Exploring Homogeneous Conditions for Mild Buchwald–Hartwig Amination in Batch and Flow

Cross-Coupling Reactions with Nickel, Visible Light, and tert-Butylamine as a Bifunctional Additive

Transition metal catalysis is crucial for the synthesis of complex molecules, with ligands and bases playing a pivotal role in optimizing cross-coupling reactions. Despite advancements in ligand design and base selection, achieving effective synergy between these components remains challenging. We present here a general approach to nickel-catalyzed photoredox reactions employing tert-butylamine as a cost-effective bifunctional additive, acting as the base and ligand. This method proves effective for C-O and C-N bond-forming reactions with a diverse array of nucleophiles, including phenols, aliphatic alcohols, anilines, sulfonamides, sulfoximines, and imines. Notably, the protocol demonstrates significant applicability in biomolecule derivatization and facilitates sequential one-pot functionalizations. Spectroscopic investigations revealed the robustness of the dynamic catalytic system, while elucidation of structure-reactivity relationships demonstrated how computed molecular properties of both the nucleophile and electrophile correlated to reaction performance, providing a foundation for effective reaction outcome prediction.

Novel purine derivatives as selective CDK2 inhibitors with potential anticancer activities: Design, synthesis and biological evaluation

Purine analogues were discovered to be inhibitors of CDK2, suggesting a potential therapeutic scaffold. This paper addresses the design, synthesis, and anticancer evaluation of purine analogues as kinase inhibitors. In the early stages of the investigation, the designed compounds demonstrated a promising docking score and greater protein-ligand stability in MD simulation than the standard, indicating a higher affinity against CDK2. Thus, we synthesised new purine analogues under simple and optimised reaction conditions. Among the studies under NCI-60, 5g and 5i were the most effective, with a percentage GI of 98.09 and 90 against OVCAR-4 and SNB-75, respectively, at a dose of 10 µM. Additionally, 5g and 5i demonstrated 7.80-fold and 1.54-fold greater cytotoxicity against PA-1 and MCF-7, with IC50s of 1.08 µM and 3.54 µM, respectively, compared to seliciclib (8.43 µM and 5.46 µM). In addition, 5g and 5i showed selective cytotoxicity against PA-1 and MCF-7 than normal cells, with selectivity indexes of 26.40 and 15.45, respectively, as compared to the standard (SI=3.83 and 5.91). In the kinase selectivity assay, both compounds demonstrated greater affinity against CDK2 than other kinases, with IC50 of 0.21 µM and 0.59 µM, in contrast to the standard (IC50 = 0.63 µM). Furthermore, 5g confirmed kinase inhibition in the western blot by lowering CDK2, cyclin A2, and other downstream substrates. Moreover, it triggered cell death by apoptosis and cell cycle arrest in G2/M. Taken together, 5g merits further investigation in PKPD research to discover a potential therapeutic candidate against cancer.

A strategy for the controllable generation of organic superbases from benchtop-stable salts

Organic superbases are a distinct class of strong base that enable numerous modern reaction applications. Despite their great synthetic potential, widespread use and study of superbases are limited by their air sensitivity and difficult preparation. To address this, we report air-stable carboxylate salts of BTPP and P2-t-Bu phosphazene superbases that, when added to solution with an epoxide, spontaneously generate freebase. These systems function as effective precatalysts and stoichiometric prereagents for superbase-promoted addition, substitution and polymerization reactions. In addition to improving the synthesis, shelf stability, handling and recycling of phosphazenes, this approach enables precise regulation of the rate of base generation in situ. The activation strategy effectively mimics manual slow addition techniques, allowing for control over a reaction's rate or induction period and improvement of reactions that require strong base but are also sensitive to its presence, such as Pd-catalyzed coupling reactions.

A green, facile, and practical preparation of capsaicin derivatives with thiourea structure

Capsaicin derivatives with thiourea structure (CDTS) is highly noteworthy owing to its higher analgesic potency in rodent models and higher agonism in vitro. However, the direct synthesis of CDTS remains t one or more shortcomings. In this study, we present reported a green, facile, and practical synthetic method of capsaicin derivatives with thiourea structure is developed by using an automated synthetic system, leading to a series of capsaicin derivatives with various electronic properties and functionalities in good to excellent yields.

