Enabling the Scale-Up of a Key Asymmetric Hydrogenation Step in the Synthesis of an API Using Continuous Flow Solid-Supported Catalysis

Self-Driving Laboratories for Chemistry and Materials Science

Self-driving laboratories (SDLs) promise an accelerated application of the scientific method. Through the automation of experimental workflows, along with autonomous experimental planning, SDLs hold the potential to greatly accelerate research in chemistry and materials discovery. This review provides an in-depth analysis of the state-of-the-art in SDL technology, its applications across various scientific disciplines, and the potential implications for research and industry. This review additionally provides an overview of the enabling technologies for SDLs, including their hardware, software, and integration with laboratory infrastructure. Most importantly, this review explores the diverse range of scientific domains where SDLs have made significant contributions, from drug discovery and materials science to genomics and chemistry. We provide a comprehensive review of existing real-world examples of SDLs, their different levels of automation, and the challenges and limitations associated with each domain.

Copper-Catalyzed Continuous-Flow Transfer Hydrogenation of Nitroarenes to Anilines: A Scalable and Reliable Protocol

A robust supported catalyst that is made up of copper nanoparticles on Celite has been successfully prepared for the selective transfer hydrogenation of aromatic nitrobenzenes to anilines under continuous flow. The method is efficient and environmentally benign thanks to the absence of hydrogen gas and precious metals. Long-term stability studies show that the catalytic system is able to achieve very high nitrobenzene conversion (>99%) when working for up to 145 h. The versatility of the transfer hydrogenation system has been tested using representative examples of nitroarenes, with moderate-to-excellent yields being obtained. The packed bed reactor (PBR) permits the use of a setup that can provide products via simple isolation by SPE without the need for further purification. The recovery and reuse of either EG or the ion-exchange resin leads to consistent waste reduction; therefore, E-factor distribution analysis has highlighted the environmental efficiency of this synthetic protocol.

Multiphasic Continuous-Flow Reactors for Handling Gaseous Reagents in Organic Synthesis: Enhancing Efficiency and Safety in Chemical Processes

The use of reactive gaseous reagents for the production of active pharmaceutical ingredients (APIs) remains a scientific challenge due to safety and efficiency limitations. The implementation of continuous-flow reactors has resulted in rapid development of gas-handling technology because of several advantages such as increased interfacial area, improved mass- and heat transfer, and seamless scale-up. This technology enables shorter and more atom-economic synthesis routes for the production of pharmaceutical compounds. Herein, we provide an overview of literature from 2016 onwards in the development of gas-handling continuous-flow technology as well as the use of gases in functionalization of APIs.

Enantioselective Transformations in the Synthesis of Therapeutic Agents

The proportion of approved chiral drugs and drug candidates under medical studies has surged dramatically over the past two decades. As a consequence, the efficient synthesis of enantiopure pharmaceuticals or their synthetic intermediates poses a profound challenge to medicinal and process chemists. The significant advancement in asymmetric catalysis has provided an effective and reliable solution to this challenge. The successful application of transition metal catalysis, organocatalysis, and biocatalysis to the medicinal and pharmaceutical industries has promoted drug discovery by efficient and precise preparation of enantio-enriched therapeutic agents, and facilitated the industrial production of active pharmaceutical ingredient in an economic and environmentally friendly fashion. The present review summarizes the most recent applications (2008-2022) of asymmetric catalysis in the pharmaceutical industry ranging from process scales to pilot and industrial levels. It also showcases the latest achievements and trends in the asymmetric synthesis of therapeutic agents with state of the art technologies of asymmetric catalysis.

How Solid Surfaces Control Stability and Interactions of Supported Cationic CuI(dppf) Complexes─A Solid-State NMR Study

Organometallic complexes are frequently deposited on solid surfaces, but little is known about how the resulting complex-solid interactions alter their properties. Here, a series of complexes of the type Cu(dppf)(L_x)⁺ (dppf = 1,1'-bis(diphenylphosphino)ferrocene, L_x = mono- and bidentate ligands) were synthesized, physisorbed, ion-exchanged, or covalently immobilized on solid surfaces and investigated by ³¹P MAS NMR spectroscopy. Complexes adsorbed on silica interacted weakly and were stable, while adsorption on acidic γ-Al₂O₃ resulted in slow complex decomposition. Ion exchange into mesoporous Na-[Al]SBA-15 resulted in magnetic inequivalence of ³¹P nuclei verified by ³¹P-³¹P RFDR and ¹H-³¹P FSLG HETCOR. DFT calculations verified that a MeCN ligand dissociates upon ion exchange. Covalent immobilization via organic linkers as well as ion exchange with bidentate ligands both lead to rigidly bound complexes that cause broad ³¹P CSA tensors. We thus demonstrate how the interactions between complexes and functional surfaces determine and alter the stability of complexes. The applied Cu(dppf)(L_x)⁺ complex family members are identified as suitable solid-state NMR probes for investigating the influence of support surfaces on deposited inorganic complexes.

