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The Fujiwara-Moritani reaction has had a profound contribution in the emergence of contemporary C-H activation protocols. Despite the applicability of the traditional approach in different fields, the associated reactivity and regioselectivity issues had rendered it redundant. The revival of this exemplary reaction requires the development of a mechanistic paradigm that would have simultaneous control on both the reactivity and regioselectivity. Often, the high thermal energy required to promote olefination leads to multiple site functionalizations. To this aim, we established a photoredox catalytic system constituting a merger of palladium/organo-photocatalyst (PC) that forges oxidative olefination in an explicit regioselective fashion with diverse arenes and heteroarenes. Visible light plays a significant role in executing "regioresolved" Fujiwara-Moritani reactions without the requirement of silver salts and thermal energy. The catalytic system is also amenable toward proximal and distal olefination aided by the respective directing groups (DGs), which entails the versatility of the protocol in engaging the entire spectrum of C(sp

First ever catalyst-free electro-photochemical generation of carbene radical anion from aryl diazoester with direct application into synthesis of interesting N-heterocycles with broad substrate scope and excellent diastereo-selectivity.

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.

Transition metal catalyzed C-H activation has developed a contemporary approach to the omnipresent area of retrosynthetic disconnection. Scientific researchers have been tempted to take the help of this methodology to plan their synthetic discourses. This paradigm shift has helped in the development of industrial units as well, making the synthesis of natural products and pharmaceutical drugs step-economical. In the vast zone of C-H bond activation, the functionalization of proximal C-H bonds has gained utmost popularity. Unlike the activation of proximal C-H bonds, the distal C-H functionalization is more strenuous and requires distinctly specialized techniques. In this review, we have compiled various methods adopted to functionalize distal C-H bonds, mechanistic insights within each of these procedures, and the scope of the methodology. With this review, we give a complete overview of the expeditious progress the distal C-H activation has made in the field of synthetic organic chemistry while also highlighting its pitfalls, thus leaving the field open for further synthetic modifications.

Transition metal catalyzed C(sp3)–H functionalization is a rapidly growing field. Despite severe challenges, distal C–H functionalizations of aliphatic molecules by overriding proximal positions have witnessed tremendous progress. While usage of stoichiometric directing groups played a crucial role, reactions with catalytic transient directing groups or methods without any directing groups are gaining more attention due to their practicality. Various innovative strategies, slowly but steadily, circumvented issues related to remote functionalizations of aliphatic molecules. A systematic compilation has been presented here to provide insights into the recent developments and future challenges in the field. The Present perspective is expected to open up a new dimension and provide an avenue for deep insights into the distal C(sp3)–H functionalizations that could be applied routinely in various pharmaceutical and agrochemical industries.

Directed C-H functionalization has been realized as a complementary tool to the traditional approaches for a straightforward access of non-proteinogenic amino acids; albeit such a process is restricted mostly up to the γ-position. In the present work, we demonstrate the diversification [(hetero)arylation] of amino acids and analogous aliphatic amines selectively at the remote δ-position by tuning the reactivity controlled by ligands. An organopalladium δ-C(sp3)-H activated intermediate has been isolated and crystallographically characterized. Mechanistic investigations carried out experimentally in conjunction with computational studies shed light on the difference in the mechanistic picture depending on the substrate structure.

Transition metal catalyzed C(sp3)–H functionalization is a rapidly growing field. Despite severe challenges, distal C–H functionalizations of aliphatic molecules by overriding proximal positions have witnessed tremendous progress. While usage of stoichiometric directing groups played a crucial role, reactions with catalytic transient directing groups or methods without any directing groups are gaining more attention due to their practicality. Various innovative strategies, slowly but steadily, circumvented issues related to remote functionalizations of aliphatic molecules. A systematic compilation has been presented here to provide insights into the recent developments and future challenges in the field. The Present perspective is expected to open up a new dimension and provide an avenue for deep insights into the distal C(sp3)–H functionalizations that could be applied routinely in various pharmaceutical and agrochemical industries., Transition metal catalyzed C(sp3)–H functionalization is a rapidly growing field.

