Ligand-enabled cross-coupling of C(sp3)-H bonds with arylboron reagents via Pd(II)/Pd(0) catalysis

Ligand-Enabled Palladium(II)-Catalyzed γ-C(sp3)-H Arylation of Primary Aliphatic Amines

The Pd(II)/sulfoxide-2-hydroxypyridine catalytic system shows promising activity in C-H activation chemistry. In this study, we showcase how this catalytic system solves the problem of native primary amine-directed γ-C(sp3)-H arylation. Primary amines with different complexities are compatible with the established methodology, and the range of applicable substrates can be expanded to include pyridine, oxime ether, and pyridine N-oxide.

The Development of Aldehyde Catalytic System

Aldehyde catalysts have proven to be highly effective in facilitating and accelerating a wide range of challenging transformations in organic chemistry. This article is structured into three main sections, focusing on the utilization of aldehydes as organocatalysts, the aldehydes/transition metals catalytic systems, and photochemical initiators. Finally, we provide a concise summary of the advancements in this fascinating research field, offering our perspectives and insights.

A recyclable stereoauxiliary aminocatalyzed strategy for one-pot synthesis of indolizine-2-carbaldehydes

Indolizine-carbaldehydes with the easily modifiable carbaldehyde group are important synthetic targets as versatile precursors for distinct indolizines. However, the efficient one-pot construction of trisubstituted indolizine-2-carbaldehydes represents a long-standing challenge. Herein, we report an unprecedented recyclable stereoauxiliary aminocatalytic approach via aminosugars derived from biomass, which enable the efficient one-pot synthesis of desired trisubstituted indolizine-2-carbaldehydes via [3+2] annulations of acyl pyridines and α,β-unsaturated aldehyde. Compared to the steric shielding effect from α-anomer, a stereoauxiliary effect favored by β-anomer of D-glucosamine is supported by control experiments. Furthermore, polymeric chitosan containing predominantly β-D-anhydroglucosamine units also shows excellent catalytic performance in aqueous solutions for the conversion of various substrates, large-scale synthesis and catalytic cycling experiments. Thus, our approach advances the existing methodologies by providing a rich library of indolizine-2-aldehydes. In addition, it delivers an efficient protocol for a set of late-stage diversification and targeted modifications of bioactive molecules or drugs, as showcased with 1,2,3-trisubstituted indolizine-2-carbaldehydes.

A new transient directing group diethoxyethyl-L-proline facilitates ortho-arylation of aryl-amines/-amino acids via Pd-catalyzed C(sp2)-H activation

Mono-ortho-arylated arylamines are constituents of various natural products but their syntheses are challenging. This report describes a new synthetic methodology for the ortho-arylation of arylamines and α-aromatic amino acids (phenylglycine and phenylalanine) through a Pd-catalyzed C(sp²)-H activation using the synthetic transient directing group diethoxyethyl-L-proline (DEP). A catalytic amount of diethoxyethyl-L-proline is sufficient to form mono-arylated arylamines as the major products using aryliodides. This method could be useful for the synthesis of various biphenyl amines and novel peptidomimetics.

Ligand-Enabled Sequential C(sp3)-H and C(sp2)-H Diolefination Reaction via Palladium Catalyst

Palladium-catalyzed sequential C(sp³)-H and C(sp²)-H bond diolefination reaction of o-toluidine has been realized for the first time using acetyl-protected aminoethyl phenyl thioether ligands. This novel reaction allows for preparation of the conjugated diene structure via an immediate second olefination on the basis of the first C(sp³)-H olefination in one pot. Various triflyl-protected anilines and acrylates were used as coupling partners elegantly. Furthermore, the unpurified diolefination products can be easily converted to tetrahydroquinoline derivatives.

