Odorless Isocyanide Chemistry: An Integrated Microfluidic System for a Multistep Reaction Sequence

α-Substituted ketones as reagent for Passerini modification of carboxymethyl cellulose: Toward dually functionalized derivatives and thermo-sensitive chemical hydrogels

The present works describes the Passerini modification of carboxymethyl cellulose (CMC) by using a library of nine α-substituted ketones derivatives, differing in their hydrophobicity and reactivity, conjointly with cyclohexyl isocyanide. The Passerini ligation, achieved in aqueous and mild conditions, was shown to be successful, leading to a large panel of dually functionalized CMC derivatives, in an eco-friendly manner. A particular attention was dedicated to the influence of the experimental parameters such as the stoichiometry, the nature of a co-solvent or the temperature, which allowed to tune the extent of modification. The reactivity of the ketone was proven to be governed by its i) compatibility with water, ii) sterical accessibility, and by iii) the presence of neighboring electron-withdrawing group. The resulting Passerini CMC products modified by methacrylate moieties (CMC-MA) were used as reactive macromonomer under a "grafting through" approach. The copolymerization of CMC-MA with oligoethylene glycol methacrylate (OEGMA) and diethylene glycol methacrylate (DEGMA) upon thermal radical reaction conditions enabled to generate tightly cross-linked chemical hydrogels, with a thermo-sensitive and thermo-reversible behavior, reflected by a macroscopical shrinkage/swelling response, and confirmed by SAXS analysis. Such chemical strategy paves the way toward multifunctional polysaccharide-based networks with potential utilizations as drug delivery devices, dye removals or actuators.

Efficient degassing and ppm-level oxygen monitoring flow chemistry system

Low oxygen levels are critical for a long range of chemical transformations carried out in both flow and batch chemistry. Here, we present an inline continuous flow degassing system based on a gas-permeable membrane inside a vacuum chamber for achieving and monitoring ppm-level oxygen concentrations in solutions. The oxygen presence was monitored with a molecular oxygen probe and a continuously running UV-vis spectrometer. An automated setup for discovering optimal reaction conditions for minimal oxygen presence was devised. The parameters tested were: flow rate, vacuum pressure, solvent back-pressure, tube material, tube length and solvent oxygen solubility. The inline degassing system was proven to be effective in removing up to 99.9% of ambient oxygen from solvents at a flow rate of 300 μl min^-1 and 4 mbar vacuum pressure inside the degassing chamber. Reaching lower oxygen concentrations was limited by gas permeation in the tubing following the degassing unit, which could be addressed by purging large volume flow reactors with an inert gas after degassing or by using tubing with lower gas permeability, such as stainless steel tubing. Among all factors, oxygen solubility in solvents was found to play a significant role in achieving efficient degassing of solvents. The data presented here can be used to choose optimal experimental parameters for oxygen-sensitive reactions in flow chemistry reaction setups. The data were also fitted to an analytically derived model from simple differential equations in physical context of the experiment.

Ugi Four-Component Reactions Using Alternative Reactants

The Ugi four-component reaction (Ugi-4CR) undoubtedly is the most prominent multicomponent reaction (MCRs) that has sparked organic chemists' interest in the field. It has been widely used in the synthesis of diverse heterocycle molecules such as potential drugs, natural product analogs, pseudo peptides, macrocycles, and functional materials. The Ugi-4CRs involve the use of an amine, an aldehyde or ketone, an isocyanide, and a carboxylic acid to produce an α-acetamido carboxamide derivative, which has significantly advanced the field of isocyanide-based MCRs. The so-called intermediate nitrilium ion could be trapped by a nucleophile such as azide, N-hydroxyphthalimide, thiol, saccharin, phenol, water, and hydrogen sulfide instead of the original carboxylic acid to allow for a wide variety of Ugi-type reactions to occur.β In addition to isocyanide, there are alternative reagents for the other three components: amine, isocyanide, and aldehyde or ketone. All these alternative components render the Ugi reaction an aptly diversity-oriented synthesis of a myriad of biologically active molecules and complex scaffolds. Consequently, this review will delve deeper into alternative components used in the Ugi MCRs, particularly over the past ten years.

An Automated Computer-Vision "Bubble-Counting" Technique to Characterise CO2 Dissolution into an Acetonitrile Flow Stream in a Teflon AF-2400 Tube-in-Tube Flow Device

A Teflon AF-2400 based tube-in-tube device was used to generate flow streams of CO₂ in acetonitrile and a computer-vision based 'bubble counting' technique was used to estimate the amount of CO₂ that had passed into solution whilst in the tube-in-tube device by quantifying the amount of CO₂ that left solution (forming separate gas-phase segments) downstream of the back-pressure regulator. For both CO₂ pressures used, there appeared to be a minimum residence time below which no CO₂ was observed to leave solution. This was assumed to be due to residual CO₂ below (or close to) the saturation concentration at atmospheric pressure and, by taking this into account, we were able to fit curves corresponding to simple gradient-driven diffusion and which closely matched previously obtained colorimetric titration data for the same system. The estimated value for the residual concentration of CO₂ (0.37 M) is higher than, but in reasonable general correspondence with, saturation concentrations previously reported for CO₂ in acetonitrile (0.27 M).

