strategy, which is different from classical tandem reactions.
As shown in Scheme 2, two parallel tandem reactions
by iodination of acetophenone 1 under acid conditions, can
be sequentially oxidized by dimethyl sulfoxide to phenylg-
lyoxal 4.6,7 Second, 2 is reacted with dimethyl sulfide (DMS),
which is readily reduced from dimethyl sulfoxide in high
yield in the presence of HI formed in the first step8 to give
dimethyl (phenacyl)-sulfonium iodine 3.9 Furthermore, 3
could condense with 4 in an aldol-type reaction to produce
intermediate 2-hydroxy-3-(methylthio)-1,4-diphenyl butane-
1,4-dione 5 after loss of MeI, which is then dehydrated to
yield 6b and 6c.10
Scheme 2. Self-Sorting Tandem Reaction Strategy
On the basis of these analyses, we believe that it is possible
to obtain isomers 6b,c from 1 in a one-pot reaction.
Surprisingly, as early as the 1970s, Furukawa reported that
the unexpected olefinic products 6b,c were obtained in poor
yield when the dimethyl sulfoxide-iodine-sulfuric acid
system was employed to oxidize 1.10 Additionally, under acid
conditions, the yield for direct oxidation of 1 to 4 by dimethyl
sulfoxide was reported to be only 10%,11 which could explain
the poor yield of the above-mentioned reaction. Therefore,
to obtain isomers 6b,c from 1 in one pot, the generation of
intermediate 2 is a key step. Moreover, iodine and dimethyl
sulfoxide are indispensable. On the basis of our research
results, we found that a CuO-iodine system could iodinate
1 to 2 in excellent yield12 after screening various metal
catalysts, such as Ag2O, CuCl, CuCl2, and CuBr. As a result,
the experiments indicated that the dimethyl sulfoxide-CuO-
iodine system (the optimal molar ratio of n(substrate)/
n(CuO)/n(iodine) equals 1:3:2) was more efficient for this
desired reaction.
proceed independently, starting from the same reactant A
and yielding the corresponding intermediates C and N; then,
C and N combine effectively together to provide the target
molecule P. We refer to this type of reaction as a self-sorting
tandem reaction.
Herein, we report a novel and efficient carbon-carbon
double-bond-forming reaction starting from aryl or heteroaryl
methyl ketones via the self-sorting tandem reaction strategy
(Scheme 3). These olefinic products containing 1,4-dicar-
Scheme 3. Synthesis of Compounds 6b,c via the Self-Sorting
Tandem Reaction
Next, we also successfully obtained the target products
6b,c using phenacyl iodine 2 as the reactant, which was
powerful evidence in support of the above hypothesis
(Scheme 3). In addition, to ensure the self-sorting tandem
reaction could be carried out efficiently, the same or
approximate reactive rates between the oxidation step from
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obtained in 96% yield.
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Org. Lett., Vol. 8, No. 11, 2006