Emerging trends in the optimization of organic synthesis through high-throughput tools and machine learning

• Pablo Quijano Velasco,
• Kedar Hippalgaonkar and
• Balamurugan Ramalingam

Beilstein J. Org. Chem. 2025, 21, 10–38, doi:10.3762/bjoc.21.3

• chemistry. Packed bed reactors are used when solid heterogeneous catalysts and reagents (e.g., inorganic bases) are handled. Specialized reactors for electro- [36][37] and photochemical [38][39][40] experiments have also been developed. Depending on the flow of the reaction mixture, flow reactions can be

• system comprised of a flow chemistry synthesis platform, a reagent delivery system, a packed bed reactor, process-analytical tools, and an integrated software control system that automates end-to-end process operations and monitoring. The system has been used to demonstrate the synthesis of at least ten

• Bédard et al. [62] to mitigate some of the challenges in traditional organic synthesis by the integration of hardware, software, and analytics. Comprising an array of modular components, including units for heating, cooling, LED light exposure, and packed bed reactors, it provides a flexible platform for

C3-Alkylation of furfural derivatives by continuous flow homogeneous catalysis

• Grédy Kiala Kinkutu,
• Catherine Louis,
• Myriam Roy,
• Juliette Blanchard and
• Julie Oble

Beilstein J. Org. Chem. 2023, 19, 582–592, doi:10.3762/bjoc.19.43

• with dried toluene to a total volume of 3.5 mL. The mixture was stirred at room temperature to completely dissolve the catalyst. The solution A is pumped into pump 1 (0.1 mL·min−1) and passed through the packed bed reactor which is set at 130 °C containing MgSO4. The residence time depends on the

Heterogeneous metallaphotoredox catalysis in a continuous-flow packed-bed reactor

• Wei-Hsin Hsu,
• Susanne Reischauer,
• Peter H. Seeberger,
• Bartholomäus Pieber and
• Dario Cambié

Beilstein J. Org. Chem. 2022, 18, 1123–1130, doi:10.3762/bjoc.18.115

• and scalable reaction conditions. Here, we report a continuous-flow approach to metallaphotoredox catalysis using a heterogeneous catalyst that combines the function of a photo- and a nickel catalyst in a single material. The catalyst is embedded in a packed-bed reactor to combine reaction and

• (catalyst) separation in one step. The use of a packed bed simplifies the translation of optimized batch reaction conditions to continuous flow, as the only components present in the reaction mixture are the substrate and a base. The metallaphotoredox cross-coupling of sulfinates with aryl halides was used

• ; heterogeneous catalysis; metallaphotoredox catalysis; packed bed; photochemistry; Introduction The amount and impact of visible-light-mediated protocols in organic synthesis have increased dramatically since the late 2000s [1]. The main driving force of this phenomenon is the novel reactivity afforded by

Synthesis of odorants in flow and their applications in perfumery

• Merlin Kleoff,
• Paul Kiler and
• Philipp Heretsch

Beilstein J. Org. Chem. 2022, 18, 754–768, doi:10.3762/bjoc.18.76

• of up to 0.35 kg/h for enone 4. In the second step, the obtained 4-aryl-3-buten-2-ones 3 and 4 are selectively hydrogenated in flow using a packed-bed reactor with Raney nickel as catalyst affording raspberry ketone (5) in 91% yield and raspberry ketone methyl ether (6) in 94% yield, respectively

• min isoamyl acetate (10) is obtained in 59% yield according to GC analysis [26]. Related methods for the enzyme-catalyzed acetylation of isoamyl alcohol (9) have been developed utilizing biphasic systems, supercritical carbon dioxide as a solvent, or packed-bed reactors with immobilized enzymes [27

• smegmatis (Scheme 4) [32]. A solution of the acyl donor 12 in ethyl acetate and an aqueous buffer solution of the corresponding alcohols 11 are mixed in a T-piece and the resulting segmented flow is pumped through a packed-bed reactor containing the immobilized transferase. The reaction mixture is directly

Inductive heating and flow chemistry – a perfect synergy of emerging enabling technologies