Efficacy of Selenourea Organocatalysts in Asymmetric Michael Reactions under Standard and Solvent-Free Conditions

By varying the steric and electronic surroundings of the hydrogen-bonding motif, the novel chiral Cinchona-alkaloid based selenoureas were developed. Acting as bifunctional catalysts, they were applied in the Michael reactions of dithiomalonate and nitrostyrene providing chiral adducts with up to 96% ee. The asymmetric Michael–-hemiacetalization reaction of benzylidene pyruvate and dimedone, performed with the assistance of 5 mol% of selenoureas, furnished the product with up to 93% ee and excellent yields. The effectiveness of the new hydrogen-bond donors was also proved in solvent-free reactions under ball mill conditions, supporting the sustainability of the devised catalytic protocol.

The chemistry and applications of hafnium and cerium(iv) metal-organic frameworks

The coordination connection of organic linkers to the metal clusters leads to the formation of metal-organic frameworks (MOFs), where the metal clusters and ligands are spatially entangled in a periodic manner. The immense availability of tuneable ligands of different length and functionalities gives rise to robust molecular porosity ranging from several angstroms to nanometres. Among the large family of MOFs, hafnium (Hf) based MOFs have been demonstrated to be highly promising for practical applications due to their unique and outstanding characteristics such as chemical, thermal, and mechanical stability, and acidic nature. Since the report of UiO-66(Hf) and DUT-51(Hf) in 2012, less than 200 Hf-MOFs (ca. 50 types of structures) have been reported. Besides, tetravalent cerium [Ce(iv)] has been proven to be capable of forming similar topological MOF structures to Zr and Hf since its first discovery in 2015. So far, ca. 40 Ce(iv) MOFs with 60% having UiO-66-type structure have been reported. This review will offer a holistic summary of the chemistry, uniqueness, synthesis, and applications of Hf/Ce(iv)-MOFs with a focus on presenting the development in the Hf/Ce(iv)-clusters, topologies, ligand structures, synthetic strategies, and practical applications of Hf/Ce(iv)-MOFs. In the end, we will present the research outlook for the development of Hf/Ce(iv)-MOFs in the future, including fundamental design of Hf/Ce(iv)-clusters, defect engineering, and various applications including membrane development, diversified types of catalytic reactions, irradiation absorption in nuclear waste treatment, water production and wastewater treatment, etc. We will also present the emerging computational approaches coupled with machine-learning algorithms that can be applied in screening Hf and Ce(iv) based MOF structures and identifying the best-performing MOFs for tailor-made applications in future practice.

Novel Selenoureas Based on Cinchona Alkaloid Skeleton: Synthesis and Catalytic Investigations

An efficient approach to the synthesis of chiral selenoureas consisting of Cinchona alkaloid scaffolds was described. The new selenoureas were assessed as bifunctional organocatalysts in the asymmetric Michael addition reactions under mild conditions. The best results were obtained for selenoureas bearing the 4-fluorophenyl group. These catalysts promoted the reactions with enantioselectivities of up to 96% ee. Additionally, the catalytic performance of the thiourea and selenourea counterpart was compared.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass

The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C₂ to C₆ bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Bis-Selenoureas for Anion Binding: A 1H NMR and Theoretical Study

The anion binding ability of a family of bis-selenoureas L1-L3 obtained by the reaction of 1,3-bis(aminomethyl)-benzene and phenylisoselenocyanate, p-methoxyphenylisoselenocyanate and naphtylisoselenocyanate, for L1, L2, and L3, respectively, has been tested and compared to that of previously described bis-urea analogues. Results suggest that the introduction of selenium leads to an increase in the acidity of the urea NH hydrogen atoms, and therefore to a stronger affinity (more than three-fold higher) towards anion species, in particular dihydrogen phosphate, in DMSO-d₆ . Theoretical calculations allowed for the optimization of the adducts receptors corroborating the experimental results.

A Mild, Fast, and Scalable Synthesis of Substituted α-Acyloxy Ketones via Multicomponent Reaction Using a Continuous Flow Approach

A continuous flow approach for the synthesis of α-acyloxy ketone derivatives from the corresponding arylglyoxals, isocyanides, and carboxylic acids is described. The target products were obtained in excellent yields in short residence times and with high purities via the first transcription of the microwave-to-flow paradigm to the isocyanide-based Passerini reaction. Furthermore, this methodology allowed a 10-fold scale-up using the same experimental conditions initially established.

