267
through C–H/N–N functionalization. The developed methodology is more costeffective and greener due to reusability of catalytic system, easy extraction process,
shorter reaction duration, biodegradable solvent, and adaptivity up to the gram scale.
Further, this catalytic system has been explored in order to activate ortho C–H
bond of ketazines using microwave approach in favour of rapid, atom economic and
sustainable synthesis of isoquinolines (Scheme 14) [107]. In the same report, the
methodology has been extended successfully with the purpose of construction of
isoquinolinones by ortho C–H functionalization of dibenzoylhydrazine. The protocol is highly atom economic as both the nitrogen atoms of directing groups could be
incorporated to the anticipated products by annulation with alkynes through C–H/
N–N bond functionalization. In addition, the method is environmentally benign due
to considerably reduced duration with easy extraction process, catalyst reusability,
external oxidant and silver or antimony salt-free conditions, gram-scale synthesis
and employment of biodegradable solvent.
Besides the extensive exploration of [RuCl 2 (p-cymene)] 2 as homogeneous recyclable catalyst for C–H activation reactions, in 2017, Jian et al. employed the facile
and reusable catalytic system for the straightforward arylation of heteroarenes by
C–H bond activation utilizing reasonable aryl chlorides by means of electrophilic
reagents (Scheme 15) [108]. A moderately economical catalyst RuCl 3 ·xH 2 O and
environmentally benign solvent PEG-400 have been utilized in presence of air
excluding any additive or ligand. The protocol enables the control of proportion of
mono- to diarylated products easily by modifying the reaction circumstances.
Moreover, the catalyst could be recycled for six times and the methodology could
be effortlessly scaled up to the gram level using 0.3 mol% Ru catalyst.
In 2019, Ackermann group applied the extensively appropriate oxidative
palladium- catalyst for the formulation of an effective protocol for the aerobic
N
R 2
N
N
R 2
R 4
R 3
Ru(p-cymene)Cl2 2 (5 mol%)
PEG-400,
150
o C, 10 min
(microwave heating)
R 3
R 4
R 2
2
R 1
R 1
R 1
2
KPF 6 (50 mol%)
Scheme 14 Ru catalysed rapid annulation of ketazines
R 1
(5 mol%)
PEG-400
120
o
C, under air
N
Cl
R 2
R 1
N
R 2
R 1
N
R 2
R 2
RuCl 3 xH 2 O
LiOH H 2 O or CH 3 COOK (2-3 equiv)
Scheme 15 Ru-catalysed direct arylation of heteroarenes
Insights into Sustainable C–H Bond Activation
through C–H/N–N functionalization. The developed methodology is more costeffective and greener due to reusability of catalytic system, easy extraction process,
shorter reaction duration, biodegradable solvent, and adaptivity up to the gram scale.
Further, this catalytic system has been explored in order to activate ortho C–H
bond of ketazines using microwave approach in favour of rapid, atom economic and
sustainable synthesis of isoquinolines (Scheme 14) [107]. In the same report, the
methodology has been extended successfully with the purpose of construction of
isoquinolinones by ortho C–H functionalization of dibenzoylhydrazine. The protocol is highly atom economic as both the nitrogen atoms of directing groups could be
incorporated to the anticipated products by annulation with alkynes through C–H/
N–N bond functionalization. In addition, the method is environmentally benign due
to considerably reduced duration with easy extraction process, catalyst reusability,
external oxidant and silver or antimony salt-free conditions, gram-scale synthesis
and employment of biodegradable solvent.
Besides the extensive exploration of [RuCl 2 (p-cymene)] 2 as homogeneous recyclable catalyst for C–H activation reactions, in 2017, Jian et al. employed the facile
and reusable catalytic system for the straightforward arylation of heteroarenes by
C–H bond activation utilizing reasonable aryl chlorides by means of electrophilic
reagents (Scheme 15) [108]. A moderately economical catalyst RuCl 3 ·xH 2 O and
environmentally benign solvent PEG-400 have been utilized in presence of air
excluding any additive or ligand. The protocol enables the control of proportion of
mono- to diarylated products easily by modifying the reaction circumstances.
Moreover, the catalyst could be recycled for six times and the methodology could
be effortlessly scaled up to the gram level using 0.3 mol% Ru catalyst.
In 2019, Ackermann group applied the extensively appropriate oxidative
palladium- catalyst for the formulation of an effective protocol for the aerobic
N
R 2
N
N
R 2
R 4
R 3
Ru(p-cymene)Cl2 2 (5 mol%)
PEG-400,
150
o C, 10 min
(microwave heating)
R 3
R 4
R 2
2
R 1
R 1
R 1
2
KPF 6 (50 mol%)
Scheme 14 Ru catalysed rapid annulation of ketazines
R 1
(5 mol%)
PEG-400
120
o
C, under air
N
Cl
R 2
R 1
N
R 2
R 1
N
R 2
R 2
RuCl 3 xH 2 O
LiOH H 2 O or CH 3 COOK (2-3 equiv)
Scheme 15 Ru-catalysed direct arylation of heteroarenes
Insights into Sustainable C–H Bond Activation