3
O
O
We thank the Natural Science Foundation of Zhejiang Province
(No. LY12B02006 and LY13B020005) the National Students
O
O
ʹ
O
Innovation and Entrepreneurship Training Program (No.
201410352004) for financial support.
6aa,b
6b
6c
6d
a Unless otherwise noted, the reaction conditions are: 1a (0.3
mmol), 6a-6d (2 mL), DTBP(1.0 equiv), TBHP (2.0 equiv), 24
h. b In presence of solvents like MeCN, DCE, CH2Cl2 and CCl4
Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.tetlet.xxx.
The exact mechanism of the reaction is not clear at this moment.
We believe that there is a radical reaction path since the use of
References and notes
2,2,6,6 tetramethylpiperidine-N-oxide (TEMPO),
a radical-
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trapping reagent, completely suppressed the formation of the
desired product 3a (Scheme 2) and formation of the adduct 7a
(38% yield) was confirmed by GC-Mass and NMR data.
DTBP/TBHP (1.0/2.0 equiv)
O
TEMPO (1.0 equiv)
O
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O N
+
+
PhSSPh
SPh
120 oC, 24 h
1a
2a
3a, trace
7a, 38%
Scheme 2. Mechanism studies of thiolation
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On the basis of the above experimental results, we have
proposed a plausible mechanism for this reaction (Figure 1). We
believe that TBHP undergoes better homolytic cleavage under
heating condition in presence of the DTBP oxidant and provides
the hydroxyl radical A. The radical A abstracts a hydrogen from
acetone to form the radical intermediate B. The ketone radical B
reacts with disulfide to form the desired product (3a) along with
a PhS radical which can be further trapped by another ketone
radical.
tBuOOH
Heat
2 tBuO
tBuOOtBu
OH
A
tBuOOtBu
O
O
OH
+
H2O
O
A
B
O
+
PhSSPh
+
PhS
SPh
3a
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B
O
O
PhS
+
SPh
B
3a
Figure 1. Possible mechanism
In conclusion, we have reported an very effective direct
oxidative α-thiolation and α-selenylation process of acetone
using a mixture of DTBP and TBHP oxidant via C(sp3)-H bond
functionalization. The method exhibits good functional group
tolerance and α-arylchalcogenation products can be obtained in
satisfied yields. Fluro-substitution on aromatic ring of the
dichalcogenides can noticeably enhance the yield of the desired
product in both thiolation and selenylation process. Investigation
has been going on to get detailed insight into the reaction
mechanism and to expand the scope of current method to various
ketones.
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Acknowledgments