65
Later, Zhang and co-workers demonstrated another oxidative cross-coupling
between heteroarenes and arylsiloxanes, mainly focusing on indole derivatives
(Scheme 3.35) [81]. In the presence of Pd(OAc) 2 as the catalyst, Ag 2 O as the oxidant, and tetrabutylammonium fluoride (TBAF) as the fluoride source for activation
of organosilanes, various substituted indoles reacted smoothly with arylsiloxanes in
good yields with high regioselectivity on the 2-position of the indole ring. Electronrich indoles are more reactive than the electron-deficient ones, which may indicate
an electrophilic substitution mechanism in this transformation.
In 2012, Oi and co-workers demonstrated the oxidative arylation of thiophenes
and benzothiophenes with aryltrimethylsilanes catalyzed by PdCl 2 (MeCN) 2 in the
presence of CuCl 2 as the oxidant at 80 °C (Scheme 3.36) [82]. The reaction preferentially occurred at the β-position of both thiophenes and benzothiophenes. Notably,
this approach is operationally simple, as it can be performed under aerobic conditions, and no base or additional ligand is required.
Recently, trifluoromethyltrimethylsilane (Ruppert’s reagent) is widely used in
organic synthesis for the introduction of the trifluoromethyl group. The direct
oxidative trifluoromethylations of heteroarene C−H bonds were developed by
Qing and co-workers. In the presence of Cu(OAc) 2 , 1,10-Phen, NaOAc, t-BuONa,
and DTBP, the direct C−H oxidative trifluoromethylation of various functionalized heteroarenes, including 1,3,4-oxadiazole, benzo[d]-oxazoles, benzo[d]imidazoles, imidazole, benzo[d]thiazole, as well as polyfluoroarene, could be
X
+
NiBr 2
. diglyme (10 mol%)
bpy (20 mol%)
CuF 2 (2 equiv)
DMAc
150
o
C, 2.5 h
Y
N
H
O
N
80%
X = C, N
Y = O, S, NMe
X
Y
N
R
S
N
64%
O
N
86%
Ph
(RO) 3 Si R
N
O
N
63%
Ph
N
N
65%
Me
Me
O
N
70% (E/Z = 26:74)
nC 6 H 13
CsF (3 equiv)
Scheme 3.34 Ni-catalyzed oxidative cross-coupling between heteroarenes and arylsilanes/
alkenylsilane
3 Oxidative Coupling Reactions Between Hydrocarbons and Organometallic Reagents…
Later, Zhang and co-workers demonstrated another oxidative cross-coupling
between heteroarenes and arylsiloxanes, mainly focusing on indole derivatives
(Scheme 3.35) [81]. In the presence of Pd(OAc) 2 as the catalyst, Ag 2 O as the oxidant, and tetrabutylammonium fluoride (TBAF) as the fluoride source for activation
of organosilanes, various substituted indoles reacted smoothly with arylsiloxanes in
good yields with high regioselectivity on the 2-position of the indole ring. Electronrich indoles are more reactive than the electron-deficient ones, which may indicate
an electrophilic substitution mechanism in this transformation.
In 2012, Oi and co-workers demonstrated the oxidative arylation of thiophenes
and benzothiophenes with aryltrimethylsilanes catalyzed by PdCl 2 (MeCN) 2 in the
presence of CuCl 2 as the oxidant at 80 °C (Scheme 3.36) [82]. The reaction preferentially occurred at the β-position of both thiophenes and benzothiophenes. Notably,
this approach is operationally simple, as it can be performed under aerobic conditions, and no base or additional ligand is required.
Recently, trifluoromethyltrimethylsilane (Ruppert’s reagent) is widely used in
organic synthesis for the introduction of the trifluoromethyl group. The direct
oxidative trifluoromethylations of heteroarene C−H bonds were developed by
Qing and co-workers. In the presence of Cu(OAc) 2 , 1,10-Phen, NaOAc, t-BuONa,
and DTBP, the direct C−H oxidative trifluoromethylation of various functionalized heteroarenes, including 1,3,4-oxadiazole, benzo[d]-oxazoles, benzo[d]imidazoles, imidazole, benzo[d]thiazole, as well as polyfluoroarene, could be
X
+
NiBr 2
. diglyme (10 mol%)
bpy (20 mol%)
CuF 2 (2 equiv)
DMAc
150
o
C, 2.5 h
Y
N
H
O
N
80%
X = C, N
Y = O, S, NMe
X
Y
N
R
S
N
64%
O
N
86%
Ph
(RO) 3 Si R
N
O
N
63%
Ph
N
N
65%
Me
Me
O
N
70% (E/Z = 26:74)
nC 6 H 13
CsF (3 equiv)
Scheme 3.34 Ni-catalyzed oxidative cross-coupling between heteroarenes and arylsilanes/
alkenylsilane
3 Oxidative Coupling Reactions Between Hydrocarbons and Organometallic Reagents…