Directed C-H functionalization has been realized as a complimentary technique to achieve borylation at a distal position of aliphatic amines. Here, we demonstrated the oxidative borylation at the distal δ-position of aliphatic amines using various borylating agents, a palladium catalyst, and a rightly tuned ligand in the presence of a cheap oxidant. Moreover, an organopalladium δ-C(sp

The Fujiwara-Moritani reaction has had a profound contribution in the emergence of contemporary C-H activation protocols. Despite the applicability of the traditional approach in different fields, the associated reactivity and regioselectivity issues had rendered it redundant. The revival of this exemplary reaction requires the development of a mechanistic paradigm that would have simultaneous control on both the reactivity and regioselectivity. Often high thermal energy required to promote olefination leads to multiple site functionalization. To this aim we established a photoredoxcatalytic system constituting a merger of palladium/organo-photocatalyst that forges oxidative olefination in an explicit regioselective fashion of diverse arenes and heteroarenes. Visible light plays a significant role in executing ‘regio-resolved’ Fuijiwara-Moritani reaction without the requirement of silver salts and thermal energy. The catalytic system is also amenable towards proximal and distal olefination aided by respective directing groups (DGs), which entails the versatility of the protocol in engaging the entire spectrum of C(sp2)-H olefination. Furthermore, streamlining the synthesis of natural products, chiral molecules, drugs and diversification through late-stage functionalizations underscore the importance of this sustainable protocol. The photoinduced attainment of this regioselective transformation is mechanistically established through control reactions, kinetic studies and theoretical calculations.

A Pd(II)-catalyzed highly regioselective γ-chalcogenation, thioarylation, and selenoarylation of aliphatic carboxylic acids has been demonstrated. The present protocol provides a direct access to make structural modifications of α-amino acids such as valine, isoleucine, and tert-leucine with high diastereoselectivity (up to 52:1). Sequential heterobifunctionalizations have been carried out at γ-sp3 C–Hs, resulting in desymmetrization of quaternary centers. The applicative potential of the chalcogenated products was exhibited by using them as precursors for the synthesis of the biologically relevant benzothiepinone moiety. Preliminary studies were carried out to gain insights into the mechanism.

A Pd(II)-catalyzed protocol for highly regioselective distal γ-C–H silylation and germanylation of aliphatic carboxylic acids is reported. Bidentate 8-aminoquinoline as the directing group was found to stabilize the six-membered palladacycle. A variety of aliphatic carboxylic acids and amino acids were silylated and germanylated in good yields and high diasteroselectivities. Detailed mechanistic studies involving isolation of a Pd(II) intermediate, determination of the reaction rate and order, control experiments, and isotopic labeling and DFT studies were found to be crucial for elucidating the elementary steps involved in this distal aliphatic functionalization.

The late-stage functionalization (LSF) of pharmaceutical and agrochemical compounds by the site-selective activation of C-H bonds provides access to diverse structural analogs and expands synthetically-accessible chemical space. We report a C-H functionalization LSF strategy that hinges on the use of an alkyne linchpin to assemble conjugates of sp

The late-stage functionalization (LSF) of pharmaceutical and agrochemical compounds by the site-selective activation of C-H bonds offers immediate access to diverse structural analogs and expands the accessible chemical space. We report an C-H functionalization LSF strategy that hinges on the use of an alkyne linchpin to assemble conjugates of sp2-rich marketed pharmaceuticals and agrochemicals with sp3-rich 3D-fragments and natural products. This is accomplished through a template-assisted inverse Sonogashira reaction that displays high levels of selectivity for the meta-position. This protocol is also amenable to distal structural modifications of a-amino acids. The transformation of alkyne functionality to other functional groups further highlights the applicative potential. Computational and experimental mechanistic studies shed light on the detailed mechanism. Turnover-limiting 1,2-migratory insertion of the bromoalkyne coupling partner occurs after relatively fast C-H activation. While this insertion occurs unselectively, regioconvergence results from one of the adducts undergoing a 1,2-trialkylsilyl migration to form the alkynylated product. A heterobimetallic Pd–Ag TS, which is essential for product formation, is explicitly implicated in the β-bromide elimination step.