Catalytic hydrogenation of nitrocyclohexane as an alternative pathway for the synthesis of value-added products

Catalytic hydrogenation of nitrocyclohexane could be an alternative source of various useful chemicals: cyclohexanone oxime, cyclohexanone, cyclohexanol, cyclohexylamine and dicyclohexylamine. Each one of these compounds found application in the modern...

Supramolecular Strategies for the Recycling of Homogeneous Catalysts

Supramolecular approaches are increasingly used in the development of homogeneous catalysts and they also provide interesting new tools for the recycling of metal-based catalysts. Various non-covalent interactions have been utilized for the immobilization homogeneous catalysts on soluble and insoluble support. By non-covalent anchoring the supported catalysts obtained can be recovered via (nano-) filtration or such catalytic materials can be used in continuous flow reactors. Specific benefits from the reversibility of catalyst immobilization by non-covalent interactions include the possibility to re-functionalize the support material and the use as "boomerang" type catalyst systems in which the catalyst is captured after a homogeneous reaction. In addition, new reactor design with implemented recycling strategies becomes possible, such as a reverse-flow adsorption reactor (RFA) that combines a homogeneous reactor with selective catalyst adsorption/desorpion. Next to these non-covalent immobilization strategies, supramolecular chemistry can also be used to generate the support, for example by generation of self-assembled gels with catalytic function. Although the stability is a challenging issue, some self-assembled gel materials have been successfully utilized as reusable heterogeneous catalysts. In addition, catalytically active coordination cages, which are frequently used to achieve specific activity or selectivity, can be bound to support by ionic interactions or can be prepared in structured solid materials. These new heterogenized cage materials also have been used successfully as recyclable catalysts.

Sampling and Analysis in Flow: The Keys to Smarter, More Controllable, and Sustainable Fine-Chemical Manufacturing

Process analytical technology (PAT) is a system designed to help chemists better understand and control manufacturing processes. PAT systems operate through the combination of analytical devices, reactor control elements, and mathematical models to ensure the quality of the final product through a quality by design (QbD) approach. The expansion of continuous manufacturing in the pharmaceutical and fine-chemical industry requires the development of PAT tools suitable for continuous operation in the environment of flow reactors. This requires innovative approaches to sampling and analysis from flowing media to maintain the integrity of the reactor content and the analyte of interest. The following Review discusses examples of PAT tools implemented in flow chemistry for the preparation of small organic molecules, and applications of self-optimization tools.

Reducing Challenges in Organic Synthesis with Stereoselective Hydrogenation and Tandem Catalysis

Tandem catalysis enables the rapid construction of complex architectures from simple building blocks. This Perspective shares our interest in combining stereoselective hydrogenation with transformations such as isomerization, oxidation, and epimerization to solve diverse challenges. We highlight the use of tandem hydrogenation for preparing complex natural products from simple prochiral building blocks and present tandem catalysis involving transfer hydrogenation and dynamic kinetic resolution. Finally, we underline recent breakthroughs and opportunities for asymmetric hydrogenation.

Recent Developments in Transition-Metal-Catalyzed Asymmetric Hydrogenation of Enamides

The catalytic asymmetric hydrogenation of prochiral olefins is one of the most widely studied and utilized transformations in asymmetric synthesis. This straightforward, atom economical, inherently direct and sustainable strategy induces chirality in a broad range of substrates and is widely relevant for both industrial applications and academic research. In addition, the asymmetric hydrogenation of enamides has been widely used for the synthesis of chiral amines and their derivatives. In this review, we summarize the recent work in this field, focusing on the development of new catalytic systems and on the extension of these asymmetric reductions to new classes of enamides.

1 Introduction

2 Asymmetric Hydrogenation of Trisubstituted Enamides

2.1 Ruthenium Catalysts

2.2 Rhodium Catalysts

2.3 Iridium Catalysts

2.4 Nickel Catalysts

2.5 Cobalt Catalysts

3 Asymmetric Hydrogenation of Tetrasubstituted Enamides

3.1 Ruthenium Catalysts

3.2 Rhodium Catalysts

3.3 Nickel Catalysts

4 Asymmetric Hydrogenation of Terminal Enamides

4.1 Rhodium Catalysts

4.2 Cobalt Catalysts

5 Rhodium-Catalyzed Asymmetric Hydrogenation of Miscellaneous Enamides

6 Conclusions

Development of Robust Heterogeneous Chiral Rhodium Catalysts Utilizing Acid-Base and Electrostatic Interactions for Efficient Continuous-Flow Asymmetric Hydrogenations

Heterogeneous chiral Rh catalysts based on acid-base and electrostatic interactions have been developed. The robust catalysts demonstrate high activity and selectivity in the continuous-flow asymmetric hydrogenation of a wide variety of enamides and dehydroamino acids, providing optically active amides without leaching of metal species. The chiral environments can be easily tuned by changing the chiral ligands, demonstrating the high versatility of the heterogeneous catalysts. By applying these efficient catalysts, continuous synthesis of several active pharmaceutical ingredient intermediates was achieved.

