Advances in Base-Metal Catalysis: Development of a Screening Platform for Nickel-Catalyzed Borylations of Aryl (Pseudo)halides with B2(OH)4

A Simple Nickel Metal-Organic Framework-Catalyzed Borylation of Aryl Chlorides and Bromides

We report a recyclable and efficient catalyst system based on a nickel-benzene tricarboxylic acid metal-organic framework (Ni-BTC MOF) for the borylation of aryl halides, including aryl chlorides, with bis(pinacolato)diboron, affording aryl boronate esters in high yields (up to >99% yield) with high selectivity. This protocol demonstrates broad functional group tolerance. Catalyst can be recyclable up to four times, and gram-scale reactions further highlights the usefulness of this method. In situ EPR experiments confirmed the formation of catalytically active Ni(I) species.

B2(OH)4-Mediated Reductive Transamidation of N-Acyl Benzotriazoles with Nitro Compounds En Route to Aqueous Amide Synthesis

We herein developed a reductive transamidation reaction between N-acyl benzotriazoles (AcBt) and organic nitro compounds or NaNO₂ under mild conditions. This protocol employed the stable and readily available B₂(OH)₄ as the reducing agent and H₂O as the ideal solvent. N-Deuterated amides can be synthesized when conducting the reaction in D₂O. A reasonable reaction mechanism involving bond metathesis between the AcBt amide and amino boric acid intermediate was proposed to explain the unique nature of AcBt.

Enabling Suzuki-Miyaura coupling of Lewis-basic arylboronic esters with a nonprecious metal catalyst

The high cost and negative environmental impact of precious metal catalysts has led to increased demand for nonprecious alternatives for widely practiced reactions such as the Suzuki-Miyaura coupling (SMC). Ni-catalyzed versions of this reaction have failed to achieve high reactivity with Lewis-basic arylboron nucleophiles, especially pinacolboron esters. We describe the development of (PPh2Me)2NiCl2 as an inexpensive and air-stable precatalyst that addresses this challenge. Under activation by n-BuMgCl, this complex can catalyze the coupling of synthetically important heteroaryl pinacolborons with heteroaryl halides. Mildly basic conditions (aqueous K3PO4) allow the reaction to tolerate sensitive functional groups that were incompatible with other Ni-SMC methods. Experimental and computational studies suggest that catalyst inhibition by substitution of PPh2Me from Ni(ii) intermediates by Lewis basic reactants and products is disfavored relative to more commonly employed ligands in the Ni-SMC, which allows it to operate efficiently in the presence of Lewis bases such as unhindered pyridines.

Structure-Reactivity Relationships of Buchwald-Type Phosphines in Nickel-Catalyzed Cross-Couplings

The dialkyl-ortho-biaryl class of phosphines, commonly known as Buchwald-type ligands, are among the most important phosphines in Pd-catalyzed cross-coupling. These ligands have also been successfully applied to several synthetically valuable Ni-catalyzed cross-coupling methodologies and, as demonstrated in this work, are top performing ligands in Ni-catalyzed Suzuki Miyaura Coupling (SMC) and C-N coupling reactions, even outperforming commonly employed bisphosphines like dppf in many circumstances. However, little is known about their structure-reactivity relationships (SRRs) with Ni, and limited examples of well-defined, catalytically relevant Ni complexes with Buchwald-type ligands exist. In this work, we report the analysis of Buchwald-type phosphine SRRs in four representative Ni-catalyzed cross-coupling reactions. Our study was guided by data-driven classification analysis, which together with mechanistic organometallic studies of structurally characterized Ni(0), Ni(I), and Ni(II) complexes allowed us to rationalize reactivity patterns in catalysis. Overall, we expect that this study will serve as a platform for further exploration of this ligand class in organonickel chemistry as well as in the development of new Ni-catalyzed cross-coupling methodologies.

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

Univariate classification of phosphine ligation state and reactivity in cross-coupling catalysis

[Figure: see text].

A Process Chemistry Benchmark for sp2-sp3 Cross Couplings

As sp²-sp³ disconnections gain acceptance in the medicinal chemist's toolbox, an increasing number of potential drug candidates containing this motif are moving into the pharmaceutical development pipeline. This raises a new set of questions and challenges around the novel, direct methodologies available for forging these bonds. These questions gain further importance in the context of process chemistry, where the focus is the development of scalable processes that enable the large-scale delivery of clinical supplies. In this paper, we describe our efforts to apply a wide variety of standard, photo-, and electrochemical sp²-sp³ cross-coupling methods to a pharmaceutically relevant intermediate and optimize each through a combination of high throughput and mechanistically guided experimentation. With data regarding the performance, benefits, and limitations of these novel methods, we evaluate them against a more traditional two-step palladium-catalyzed process. This work reveals trends and similarities between these sp²-sp³ bond-forming methods and suggests a path forward for further refinements.

Increasing saturation: development of broadly applicable photocatalytic Csp2–Csp3 cross-couplings of alkyl trifluoroborates and (hetero)aryl bromides for array synthesis

HTE was used to systematically investigate the reaction of alkyl trifluoroborates and aryl bromides under photocatalytic conditions. General conditions were identified for coupling of activated primary, benzylic and secondary alkyl trifluoroborates.

Transition-Metal-Free Borylation of Aryl Bromide Using a Simple Diboron Source

In this study, we developed a simple transition-metal-free borylation reaction of aryl bromides. Bis-boronic acid (BBA), was used, and the borylation reaction was performed using a simple procedure at a mild temperature. Under mild conditions, aryl bromides were converted to arylboronic acids directly without any deprotection steps and purified by conversion to trifluoroborate salts. The functional group tolerance was considerably high. The mechanism study suggested that this borylation reaction proceeds via a radical pathway.

Photochemically-Mediated, Nickel-Catalyzed Synthesis of N-(Hetero)aryl Sulfamate Esters

A general method is described for the coupling of (hetero)aryl bromides with O-alkyl sulfamate esters. The protocol relies on catalytic amounts of nickel and photoexcitable iridium complexes and proceeds under visible light irradiation at ambient temperature. This technology engages a broad range of simple and complex O-alkyl sulfamate ester substrates under mild conditions. Furthermore, it is possible to avoid undesirable N-alkylation, which was found to plague palladium-based protocols for N-arylation of O-alkyl sulfamate esters. These investigations represent the first use of sulfamate esters as nucleophiles in transition metal-catalyzed C-N coupling processes.

Rapid route design of AZD7594

Multidisciplinary collaboration enables the rapid and efficient design and selection of an improved manufacturing route to a new potential medicine for the treatment of asthma.