Continuous Flow Coupling and Decarboxylation Reactions Promoted by Copper Tubing

Complementary catalysis and analysis within solid state additively manufactured metal micro flow reactors

Additive Manufacturing is transforming how researchers and industrialists look to design and manufacture chemical devices to meet their specific needs. In this work, we report the first example of a flow reactor formed via the solid-state metal sheet lamination technique, Ultrasonic Additive Manufacturing (UAM), with directly integrated catalytic sections and sensing elements. The UAM technology not only overcomes many of the current limitations associated with the additive manufacturing of chemical reactionware but it also significantly increases the functionality of such devices. A range of biologically important 1, 4-disubstituted 1, 2, 3-triazole compounds were successfully synthesised and optimised in-flow through a Cu mediated Huisgen 1, 3-dipolar cycloaddition using the UAM chemical device. By exploiting the unique properties of UAM and continuous flow processing, the device was able to catalyse the proceeding reactions whilst also providing real-time feedback for reaction monitoring and optimisation.

Flow chemistry as a tool to access novel chemical space for drug discovery

This perspective scrutinizes flow chemistry as a useful tool for medicinal chemists to expand the current chemical capabilities in drug discovery. This technology has demonstrated his value not only for the traditional reactions used in Pharma for the last 20 years, but also for bringing back to the lab underused chemistries to access novel chemical space. The combination with other technologies, such as photochemistry and electrochemistry, is opening new avenues for reactivity that will smoothen the access to complex molecules. The introduction of all these technologies in automated platforms will improve the productivity of medicinal chemistry labs reducing the cycle times to get novel and differentiated bioactive molecules, accelerating discovery cycle times.

A numbering-up metal microreactor for the high-throughput production of a commercial drug by copper catalysis

Microreactors are emerging as an efficient, sustainable synthetic tool compared to conventional batch reactors. Here, we present a new numbering-up metal microreactor by integrating a flow distributor and a copper catalytic module for high productivity of a commercial synthetic drug. A flow distributor and an embedded baffle disc were manufactured by CNC machining and 3D printing of stainless steel (S/S), respectively, whereas a catalytic reaction module was composed of 25 copper coiled capillaries configured in parallel. Eventually, the numbering-up microreactor system assembled with functional modules showed uniform flow distribution and high mixing efficiency regardless of clogging, and achieved high-throughput synthesis of the drug "rufinamide", an anticonvulsant medicine, via a Cu(i)-catalyzed azide-alkyne cycloaddition reaction under optimized conditions.

C-H functionalization reactions under flow conditions

C-H functionalization technologies have progressed enormously in the last decade as testified by the great number of publications that have appeared in the literature, which are receiving great attention from researchers from different areas of expertise. While most of the protocols reported realize the C-H functionalization processes under batch conditions, there is a growing interest in the development of continuous-flow procedures aiming at increasing the performances of established methodologies or the definition of otherwise unfeasible transformations. This review summarizes the application of flow technologies for the realization of C-H functionalization reactions. According to the type of flow reactors necessary, two main general approaches are possible for the application of flow techniques, namely the use of homogeneous or heterogeneous conditions. Each example is discussed and accompanied by the description of the main features and benefits of the use of flow compared to batch conditions.

Continuous flow biocatalysis

The continuous flow synthesis of active pharmaceutical ingredients, value-added chemicals, and materials has grown tremendously over the past ten years. This revolution in chemical manufacturing has resulted from innovations in both new methodology and technology. This field, however, has been predominantly focused on synthetic organic chemistry, and the use of biocatalysts in continuous flow systems is only now becoming popular. Although immobilized enzymes and whole cells in batch systems are common, their continuous flow counterparts have grown rapidly over the past two years. With continuous flow systems offering improved mixing, mass transfer, thermal control, pressurized processing, decreased variation, automation, process analytical technology, and in-line purification, the combination of biocatalysis and flow chemistry opens powerful new process windows. This Review explores continuous flow biocatalysts with emphasis on new technology, enzymes, whole cells, co-factor recycling, and immobilization methods for the synthesis of pharmaceuticals, value-added chemicals, and materials.

Batch–flow hybrid synthesis of the antipsychotic clozapine

The development of batch–flow hybrid processes is becoming an attractive prospect through which chemists can make use of the best aspects of both technologies.