Recent Progress in Continuous-Flow Hydrogenation

To achieve a safe, efficient, and sustainable (even fully automated) production for the continuous-flow hydrogenation reactions, which is among the most often used reactions in chemical synthesis, new catalyst types and immobilization methods as well as flow reactors and technologies have been developed over the last years; in addition, these approaches have been combined with new and transformational technologies in other fields such as artificial intelligence. Thus, attention from academic and industry practitioners has increasingly focused on improving the performance of hydrogenation in flow mode by reducing the reaction times, increasing selectivities, and achieve safe operation. This Minireview aims to summarize the most recent research results on this topic with focus on the advantages, current limitations, and future directions of flow chemistry.

Continuous Hydrogenation of Aqueous Furfural Using a Metal-Supported Activated Carbon Monolith

Continuous hydrogenation of aqueous furfural (4.5%) was studied using a monolith form (ACM) of an activated carbon Pd catalyst (∼1.2% Pd). A sequential reaction pathway was observed, with ACM achieving high selectivity and space time yields (STYs) for furfuryl alcohol (∼25%, 60-70 g/L-cat/h, 7-15 1/h liquid hourly space velocity, LHSV), 2-methylfuran (∼25%, 45-50 g/L-cat/h, 7-15 1/h LHSV), and tetrahydrofurfuryl alcohol (∼20-60%, 10-50 g/L-cat/h, <7 1/h LHSV). ACM showed a low loss of activity and metal leaching over the course of the reactions and was not limited by H2 external mass transfer resistance. Acetic acid (1%) did not significantly affect furfural conversion and product yields using ACM, suggesting Pd/ACM's potential for conversion of crude furfural. Limited metal leaching combined with high metal dispersion and H2 mass transfer rates in the composite carbon catalyst (ACM) provides possible advantages over granular and powdered forms in continuous processing.

Recent Advances in Continuous-Flow Enantioselective Catalysis

The increased demand for more efficient, safe, and green production in fine chemical and pharmaceutical industry calls for the development of continuous-flow manufacturing, and for chiral chemicals in particular, enantioselective catalytic processes. In recent years, this emerging direction has received considerable attention and has seen rapid progress. In most cases, catalytic enantioselective flow processes using homogeneous, heterogeneous, or enzymatic catalysts have shown significant advantages over the conventional batch mode, such as shortened reaction times, lower catalysts loadings, and higher selectivities in addition to the normal merits of non-enantioselective flow operations. In this Minireview, the advancements, key strategies, methods, and technologies developed the last six years as well as remaining challenges are summarized.

Reworking Organic Synthesis for the Modern Age: Synthetic Strategies Based on Continuous-Flow Addition and Condensation Reactions with Heterogeneous Catalysts

While organic synthesis carried out in most laboratories uses batch methods, there is growing interest in modernizing fine chemical synthesis through continuous-flow processes. As a synthetic method, flow processes have several advantages over batch systems in terms of environmental compatibility, efficiency, and safety, and recent advances have allowed for the synthesis of several complex molecules, including active pharmaceutical ingredients (APIs). Nevertheless, due to several reasons related to the difficulties arising from byproduct formation during the flow process, such as lower yields, poor selectivities, clogging of columns due to poor solubility, catalyst poisoning, etc., successful examples of continuous-flow synthesis of complex organic molecules are still limited. In order to solve this bottleneck, the development of selective and atom-economical continuous-flow organic transformations are needed. This perspective highlights examples of atom-economical addition and condensation reactions with heterogeneous catalysts under continuous-flow conditions and their applications for the synthesis of complex organic molecules such as natural products and APIs. In order to realize new continuous-flow methodologies, based on addition and condensation reactions, in place of substitution reactions, the development of novel reactions and heterogeneous catalysts is required.

Recent advances in continuous-flow organocatalysis for process intensification

The progresses on continuous-flow organocatalysis from 2016 to early 2020 are reviewed with focus on transition from batch to flow.

Continuous flow chemistry: where are we now? Recent applications, challenges and limitations

A general outlook of the changing face of chemical synthesis is provided in this article through recent applications of continuous flow processing in both industry and academia. The benefits, major challenges and limitations associated with the use of this mode of processing are also given due attention as an attempt to put into perspective the current position of continuous flow processing, either as an alternative or potential combinatory technology for batch processing.

Chiral catalysts immobilized on achiral polymers: effect of the polymer support on the performance of the catalyst

Achiral polymeric supports can have important positive effects on the activity, stability and selectivity of supported chiral catalysts.

Safety assessment in development and operation of modular continuous-flow processes

Improved safety is one of the main drivers for microreactor application in chemical process development and small-scale production.