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

• employs silicon-glass and tubular reactors packed with nanoparticle supported catalysts. The apparatus allows the desired material to be prepared in 48% yield. The authors pointed out better outcomes were obtained in batch using a MgO-based catalyst, whose usage proved troublesome in flow due to clogging

• . In 2008, the group of Sartori developed a flow setup for nitroaldol condensations of different benzaldehydes exploiting a silica-supported amine (KG-60-NH2) as a heterogeneous catalyst (Scheme 21) [133]. Secondary and tertiary amine-supported catalysts were also investigated, although they were found

Activation of pentafluoropropane isomers at a nanoscopic aluminum chlorofluoride: hydrodefluorination versus dehydrofluorination

• Maëva-Charlotte Kervarec,
• Thomas Braun,
• Mike Ahrens and
• Erhard Kemnitz

Beilstein J. Org. Chem. 2020, 16, 2623–2635, doi:10.3762/bjoc.16.213

• pentafluoropropanes (HFC-245 isomers) using chromia-based catalysts, or metal chloride/fluoride (AlF3, MgF2)-supported catalysts at elevated temperatures (350 °C) [11][14][15][17][18]. The group of Lu recently reported the gas-phase transformation of 1,1,1,3,3-pentafluoropropane (HFC-245eb) into 1,3,3,3

Synergy between supported ionic liquid-like phases and immobilized palladium N-heterocyclic carbene–phosphine complexes for the Negishi reaction under flow conditions

• Edgar Peris,
• Raúl Porcar,
• María Macia,
• Jesús Alcázar,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2020, 16, 1924–1935, doi:10.3762/bjoc.16.159

• performance in the presence of one equivalent of the phosphine. The catalysts prepared by NaBH4 reduction were slightly less reactive than those obtained with EtOH as reducing agent. Noteworthy, the supported catalysts were active in further catalytic cycles after separation of the product by filtration and

• distribution 3.12 ± 0.97 nm. Synthesis of NHC-supported catalysts. Negishi benchmark reaction. Synthesis of immobilized NHC–Pd–RuPhos. Pd species immobilized onto SILLPs. i) 1 g SILLP 10, 100 mg PdCl2 in milli-Q® water (100 mL 1% HCl, 1000 ppm PdCl2), orbitalic stirring, rt, 5 h. ii) 250 mg Pd-SILLP 11, 0.2 g

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

Activated carbon as catalyst support: precursors, preparation, modification and characterization

• Melanie Iwanow,
• Tobias Gärtner,
• Volker Sieber and
• Burkhard König

Beilstein J. Org. Chem. 2020, 16, 1188–1202, doi:10.3762/bjoc.16.104

• of the carbon surface influence the acid–base and hydrophilic character and thus can affect the preparation of carbon-supported catalysts. Different types of active phase–support interactions can be induced by the introduction of heteroatoms on the carbon surface, which is only marginally possible in

• other catalyst supports, e.g., silica or alumina [2]. Depending on the application of the carbon-supported catalysts, different possibilies are available for the modification of the properties on the surface of the activated carbon materials. Oxygen-containing surface groups: The amount and composition

• impregnation method is comparatively simple and thus widely used in the preparation of supported catalysts. Three different methods are available: wet impregnation, incipient-wetness impregnation and ionic adsorption. Using these methods for the preparation of supported metal catalysts, the interaction between

Ugi reaction-derived prolyl peptide catalysts grafted on the renewable polymer polyfurfuryl alcohol for applications in heterogeneous enamine catalysis

• Alexander F. de la Torre,
• Gabriel S. Scatena,
• Oscar Valdés,
• Daniel G. Rivera and
• Márcio W. Paixão

Beilstein J. Org. Chem. 2019, 15, 1210–1216, doi:10.3762/bjoc.15.118

• polyfurfuryl alcohol-supported catalysts for applications in heterogeneous enamine catalysis. The utilization of the polymer-supported catalysts in both batch and continuous-flow organocatalytic procedures proved moderate catalytic efficacy and enantioselectivity, but excellent diastereoselectivity in the