The assembly and use of continuous flow systems for chemical synthesis

The adoption of and opportunities in continuous flow synthesis ('flow chemistry') have increased significantly over the past several years. Continuous flow systems provide improved reaction safety and accelerated reaction kinetics, and have synthesised several active pharmaceutical ingredients in automated reconfigurable systems. Although continuous flow platforms are commercially available, systems constructed 'in-lab' provide researchers with a flexible, versatile, and cost-effective alternative. Herein, we describe the assembly and use of a modular continuous flow apparatus from readily available and affordable parts in as little as 30 min. Once assembled, the synthesis of a sulfonamide by reacting 4-chlorobenzenesulfonyl chloride with dibenzylamine in a single reactor coil with an in-line quench is presented. This example reaction offers the opportunity to learn several important skills including reactor construction, charging of a back-pressure regulator, assembly of stainless-steel syringes, assembly of a continuous flow system with multiple junctions, and yield determination. From our extensive experience of single-step and multistep continuous flow synthesis, we also describe solutions to commonly encountered technical problems such as precipitation of solids ('clogging') and reactor failure. Following this protocol, a nonspecialist can assemble a continuous flow system from reactor coils, syringes, pumps, in-line liquid-liquid separators, drying columns, back-pressure regulators, static mixers, and packed-bed reactors.

A Modular Flow Design for the meta-Selective C-H Arylation of Anilines

Described herein is an effective and practical modular flow design for the meta-selective C-H arylation of anilines. The design consists of four continuous-flow modules (i.e., diaryliodonium salt synthesis, meta-selective C-H arylation, inline copper extraction, and aniline deprotection) which can be operated either individually or consecutively to provide direct access to meta-arylated anilines. With a total residence time of 1 hour, the desired product could be obtained in high yield and excellent purity without the need for column chromatography, and the residual copper content meets the standards for parenterally administered pharmaceutical substances.

The Hitchhiker's Guide to Flow Chemistry ∥

Flow chemistry involves the use of channels or tubing to conduct a reaction in a continuous stream rather than in a flask. Flow equipment provides chemists with unique control over reaction parameters enhancing reactivity or in some cases enabling new reactions. This relatively young technology has received a remarkable amount of attention in the past decade with many reports on what can be done in flow. Until recently, however, the question, "Should we do this in flow?" has merely been an afterthought. This review introduces readers to the basic principles and fundamentals of flow chemistry and critically discusses recent flow chemistry accounts.

Continuous flow-ultrasonic synergy in click reactions for the synthesis of novel 1,2,3-triazolyl appended 4,5-unsaturated l-ascorbic acid derivatives

A combination of flow chemistry and batch-based synthetic procedures has been successfully applied to the assembly of novel 4,5-unsaturated l-ascorbic acid series 6a–6n with diverse C-6-substituted 1,2,3-triazole moiety.

Taming hazardous chemistry by continuous flow technology

Over the last two decades, flow technologies have become increasingly popular in the field of organic chemistry, offering solutions for engineering and/or chemical problems. Flow reactors enhance the mass and heat transfer, resulting in rapid reaction mixing, and enable a precise control over the reaction parameters, increasing the overall process selectivity, efficiency and safety. These features allow chemists to tackle unexploited challenges in their work, with the ultimate objective making chemistry more accessible for laboratory and industrial applications, avoiding the need to store and handle toxic, reactive and explosive reagents. This review covers some of the latest and most relevant developments in the field of continuous flow chemistry with the focus on hazardous reactions.

The utilization of copper flow reactors in organic synthesis

The use of flow chemistry techniques has flourished over the past decade, with the field expanding to include the use of copper flow reactors in bench-top organic synthesis in recent years. These reactors are available in a variety of forms and possess a number of advantages over their batch reaction counterparts, in terms of both safety and yield. This review will highlight the current research employing copper flow reactors, such as 1,3-dipolar cycloadditions ('click' chemistry), macrocyclizations (via 'click' chemistry), Sonogashira C-C couplings, Ullmann couplings, decarboxylations, and other reported findings.

Decarboxylative Reissert type trifluoro- and trichloro-methylation of (iso)quinoline derivatives in batch and continuous flow

Copper-free decarboxylative trifluoro- and trichloromethylation of isoquinoline and quinoline derivatives through Reissert type reactions in batch and telescoped continuous flow.

Tandem Click-Suzuki reactions in a novel flow reactor incorporating immobilized and exchangeable reagents

A custom-built modular flow reactor featuring immobilized reagents in exchangeable cartridges has been developed.