Pd(II)-Catalyzed Enantioselective C(sp3)-H Arylation of Cyclopropanes and Cyclobutanes Guided by Tertiary Alkylamines

Strained aminomethyl-cycloalkanes are a recurrent scaffold in medicinal chemistry due to their unique structural features that give rise to a range of biological properties. Here, we report a palladium-catalyzed enantioselective C(sp³)-H arylation of aminomethyl-cyclopropanes and -cyclobutanes with aryl boronic acids. A range of native tertiary alkylamine groups are able to direct C-H cleavage and forge carbon-aryl bonds on the strained cycloalkanes framework as single diastereomers and with excellent enantiomeric ratios. Central to the success of this strategy is the use of a simple N-acetyl amino acid ligand, which not only controls the enantioselectivity but also promotes γ-C-H activation of over other pathways. Computational analysis of the cyclopalladation step provides an understanding of how enantioselective C-H cleavage occurs and revealed distinct transition structures to our previous work on enantioselective desymmetrization of N-isobutyl tertiary alkylamines. This straightforward and operationally simple method simplifies the construction of functionalized aminomethyl-strained cycloalkanes, which we believe will find widespread use in academic and industrial settings relating to the synthesis of biologically active small molecules.

Diastereoselective palladium-catalyzed functionalization of prochiral C(sp3)-H bonds of aliphatic and alicyclic compounds

We highlight the reported developments of the palladium-catalyzed C-H activation and functionalization of the inactive/unreactive prochiral C(sp³)-H bonds of aliphatic and alicyclic compounds. There exist numerous classical methods for generating contiguous stereogenic centers in a compound with a high degree of stereocontrol. Along similar lines, the Pd(II)-catalyzed, directing group-aided functionalization of inactive prochiral/diastereotopic C(sp³)-H bonds have been exploited to accomplish the stereoselective construction of stereo-arrays in organic compounds. We present a concise discussion on how specific strategies consisting of Pd(II)-catalyzed, directing group-aided C(sp³)-H functionalization have been utilized to generate two or more stereogenic centers in aliphatic and alicyclic compounds.

Theoretical Investigate of the α-Substitution Effect on γ-C(sp3)−H Arylation of Amines: Structure-Reactivity Relationship (SRR) Studies

Structure-reactivity relationship (SRR) studies to understand the α-substitution effect toward Pd-catalyzed γ-C(sp3)−H arylation enabled by catalytic transient directing groups have carefully been performed by DFT calculations. Selected transient directing groups...

Transition-Metal-Catalyzed, Coordination-Assisted Functionalization of Nonactivated C(sp3)-H Bonds

Transition-metal-catalyzed, coordination-assisted C(sp³)-H functionalization has revolutionized synthetic planning over the past few decades as the use of these directing groups has allowed for increased access to many strategic positions in organic molecules. Nonetheless, several challenges remain preeminent, such as the requirement for high temperatures, the difficulty in removing or converting directing groups, and, although many metals provide some reactivity, the difficulty in employing metals outside of palladium. This review aims to give a comprehensive overview of coordination-assisted, transition-metal-catalyzed, direct functionalization of nonactivated C(sp³)-H bonds by covering the literature since 2004 in order to demonstrate the current state-of-the-art methods as well as the current limitations. For clarity, this review has been divided into nine sections by the transition metal catalyst with subdivisions by the type of bond formation. Synthetic applications and reaction mechanism are discussed where appropriate.

Progress and perspectives on directing group-assisted palladium-catalysed C-H functionalisation of amino acids and peptides

Peptide modifications can unlock a variety of compounds with structural diversity and abundant biological activity. In nature, peptide modifications, such as functionalisation at the side-chain position of amino acids, are performed using post-translational modification enzymes or incorporation of unnatural amino acids. However, accessing these modifications remains a challenge for organic chemists. During the past decades, selective C-H activation/functionalisation has attracted considerable attention in synthetic organic chemistry as a pathway to peptide modification. Various directing group strategies have been discovered that assist selective C-H activation. In particular, bidentate directing groups that enable tuneable and reversible coordination are now recognised as one of the most efficient methods for the site-selective C-H activation and functionalisation of numerous families of organic compounds. Synthetic peptide chemists have harnessed bidentate directing group strategies for selective functionalisation of the β- and γ-positions of amino acids. This method has been expanded and recognised as an effective device for the late stage macrocyclisation and total synthesis of complex peptide natural products. In this review, we discuss various β-, γ-, and δ-C(sp³)-H bond functionalisation reactions of amino acids for the formation of C-X bonds with the aid of directing groups and their application in late-stage macrocyclisation and the total synthesis of complex peptide natural products.