• -supported catalysts amenable for continuous-flow asymmetric enamine catalysis [9][10]. The acid-catalyzed polymerization of furfuryl alcohol renders a dark polymer featuring a complex cross-linked polyunsaturated scaffold derived from polycondensation and Diels–Alder reactions [11][12]. Worldwide, there is

• the peptide moieties into the PFA matrix, while proving the good stability of the PFA-supported catalysts under classic working temperatures (i.e., up to 100 °C). To assess the catalytic performance of the PFA-supported catalysts, the model system consisting in organocatalytic conjugate addition of n

Encaging palladium(0) in layered double hydroxide: A sustainable catalyst for solvent-free and ligand-free Heck reaction in a ball mill

• Wei Shi,
• Jingbo Yu,
• Zhijiang Jiang,
• Qiaoling Shao and
• Weike Su

Beilstein J. Org. Chem. 2017, 13, 1661–1668, doi:10.3762/bjoc.13.160

• %), TBAB (1.5 mmol), K2CO3 (3.6 mmol), and silica gel 5 g were placed in a 80 mL stainless-steel vessel (ΦMB = 0.25, dMB = 5 mm). HSBM conditions: 60 min at 800 rpm. Supported catalysts in cross-coupling reactions. MM represents mixer mill; PM represents planetary mill. Selected model reaction. Pd/MgAl

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

• under continuous-flow conditions using supported catalysts. The substrates and the commonly observed products with the labelling adopted in the present review are shown in Scheme 2. Representative data are summarized in Table 1, in which conversions are indicated and catalysts’ efficiencies are

• the earlier discussed hydrogenation of 1-hexyne (see above), the continuous flow, partial hydrogenation of 3-hexyne (10) to cis-3-hexene (10a) has been extensively examined by comparing the efficiency of various packed-bed supported catalysts [119][121][123]. In all cases, irrespective of the metal or

Tunable microwave-assisted method for the solvent-free and catalyst-free peracetylation of natural products

• Manuela Oliverio,
• Paola Costanzo,
• Monica Nardi,
• Carla Calandruccio,
• Raffaele Salerno and
• Antonio Procopio

Beilstein J. Org. Chem. 2016, 12, 2222–2233, doi:10.3762/bjoc.12.214

• heterogeneous or supported catalysts [15][16][17], solid nanopowders or nanoparticles [18][19], non-metal-based heterogeneous acetylation catalysts [20][21][22], as well as natural marine clays instead of homogeneous catalysts as reaction activators [23]. Even if these methods allow a complete peracetylation of

Supported bifunctional thioureas as recoverable and reusable catalysts for enantioselective nitro-Michael reactions

• José M. Andrés,
• Miriam Ceballos,
• Alicia Maestro,
• Isabel Sanz and
• Rafael Pedrosa

Beilstein J. Org. Chem. 2016, 12, 628–635, doi:10.3762/bjoc.12.61

• nitro-Michael addition; supported catalysts; thioureas; Introduction The use of chiral bifunctional thioureas that allow the simultaneous activation of a electrophile, by hydrogen bonding, and a nucleophile, by deprotonation, plays a major role in the stereoselective formation of C–C bonds in different

• organocatalysts in the stereoselective aza-Henry reaction [31]. Now we describe the results obtained in different stereoselective nitro-Michael additions promoted by these materials. Results and Discussion The ability of the supported catalysts (II–V) to promote the stereoselective nitro-Michael reaction was

• next consider the reaction of some 4-substituted nitrostyrenes (1b–d) with diethyl malonate (2a), and the addition of a range of β-functionalized nucleophiles 2b–g to 1a promoted by supported catalysts IV (5 mol %) and V (2 mol %), respectively (Scheme 2 and Table 2). The results obtained in the

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

• Krzysztof Skowerski,
• Jacek Białecki,
• Stefan J. Czarnocki,
• Karolina Żukowska and
• Karol Grela

