Chemistry Reference
In-Depth Information
Et
2
BO
2
.
Et
.
O
2
+
Et
3
B
+
XCHR
1
R
2
Et
.
.
CHR
1
R
2
EtX
+
+
X=I,R
1
=CO
2
Et, R
2
=H; X = Br,R
1
=CO
2
Et , R
2
=CH
3
Scheme 146
Autooxidation of triethylborane thence formation of reactive electrophilic carbon
radicals [
210
]
CHR
1
R
2
+
CHR
1
R
2
S
S
H
CHR
1
R
2
CHR
1
R
2
H
+
-H
+
Fe
3+
+
CHR
1
R
2
+
Fe
2+
S
S
S
H
94
R
1
=CO
2
Et, R
2
=CH
3
(47 %); R
1
=CO
2
Et, R
2
=H(56%)
Scheme 147
Radical substitution of thiophene with electrophilic CHR
1
R
2
[
210
]
R
Cl
R'
R = Cl, F, NMe
2
N
N
S
N
R' = Cl, SBn, SO N
22
S
Cl
Fig. 4
Thiophene-containing compounds as potential radical scavengers [
149
]
In this way, ethyl esters
94
of thien-2-ylacetic acids were formed (Scheme
147
)
[
210
]. The presence of oxidant Fe
2
(SO
4
)
3
H
2
O was necessary for the oxidation of
the intermediate
-complex and thus for reaction progress (Scheme
147
)[
210
].
Concluding this radical substitution section, one can cite examples of thiophene-
containing molecules which were assessed for their antioxidant potential and
free radical scavenging activity,
˃
in work seeking a good xanthine oxidase
inhibitor [
149
].
It was demonstrated that both activities are dependent on substituents on the
thiophene ring (R
1
). The best compound had R
NMe
2
and R
1
SBn (Fig.
4
)
[
149
]. Thus, the capability of a thiophene ring to accept electrons from radicals
was confirmed again.
¼
¼