A palladium(II)-catalyzed protocol for the highly regioselective remote γ-C–H arylation of aliphatic carboxylic acid has been disclosed. The 8-aminoquinoline moiety as an intramolecular bidentate chelator was found to be suitable for this γ-C–H arylation. Various aryl iodides successfully produced the regioselectively mono-arylated products with negligible diarylation. Functional group tolerance and easy-to-handle reaction conditions make this method attractive.

Directed C-H functionalization has been realized as a complementary tool to the traditional approaches for a straightforward access of non-proteinogenic amino acids; albeit such a process is restricted mostly up to the γ-position. In the present work, we demonstrate the diverse (hetero)arylation of amino acids and analogous aliphatic amines selectively at the remote δ-position by tuning the reactivity controlled by ligands. An organopalladium δ-C(sp

Enzymes are most efficient catalyst for organic transformations including halogenation of C–H bonds. Most of the halogenating enzymes utilize high valent metal-oxo intermediates for hydrogen atom abstraction (HAA) and subsequent haloalkane formation. Due to high demand of organohalide compounds, many attempts have been made to mimic the active sites of halogenating enzymes in order to achieve efficacy of enzymes. Different first row transition metals complexes have been synthesized using various ligand systems. In this review, we have summarized the efforts made towards development of halogenation using high valent metal-oxo complexes and understanding the mechanism of their activity.

A Cu-catalyzed synthesis of indoloquinoxalin-6-one has been developed that starts from o-indolyl-N,N-dialkylamines through sp3 C–H bond oxidation α to the nitrogen atom with di-tert-butyl peroxide as oxidant. Other heterocycles, such as pyrrole, imidazole and benzimidazole derivatives also reacted successfully to give their respective fused quinoxalin-6-one derivatives. In this process, one of the methyl groups is transformed into a carbonyl group.

The higher propensity of C-N over C-S bond forming ability was demonstrated, through formal C-H functionalization during the construction of 4,5-disubstituted 1,2,4-triazole-3-thiones from arylidenearylthiosemicarbazides catalyzed by Cu(II). However, steric factors imparted by the o-disubstituted substrates tend to change the reaction path giving thiodiazole as the major or an exclusive product. Upon prolonging the reaction time, the in situ generated thiones are transformed to 4,5-disubstituted 1,2,4-triazoles via a desulfurization process. Two classes of heterocycles viz. 4,5-disubstituted 1,2,4-triazole-3-thiones and 4,5-disubstituted 1,2,4-triazoles can be synthesized from arylidenearylthiosemicarbazides by simply adjusting the reaction time. Desulfurization of 1,2,4-triazole-3-thiones is assisted by thiophilic Cu to provide 1,2,4-triazoles with concomitant formation of CuS and polynuclear sulfur anions as confirmed from scanning electron microscope and energy dispersive X-ray spectroscopy measurements. A one-pot synthesis of an antimicrobial compound has been successfully achieved following this strategy.

A regioselective cross-dehydrogenative coupling between electron-deficient N-heterocycles (isoquinoline, quinolines, and quinoxalines) and methylbenzenes leading to regiospecific C-aroylation has been accomplished using AlCl3 as the catalyst in the presence of oxidant TBHP. This protocol is a practical alternative to the classical Minisci reaction.

An efficient copper‐catalyzed protocol has been developed for the synthesis of carbamates from dialkylformamides and phenols possessing directing groups such as benzothiazole, quinoline and formyl at the ortho‐position. In this chelation assisted approach, C-O bond formation takes place via a Cross Dehydrogenative Coupling (CDC) between the formyl C-H of dialkylformamide and phenolic O-H in the presence of copper(II)acetate/aqueous tert‐butyl hydroperoxide. Under identical reaction conditions, salicylic acid derivatives underwent amidation with the carboxylic group rather than formamidation of the phenolic OH. The use of a cheap and environmentally benign catalyst along with the tolerance of a wide range of functional groups makes this an easy, phosgene‐free route to carbamates.

An oxidative cross-coupling between directing substrates and benzyl bromides via the combined effect of oxidants TBHP and NMO, catalysed by Pd(II) has been investigated. Benzyl bromides served as efficient aroyl surrogates in this substrate directed C–H functionalisation. The in situ generated benzaldehyde originating from benzyl bromide is the active aroylating source.