Copper catalysed Ullmann type chemistry: from mechanistic aspects to modern development

Cu-catalysed arylation reactions devoted to the formation of C-C and C-heteroatom bonds (Ullmann-type couplings) have acquired great importance in the last decade. This review discusses the history and development of coupling reactions between aryl halides and various classes of nucleophiles, focusing mostly on the different mechanisms proposed through the years. Selected mechanistic investigations are treated more in depth than others. For example, evidence in favour or against radical mechanisms is discussed. Cu(I) and Cu(III) complexes involved in the Ullmann reaction and N/O selectivity in aminoalcohol arylation are discussed. A separate section has been dedicated to the synthesis of heterocyclic rings through intramolecular couplings. Finally, recent developments in green chemistry for these reactions, such as reactions in aqueous media and heterogeneous catalysis, have also been reviewed.

Sonogashira cross-coupling under non-basic conditions. Flow chemistry as a new paradigm in reaction control

The Sonogashira reaction under non-basic conditions.

Ru-catalyzed decarboxylative cyclization of mandelic acids with acrylates: facile access to the phthalide skeleton

A Ru-catalyzed decarboxylative cyclization of mandeic acids with acrylates was developed, which provides an efficient route to the phthalide skeleton.

Cross-coupling reactions catalyzed by an N-heterocyclic carbene–Pd(ii) complex under aerobic and CuI-free conditions

The catalytic reactions proceed with good yields with a low catalyst loading (1 mol%) under aerobic and CuI-free conditions for Sonogashira and Heck reactions.

Rapid and efficient trifluoromethylation of aromatic and heteroaromatic compounds using potassium trifluoroacetate enabled by a flow system

Going to the source: The trifluoromethylation of aryl/heteroaryl iodides has been demonstrated using a flow system, thus enabling a rapid rate of reaction. A broad spectrum of trifluoromethylated compounds was prepared in good to excellent yields using CF3 CO2 K as the trifluoromethyl source. The process has the advantage of short reaction times and uses convenient [CF3 ] sources.

Rapid discovery of a novel series of Abl kinase inhibitors by application of an integrated microfluidic synthesis and screening platform

Drug discovery faces economic and scientific imperatives to deliver lead molecules rapidly and efficiently. Using traditional paradigms the molecular design, synthesis, and screening loops enforce a significant time delay leading to inefficient use of data in the iterative molecular design process. Here, we report the application of a flow technology platform integrating the key elements of structure-activity relationship (SAR) generation to the discovery of novel Abl kinase inhibitors. The platform utilizes flow chemistry for rapid in-line synthesis, automated purification, and analysis coupled with bioassay. The combination of activity prediction using Random-Forest regression with chemical space sampling algorithms allows the construction of an activity model that refines itself after every iteration of synthesis and biological result. Within just 21 compounds, the automated process identified a novel template and hinge binding motif with pIC50 > 8 against Abl kinase--both wild type and clinically relevant mutants. Integrated microfluidic synthesis and screening coupled with machine learning design have the potential to greatly reduce the time and cost of drug discovery within the hit-to-lead and lead optimization phases.

Rapid access to compound libraries through flow technology: fully automated synthesis of a 3-aminoindolizine library via orthogonal diversification

A novel methodology for the synthesis of druglike heterocycle libraries has been developed through the use of flow reactor technology. The strategy employs orthogonal modification of a heterocyclic core, which is generated in situ, and was used to construct both a 25-membered library of druglike 3-aminoindolizines, and selected examples of a 100-member virtual library. This general protocol allows a broad range of acylation, alkylation and sulfonamidation reactions to be performed in conjunction with a tandem Sonogashira coupling/cycloisomerization sequence. All three synthetic steps were conducted under full automation in the flow reactor, with no handling or isolation of intermediates, to afford the desired products in good yields. This fully automated, multistep flow approach opens the way to highly efficient generation of druglike heterocyclic systems as part of a lead discovery strategy or within a lead optimization program.

Diisobutylaluminum hydride reductions revitalized: a fast, robust, and selective continuous flow system for aldehyde synthesis

A continuous flow system for the multiparameter (flow rate, temperature, residence time, stoichiometry) optimization of the DIBALH reduction of esters to aldehydes is described. Incorporating an in-line quench (MeOH), these transformations are generally complete in fewer than 60 s. Mixing of the DIBALH and ester solutions was observed to be an exceptionally critical parameter for optimum results. This system thus provides general guidelines based on the structure of the ester for selective reduction of an ester without overreduction.