Ligand-Enabled δ-C(sp3 )-H Borylation of Aliphatic Amines

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(sp³ )-H-activated intermediate has been isolated and crystallographically characterized to get mechanistic insight.

Assembly of Tetrahydroquinolines and 2-Benzazepines by Pd-Catalyzed Cycloadditions Involving the Activation of C(sp3)-H Bonds

Cycloaddition reactions are among the most practical strategies to assemble cyclic products; however, they usually require the presence of reactive functional groups in the reactants. Here, we report a palladium-catalyzed formal (4 + 2) cycloaddition that involves the activation of C(sp³)–H bonds and provides a direct, unconventional entry to tetrahydroquinoline skeletons. The reaction utilizes amidotolyl precursors and allenes as annulation partners, and is catalyzed by Pd(II) precursors in combination with specific N-acetylated amino acid ligands. The reactivity can be extended to ortho-methyl benzylamides, which provide for the assembly of appealing tetrahydro-2-benzazepines in a formal (5 + 2) annulation process.

Direct C4-Acetoxylation of Tryptophan and Tryptophan-Containing Peptides via Palladium(II)-Catalyzed C-H Activation

An efficient regioselective palladium(II)-catalyzed C(sp2)-H 4-acetoxylation of tryptophan and tryptophan-containing peptides is described. This transformation achieves the direct construction of C-O bonds at the tryptophan C4-position and features good functional group tolerance. The 4-hydroxyl compound was obtained by removing acetyl after C4-acetoxylation of tryptophan derivatives and tryptophan-containing dipeptides. This method provides a novel strategy for the synthesis of 4-substituted tryptophan derivatives and modification of tryptophan-containing peptides.

Transition-Metal-Free α Csp3 -H Cyanation of Sulfonamides

This report describes the site-selective α-functionalization of sulfonylamide derivatives through the in-situ generation of imine intermediates. The N-F sulfonylamides, which could facilitate the elimination to generate imines, are coupled with TBACN to efficiently and mildly afford α-amino cyanides. Comparing with Strecker reaction, this transformation offers a complementary strategy to efficiently construct α-amino cyanides from direct α C-H functionalization of sulfonylamindes. The reaction is also characterized by broad substrate scope and flash chromatography column free workup. More importantly, the new two-electron pathway to generate imines through manipulation of the leaving group allows us to achieve excellent α site-selectivity.

Transition-Metal-Catalyzed C–H Arylation Using Organoboron Reagents

Aryl rings are ubiquitous in the core of numerous natural product and industrially important molecules and thus their facile synthesis is of major interest in the scientific community and industry. Although multiple strategies enable access to these skeletons, metal-catalyzed C–H activation is promising due to its remarkable efficiency. Commercially available organoboron reagents, a prominent arylating partner in the cross-coupling domain, have also been utilized for direct arylation. Organoborons are bench-stable, inexpensive, and readily available coupling partners that promise regioselectivity, chemodivergence, cost-efficiency, and atom-economy without requiring harsh and forcing conditions. This critical, short review presents a summary of all major studies of arylation using organoborons in transition-metal catalysis since 2005.