A Slug Flow Platform with Multiple Process Analytics Facilitates Flexible Reaction Optimization

Flow processing offers many opportunities to optimize reactions in a rapid and automated manner, yet often requires relatively large quantities of input materials. To combat this, the use of a flexible slug flow reactor, equipped with two analytical instruments, for low-volume optimization experiments are reported. A Buchwald-Hartwig amination toward the drug olanzapine, with 6 independent optimizable variables, is optimized using three different automated approaches: self-optimization, design of experiments, and kinetic modeling. These approaches are complementary and provide differing information on the reaction: pareto optimal operating points, response surface models, and mechanistic models, respectively. The results are achieved using <10% of the material that would be required for standard flow operation. Finally, a chemometric model is built utilizing automated data handling and three subsequent validation experiments demonstrate good agreement between the slug flow reactor and a standard (larger scale) flow reactor.

Controlling Reactivity and Selectivity in the Mizoroki-Heck Reaction: High Throughput Evaluation of 1,5-Diaza-3,7-diphosphacyclooctane Ligands

We report a high throughput evaluation of the Mizoroki-Heck reaction of diverse olefin coupling partners. Comparison of different ligands revealed the 1,5-diaza-3,7-diphosphacyclooctane (P2N2) scaffold to be more broadly applicable than common "gold standard" ligands, demonstrating that this family of readily accessible diphosphines has unrecognized potential in organic synthesis. In particular, two structurally related P2N2 ligands were identified to enable the regiodivergent arylation of styrenes. By simply altering the phosphorus substituent from a phenyl to tert-butyl group, both the linear and branched Mizoroki-Heck products can be obtained in high regioisomeric ratios. Experimental and computational mechanistic studies were performed to further probe the origin of selectivity, which suggests that both ligands coordinate to the metal in a similar manner but that rigid positioning of the phosphorus substituent forces contact with the incoming olefin in a π-π interaction (for P-Ph ligands) or with steric clash (for P-tBu ligands), dictating the regiocontrol.

A deep learning framework for accurate reaction prediction and its application on high-throughput experimentation data

In recent years, it has been seen that artificial intelligence (AI) starts to bring revolutionary changes to chemical synthesis. However, the lack of suitable ways of representing chemical reactions and the scarceness of reaction data has limited the wider application of AI to reaction prediction. Here, we introduce a novel reaction representation, GraphRXN, for reaction prediction. It utilizes a universal graph-based neural network framework to encode chemical reactions by directly taking two-dimension reaction structures as inputs. The GraphRXN model was evaluated by three publically available chemical reaction datasets and gave on-par or superior results compared with other baseline models. To further evaluate the effectiveness of GraphRXN, wet-lab experiments were carried out for the purpose of generating reaction data. GraphRXN model was then built on high-throughput experimentation data and a decent accuracy (R2 of 0.712) was obtained on our in-house data. This highlights that the GraphRXN model can be deployed in an integrated workflow which combines robotics and AI technologies for forward reaction prediction.

Applications of palladium-catalyzed C-N cross-coupling reactions in pharmaceutical compounds

C-N cross-coupling bond formation reactions have become valuable approaches to synthesizing anilines and their derivatives, known as important chemical compounds. Recent developments in this field have focused on versatile catalysts, simple operation methods, and green reaction conditions. This review article presents an overview of C-N cross-coupling reactions in pharmaceutical compound synthesis reports. Selected examples of N-arylation reactions of various nitrogen-based compounds and aryl halides are defined for preparing pharmaceutical molecules.

