates to yield an allylsamarium(III) intermediate and
alkyl disul®de, which further react to form allyl sul®des at
60 8C.
of allylsamarium(II) with imine,11 the synthesis of allyl
selenides by allylsamarium(II) reagents12 and homoallyl-
amines by the addition of allylsamarium(II) reagents to
nitriles,13 and the synthesis of allyl sul®des by treating
allylsamarium(II) reagents with disul®des.14
Sul®des are a class of useful synthetic intermediates, and
many syntheses have been reported for their preparation,
for example, the alkylation of thiols,16 the reaction of alkyl
halide with sodium sul®de,17 addition of hydrogen sul®de to
alkene,18 reduction of disul®des with copper in the presence
of halide,19 reduction of sulfoxides with titanium(II) chlor-
ide,20 deoxygenation of sulfoxides with triphenylphosphine±
iodide±sodium iodide,21 and the synthesis of allyl sul®des
via allyldialkyltelluronium salts.22 The advantages of this
present method are readily available starting materials,
simple operation, mild and neutral conditions, as well as
good yield. The results are summarized in Table 1.
Up until now, no reaction mechanism involving both
the organosamarium(III) and the organosamarium(II) inter-
mediate has been suggested. The organosamarium(III)
intermediate is more stable than the corresponding
organosamarium(II) intermediate. In some reactions, the
organosamarium(II) intermediate may act as a reductive
reagent rather than
a general organometallic reagent.
Recently, there has been an increase in the interest on the
application of organosamarium reagents in organic synthesis
which prompted us to investigate the reaction mechanism of
organosamarium intermediates. Here we report the reaction
of allylsamarium(II) reagents with sodium alkyl thiosulfates
to aord allyl sul®des. In our experiments, mixtures
of sodium alkyl thiosulfates and allylsamarium(II) reagent,
prepared as described in the Experimental section, were
stirred for 0.5 h at room temperature. Only alkyl disul®des
Experimental
Typical procedure.ÐSamarium (0.33 g, 2.2 mmol), THF (20 ml)
and allyl bromide (0.30 g, 2.5 mmol) were added to a three necked
¯ask with stirring at room temperature under nitrogen. When the
mixture turned purple, the stirring was continued for 1 h until the
samarium powder disappeared. Sodium alkyl thiosulfates were then
added to the solution. The solution turned brownish red within a
few seconds and the mixture was further stirred for 2.5 h at room
temperature under nitrogen and then at 60 8C for a given time.
Water (10 ml) was then added and the resulting mixture extracted
with diethyl ether (3Â 40 ml) and the ether layer separated. The
ethereal solution was washed with water (3 Â 40 ml) and the organic
layer dried (MgSO4). The solvent was removed by evaporation
under reduced pressure and the crude product obtained puri®ed
by preparative TLC on silica gel (cyclohexane and ethyl acetate as
*To receive any correspondence.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
Zhan, Zhuangping