A unique copper-catalyzed cross-dehydro- genative coupling (CDC) of thiols and alkylbenzenes has been developed for the synthesis of thioesters without the assistance of any directing group. A thio- ester moiety is created via successive CS and CO bond formation at the expense of three sp 3 CH bonds of the alkylbenzene and one sp 3 SH bond of the thiol.

An acyl moiety generated from a-oxocar- boxylic acids via decarboxylation undergoes a palladi- um-catalyzed chemoselective insertion into organic cyanamides to afford N-monosubstituted a-keto- A

A copper-catalyzed cross-dehydrogenative coupling strategy has been developed for the synthesis of two classes of esters from simple solvents. The reaction of methylarenes with cyclic ethers resulted in α-acyloxy ethers involving four sp(3) C-H cleavages, while treatment of methylarenes with cycloalkanes led to the formation of allyl esters at the expense of six consecutive sp(3) C-H bonds.

A variety of styrenes and phenylacetylenes serve as excellent arylcarboxy sources in bringing about substrate directed o-benzoxylation of 2-phenylpyridine derivatives catalyzed by Cu(II) in the presence of TBHP. This reaction proceeds via formation of phenylglyoxal followed by decarbonylation to benzoyl radical/benzaldehyde which acts as the arylcarboxy source.

A Cu(I)-catalysed synthesis of substituted 3-methyleneisoindolin-1-ones using alkynyl acids as an alkyne source has been developed. The reaction involves the decarboxylative cross-coupling of 2-halobenzamides with aryl alkynyl acids, followed by 5-exo-dig heteroannulation. While reactions of 2-iodo benzamides proceeded without a ligand, for 2-bromo substrates, the assistance of a ligand is essential.

Different reactivities and selectivities of Cu and Pd catalysts have been demonstrated in the reactions of benzylamines with 2-phenylpyridines. Although Pd is reported to give o-arylation (ArCO–), Cu introduces an arylcarboxy group (ArCOO–) at the proximal site of the directing group. For the first time benzylamine has been utilised as a synthetic equivalent of an arylcarboxy group.

An efficient metal free oxidative esterification of sp(3) C-H bonds (adjacent to an oxygen atom) in simple solvents like 1,4-dioxane, tetrahydropyran, tetrahydrofuran and ethyl acetate has been achieved using terminal aryl alkenes and alkynes as the ArCOO(-) sources.

An efficient Cu(I)-catalyzed synthesis of 3-aroylindoles has been achieved from o-alkynylated N,N-dimethylamines via a sp(3) C-H bond activation α to the nitrogen atom followed by an intramolecular nucleophilic attack with the alkyne using an aqueous solution of tert-butyl hydroperoxide (TBHP) as the oxidant. In this tandem catalytic synthesis of 3-aroylindoles both C-C and C-O bonds are installed at the expense of two sp(3) C-H bond cleavages.

An efficient protocol has been developed for the direct ortho-hydroxylation of 2-arylbenzothiazole using Pd(OAc)2 as the catalyst and either of DIB/AcOH or Oxone®/TFA combinations under air atmosphere. Under both these conditions, the methodology tolerates a diverse array of substituents giving good to excellent yields of corresponding ortho-hydroxylated products. Regioselective hydroxylation is observed at the less sterically hindered site of the phenyl ring possessing substituents at its meta position.

An efficient protocol for the ortho-aroylation of 2-arylbenzothiazoles and 2-arylbenzoxazoles has been developed using aldehydes as the aroyl source. This Pd-catalyzed substrate-directed sp2-hybridized C–H bond functionalization occurs in the presence of the oxidant tert-butyl hydroperoxide. A variety of functional groups on the 2-arylbenzothiazoles, 2-arylbenzoxazoles, and aldehydes are tolerated under the reaction conditions. Regioselective aroylation at the less hindered ortho position was observed for meta-substituted 2-arylbenzothiazoles.

Oxidative C-O bond formation via sp(3) C-H functionalisation represents an attractive approach for the synthesis of esters. This review focuses on the recent advances of sp(3) C-H bond functionalisation strategies for ester synthesis from unconventional precursors using transition metal/metal free catalysts in combination with various oxidants. Various classes of esters and the mechanisms of their formation are discussed with numerous examples.