Comparative Screening of DalPhos/Ni Catalysts in C-N Cross-couplings of (Hetero)aryl Chlorides Enables Development of Aminopyrazole Cross-couplings with Amine Base

A systematic competitive evaluation of the DalPhos ligand family in nickel-catalyzed N-arylation chemistry is reported, involving primary (linear and branched) and secondary alkylamines, as well as a primary five-membered heteroarylamine (aminopyrazole), in combination with a diverse set of test electrophiles and bases (NaOtBu, K₂ CO₃ , DBU/NaTFA). In addition to providing optimal ligand/catalyst identification, and bringing to light methodology limitations (e. g., unwanted C-O cross-coupling with NaOtBu), our survey enabled the development of the first efficient catalyst system for heteroatom-dense C-N cross-coupling of aminopyrazoles and related nucleophiles with (hetero)aryl chlorides by use of an amine 'dual-base' system.

Adamantane-Functionalized Phthalimide Scaffold: Pathways to Supramolecular Interactions and Drug Discovery

Herein, the synthesis of a novel adamantanyl-functionalized phthalimide scaffold is demonstrated. The novel compound could be used as a precursor for various synthetic pathways owing to the generic use of adamantane substituents as the driving force for supramolecular interactions with macrocycles and N-substituted phthalimide derivatives as a core structure in numerous drugs. The adamantanyl-functionalized phthalimide scaffold contains bromide groups on the C4 and C5 positions of the benzene ring, effectively allowing further facile modifications of the scaffold. The structure was fully characterized including single-crystal X-ray crystallography. The crystal structure shows an adamantane moiety at an angle of 115.57(7)° to the phthalimide core, hence sterically freeing the adamantane unit for host–guest interactions.

Rapid Optimization of Photoredox Reactions for Continuous-Flow Systems Using Microscale Batch Technology

Photoredox catalysis has emerged as a powerful and versatile platform for the synthesis of complex molecules. While photocatalysis is already broadly used in small-scale batch chemistry across the pharmaceutical sector, recent efforts have focused on performing these transformations in process chemistry due to the inherent challenges of batch photocatalysis on scale. However, translating optimized batch conditions to flow setups is challenging, and a general approach that is rapid, convenient, and inexpensive remains largely elusive. Herein, we report the development of a new approach that uses a microscale high-throughput experimentation (HTE) platform to identify optimal reaction conditions that can be directly translated to flow systems. A key design point is to simulate the flow-vessel pathway within a microscale reaction plate, which enables the rapid identification of optimal flow reaction conditions using only a small number of simultaneous experiments. This approach has been validated against a range of widely used photoredox reactions and, importantly, was found to translate accurately to several commercial flow reactors. We expect that the generality and operational efficiency of this new HTE approach to photocatalysis will allow rapid identification of numerous flow protocols for scale.

Nickel-Catalyzed N-Arylation of Fluoroalkylamines

The Ni-catalyzed N-arylation of β-fluoroalkylamines with broad scope is reported for the first time. Use of the air-stable pre-catalyst (PAd2-DalPhos)Ni(o-tol)Cl allows for reactions to be conducted at room temperature (25 °C, NaOtBu), or by use of a commercially available dual-base system (100 °C, DBU/NaOTf), to circumvent decomposition of the N-(β-fluoroalkyl)aniline product. The mild protocols disclosed herein feature broad (hetero)aryl (pseudo)halide scope (X=Cl, Br, I, and for the first time phenol-derived electrophiles), encompassing base-sensitive substrates and enantioretentive transformations, in a manner that is unmatched by any previously reported catalyst system.

Reaction screening in multiwell plates: high-throughput optimization of a Buchwald-Hartwig amination

Chemical space is vast, and chemical reactions involve the complex interplay of multiple variables. As a consequence, reactions can fail for subtle reasons, necessitating screening of conditions. High-throughput experimentation (HTE) techniques enable a more comprehensive array of data to be obtained in a relatively short amount of time. Although HTE can be most efficiently achieved with automated robotic dispensing equipment, the benefits of running reaction microarrays can be accessed in any regularly equipped laboratory using inexpensive consumables. Herein, we present a cost-efficient approach to HTE, examining a Buchwald-Hartwig amination as our model reaction. Experiments are carried out in a machined aluminum 96-well plate, taking advantage of solid transfer scoops and pipettes to facilitate rapid reagent transfer. Reaction vials are simultaneously heated and mixed, using a magnetic stirrer, and worked up in parallel, using a plastic filter plate. Analysis by gas chromatography provides the chemist with 96 data points with minimal commitment of time and resources. The best-performing experiment can be selected for scale-up and isolation, or the data can be used for designing future optimization experiments.

