BBr3 -Mediated P(III)-Directed C-H Borylation of Phosphines

Ortho Arylation of N-Aryl Amides and the Construction of Diagonal Tetraarylbenzenediamines and N-Doped Fulminenes via BBr3-Derived Dibromoboracycles

The synthesis of biaryl amides, which are prevalent motifs in bioactive molecules, often necessitates lengthy and inefficient procedures. To address these limitations, catalytic C-H activation protocols have emerged, enabling the direct ortho-arylation of aryl amides. However, these protocols often suffer from issues such as lack of selectivity, reliance on stoichiometric oxidants, and the requirement for excess reagents and harsh reaction conditions. To overcome these challenges, we present a novel and highly selective protocol for the ortho-arylation of N-aryl amides and ureas. The high selectivity originates from the directed installation of BBr3 to form a boracycle, which then undergoes cross-coupling with an aryl halide. Our method offers significant advantages, including mild reaction conditions, excellent site-specificity, and scalability. The protocol demonstrates broad compatibility with a diverse range of readily accessible functionalized anilides and aryl iodides, as evidenced by 55 successful examples yielding products in the 30-95 % range. Furthermore, our methodology surpasses conventional approaches by facilitating the one-pot selective diagonal diarylation of dianilides. This capability unlocks the construction of previously unattainable diagonal aryl systems, which serve as valuable precursors for the synthesis of diagonal tetraarylbenzenediamines and N-doped fulminenes, two crucial compound classes in materials science.

Chemoselective C-H Hydroxylation and Borylation of N-Phenylbenzamides using BBr3

A novel metal-free chemoselective C-H hydroxylation and borylation of N-phenylbenzamides using BBr3 is described. The protocol generates the corresponding phenols and arylboronic esters in moderate to excellent yields under mild conditions with brilliant chemoselectivity. Additionally, this strategy can be realized in one pot, and several potential bioactive derivatives can be synthesized efficiently. Density functional theory calculations certify that the preferred pathway for this metal-free C-H hydroxylation process is the formation of a five-membered boracycle.

Metal-Free ortho C-H Borylation of Thiobenzamides

A BBr3-mediated S-directed ortho C-H borylation of thiobenzamides was developed. A variety of ortho-borylated thiobenzamides were obtained in moderate to good yields with a wide functional group tolerance under simple and metal-free conditions. This transformation provided a convenient and practical route to important functionalized thiobenzamides.

Late-Stage Diversification of Phosphines by C-H Activation: A Robust Strategy for Ligand Design and Preparation

ConspectusThe advent of the twenty-first century marked a golden era in the realm of synthetic chemistry, exemplified by groundbreaking advancements in the field of C-H activation, which is a concept that quickly transitioned from mere academic fascination to an essential element within the synthetic chemist's toolkit. This methodological breakthrough has given rise to a wealth of opportunities spanning a wide range of chemical disciplines. It has facilitated the late-stage diversification of elaborate organic frameworks, encompassing the spectrum from simple methane to complex polymers, thus refining the lead optimization process and easing the production of diverse molecular analogues. Among these strides forward, the development of phosphorus(III)-directed C-H activation stands out as an increasingly significant and inventive approach for the design and synthesis of ligands, substantially redefining the contours of synthetic methodology.Phosphines, renowned for their roles as ligands and organocatalysts, have become fundamentally important in modern organic chemistry. Their efficiency as ligands is significantly affected by coordination with transition metals, which is essential for their involvement in catalytic processes, influencing both the catalytic activity and the selectivity. Historically, the fabrication of phosphines predominantly relied on synthesis employing complex, multistep procedures. Addressing this limitation, our research has delved into ligand design and synthesis through innovative catalytic P(III)-directed C-H activation strategies. In this Account, we have explored a spectrum of procedures, including direct arylation using metal catalysis, and ventured further into domains such as C-H alkylation, alkenylation, aminocarbonylation, alkynylation, borylation, and silylation. These advances have enriched the field by providing efficient methods for the late-stage diversification of biaryl-type monophosphines as well as enabled the C-H activation of triphenylphosphine and its derivatives. Moreover, we have successfully constructed libraries of diverse axially chiral binaphthyl phosphine ligands, showcasing their potency in asymmetric catalysis. Through this Account, we aim to illuminate the exciting possibilities presented by P(III)-directed C-H activation in propelling the boundaries of organic synthesis. By highlighting our pioneering work, we hope to inspire further developments in this promising field of chemistry.

Regioselective ortho halogenation of N-aryl amides and ureas via oxidative halodeboronation: harnessing boron reactivity for efficient C-halogen bond installation

The installation of the C-halogen bond at the ortho position of N-aryl amides and ureas represents a tool to prepare motifs that are ubiquitous in biologically active compounds. To construct such prevalent bonds, most methods require the use of precious metals and a multistep process. Here we report a novel protocol for the long-standing challenge of regioselective ortho halogenation of N-aryl amides and ureas using an oxidative halodeboronation. By harnessing the reactivity of boron over nitrogen, we merge carbonyl-directed borylation with consecutive halodeboronation, enabling the precise introduction of the C-X bond at the desired ortho position of N-aryl amides and ureas. This method offers an efficient, practical, and scalable solution for synthesizing halogenated N-heteroarenes under mild conditions, highlighting the superiority of boron reactivity in directing the regioselectivity of the reaction.

Metal-Free Stereoconvergent C-H Borylation of Enamides

Enamides, functional derivatives of enamines, play a significant role as synthetic targets. However, the stereoselective synthesis of these molecules has posed a longstanding challenge in organic chemistry, particularly for acyclic enamides that are less thermodynamically stable. In this study, we present a general strategy for constructing β-borylenamides by C-H borylation, which provides a versatile platform for generating the stereodefined enamides. Our approach involves the utilization of metalloid borenium cation, generated through the reaction of BBr3 and enamides in the presence of two different additives, avoiding any exogenous catalyst. Importantly, the stereoconvergent nature of this methodology allows for the use of starting materials with mixed E/Z configurations, thus highlighting the unique advantage of this chemistry. Mechanistic investigations have shed light on the pivotal roles played by the two additives, the reactive boron species, and the phenomenon of stereoconvergence.

Borylation Directed Borylation of Indoles Using Pyrazabole Electrophiles: A One-Pot Route to C7-Borylated-Indolines

Pyrazabole (1) is a readily accessible diboron compound that can be transformed into ditopic electrophiles. In 1 (and derivatives), the B⋅⋅⋅B separation is ca. 3 Å, appropriate for one boron centre bonding to N and one to the C7 of indoles and indolines. This suitable B⋅⋅⋅B separation enables double E-H (E=N/C) functionalisation of indoles and indolines. Specifically, the activation of 1 with HNTf₂ generates an electrophile that transforms N-H indoles and indolines into N/C7-diborylated indolines, with N-H borylation directing subsequent C7-H borylation. Indole reduction to indoline occurs before C-H borylation and our studies indicate this proceeds via hydroboration-C3-protodeboronation to produce an intermediate that then undergoes C7 borylation. The borylated products can be converted in situ into C7-BPin-N-H-indolines. Overall, this represents a transient directed C-H borylation to form useful C7-BPin-indolines.

Facile Synthesis and Utilization of Bis(o-phosphinophenyl)zinc as Isolable PZnP-pincer Ligands Enabled by Boron-Zinc Double Transmetallation

Bis(o-phosphinophenyl)zinc derivatives were successfully synthesized by the reaction of o-phosphinophenylboronates with dimethylzinc via boron-zinc double transmetallation. The transmetallation was significantly accelerated by the presence of the ortho PR2 substituent to...