Beilstein J. Org. Chem. 2016, 12, 5–15, doi:10.3762/bjoc.12.2

• of remotely functionalised ligands within the metal coordination sphere. A very efficient covalent immobilisation through anionic ligands was reported by Buchmeiser et al., who synthesised a series of monolith-supported catalysts (such as 1) which gave metathesis products with extremely low residual

• designed to facilitate straightforward removal of the metal-containing species after the reaction is completed. Although this idea is simple, the preparation of such sophisticated nanoparticle-supported catalysts is often a complicated multistep procedure. Definitely, the simplest and quickest

Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave-assisted green protocol

• Marina Caporaso,
• Giancarlo Cravotto,
• Spyros Georgakopoulos,
• George Heropoulos,
• Katia Martina and
• Silvia Tagliapietra

Beilstein J. Org. Chem. 2014, 10, 1454–1461, doi:10.3762/bjoc.10.149

• developed for the aerobic oxidation of primary and secondary alcohols to aldehydes and ketones using Au [4][5][6][7][8], Pd [9][10][11][12], Ru [13][14][15][16] and Cu [17][18][19] supported catalysts. An elegant approach to the direct oxidative esterification of alcohols has been described in recent years

• catalysts, the common Pd/C is easily handled and filtered off from the reaction mixture. It is remarkably stable under acidic and basic conditions and features a much higher surface area than alumina- and silica-supported catalysts [45]. Moreover, charcoal is rapidly heated under microwave (MW) irradiation

Organocatalysis

• Benjamin List

Beilstein J. Org. Chem. 2012, 8, 1358–1359, doi:10.3762/bjoc.8.156

• on the other hand. There are additional aspects that belong to the field and that are being actively researched, including supported catalysts, organocatalysis in unusual reaction media, and applications in polymerizations, in total synthesis and drug-discovery, as well as in drug manufacturing

Combined bead polymerization and Cinchona organocatalyst immobilization by thiol–ene addition

• Kim A. Fredriksen,
• Tor E. Kristensen and
• Tore Hansen

Beilstein J. Org. Chem. 2012, 8, 1126–1133, doi:10.3762/bjoc.8.125

• 23% ee), and probably not very useful for benchmarking, the supported catalysts 10a–d were obviously catalytically active, albeit modestly selective compared to the free catalyst, giving quantitative yields and a selectivity of 11–14% ee. Of greater interest was the performance of the primary amine

• organocatalysts 11. Polymer-supported catalysts 11a,b were tried out in the asymmetric preparation of the anticoagulant warfarin from benzylideneacetone and 4-hydroxycoumarin, a transformation that we have investigated in our group as part of developmental work in primary amine organocatalysis on a previous

• occasion (Table 2) [18]. Compared to the free catalyst 2, the yields obtained by using supported catalysts 11a,b are inferior, but this is most probably due to the lack of solubility of the hydroxycoumarin, a very insoluble compound, in the reaction medium (CH2Cl2) and probably not so much a lack of

Continuous-flow enantioselective α-aminoxylation of aldehydes catalyzed by a polystyrene-immobilized hydroxyproline

• Xacobe C. Cambeiro,
• Rafael Martín-Rapún,
• Pedro O. Miranda,
• Sonia Sayalero,
• Esther Alza,
• Patricia Llanes and
• Miquel A. Pericàs

Beilstein J. Org. Chem. 2011, 7, 1486–1493, doi:10.3762/bjoc.7.172

• chemistry with solid-supported catalysts allows the advantages inherent to both technologies to be added together. Thus, the physical immobilization of the catalyst in a packed-bed reactor allows it to be submitted constantly to the reaction conditions, avoiding possible degradation of the catalyst during

Continuous preparation of carbon-nanotube-supported platinum catalysts in a flow reactor directly heated by electric current

• Alicja Schlange,
• Antonio Rodolfo dos Santos,
• Ulrich Kunz and
• Thomas Turek