A Cu-catalyzed synthesis of indoloquinoxalin-6-ones is developed, starting from o-indolyl-N,N-dialkylamines through sp3 C—H bond oxidation in the α-position to the nitrogen atom with di-tert-butyl peroxide as oxidant.

An unprecedented aroylation at the ortho C-H bond with respect to a directing group has been accomplished via a Pd(II)-catalyzed cross dehydrogenative coupling approach using alkylbenzene as the synthetic equivalent of an aroyl moiety. The reaction proceeds through sequential C-C and C-O bond making at the expense of four consecutive C-H bond cleavages (three sp(3) benzylic C-H's and one sp(2) arene C-H) to selectively install an aroyl functionality at the proximal site of substrates containing various directing groups.

A tandem and convergent approach to var- ious N-, O-, or S-containing azoles has been devel- oped by exploiting the thiophilic property of cop- per(I) iodide used in a catalytic quantity. The present protocol gives access to amino-substituted tetrazoles, triazoles, oxadiazoles and thiadiazoles via oxidative desulfurization of their respective precursors fol- lowed by inter- or intramolecular attack of suitable nucleophiles. For aminotetrazoles and triazoles an excellent regioselectivity has been achieved through proper tuning of the pKa values of the parent amines attached to unsymmetrical thioureas. The method represents an autocatalytic process in which cop- per(I) iodide gets converted to copper(II) sulfide which in turn transforms to active copper(II) oxide that effectively carries forward the catalytic cycle. The fate of the copper catalyst has also been studied using scanning electron microscopic (SEM) and energy-dispersive X-ray spectroscopic (EDS) analy- ses which give an insight into the mechanism for this catalytic process.

Copper(II) as the catalyst in a cross dehydrogenative coupling (CDC) reaction has been demonstrated for the synthesis of benzylic esters using aldehydes and alkylbenzenes as coupling partners.

A tandem regioselective one-pot synthesis of 3-amino-[1,2,4]-triazoles has been achieved from 1,3-disubstituted thioureas using molecular iodine. In this one-pot strategy, the intermediate carbodiimide generated in situ from thiourea upon reaction with HCONHNH2 gives diaryl/alkylhydrazinecarboximidamide or acylureidrazone, which then undergoes an intramolecular cyclodehydration to afford the corresponding 3-amino-[1,2,4]-triazole. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas correlate well with the pKas of the parent amines attached, in which the amine having higher pKa goes to the ring nitrogen while the other nitrogen remains flanked as an exocyclic nitrogen of the triazole core. This method is milder and environmentally sustainable giving good to excellent yields of the desired products.

A direct access to symmetrical and unsymmetrical 2,5-disubstituted [1,3,4]-oxadiazoles has been accomplished through an imine C-H functionalization of N-arylidenearoylhydrazide using a catalytic quantity of Cu(OTf)(2). This is the first example of amidic oxygen functioning as a nucleophile in a Cu-catalyzed oxidative coupling of an imine C-H bond. These reactions can be performed in air atmosphere and moisture making it exceptionally practical for application in organic synthesis.

We have developed a ligand-assisted copper(I)-catalyzed two sequential heteroarylation sequence. An intramolecular S-arylation is followed by an intermolecular N-arylation leading to the direct synthesis of N-aryl-2-aminobenzothiazoles. In most cases however, the 2-arylsulfanyl-arylcyanamide was the major product obtained via an intramolecular C―S bond formation, associated with C―S bond breakage, followed by an intermolecular S-arylation. The selectivity of this ligand-assisted reaction is quite different as compared to that of ligand-free reactions and the rates are much faster giving good yields of products. Various cyanamides can be prepared in excellent yields from their corresponding 1-substituted thioureas with or without the assistance of a ligand with a catalytic quantity of copper(I).

Either 1,2,4-triazole-thiones or 1,2,4-triazoles are efficiently obtained from arylidenearylthiosemicarbazides by simple tuning of the reaction time.

A regioselective cross-dehydrogenative coupling between electron-deficient N-heterocycles (isoquinoline, quinolines, and quinoxalines) and methylbenzenes leading to regiospecific C–aroylation has been accomplished using AlCl3 as the catalyst in the presence of oxidant TBHP. This protocol is a practical alternative to the classical Minisci reaction.