1 Introduction

2 Arylation without Directing Group Assistance

2.1 Palladium Catalysis

2.2 Iron Catalysis

2.3 Gold Catalysis

3 Arylation with Directing Group Assistance

3.1 Palladium Catalysis

3.2 Ruthenium Catalysis

3.3 Rhodium Catalysis

3.4 Nickel Catalysis

3.5 Cobalt Catalysis

3.6 Copper Catalysis

4 Conclusion

Palladium-catalyzed functionalizations of acidic and non-acidic C(sp3)-H bonds - recent advances

A tremendous upsurge has been seen in the recent decade for the proximal and remote functionalization of activated and unactivated substrates via palladium redox pathways. This feature article discusses some of the recent reports on direct as well as indirect C(sp3)-H functionalization via cross-coupling reactions under palladium catalysis. Activated substrates (possessing acidic C(sp3)-H) including enones, ketones, aldehydes, silylenol ethers, esters, silyl ketene acetals, amides, cyano, α-amino esters, and O-carbamates, capable of undergoing cross-coupling reactions at the α-, β-, γ-, δ- and ε-positions, will be discussed. To overcome the challenging task of achieving regioselectivity, a variety of innovative modifications have been reported. The reports of C-H activations based on directing group, and as native functionality have been illustrated at the β-, γ- and δ-positions. Substrates such as α-amino esters, carbonyls, carboxylic acids and their derivatives, afford site-selective C(sp3)-H functionalization via varied-sized reactive metallacycles and are a unique class of substrates whose C(sp3)-H functionalizations were earlier considered as very difficult.

Intramolecular Oxidative Coupling between Unactivated Aliphatic C-H and Aryl C-H Bonds

Direct oxidative coupling of different inert C-H bonds is the most straightforward and environmentally benign method to construct C-C bonds. In this paper, we developed a Pd-catalyzed intramolecular oxidative coupling between unactivated aliphatic and aryl C-H bonds. This chemistry showed great potential to build up fused cyclic scaffolds from linear substrates through oxidative couplings. Privileged chromane and tetralin scaffolds were constructed from readily available linear starting materials in the absence of any organohalides and organometallic partners.

Site-selective and diastereoselective functionalization of α-amino acid and peptide derivatives via palladium-catalyzed sp3 C–H activation

This review introduces palladium-catalyzed C–H functionalization of amino acids and peptides.

Tailored quinones support high-turnover Pd catalysts for oxidative C-H arylation with O2

Palladium(II)-catalyzed carbon-hydrogen (C-H) oxidation reactions could streamline the synthesis of pharmaceuticals, agrochemicals, and other complex organic molecules. Existing methods, however, commonly exhibit poor catalyst performance with high palladium (Pd) loading (e.g., 10 mole %) and a need for (super)stoichiometric quantities of undesirable oxidants, such as benzoquinone and silver(I) salts. The present study probes the mechanism of a representative Pd-catalyzed oxidative C-H arylation reaction and elucidates mechanistic features that undermine catalyst performance, including substrate-consuming side reactions and sequestration of the catalyst as an inactive species. Systematic tuning of the quinone cocatalyst overcomes these deleterious features. Use of 2,5-di-tert-butyl-p-benzoquinone enables efficient use of molecular oxygen as the oxidant, high reaction yields, and >1900 turnovers by the Pd catalyst.

Thioether Ligand-Enabled Cationic Palladium(II)-Catalyzed Electrophilic C-H Arylation of α,β-Unsaturated Oxime Ethers

The use of the cationic palladium(II) catalyst realized electrophilic C-H arylation of α,β-unsaturated O-SEM oximes with arylboronic acids. This Pd-catalyzed electrophilic C-H arylation is facilitated by employing alkyl aryl thioether ligands, and optimization of the ligand structure greatly improves the yield. The resulting α,β-unsaturated oximes would provide access to multisubstituted heterocyclic compounds.

Diverse strategies for transition metal catalyzed distal C(sp3)-H functionalizations

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.

Rh(III)-Catalyzed C(sp3)-H Acetoxylation of 8-Methylquinolines

A mild and efficient Rh(III)-catalyzed aliphatic C-H acetoxylation directed by quinolines has been developed with widespread functional groups, including various halogens, which usually can provide precursors for further organic synthesis but easily results in selectivity issues in the Pd- and Ni-catalyzed reaction. Interestingly, Ac₂O plays an essential role in promoting the transformation.

