302
cobalt- catalysed electrooxidative annulation with hydrazide as a directing
group [291].
Recently, Tang et al. accomplished the first illustration of electrochemical double
C–H functionalization of amides and alkynes by dehydrogenative annulation to
develop polycyclic isoquinolinones (Scheme 93) [292]. This strategy without any
oxidant delivered the products with improved chemo and regioselectivity and was
found to be very competent as compared to other traditional methods using strong
oxidant conditions. Ackermann et al. in 2019 demonstrated the first report of
rhodaelectro- catalysed C–H activation of imidate and unsymmetrical alkyne in electrochemical flow reactor (Scheme 94) [293]. This electrochemical-flow annulation
reaction was recognized to be operative for both intra- and intermolecular annulation
with a variety of substrates and led to the synthesis of isoquinoline products with
excellent chemoselectivity. The concept of rhodaelectro-catalysed C–H bond activation was again combined with [2 + 2 + 2] alkyne annulation of boronic acids and
cyclodehydrogenation to construct the varyingly substituted polycyclic aromatic
hydrocarbons (PAHs) (Scheme 95) [294]. This concept offers several advantages of
being green and sustainable over conventional chemical oxidants with the use of
electricity as a green oxidant, wide substrate scope and easy operational set up.
Huang et al. demonstrated mild and oxidant-free electrochemical protocol for
C–H phosphorylation of secondary amine with diethyl phosphate (Scheme 96)
[295]. This approach was effective to tolerate wide functionality of a series of cyclic
and chain secondary amines and produced products with satisfactory yields.
Fine chemicals with nitrile group incorporated in it is of specific interest using
C–H activation of alkyl nitriles as it offers high economy. Noteworthy achievement
in the extent of electrochemical C–H bond functionalization was accomplished
recently by He et al. [296] to synthesize sulphur-comprising β-enaminonitrile molecules in a stereoselective manner via Csp
3
–H oxidative activation of acetonitrile by
Cp*RhCl2 2 (2.5 mol%)
HOPiv (10 mol%)
NaOPiv (2 equiv)
MeOH, 25
o C, O 2 18-22 h
CPE at 1.5 mA
O
NH
Me
R 2
R 1
R
R
N
OMe
R 2
R 1
Scheme 94 Flow-rhodaelectro-enabled C–H bond activation of imidates and alkynes
Cp*RhCl2 2 (2.5 mol%)
KOAc, t-AmOH/H 2 O (3/ 1 )
80
o C, 12 h
CCE at 4.0 mA
RVC
Pt
B
R 1
R 2
OH
OH
R
R
R 1
R 2
R 2
R 1
Scheme 95 C−H activation of boronic acids and alkynes via rhodaelectro catalysis
D. S. Deshmukh et al.
cobalt- catalysed electrooxidative annulation with hydrazide as a directing
group [291].
Recently, Tang et al. accomplished the first illustration of electrochemical double
C–H functionalization of amides and alkynes by dehydrogenative annulation to
develop polycyclic isoquinolinones (Scheme 93) [292]. This strategy without any
oxidant delivered the products with improved chemo and regioselectivity and was
found to be very competent as compared to other traditional methods using strong
oxidant conditions. Ackermann et al. in 2019 demonstrated the first report of
rhodaelectro- catalysed C–H activation of imidate and unsymmetrical alkyne in electrochemical flow reactor (Scheme 94) [293]. This electrochemical-flow annulation
reaction was recognized to be operative for both intra- and intermolecular annulation
with a variety of substrates and led to the synthesis of isoquinoline products with
excellent chemoselectivity. The concept of rhodaelectro-catalysed C–H bond activation was again combined with [2 + 2 + 2] alkyne annulation of boronic acids and
cyclodehydrogenation to construct the varyingly substituted polycyclic aromatic
hydrocarbons (PAHs) (Scheme 95) [294]. This concept offers several advantages of
being green and sustainable over conventional chemical oxidants with the use of
electricity as a green oxidant, wide substrate scope and easy operational set up.
Huang et al. demonstrated mild and oxidant-free electrochemical protocol for
C–H phosphorylation of secondary amine with diethyl phosphate (Scheme 96)
[295]. This approach was effective to tolerate wide functionality of a series of cyclic
and chain secondary amines and produced products with satisfactory yields.
Fine chemicals with nitrile group incorporated in it is of specific interest using
C–H activation of alkyl nitriles as it offers high economy. Noteworthy achievement
in the extent of electrochemical C–H bond functionalization was accomplished
recently by He et al. [296] to synthesize sulphur-comprising β-enaminonitrile molecules in a stereoselective manner via Csp
3
–H oxidative activation of acetonitrile by
Cp*RhCl2 2 (2.5 mol%)
HOPiv (10 mol%)
NaOPiv (2 equiv)
MeOH, 25
o C, O 2 18-22 h
CPE at 1.5 mA
O
NH
Me
R 2
R 1
R
R
N
OMe
R 2
R 1
Scheme 94 Flow-rhodaelectro-enabled C–H bond activation of imidates and alkynes
Cp*RhCl2 2 (2.5 mol%)
KOAc, t-AmOH/H 2 O (3/ 1 )
80
o C, 12 h
CCE at 4.0 mA
RVC
Pt
B
R 1
R 2
OH
OH
R
R
R 1
R 2
R 2
R 1
Scheme 95 C−H activation of boronic acids and alkynes via rhodaelectro catalysis
D. S. Deshmukh et al.