• Conrad Kuhwald,
• Sibel Türkhan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2022, 18, 688–706, doi:10.3762/bjoc.18.70

• dioxide (core-shell nanostructured particles), called MagSilicaTM to be used as fixed-bed materials in many different continuous flow processes (Figure 4A) [50]. These materials are excited very rapidly in a medium frequency (25 kHz) electromagnetic field, heating reaction mixtures in packed bed reactors

• electromagnetic field. Other comparisons include the Pd-mediated transfer hydrogenations using ethanol in cyclohexene (Scheme 9, case A), multicomponent reactions (Scheme 9, case B), pericyclic reactions (Scheme 10, case A) and Pd-catalyzed reactions (Scheme 10, case B) [53]. Noteworthy, packed bed fillings used

• fixed-bed material (Scheme 11, case A) [72][73]. The reaction was carried out at 150 °C and an internal pressure of 7 bar. Remarkably, the process could be operated for 15 h with a slight decrease of effciency. Importantly, the catalyst activity can completely be restored when heating the packed bed to

Shift of the reaction equilibrium at high pressure in the continuous synthesis of neuraminic acid

• Jannis A. Reich,
• Miriam Aßmann,
• Kristin Hölting,
• Paul Bubenheim,
• Jürgen Kuballa and
• Andreas Liese

Beilstein J. Org. Chem. 2022, 18, 567–579, doi:10.3762/bjoc.18.59

• 2018a using the trapz function. The given values for τ do not account for the porosity of the packed bed. They are calculated via Equation 1 with V as the volume of the empty reactor and as the volumetric flow rate. Kinetics To investigate the influence of pressure on the selected reaction, a

Flow synthesis of oxadiazoles coupled with sequential in-line extraction and chromatography

• Kian Donnelly and
• Marcus Baumann

Beilstein J. Org. Chem. 2022, 18, 232–239, doi:10.3762/bjoc.18.27

• approach. This entails the use of a heated packed-bed reactor filled with solid K2CO3 as a base. Using DMSO as solvent, this flow method generates the target heterocycles within short residence times of 10 minutes and in yields up to 93%. Scale-up of this flow process was achieved (34 mmol/h) and featured

• batch mode to continuous flow mode. The use of an insoluble reagent (e.g. K2CO3) is generally problematic with continuous flow reactors, due to the high probability of blockages occurring within the reactor tubing. To overcome this, we opted to incorporate a packed bed reactor into the continuous flow

• setup. The initial setup consisted of a heated glass column (i.d. 7 mm, length 7 cm), packed with K2CO3, through which a solution of acyl hydrazone and iodine were passed. It was anticipated that the larger excess of K2CO3 present in the packed bed reactor (when compared to batch mode), in addition to

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

• areas of chemistry improving performance and utility, for example, reinvigorating the area of solid-supported reagents [78]. The incorporation of solid reagents is facilitated in flow through the use of packed bed columns and channels. Consequently, the filtration necessary as part of a batch process

• carrying out aldol processes in flow is the possibility to incorporate heterogeneous solid-supported reagents as catalysts. The ways in which these are used fall into three main categories; monolithic (a), wall-coated (b) and packed bed (c) reactors (Figure 6) [105]. Monolithic columns are prepared by

• reagent incorporation into a mixture of monomers which are co-polymerised to create a network of micro- and mesoporous channels that fill the entirety of the tube/column. In a coated wall reactor, the reagent is immobilised onto the inner surface of the reactor. Finally, packed bed reactor columns are

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• ]. Zhou and co-workers employed 4-methoxycalix[7]arene and quartz beads as the host and packing material, respectively (Figure 13). The formed packed bed could then immobilize TiO2. Therein, the 4-methoxycalix[7]arene not only led to a decrease in the band gap of TiO2 but also prohibited the recombination

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors

• Emine Kayahan,
• Mathias Jacobs,
• Leen Braeken,
• Leen C.J. Thomassen,
• Simon Kuhn,
• Tom van Gerven and
• M. Enis Leblebici

