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Molecules
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Current Developments in Continuous-Flow Organocatalysis
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Current Developments in Continuous-Flow Organocatalysis

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (31 October 2023) | Viewed by 9349

Special Issue Editors

Dr. Graziano Di Carmine

E-Mail Website
Guest Editor
Department of Environmental and Prevention Sciences, University of Ferrara, Via L. Borsari 46, 44121 Ferrara, Italy
Interests: organocatalysis; photocatalysis; the immobilization of molecular catalysts; flow chemistry and green chemistry
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Alessandro Massi

E-Mail Website
Guest Editor
Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari 46, 44121 Ferrara, Italy
Interests: flow chemistry; catalysis; green chemistry; microreactors; organic chemistry
Special Issues, Collections and Topics in MDPI journals
Dr. Carmine D'Agostino

E-Mail Website
Guest Editor
Department of Chemical Engineering, The University of Manchester, The Mill, Sackville Street, Manchester M13 9PL, UK
Interests: heterogeneous catalysis; reaction kinetics; hydrogen bonding; ionic liquids; NMR relaxometry; porous materials

Special Issue Information

Dear Colleagues,

Since its rediscovery in 2000 by List and MacMillan, organocatalysis has grown in prominence, becoming one of the pillars in the field of catalysis. In organocatalysis, all reactions are catalyzed by small organic molecules, and metals are generally not involved. This feature makes organocatalysis a greener alternative to reactions mediated by toxic and/or low-abundance metals; it also paves the way to unexplored reactivities. Unfortunately, some drawbacks arise when employing organocatalysis in comparison to biological and metal analogues. Main concerns relate to the high catalytic loading required for performing the reaction in acceptable yield and time, along with tedious purification steps needed to remove catalyst from the reaction mixture. Immobilization of these molecular catalysts onto inert and stable supports, such as silicas and organic polymers, has been the most promising solution explored so far. After catalyst immobilization, the implementation of the process in flow is generally straightforward, and important benefits are often observed, enabling this technology. The aim of this Special Issue is to provide broad perspective of the state of the art in continuous-flow organocatalysis, focusing on new catalysts supported, spectroscopic characterizations, and potential applications in the valorization of biomass and the industrial synthesis of fine chemicals.

Dr. Graziano Di Carmine
Prof. Dr. Alessandro Massi
Dr. Carmine D'Agostino
Guest Editors

Manuscript Submission Information

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Keywords

  • sustainable processes in organic chemistry
  • continuous-flow chemistry
  • immobilization of organocatalysts
  • heterogenous organocatalysis
  • asymmetric synthesis
  • microreactors and mesoreactors

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Published Papers (4 papers)