Pd(II)-Catalyzed Enantioselective γ-C(sp3)-H Functionalizations of Free Cyclopropylmethylamines

Prized for their ability to reliably forge stereocenters with precise regiocontrol from simple and abundant starting materials, substrate-directable enantioselective reactions are widely used in modern organic synthesis. As such, enantioselective C(sp3)-H functionalization reactions directed by innate functional groups could provide new routes to introduce molecular complexity within the inert hydrocarbon moiety, but to date this approach has been met with little success. While free primary aliphatic amines are common, versatile intermediates in synthesis, they are traditionally unreactive in C(sp3)-H activation reactions. Herein we report the Pd-catalyzed enantioselective C(sp3)-H functionalization of free aliphatic amines (cyclopropylmethylamines) enabled by a chiral bidentate thioether ligand. This ligand's privileged bidentate coordination mode and thioether motif favor the generation of the requisite mono(amine)-Pd(II) intermediate, thus enabling the enantioselective C-H activation of free amines. The resulting C-Pd(II) species could engage in either Pd(II)/Pd(IV) or Pd(II)/Pd(0) catalytic cycles, enabling access to a diverse range of products through (hetero)arylation, carbonylation, and olefination reactions. Consequently, this versatile reactivity offers medicinal chemists a general strategy to rapidly prepare and functionalize biologically relevant amines.

Design and biological evaluation of novel HIV-1 protease inhibitors with isopropanol as P1' ligand to enhance binding with S1' subsite

Newly designed HIV-1 protease inhibitors that maximize interactions with the protein backbone, especially in the form of hydrogen bonds, may enhance the antiviral potency of these compounds and minimize acquisition of drug-resistant mutations. Herein, we described a series of new HIV-1 PIs containing phenols as the P2 ligands and chiral isopropanol as the P1' ligands, in combination with 4-trifluoromethylphenylsulfonamide or 4-nitrophenylsulfonamide as the P2' ligands. And most of these compounds exhibited nanomolar inhibitory potency. In particular, inhibitors 13c and 13e with 4-trifluoromethylphenylsulfonamide as the P2' ligand and (R) - isopropanol as the P1' ligand, exhibited antiviral IC₅₀ values of 1.64 nM and 2.33 nM, respectively. Furthermore, they also showed remarkable activity against wild-type and DRV-resistant HIV-1 variants that raised the prospect of designing more effective PIs further.

Pd(II)-Catalyzed Direct γ-C(sp3)-H Arylation between Free β2-Amino Esters and β3-Amino Esters and Aryl Iodides Using a Catalytic Transient Directing Group

Pd(II)-catalyzed direct γ-C(sp³)-H arylation coupling with free β²-amino esters and β³-amino esters using a commercially available catalytic transient directing group has been developed. This approach features high efficiency, broad substrate tolerance, easily accessible starting materials, and mild reaction conditions.

Palladium-Catalyzed Oxidation of β-C(sp3)-H Bonds of Primary Alkylamines through a Rare Four-Membered Palladacycle Intermediate

Site-selective functionalizations of C-H bonds are often achieved with a directing group that leads to five- or six-membered metallacyclic intermediates. Analogous reactions that occur through four-membered metallacycles are rare. We report a challenging palladium-catalyzed oxidation of primary C-H bonds β to nitrogen in an imine of an aliphatic amine, a process that occurs through a four-membered palladacyclc intermediate. The success of the reaction relies on the identification, by H/D exchange, of a simple directing group (salicylaldehyde) capable of inducing the formation of this small ring. To gain insight into the steps of the catalytic cycle of this unusual oxidation reaction, a series of mechanistic experiments and density functional theory (DFT) calculations were conducted. The experimental studies showed that cleavage of the C-H bond is rate-limiting and formation of the strained four-membered palladacycle is thermodynamically uphill. DFT calculations corroborated these conclusions and suggested that the presence of an intramolecular hydrogen bond between the oxygen of the directing group and hydroxyl group of the ligating acetic acid is crucial for stabilization of the palladacyclic intermediate.

