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Biaryl scaffolds are found in natural products and drug molecules and exhibit a wide range of biological activities. In past decade, the transition metal-catalyzed C–H arylation reaction came out as an effective tool for the construction of biaryl motifs. However, traditional transition metal-catalyzed C–H arylation reactions have limitations like harsh reaction conditions, narrow substrate scope, use of additives etc. and therefore encouraged synthetic chemists to look for alternate greener approaches. This review aims to draw a general overview on C–H bond arylation reactions for the formation of C–C bonds with the aid of different methodologies, majorly highlighting on greener and sustainable approaches. Transition-metal-catalyzed C–H arylations are an effective tool for the construction of biaryl motifs in an efficient and selective manner. Here the authors provide an overview of the state-of-the-art of the field and perspectives on emerging directions toward increased sustainability.

The study of carbon-based nanomaterials (CBNs) for biomedical applications has attracted great attention due to their unique chemical and physical properties including thermal, mechanical, electrical, optical and structural diversity. With the help of these intrinsic properties, CBNs, including carbon nanotubes (CNT), graphene oxide (GO), and graphene quantum dots (GQDs), have been extensively investigated in biomedical applications. This review summarizes the most recent studies in developing of CBNs for various biomedical applications including bio-sensing, drug delivery and cancer therapy.

C–H activation is a ‘simple-to-complex’ transformation that nature has perfected over millions of years of evolution. Transition-metal-catalysed C–H activation has emerged as an expeditious means to expand the chemical space by introducing diverse functionalities. Notably, among the strategies to selectively cleave a particular C–H bond, the catalytic use of a small molecule as co-catalyst to generate a transient directing group, which provides a balance between step economy and chemical productivity, has gained immense attention in recent years. This allows one to convert a desired C–H bond irrespective of its geometrical or stereochemical configuration. This Review describes the various transient directing groups used in C–H activation and explains their mechanistic significance. Transient directing groups enable selective metal-catalysed C–H functionalization reactions to give diverse products. These directing groups form and dissociate in situ, such that their use is an efficient route to complex organics, examples of which are summarized in this Review.

Despite the widespread applications of C–H functionalization, controlling site selectivity remains a significant challenge. Covalently attached directing groups (DGs) served as ancillary ligands to ensure ortho -, meta - and para -C–H functionalization over the last two decades. These covalently linked DGs necessitate two extra steps for a single C–H functionalization: introduction of DG prior to C–H activation and removal of DG post-functionalization. Here we report a temporary directing group (TDG) for meta -C–H functionalization via reversible imine formation. By overruling facile ortho -C–H bond activation by imine- N atom, a suitably designed pyrimidine-based TDG successfully delivered selective meta -C–C bond formation. Application of this temporary directing group strategy for streamlining the synthesis of complex organic molecules without any necessary pre-functionalization at the meta position has been explored. Site-selective C–H functionalization still faces some challenges, such as the introduction and removal of an appropriate directing group. Here, the authors introduce a temporary directing group for selective meta -C–H functionalization of 2-arylbenzaldehydes via reversible imine formation.

The emergence of visible light-mediated synthetic transformations has transpired as a promising approach to redefine traditional organic synthesis in a sustainable way. In this genre, transition metal-mediated photoredox catalysis has led the way and recreated a plethora of organic transformations. However, the use of photochemical energy solely to initiate the reaction is underexplored. With the direct utilization of photochemical energy herein, we have established a general and practical protocol for the synthesis of diversely functionalized organosilanols, silanediols, and polymeric siloxanol engaging a wide spectrum of hydrosilanes under ambient reaction conditions. Streamlined synthesis of bio-active silanols via late-stage functionalization underscores the importance of this sustainable protocol. Interestingly, this work also reveals photoinduced non-classical chlorine radical (Cl • ) generation from a readily available chlorinated solvent under aerobic conditions. The intriguing factors of the proposed mechanism involving chlorine and silyl radicals as intermediates were supported by a series of mechanistic investigations. Contrary to photocatalysis, the use of photochemical energy solely to initiate reactions is underexplored. Here, the authors demonstrate light initiated synthesis of functionalized organosilanols, silanediols, and polymeric siloxanol under ambient reaction conditions.

Facile conversion of CO 2 to commercially viable carbon feedstocks offer a unique way to adopt a net-zero carbon scenario. Synthetic CO 2 -reducing catalysts have rarely exhibited energy-efficient and selective CO 2 conversion. Here, the carbon monoxide dehydrogenase (CODH) enzyme blueprint is imitated by a molecular copper complex coordinated by redox-active ligands. This strategy has unveiled one of the rarest examples of synthetic molecular complex-driven reversible CO 2 reduction/CO oxidation catalysis under regulated conditions, a hallmark of natural enzymes. The inclusion of a proton-exchanging amine groups in the periphery of the copper complex provides the leeway to modulate the biases of catalysts toward CO 2 reduction and CO oxidation in organic and aqueous media. The detailed spectroelectrochemical analysis confirms the synchronous participation of copper and redox-active ligands along with the peripheral amines during this energy-efficient CO 2 reduction/CO oxidation . This finding can be vital in abating the carbon footprint-free in multiple industrial processes. An efficient CO 2 -to-CO conversion can provide a perfect leeway for transforming waste CO 2 into industrially viable CO. Here, the authors report a bio-inspired copper based synthetic catalyst that can convert CO 2 to CO with minimal energy penalty in both organic and aqueous media.