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Research

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16 pages, 3259 KiB  
Article
Efficiency in Carbon Dioxide Fixation into Cyclic Carbonates: Operating Bifunctional Polyhydroxylated Pyridinium Organocatalysts in Segmented Flow Conditions
by Lorenzo Poletti, Caterina Rovegno, Graziano Di Carmine, Filippo Vacchi, Daniele Ragno, Arianna Brandolese, Alessandro Massi and Paolo Dambruoso
Molecules 2023, 28(4), 1530; https://doi.org/10.3390/molecules28041530 - 4 Feb 2023
Cited by 4 | Viewed by 2460
Abstract
Novel polyhydroxylated ammonium, imidazolium, and pyridinium salt organocatalysts were prepared through N-alkylation sequences using glycidol as the key precursor. The most active pyridinium iodide catalyst effectively promoted the carbonation of a set of terminal epoxides (80 to >95% yields) at a low catalyst [...] Read more.
Novel polyhydroxylated ammonium, imidazolium, and pyridinium salt organocatalysts were prepared through N-alkylation sequences using glycidol as the key precursor. The most active pyridinium iodide catalyst effectively promoted the carbonation of a set of terminal epoxides (80 to >95% yields) at a low catalyst loading (5 mol%), ambient pressure of CO2, and moderate temperature (75 °C) in batch operations, also demonstrating high recyclability and simple downstream separation from the reaction mixture. Moving from batch to segmented flow conditions with the operation of thermostated (75 °C) and pressurized (8.5 atm) home-made reactors significantly reduced the process time (from hours to seconds), increasing the process productivity up to 20.1 mmol(product) h−1 mmol(cat)−1, a value ~17 times higher than that in batch mode. Full article
(This article belongs to the Special Issue Current Developments in Continuous-Flow Organocatalysis)
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12 pages, 2722 KiB  
Article
Laboratory Scale Continuous Flow Systems for the Enantioselective Phase Transfer Catalytic Synthesis of Quaternary Amino Acids
by Milena Krstić, Sergio Rossi, Miguel Sanz and Alessandra Puglisi
Molecules 2023, 28(3), 1002; https://doi.org/10.3390/molecules28031002 - 19 Jan 2023
Cited by 1 | Viewed by 2379
Abstract
The use of stereoselective phase-transfer catalysis as a reliable method for the enantioselective synthesis of optically active α-amino acid derivatives using achiral Schiff base esters has been well-developed in batch in the last 40 years. Recently, continuous flow technology has become of great [...] Read more.
The use of stereoselective phase-transfer catalysis as a reliable method for the enantioselective synthesis of optically active α-amino acid derivatives using achiral Schiff base esters has been well-developed in batch in the last 40 years. Recently, continuous flow technology has become of great interest in the academy and industry, since it offers safer process operating conditions and higher efficiency compared to a traditional batch processing. Herein, we wish to report the first example of enantioselective phase transfer benzylation of alanine Schiff base ester, under continuous flow conditions. Two different methodologies were investigated: a liquid-solid phase transfer catalytic benzylation using a packed-bed reactor and a liquid-liquid phase transfer catalytic benzylation in continuous stirred-tank reactors. Liquid-liquid phase transfer process in flow showed slightly better productivity than the batch process, while solid-liquid phase transfer benzylation proved much more advantageous in terms of productivity and space-time yield. Furthermore, continuous flow system allowed the isolation of benzylated product without any work up, with a significant simplification of the process. In both cases, phase transfer asymmetric benzylation promoted by Maruoka catalyst demonstrated high enantioselectivity of target quaternary amino ester in flow, up to 93% ee. Full article
(This article belongs to the Special Issue Current Developments in Continuous-Flow Organocatalysis)
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15 pages, 3531 KiB  
Article
Continuous-Flow Synthesis of Arylthio-Cyclopropyl Carbonyl Compounds
by Davide Moi, Maria Chiara Cabua, Viktoria Velichko, Andrea Cocco, Annalisa Chiappone, Rita Mocci, Stefania Porcu, Monica Piras, Stefano Bianco, Fabio Pesciaioli and Francesco Secci
Molecules 2022, 27(22), 7943; https://doi.org/10.3390/molecules27227943 - 16 Nov 2022
Cited by 2 | Viewed by 2142
Abstract
The straightforward, continuous-flow synthesis of cyclopropyl carbaldehydes and ketones has been developed starting from 2-hydroxycyclobutanones and aryl thiols. This acid-catalyzed mediated procedure allows access to the multigram and easily scalable synthesis of cyclopropyl adducts under mild conditions, using reusable Amberlyst-35 as a catalyst. [...] Read more.
The straightforward, continuous-flow synthesis of cyclopropyl carbaldehydes and ketones has been developed starting from 2-hydroxycyclobutanones and aryl thiols. This acid-catalyzed mediated procedure allows access to the multigram and easily scalable synthesis of cyclopropyl adducts under mild conditions, using reusable Amberlyst-35 as a catalyst. The resins, suitably ground and used for filling steel columns, have been characterized via TGA, ATR, SEM and BET analyses to describe the physical–chemical properties of the packed bed and the continuous-flow system in detail. To highlight the synthetic versatility of the arylthiocyclopropyl carbonyl compounds, a series of selective oxidation reactions have been performed to access sulfoxide and sulfone carbaldehyde cyclopropanes, oxiranes and carboxylic acid derivatives. Full article
(This article belongs to the Special Issue Current Developments in Continuous-Flow Organocatalysis)
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Review

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28 pages, 9697 KiB  
Review
Heterogeneous Organocatalysts for Light-Driven Reactions in Continuous Flow
by Graziano Di Carmine, Carmine D’Agostino, Olga Bortolini, Lorenzo Poletti, Carmela De Risi, Daniele Ragno and Alessandro Massi
Molecules 2024, 29(10), 2166; https://doi.org/10.3390/molecules29102166 - 7 May 2024
Cited by 2 | Viewed by 1496
Abstract
Within the realm of organic synthesis, photocatalysis has blossomed since the beginning of the last decade. A plethora of classical reactivities, such as selective oxidation of alcohol and amines, redox radical formation of reactive species in situ, and indirect activation of an organic [...] Read more.
Within the realm of organic synthesis, photocatalysis has blossomed since the beginning of the last decade. A plethora of classical reactivities, such as selective oxidation of alcohol and amines, redox radical formation of reactive species in situ, and indirect activation of an organic substrate for cycloaddition by EnT, have been revised in a milder and more sustainable fashion via photocatalysis. However, even though the spark of creativity leads scientists to explore new reactions and reactivities, the urgency of replacing the toxic and critical metals that are involved as catalysts has encouraged chemists to find alternatives in the branch of science called organocatalysis. Unfortunately, replacing metal catalysts with organic analogues can be too expensive sometimes; however, this drawback can be solved by the reutilization of the catalyst if it is heterogeneous. The aim of this review is to present the recent works in the field of heterogeneous photocatalysis, applied to organic synthesis, enabled by continuous flow. In detail, among the heterogeneous catalysts, g-CN, polymeric photoactive materials, and supported molecular catalysts have been discussed within their specific sections, rather than focusing on the types of reactions. Full article
(This article belongs to the Special Issue Current Developments in Continuous-Flow Organocatalysis)
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