Affiliation:
1. Laboratory of Organic and Medicinal Chemistry (OMC lab), Department of Chemistry, Malaviya National Institute of Technology Jaipur, Jawaharlal Nehru Marg, Jaipur-302017, India
Abstract
The formation of new bonds through C-C bond formation is of utmost importance in the
synthesis of biologically privileged scaffolds and therapeutic drugs. In recent years, extensive efforts
has been done to improve the intermolecular and intramolecular cross-coupling reaction in the
simple, mild, efficient, economical, and eco-friendly manner via transition metal-free or organocatalytic
direct C-H bond activation methodology. The traditional cross-coupling era continuously
shifted to metal-free, organocatalytic, or metal-free cross-dehydrogenative coupling strategies to
fast-track the reactions and diminishing the typical purification processes. Therefore, recent advances
on the transition-metal-free, organocatalytic inter- and intra-molecular cross-coupling reactions
have been introduced and discussed in the present article. In view of the reaction mechanism,
organocatalytic cross-coupling reactions undergo through radical pathways, radical anionic intermediate
which is completely different from traditional transition metal-catalyzed reactions. The exploration
of transition metal-free organocatalyzed cross-couplings for direct C-H arylation of arenes
has grown significantly, thereby, improving the formation of a wide range of aryl-aryl /arylheteroaryl/
heteroaryl-heteroaryl compounds. In the survey, transition metal-free/organocatalytic
cross-coupling reactions showed a higher efficiency under simple and mild conditions than the
comparative transition metal-catalyzed cross-coupling reactions. However, the higher regioselectivity
and chemoselectivity are still far ahead in organocatalytic cross-coupling reactions due to their
specific intrinsic mechanistic pathway. The tuning of many parameters such as oxidative states, ligands
coordination, and counter anions, etc., which results in the specific direct C-H functionalization
with flexible methodology are missing in the transition metal-free cross-coupling reactions.
The highly systematic transition metal-catalyzed chemistry is still playing a dominant role over
transition metal-free chemistry in organic synthesis. The organocatalyzed transition-metal-free conditions
should be more efficient, chemoselective, and regioselective for further potential development
and applications in organic synthesis. For the endless pursuit of sustainable chemistry and
green chemistry, such transition-metal-free/organocatalytic reactions should be never ceased. Additional
curious attention and interest have been developed so far, and chemists are showing their eagerness
and talents to uncover the hidden treasure of green chemistry. In this review article, we
highlighted the developments of various transition metal-free/organocatalytic C-H bond activation
reactions which further encourages the advancement in the development of sustainable C-C coupling
reactions and their further applications towards the synthesis of biologically privileged scaffolds
and drug molecules.
Publisher
Bentham Science Publishers Ltd.
Subject
Organic Chemistry,Analytical Chemistry,Catalysis
Cited by
2 articles.
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