Palladium catalyzed C–C and C–N bond forming reactions: an update on the synthesis of pharmaceuticals from 2015–2020

Some of the most prominent and promising catalysts in organic synthesis for the requisite construction of C–C and C–N bonds are palladium (Pd) catalysts, which play a pivotal role in pharmaceutical and medicinal chemistry.

Nickel-Catalyzed N-Arylation of Amides with (Hetero)aryl Electrophiles by Using a DBU/NaTFA Dual-Base System

The first nickel-catalyzed N-arylation of amides with (hetero)aryl (pseudo)halides employing an organic amine base is described. By using a bis(cyclooctadienyl)nickel/8-[2-(dicyclohexylphosphinyl)phenyl]-1,3,5,7-tetramethyl-2,4,6-trioxa-8-phosphaadamantane catalyst mixture in combination with DBU/NaTFA as a dual-base system, a diversity of (hetero)aryl chloride, bromide, tosylate, and mesylate electrophiles were successfully cross-coupled with structurally diverse primary amides, as well as a selection of secondary amide, lac­tam, and oxazolidone nucleophiles.

Aryl Amination Using Soluble Weak Base Enabled by a Water-Assisted Mechanism

The amination of aryl halides has become one of the most commonly practiced C-N bond-forming reactions in pharmaceutical and laboratory syntheses. The widespread use of strong or poorly soluble inorganic bases for amine activation nevertheless complicates the compatibility of this important reaction class with sensitive substrates as well as applications in flow and automated synthesis, to name a few. We report a palladium-catalyzed C-N coupling using Et₃N as a weak, soluble base, which allows a broad substrate scope that includes bromo- and chloro(hetero)arenes, primary anilines, secondary amines, and amide type nucleophiles together with tolerance for a range of base-sensitive functional groups. Mechanistic data have established a unique pathway for these reactions in which water serves multiple beneficial roles. In particular, ionization of a neutral catalytic intermediate via halide displacement by H₂O generates, after proton loss, a coordinatively unsaturated Pd-OH species that can bind amine substrate triggering intramolecular N-H heterolysis. This water-assisted pathway operates efficiently with even weak terminal bases, such as Et₃N. The use of a simple, commercially available ligand, PAd₃, is key to this water-assisted mechanism by promoting coordinative unsaturation in catalytic intermediates responsible for the heterolytic activation of strong element-hydrogen bonds, which enables broad compatibility of carbon-heteroatom cross-coupling reactions with sensitive substrates and functionality.

The Quest for the Ideal Base: Rational Design of a Nickel Precatalyst Enables Mild, Homogeneous C-N Cross-Coupling

Palladium-catalyzed amination reactions using soluble organic bases have provided a solution to the many issues associated with heterogeneous reaction conditions. Still, homogeneous C-N cross-coupling approaches cannot yet employ bases as weak and economical as trialkylamines. Furthermore, organic base-mediated methods have not been developed for Ni(0/II) catalysis, despite some advantages of such systems over those employing Pd-based catalysts. We designed a new air-stable and easily prepared Ni(II) precatalyst bearing an electron-deficient bidentate phosphine ligand that enables the cross-coupling of aryl triflates with aryl amines using triethylamine (TEA) as base. The method is tolerant of sterically congested coupling partners, as well as those bearing base- and nucleophile-sensitive functional groups. With the aid of density functional theory (DFT) calculations, we determined that the electron-deficient auxiliary ligands decrease both the pK_a of the Ni-bound amine and the barrier to reductive elimination from the resultant Ni(II)-amido complex. Moreover, we determined that the preclusion of Lewis acid-base complexation between the Ni catalyst and the base, due to steric factors, is important for avoiding catalyst inhibition.