Biaryl scaffolds are privileged templates used in the discovery and design of therapeutics with high affinity and specificity for a broad range of protein targets. Biaryls are found in the structures of therapeutics, including antibiotics, anti-inflammatory, analgesic, neurological and antihypertensive drugs. However, existing synthetic routes to biphenyls rely on traditional coupling approaches that require both arenes to be prefunctionalized with halides or pseudohalides with the desired regiochemistry. Therefore, the coupling of drug fragments may be challenging via conventional approaches. As an attractive alternative, directed C−H activation has the potential to be a versatile tool to form para -substituted biphenyl motifs selectively. However, existing C–H arylation protocols are not suitable for drug entities as they are hindered by catalyst deactivation by polar and delicate functionalities present alongside the instability of macrocyclic intermediates required for para -C−H activation. To address this challenge, we have developed a robust catalytic system that displays unique efficacy towards para -arylation of highly functionalized substrates such as drug entities, giving access to structurally diversified biaryl scaffolds. This diversification process provides access to an expanded chemical space for further exploration in drug discovery. Further, the applicability of the transformation is realized through the synthesis of drug molecules bearing a biphenyl fragment. Computational and experimental mechanistic studies further provide insight into the catalytic cycle operative in this versatile C−H arylation protocol. Biaryls are privileged structural motif used in the discovery and design of therapeutics with high affinity and specificity for a broad range of protein targets. Herein, the authors develop a robust strategy for para-C–H arylation of arenes with a range of (het)aryl iodides, including bioactive molecules.

Dehydrogenation chemistry has long been established as a fundamental aspect of organic synthesis, commonly encountered in carbonyl compounds. Transition metal catalysis revolutionized it, with strategies like transfer-dehydrogenation, single electron transfer and C–H activation. These approaches, extended to multiple dehydrogenations, can lead to aromatization. Dehydrogenative transformations of aliphatic carboxylic acids pose challenges, yet engineered ligands and metal catalysis can initiate dehydrogenation via C–H activation, though outcomes vary based on substrate structures. Herein, we have developed a catalytic system enabling cyclohexane carboxylic acids to undergo multifold C–H activation to furnish olefinated arenes, bypassing lactone formation. This showcases unique reactivity in aliphatic carboxylic acids, involving tandem dehydrogenation-olefination-decarboxylation-aromatization sequences, validated by control experiments and key intermediate isolation. For cyclopentane carboxylic acids, reluctant to aromatization, the catalytic system facilitates controlled dehydrogenation, providing difunctionalized cyclopentenes through tandem dehydrogenation-olefination-decarboxylation-allylic acyloxylation sequences. This transformation expands carboxylic acids into diverse molecular entities with wide applications, underscoring its importance. Dehydrogenation chemistry can be used to generate units of unsaturation that can later be functionalized, as well as create aromaticity, which fundamentally alters the properties of molecules. Here the authors show methodologies to create multiple types of units of unsaturation from aliphatic cyclic carboxylic acids via palladium catalyzed decarboxylative multifold C–H activation.

In nature, enzymatic pathways generate C aryl −C(O) bonds in a site-selective fashion. Synthetically, C aryl −C(O) bonds are synthesised in organometallic reactions using prefunctionalized substrate materials. Electrophilic routes are largely limited to electron-rich systems, non-polar medium, and multiple product formations with a limited scope of general application. Herein we disclose a directed para -selective ketonisation technique of arenes, overriding electronic bias and structural congestion, in the presence of a polar protic solvent. The concept of hard–soft interaction along with in situ activation techniques is utilised to suppress the competitive routes. Mechanistic pathways are investigated both experimentally and computationally to establish the hypothesis. Synthetic utility of the protocol is highlighted in formal synthesis of drugs, drug cores, and bioactive molecules. Electrophilic acylation of arenes is largely limited to electron rich systems, non-polar medium and often displays moderate selectivity. Here, the authors show a directed para -selective ketonisation of arenes, overriding electronic bias and structural congestion, and apply it to the synthesis of bioactive compounds.

Regioselective distal C−H functionalization of nitroarenes by overriding proximal C−H activation has remained an unsolved challenge. Herein, we present a palladium-catalyzed meta -C−H alkenylation of nitroarene substrate, achieved through leveraging the non-covalent hydrogen bonding interactions. Urea-based templates comprising an elongated biphenyl linker designed in such a way that it interacts with nitro group via strong hydrogen bonding interaction, while a cyano based directing group is attached along the template to coordinate with the palladium center, thereby facilitating the activation of the remote meta -C−H bond of nitrobenzene. Computational mechanistic investigation and the analysis of non-covalent interaction deciphers the crucial role of H-bonding in regulating the regioselectivity. Regioselective distal C-H functionalization of nitroarenes by overriding proximal C-H activation has remained an unsolved challenge. Herein, the authors present a palladium-catalyzed meta-C-H alkenylation of nitroarene substrate, achieved through leveraging the noncovalent hydrogen bonding interactions.