Beilstein J. Org. Chem. 2020, 16, 2484–2504, doi:10.3762/bjoc.16.202

• : microreactor; microreactor scale-up; monolith reactors; packed bed reactor; photoreactor scale-up; Review Introduction In the traditional chemical industry, thermochemical activation routes are mostly preferred. Light can also activate some molecules, which leads to fast and selective reaction pathways

• intrinsic kinetics, is to create micro- or mesostructures in large vessels. Translucent packed bed reactors and aerosol photoreactors are examples of such designs. Below, we will discuss several scale-up strategies applied in photochemistry. Most researchers that utilize photomicroreactors suggest that

• could not be calculated. Packed-bed structures are often used for mass transfer enhancement. Once the channel size is adjusted, translucent packed structures can be used as an alternative scale-up strategy to the numbering-up of microreactors. Claes et al. adjusted the size of the beads in a catalytic

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

Disposable cartridge concept for the on-demand synthesis of turbo Grignards, Knochel–Hauser amides, and magnesium alkoxides

• Mateo Berton,
• Kevin Sheehan,
• Andrea Adamo and
• D. Tyler McQuade

Beilstein J. Org. Chem. 2020, 16, 1343–1356, doi:10.3762/bjoc.16.115

• batch-to-batch variability. Tubular reactors of solid reagents combined with solution-phase reagents enable the continuous-flow preparation of organomagnesium reagents. The use of stratified packed-bed columns of magnesium metal and lithium chloride for the synthesis of highly concentrated turbo

• fresh organomagnesium reagents on a discovery scale and will do so independent from the operator’s experience in flow and/or organometallic chemistry. Keywords: Knochel–Hauser base; lithium chloride; magnesium; on-demand; packed-bed reactors; plug and flow reactor; synthesizer; turbo Grignard reagent

• . The design presented here is based on a disposable cartridge concept, inspired by pod-based coffee machines (Figure 1). We took inspiration from recent efforts that demonstrated that simple machines can do valuable chemistry [12]. Our “cartridge” encompasses reagent bags, tubing, and packed-bed

Low-budget 3D-printed equipment for continuous flow reactions

• Jochen M. Neumaier,
• Amiera Madani,
• Thomas Klein and
• Thomas Ziegler

Beilstein J. Org. Chem. 2019, 15, 558–566, doi:10.3762/bjoc.15.50

• ]. Unfortunately, the synthetic steps for the glycoside preparation could not be combined in a multistep reaction, due to clogging of the packed bed reactor, most likely due to the formation of silver bromide during the Koenigs–Knorr reaction. No such clogging was observed when the column was packed with Fetizon’s

• preparing acetobromo glycoses. In order to show the suitability of our flow system for the preparation of simple glycosides, we first tested Koenigs–Knorr glycosylation conditions with silver triflate as activator. Thus, silver triflate (2 equiv) was mixed with molecular sieves (4 Å) and placed in a packed

• bed reactor. Next, a solution of acetobromo glucose (2) in dichloromethane (0.25 M) and methanol were pumped through the reactor at such a rate that ca. 20 mol equivalents of methanol were present in the mixture. Scheme 2 shows the setup of the glycosylation reaction under flow conditions. Best

Assessing the possibilities of designing a unified multistep continuous flow synthesis platform

• Mrityunjay K. Sharma,
• Roopashri B. Acharya,
• Chinmay A. Shukla and
• Amol A. Kulkarni

Beilstein J. Org. Chem. 2018, 14, 1917–1936, doi:10.3762/bjoc.14.166

• in performing multiple reactions in a single platform as given above: The number of valves needed to select the desired set of equipment is much higher. The reactions which take place only in a packed bed reactor and do not involve a separator, filter, crystallizer, etc. The path required for the

• aqueous NaOH through pump P4 which is heated to 140 °C through HE1. In-line extraction and purification happen in packed bed column reactor R6 by water and hexane which are pumped through pump P35 and P36. The resulting biphasic solution passes through gravity operated liquid–liquid separator S2 with