From Pd(OAc)2 to Chiral Catalysts: The Discovery and Development of Bifunctional Mono-N-Protected Amino Acid Ligands for Diverse C-H Functionalization Reactions

The functionalization of unactivated carbon-hydrogen bonds is a transformative strategy for the rapid construction of molecular complexity given the ubiquitous presence of C-H bonds in organic molecules. It represents a powerful tool for accelerating the synthesis of natural products and bioactive compounds while reducing the environmental and economic costs of synthesis. At the same time, the ubiquity and strength of C-H bonds also present major challenges toward the realization of transformations that are both highly selective and efficient. The development of practical C-H functionalization reactions has thus remained a compelling yet elusive goal in organic chemistry for over a century.Specifically, the capability to form useful new C-C, C-N, C-O, and C-X bonds via direct C-H functionalization would have wide-ranging impacts in organic synthesis. Palladium is especially attractive as a catalyst for such C-H functionalizations because of the diverse reactivity of intermediate palladium-carbon bonds. Early efforts using cyclopalladation with Pd(OAc)₂ and related salts led to the development of many Pd-catalyzed C-H functionalization reactions. However, Pd(OAc)₂ and other simple Pd salts perform only racemic transformations, which prompted a long search for effective chiral catalysts dating back to the 1970s. Pd salts also have low reactivity with synthetically useful substrates. To address these issues, effective and reliable ligands capable of accelerating and improving the selectivity of Pd-catalyzed C-H functionalizations are needed.In this Account, we highlight the discovery and development of bifunctional mono-N-protected amino acid (MPAA) ligands, which make great strides toward addressing these two challenges. MPAAs enable numerous Pd(II)-catalyzed C(sp²)-H and C(sp³)-H functionalization reactions of synthetically relevant substrates under operationally practical conditions with excellent stereoselectivity when applicable. Mechanistic studies indicate that MPAAs operate as unique bifunctional ligands for C-H activation in which both the carboxylate and amide are coordinated to Pd. The N-acyl group plays an active role in the C-H cleavage step, greatly accelerating C-H activation. The rigid MPAA chelation also results in a predictable transfer of chiral information from a single chiral center on the ligand to the substrate and permits the development of a rational stereomodel to predict the stereochemical outcome of enantioselective reactions.We also describe the application of MPAA-enabled C-H functionalization in total synthesis and provide an outlook for future development in this area. We anticipate that MPAAs and related next-generation ligands will continue to stimulate development in the field of Pd-catalyzed C-H functionalization.

V-shaped bis-coumarin based fluorescent probe for detecting palladium in natural waters

A catalytic fluorescent probe based on V-shaped bis-coumarin has been designed and synthesized for detection of palladium (Pd). The detection mechanism of the probe is based on palladium-catalyzed Tsuji‒Trost reaction process and photoinduced electron transfer (PET), which can distinguish and detect palladium (0, +2/+4) in different valence states under different conditions. The fluorescence intensity of the probe enhances after adding the palladium in about 10 min at room temperature. The limit of detection (LOD) of the probe is as low as 40.0 nM (4.2 ng/g), and it has good selectivity and high sensitivity. Apart from that, it has been successfully applied to detection of palladium in environmental waters.

Synthesis and evaluation of potent human immunodeficiency virus 1 protease inhibitors with epimeric isopropanol as novel P1' ligands

Aim: HIV-1 protease inhibitors regimens suffered from a number of drawbacks, among which, the most egregious issue was the growing emergence of drug-resistant strains. Materials & methods: The design strategy of maximizing the protease active site interactions with the inhibitor, especially promoting extensive hydrogen bonding with the protein backbone atoms, might be in favor of combating drug resistance. A series of HIV-1 protease inhibitors that incorporated enantiomeric isopropanols as the P1' ligands in combination with phenols as the P2 ligands were reported herein. Results: A number of inhibitors displayed potent protease enzyme inhibition activity. In particular, inhibitor 14c showed comparable potency as darunavir with IC₅₀ value of 1.91 nM and activity against darunavir-resistant HIV-1 variants. Conclusion: The new kind of HIV-1 protease inhibitors deserves further study.