Beilstein J. Org. Chem. 2011, 7, 1412–1420, doi:10.3762/bjoc.7.165

• production of other metal/carbon supported catalysts. Electrocatalyst preparation methods In recent years, different methods for the synthesis of carbon-supported Pt catalysts have been studied. Among these, three methods were mainly used: impregnation method, based on the impregnation of platinum precursor

• ]. In consequence, the preparation of carbon-supported catalysts with smaller noble metal sizes and narrow size distributions is possible [21]. Amongst others, this attractive synthesis method for the production of CNT or carbon-black-supported Pt catalysts was successfully applied by several

• and Discussions Experimental setup For the continuous preparation of CNT-supported catalysts an experimental setup as depicted in Figure 1 and similar to that described in our previous publication [1] was used. As seen in Figure 1 the reaction mixture of platinum precursor, EG and carbon nanotubes was

Efficient and selective chemical transformations under flow conditions: The combination of supported catalysts and supercritical fluids

• M. Isabel Burguete,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2011, 7, 1347–1359, doi:10.3762/bjoc.7.159

Air-stable, recyclable, and time-efficient diphenylphosphinite cellulose-supported palladium nanoparticles as a catalyst for Suzuki–Miyaura reactions

• Qingwei Du and
• Yiqun Li

Beilstein J. Org. Chem. 2011, 7, 378–385, doi:10.3762/bjoc.7.48

• they can be easily separated and recovered [19][20][21][22]. Recently, numerous solid-supported palladium catalysts have been reported which can be used under mild and/or environmentally benign reaction conditions. These supported catalysts were prepared by immobilizing palladium(II) on supported

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites

• Christophe Copéret

Beilstein J. Org. Chem. 2011, 7, 13–21, doi:10.3762/bjoc.7.3

• tool to characterize active sites of heterogeneous catalysts and finally to propose strategies to improve catalysts based on the current state of the art. Keywords: active sites; metathesis; stereoselectivity; supported catalysts; Introduction Achieving high selectivity and, in particular

• how it evolves with time. Stereochemical analysis is therefore a powerful tool that will be exploited thereafter to obtain more information about supported catalysts. Stereoselectivity of heterogeneous alkene metathesis catalysts: a snapshot of the structures of active sites Well-defined silica

• supported catalysts Metathesis of propene in flow reactors can easily allow the kinetic stereoselectivity of a catalyst at low contact times (high space velocity) to be obtained. For instance, [(≡SiO)(t-BuCH2)Re(=CHt-Bu)(≡Ct-Bu)] displays a (E/Z)0 of 2, which is very close the thermodynamic equilibrium

Hydroxyapatite supported caesium carbonate as a new recyclable solid base catalyst for the Knoevenagel condensation in water

• Monika Gupta,
• Rajive Gupta and
• Medha Anand

Beilstein J. Org. Chem. 2009, 5, No. 68, doi:10.3762/bjoc.5.68

• that the catalysis is purely heterogeneous. Similarly, the reaction between 4-methoxybenzaldehyde and malonic acid was also carried out to investigate heterogeneity. The second point is the recyclability and deactivation of the heterogeneous catalyst which are equally important when supported catalysts

Asymmetric reactions in continuous flow

• Xiao Yin Mak,
• Paola Laurino and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2009, 5, No. 19, doi:10.3762/bjoc.5.19

• (in the case of transition metal-catalyzed reactions) also can be problematic in large-scale syntheses, especially in pharmaceutical applications. Consequently, reactions based on the use of supported catalysts are in many ways a more attractive option for the stereoselective synthesis of chiral

• compounds. Supported catalysts are in principle recoverable and, ideally, recyclable. With potential longer term usage, chemical processes can become more economically and environmentally friendly [16][17]. In conjunction with continuous flow, the reaction and separation of catalysts can be performed

• of asymmetric synthesis using solid-supported catalysts is the development of an immobilization strategy that maintains both good stereoselectivity and catalyst activity. Selectivities obtained using homogeneous catalysts that work well in solution phase can often be significantly reduced when