• interconnected. The first, reactor module includes different reactors types that are commonly used in the synthesis of APIs viz. tubular reactor (R1–R4), packed bed reactor (R5–R8) and stirred tank reactor (R9). The reactors are equipped with a jacket for maintaining the reaction temperatures. Additionally

High-yielding continuous-flow synthesis of antimalarial drug hydroxychloroquine

• Eric Yu,
• Hari P. R. Mangunuru,
• Nakul S. Telang,
• Caleb J. Kong,
• Jenson Verghese,
• Stanley E. Gilliland III,
• Saeed Ahmad,
• Raymond N. Dominey and
• B. Frank Gupton

Beilstein J. Org. Chem. 2018, 14, 583–592, doi:10.3762/bjoc.14.45

• synthesis of the antimalarial drug hydroxychloroquine (HCQ). Key improvements in the new process include the elimination of protecting groups with an overall yield improvement of 52% over the current commercial process. The continuous process employs a combination of packed bed reactors with continuous

• next step 6 was reacted with hydroxylamine, which was facilitated by passing through a packed-bed of K2CO3 to give oxime 11 (Table 2). As was seen with the reaction to produce 6 (Table S1 in Supporting Information File 1), reactant concentrations also had a dramatic effect on the oxime formation. A

• flushed with nitrogen gas. At room temperature, the stock solutions of 5-iodopentan-2-one (10, 1.0 M) and 2-(ethylamino)ethan-1-ol (7) in THF solution (1.0 M) were streamed in at 0.5 mL min−1 via a T-piece into a 10 mL reactor coil (tR = 10 min) and passed through a packed bed reactor of potassium

Latest development in the synthesis of ursodeoxycholic acid (UDCA): a critical review

• Fabio Tonin and
• Isabel W. C. E. Arends

Beilstein J. Org. Chem. 2018, 14, 470–483, doi:10.3762/bjoc.14.33

• the half-life (23 h) is lower and the biocatalyst can be reused for only five cycles of conversions. In order to reduce the mechanical stress that might inactivate the immobilized enzymes, the flow-system represents a valid technology. The packed-bed reactor set up by Zheng et al. partially solved

A concise flow synthesis of indole-3-carboxylic ester and its derivatisation to an auxin mimic

• Marcus Baumann,
• Ian R. Baxendale and
• Fabien Deplante

Beilstein J. Org. Chem. 2017, 13, 2549–2560, doi:10.3762/bjoc.13.251

• through a heated (55 °C) flow coil and then through a packed bed scavenging cartridge containing QP-DMA (N,N-dimethylbenzylamine polystyrene). Following solvent evaporation this gave the product as an off white solid in 91% isolated yield. In practice this approach proved far superior to the previously

Automating multistep flow synthesis: approach and challenges in integrating chemistry, machines and logic

• Chinmay A. Shukla and
• Amol A. Kulkarni

Beilstein J. Org. Chem. 2017, 13, 960–987, doi:10.3762/bjoc.13.97

• ratio using a ratio controller. This mixed stream can be passed through a packed bed reactor containing a Pd/C catalyst and maintained at 40 °C using a heating jacket. The reactor outlet concentration can be monitored inline and controlled by manipulating the jacket fluid flow rate of the reactor. The

• through a packed bed reactor containing silica-supported Ti(OiPr)4 maintained at 85 °C using a reactor jacket to obtain the olanzapine drug. While the above mentioned automated protocol can be implemented for the synthesis in Scheme 1, it is not easy to implement a few aspects that are routinely used in

• (like UV, IR or Raman spectroscopy) which may be coupled with the reactor jacket flow rate to maintain the desired conversion. The azide and amide streams can be mixed and preheated at 110 °C. The preheated stream can then flow through a copper tubing reactor or a packed bed reactor with copper packings

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

• Carmen Moreno-Marrodan,
• Francesca Liguori and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2017, 13, 734–754, doi:10.3762/bjoc.13.73

• alkynes, i.e., capillary, packed-bed, honeycomb and monolithic reactors. A schematic representation of these reactors is shown in Figure 1. Other reactor types (e.g., fluidized bed reactor, wherein the solid catalyst is suspended in a fluid) have not been reported for liquid-phase alkyne hydrogenations

