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along with the generation of dioxygen and water via Russell
fragmentation.6,20 In contrast, product 3 was also formed via
intermediate 11 followed by the elimination of [CuII-OH]+ due to
the low concentration of the hydroperoxide radical in the
Cu-catalytic system.6,21 The side product 4 might be produced by
the reduction of the hydroperoxide 12, which was generated from 9
via the abstraction of a H atom from the strong H-donor 5.6
In conclusion, we have developed an unprecedented copper-
catalyzed direct oxysulfonylation of alkenes with dioxygen and
sulfonylhydrazides to access b-ketosulfones. Isotope labeling
and radical capture experiments suggested that the carbonyl
oxygen atom of b-ketosulfones originated from O2 and a radical
pathway might be involved. Taking into account the following
desirable features, such as operation simplicity, cheap catalysts,
readily-available materials, as well as mild and environmentally
benign conditions, this novel catalytic system provides a highly
attractive approach to produce b-ketosulfones. Studies of the
detailed mechanism of this process and its application are
underway.
Scheme 1 Postulated reaction pathway.
performed in the presence of H2O (10 equiv.) under 18O2 (eqn (3),
HRMS, see ESI†). The combination of this result and oxygen
scrambling experiments also clearly indicated that the carbonyl
oxygen atom of the b-ketosulfones originated from dioxygen.
This work was supported by the Taishan Scholar Foundation
of Shandong Province and the National Natural Science Foun-
dation of China (No. 21302109, 21375075, and 21275089).
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Notes and references
It is known that radical species are formed from hydrazide
compounds via the generation of diazenes in the presence of
transition metals or dioxygen.19 Therefore, a radical pathway was
also supposed to be involved in this reaction. Radical trapping
experiments supported this assumption. As shown in eqn (4),
when TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy, a well known
radical-capturing species) was added to the reaction system, the
oxysulfonylation reaction was completely suppressed, indicating
that this reaction presumably involves a radical process.
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Furthermore, b-hydroxysulfone 4ab could be isolated from
the reaction system of 1a with p-toluenesulfonylhydrazide 2b.
However, the desired product 3ab was not obtained when 4ab
was treated under the standard conditions (eqn (5)), suggesting
that 4ab might not be an intermediate in this reaction.
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Based on the above experiments and previous reports espe-
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17 Q. Lu, J. Zhang, F. Wei, Y. Qi, H. Wang, Z. Liu and A. W. Lei,
way is described in Scheme 1. Initially, the sulfonyl radical 7
and ꢀOOH species were generated from 2 and dioxygen with the
Angew. Chem., Int. Ed., 2013, 52, 7156.
release of N2 via single electron transfer and the deprotonation 18 M. Dole, Chem. Rev., 1952, 52, 263.
process.6,19 The transformations occurred faster when high-
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to alkyl radical 8, which interacted with O2 to afford peroxy
ꢀ
radical 9. Finally, 9 coupled with the OOH species to form a
monoalkyl tetroxide 10, which decomposed to give the product 3,
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 10239--10241 10241