140
4.4.3 Oxidative C-S Coupling
Thiolation of ethers or alkanes with disulfides via oxidation of C(sp3)-H bonds can
be conducted using DTBP or TBP as the oxidants under transition-metal-free conditions (Scheme 4.61) [45]. Because disulfide bonds are weak and can undergo rapid
cleavage under mild conditions, disulfides undergo oxidative radical C-S coupling
with C(sp3)-H bonds easily. And good yields of thiolation products can be observed.
The reaction mechanism suggests that the tert-butoxyl radical is formed after the
decomposition of DTBP. And then the tert-butoxyl radical abstracts an H atom from
the ether to produce the carbon radical intermediate, which then reacts with disulfide to provide the desired product and sulfur radicals. The selective cross-coupling
of the two radicals furnishs the final C-S coupling product.
TBP or DTBP
+
120 °C
S
Ar
X
H
X
Ar
S
S
Ar
S
88%
S
79%
MeO
S
87%
Br
S
65%
S
77%
S
N
65%
X
[O]
X
X
Ar
S
S
Ar
X
S
Ar
+ ArS
X
ArS
X
S
Ar
Scheme 4.61 Thiolation of ethers or alkanes with disulfides
W. Liu