290
the use of this reaction protocol, intramolecular amoniohalogenation and a threecomponent aminoazidation reaction were conducted in a very efficient way with
remarkable regioselectivity and stereoselectivity in the products.
Various recent articles in the literature presented the major significant contributions in C–H functionalization including radical addition to N-tosylimines using
decatungstate photocatalyst [233], α-C–H alkynylation of ethers and alkynyl bromides [234], metal-free alkylheteroarylation of unactivated olefins [235], difunctionalizations of alkenes to synthesize fluoroalkyl ketones [236], nickel-catalysed
photoredox C(sp
3
)–H activation of amides with thioethers [237] and for C(sp
3
)–H
functionalization of glycine moieties to construct 1,3-oxazolidines [238].
Over the past few years, continuous flow microreactor technology has gained
significant impact and has been recognized as permitting technology to avoid mass
transfer issues occurred in various reactions. Continuous flow microreactor technology is providing means to scale operationally complex transformations including
photochemical reactions [239, 240]. Developments of C–H activation in the area of
continuous flow microreactor has been carried out very recently for benzylic C–H
oxidation [241], C(sp
3
)–H aerobic oxidation [242] and for C–H functionalization of
heteroarenes [243]. These photochemical transformations in continuous flow microreactor offered several advantages of low-cost operational simplicity, easy product
separation and good yield of products.
7 Microwave-Assisted C–H Activation Reactions
Organic synthesis by microwave-assisted reactions has been emerged as a more
straightforward and substantial platform in modern organic chemistry [244–246].
C–H activation reactions are often performed with high temperature and long reaction times; the use of microwave irradiation offers several advantages as it productively attains the need of the high temperatures necessary to accomplish C–H
activation. Hence microwave-assisted C–H activation is gaining popularity in
laboratory- scale medicinal chemistry due to its rewarding advantages such as reproducibility, operational simplicity, safety and simple scale up procedure [247–250].
Many microwave-assisted C–H activation reactions permit an efficient path to
bi(hetero)aryl compounds having applications in medicinal chemistry and organic
materials [251]. This section of book chapter gives an overview of some of the
important accomplishments in the microwave-assisted C–H activation reactions.
When compared with other transition metal catalysis, palladium catalysts represented enormous applications in microwave-assisted C–H activation reactions. With
this background, Baber et al. demonstrated the synthesis of chiral complexes of
palladium with bis(phosphite) PCP-pincer ligands via C–H activation of ligands by
thermal heating and observed enormous enhancement in the reaction rate under
microwave irradiation (Scheme 64) [252].
These complexes were utilized for allylation of aldehydes and offered promising
enantioselectivity in resulting products. Microwave-mediated palladium-catalysed
D. S. Deshmukh et al.
the use of this reaction protocol, intramolecular amoniohalogenation and a threecomponent aminoazidation reaction were conducted in a very efficient way with
remarkable regioselectivity and stereoselectivity in the products.
Various recent articles in the literature presented the major significant contributions in C–H functionalization including radical addition to N-tosylimines using
decatungstate photocatalyst [233], α-C–H alkynylation of ethers and alkynyl bromides [234], metal-free alkylheteroarylation of unactivated olefins [235], difunctionalizations of alkenes to synthesize fluoroalkyl ketones [236], nickel-catalysed
photoredox C(sp
3
)–H activation of amides with thioethers [237] and for C(sp
3
)–H
functionalization of glycine moieties to construct 1,3-oxazolidines [238].
Over the past few years, continuous flow microreactor technology has gained
significant impact and has been recognized as permitting technology to avoid mass
transfer issues occurred in various reactions. Continuous flow microreactor technology is providing means to scale operationally complex transformations including
photochemical reactions [239, 240]. Developments of C–H activation in the area of
continuous flow microreactor has been carried out very recently for benzylic C–H
oxidation [241], C(sp
3
)–H aerobic oxidation [242] and for C–H functionalization of
heteroarenes [243]. These photochemical transformations in continuous flow microreactor offered several advantages of low-cost operational simplicity, easy product
separation and good yield of products.
7 Microwave-Assisted C–H Activation Reactions
Organic synthesis by microwave-assisted reactions has been emerged as a more
straightforward and substantial platform in modern organic chemistry [244–246].
C–H activation reactions are often performed with high temperature and long reaction times; the use of microwave irradiation offers several advantages as it productively attains the need of the high temperatures necessary to accomplish C–H
activation. Hence microwave-assisted C–H activation is gaining popularity in
laboratory- scale medicinal chemistry due to its rewarding advantages such as reproducibility, operational simplicity, safety and simple scale up procedure [247–250].
Many microwave-assisted C–H activation reactions permit an efficient path to
bi(hetero)aryl compounds having applications in medicinal chemistry and organic
materials [251]. This section of book chapter gives an overview of some of the
important accomplishments in the microwave-assisted C–H activation reactions.
When compared with other transition metal catalysis, palladium catalysts represented enormous applications in microwave-assisted C–H activation reactions. With
this background, Baber et al. demonstrated the synthesis of chiral complexes of
palladium with bis(phosphite) PCP-pincer ligands via C–H activation of ligands by
thermal heating and observed enormous enhancement in the reaction rate under
microwave irradiation (Scheme 64) [252].
These complexes were utilized for allylation of aldehydes and offered promising
enantioselectivity in resulting products. Microwave-mediated palladium-catalysed
D. S. Deshmukh et al.