• . It is important mentioning that different flow regimes can be attained in miniaturized channels, depending on the gas and liquid rates, as these may affect both conversion and selectivity of the process (Figure 2). Packed-bed reactors are among the most used systems since they are relatively simple

• catalysis [103][104]. Monolithic reactors may surpass most drawbacks typical of packed-bed systems, including high pressure drops, low contacting efficiency, large distribution of residence times, formation of hot-spots or stagnation zones, which results in poorly controlled fluid dynamics, hence in low

Electron-transfer-initiated benzoin- and Stetter-like reactions in packed-bed reactors for process intensification

• Anna Zaghi,
• Daniele Ragno,
• Graziano Di Carmine,
• Carmela De Risi,
• Olga Bortolini,
• Pier Paolo Giovannini,
• Giancarlo Fantin and
• Alessandro Massi

Beilstein J. Org. Chem. 2016, 12, 2719–2730, doi:10.3762/bjoc.12.268

• (DMF) solvent to the α-diketone and generate the corresponding enediolate active species. After having identified the 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine on polystyrene (PS-BEMP) as the suitable base, packed-bed microreactors (pressure-resistant stainless-steel

• asymmetric version of acyloin-type reactions was also investigated in our laboratory operating packed-bed bioreactors functionalized with a suitable thiamine diphosphate (ThDP)-dependent enzyme supported on mesoporous silica [17]. Overall, the so far reported umpolung flow processes [12][13][14][15][16][17

Selective synthesis of thioethers in the presence of a transition-metal-free solid Lewis acid

• Federica Santoro,
• Matteo Mariani,
• Federica Zaccheria,
• Rinaldo Psaro and
• Nicoletta Ravasio

Beilstein J. Org. Chem. 2016, 12, 2627–2635, doi:10.3762/bjoc.12.259

• of thiols has also been carried out under flow conditions in the presence of a heterogeneous base in a packed bed reactor but also in this case alkyl halides were used as electrophiles [28]. The reaction we are presenting here takes place in the presence of a solid catalyst starting from the alcohol

Integration of enabling methods for the automated flow preparation of piperazine-2-carboxamide

• Richard J. Ingham,
• Claudio Battilocchio,
• Joel M. Hawkins and
• Steven V. Ley

Beilstein J. Org. Chem. 2014, 10, 641–652, doi:10.3762/bjoc.10.56

• which demonstrated the hydration of broad classes of nitriles by passing aqueous–organic solutions through a packed bed of manganese dioxide [21], we have found that heteroaromatic nitriles possessing a β-heteroatom can also be hydrolysed using hydrous zirconia [22][23] in a similar fashion (Figure 3

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• , 25 °C for aldimine formation (first step) in the MM K-10 containing packed-bed capillary reactor (PBCR), and 80 °C for the reaction with phenylacetylene (second step) in Au NP@Al2O3 containing PBCR. The system, tested with some different aryl/heteroaryl/alkylaldehydes and cyclic/acyclic secondary

Continuous flow nitration in miniaturized devices

• Amol A. Kulkarni

Beilstein J. Org. Chem. 2014, 10, 405–424, doi:10.3762/bjoc.10.38

• , can improve the selectivity of p-nitrotoluene in a conventional reactor using a mixed acid as the nitrating agent [52][53]. Continuous flow nitration of toluene in a packed bed microreactor using concentrated nitric acid as the nitrating agent was reported by Halder et al. [54]. Different ‘solid acid

Flow microreactor synthesis in organo-fluorine chemistry

• Hideki Amii,
• Aiichiro Nagaki and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2013, 9, 2793–2802, doi:10.3762/bjoc.9.314

• . Furthermore, efficient mixing becomes difficult when dealing with large quantities of insoluble CsF. They invented a packed-bed flow reactor, which allowed for easy handling of large quantities of insoluble CsF with efficient mixing (Scheme 5) [53]. As an alternative method for aromatic fluorination, Yoshida