Weak coordinated nitrogen functionality enabled regioselective C–H alkynylation via Pd(ii)/mono-N-protected amino acid catalysis

By using mono-N-protected amino acid (MPAA) ligand under Pd(ii) catalysis, regioselective C–H alkynylation of weak coordinated nitrogen functionalities was developed with great efficiency, proceeding via 5, 6 and 7-membered palladacycle intermediates.

Catalytic C(sp3)-H bond activation in tertiary alkylamines

The development of robust catalytic methods to assemble tertiary alkylamines provides a continual challenge to chemical synthesis. In this regard, transformation of a traditionally unreactive C-H bond, proximal to the nitrogen atom, into a versatile chemical entity would be a powerful strategy for introducing functional complexity to tertiary alkylamines. A practical and selective metal-catalysed C(sp³)-H activation facilitated by the tertiary alkylamine functionality, however, remains an unsolved problem. Here, we report a Pd(II)-catalysed protocol that appends arene feedstocks to tertiary alkylamines via C(sp³)-H functionalization. A simple ligand for Pd(II) orchestrates the C-H activation step in favour of deleterious pathways. The reaction can use both simple and complex starting materials to produce a range of multifaceted γ-aryl tertiary alkylamines and can be rendered enantioselective. The enabling features of this transformation should be attractive to practitioners of synthetic and medicinal chemistry as well as in other areas that use biologically active alkylamines.

Iodine-Catalyzed Functionalization of Primary Aliphatic Amines to Oxazoles, 1,4-Oxazines, and Oxazinones

Unprecedented I₂-catalyzed α,α-C(sp³)-H, decarboxylative α-C(sp³)-H, lactonized α-C(sp³)-H, and α,β-C(sp³)-H functionalized 5- and 6-annulation as well as α-C(sp³)-H activated 6-lactonization of primary aliphatic amines are devised under aerobic conditions. The metal-free sustainable strategy was employed for the diverse construction of valuable five-and six-membered polycyclic N,O-heteroaromatics such as oxazoles, 1,4-oxazines, and oxazin-2-one with a rapid reaction rate and high yield. The viability of this mild nonmetallic catalysis is successfully verified through syntheses of labile chiral heterocyclic analogues. In contrast to the common practice, this method is not limited to use of prefunctionalized amines, directing groups (DGs) and/or transient DGs, metal catalysts, and traditional oxidants. The possible mechanistic pathway of the annulation reaction is investigated by control experiments and ESI-MS data collected for a reaction mixture of the ongoing reaction. The synthesized new compounds are potent organic nanobuilding blocks to achieve valuable organic nanomaterials of different sizes, shapes, and dimensions, which are under investigation for the discovery of high-tech devices of innovative organic nanoelectronics and photophysical properties.

A Computational Mechanistic Study of Pd(II)-Catalyzed Enantioselective C(sp3)-H Borylation: Roles of APAO Ligands

A computational mechanistic study has been performed on Pd(II)-catalyzed enantioselective reactions involving acetyl-protected aminomethyl oxazolines (APAO) ligands that significantly improved reactivity and selectivity in C(sp³)-H borylation. The results support a mechanism including initiation of C(sp³)-H bond activation generating a five-membered palladacycle and ligand exchange, followed by HPO₄^2--promoted transmetalation. These resulting Pd(II) complexes further undergo sequential reductive elimination by coordination of APAO ligands and protonation to afford the enantiomeric products and deliver Pd(0) complexes, which will then proceed by oxidation and deprotonation to regenerate the catalyst. The C(sp³)-H activation is found to be the rate- and enantioselectivity-determining step, in which the APAO ligand acts as the proton acceptor to form the two enantioselectivity models. The results demonstrate that the diverse APAO ligands control the enantioselectivity by differentiating the distortion and interaction between the major and minor pathways.