A methanol and protic ionic liquid Ugi multicomponent reaction path to cytotoxic α-phenylacetamido amides

The Ugi four component reaction of an aldehyde, amine, isocyanide and an ethanoic acid was effected smoothly in protic ionic liquids ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) to afford analogues of α-phenylacetamido amides in good to excellent isolated yields. The corresponding reactions in [BMIM][PF₆] and the protic ionic liquid ethanolammonium nitrate (ETAN) failed. Microwave irradiation in EAN facilitated rapid access to three focused libraries, based on the parent isocyanide: cyclohexyl isocyanide, benzyl isocyanide and ethyl isocyanoacetate. Analysis of the structure activity relationship data suggested the presence of a bulky moiety originating from the isocyanide (cyclohexyl and benzyl) enhanced cytotoxicity. Removal of the acetylenic H-atom from the ethanoic acid moiety was detrimental to cytotoxicity. The most active analogues produced, N-(2-cyclohexylamino)-1-(4-methoxyphenyl)-2-oxoethyl-N-(3,5-dimethoxyphenyl)propiolamide, returned average GI₅₀ values of ≤1 μM across the cancer cell lines evaluated. Combined, these data suggest that analogues of this nature are interesting potential anti-cancer development leads.

The Ugi reaction (aldehyde, amine, isocyanide and an ethanoic acid) in the protic ionic liquids ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) gave excellent yields of α-phenylacetamido amides.

Photocatalysis in a multi-capillary assembly microreactor: toward up-scaling the synthesis of 2H-indazoles as drug scaffolds

Visible-light-promoted direct arylation of 2H-indazoles using phenyldiazonium salt enabled a single-step and fast synthesis (<1 min) of C3 arylated products in high yields (>65%) in an eosin Y immobilized capillary microreactor.

Integrated continuous flow/batch protocol for the photoreduction of ortho-methyl phenyl ketones using water as the hydrogen source

The direct hydrogenation of ketones (RRCO) with water to secondary alcohols under catalyst-free, minimal risk conditions, through the light-driven transfer hydrogenation platform.

A platform for accelerated continuous-flow radical polymerization of acrylates and styrene with copper-wire threads

Accelerated Cu(0)-mediated homo-/block (co)polymerization of the vinyl monomers is conducted via continuous-flow process with a copper metal-wire catalyst threaded through perfluoroalkoxy alkane (PFA) tube.

Flow-Assisted Switchable Catalysis of Metal Ions in a Microenvelope System Embedded with Core-Shell Polymers

Many efforts have been made on stimuli-responsive switchable catalysis to trigger catalytic activity over various chemical reactions. However, the reported light-, pH- or chemically responsive organocatalysts are mostly incomplete in the aspects of shielding efficiency and long-term performance. Here, we advance the flow-assisted switchable catalysis of metal ions in a microenvelope system that allows  the on-off catalysis mode on demand for long-lasting catalytic activity. Various metal-ion catalysts can be selectively embedded in a novel polymeric core-shell of the heteroarm star copolymer of poly(styrene) and poly(4-vinylpyridine) emanated from a polyhedral oligomeric silsesquioxane center. The immobilized core-shell polymer on the inner wall of a poly(dimethylsiloxane) envelope microreactor shows on-off switching catalysis between the expanded active mode and contracted protective mode under continuous flow of solvents or subsequent dry conditions. In particular, the preserved catalytic activity of toxic Hg²⁺ for oxymercuration was demonstrated even for 2 weeks without leaching, whereas the activity of moisture-sensitive Ru³⁺ ions for polymerization of methyl methacrylate was maintained even after 5 days from an open atmosphere. It is practical that the tight environment of the enveloped microfluidic system facilitates cyclic switching between the reaction-"on" and -"off" modes of such toxic, sensitive/expensive catalysts for long-term prevention and preservation.

In situ epoxide generation by dimethyldioxirane oxidation and the use of epichlorohydrin in the flow synthesis of a library of β-amino alcohols

The flow coupling of epichlorohydrin with substituted phenols, while efficient, limits the nature of the epoxide available for the development of focused libraries of β-amino alcohols. This limitation was encountered in the production of analogues of 1-(4-nitrophenoxy)-3-((2-((4-(trifluoromethyl)pyrimidin-2-yl)amino)ethyl)amino)propan-2-ol 1, a potential antibiotic lead. The in situ (flow) generation of dimethyldoxirane (DMDO) and subsequent flow olefin epoxidation abrogates this limitation and afforded facile access to structurally diverse β-amino alcohols. Analogues of 1 were readily accessed either via (i) a flow/microwave hybrid approach, or (ii) a sequential flow approach. Key steps were the in situ generation of DMDO, with olefin epoxidation in typically good yields and a flow-mediated ring opening aminolysis to form an expanded library of β-amino alcohols 1 and 10a-18g, resulting in modest (11a, 21%) to excellent (12g, 80%) yields. Alternatively flow coupling of epichlorohydrin with phenols 4a-4m (22%-89%) and a Bi(OTf)₃ catalysed microwave ring opening with amines afforded a select range of β-amino alcohols, but with lower levels of aminolysis regiocontrol than the sequential flow approach.

To each his own: isonitriles for all flavors. Functionalized isocyanides as valuable tools in organic synthesis

The term functionalized isocyanides refers to all those isocyanides in which a neighbouring functional group can finely tune the reactivity of the isocyano group or can be exploited in post-functionalization processes. In this manuscript, we have reviewed all the isocyanides in which the pendant functional group causes either deviation from or reinforces the normal reactivity of the isocyano group and categorized them to highlight their common features and differences. An analysis of their synthetic potential and the possible unexplored directions for future research studies is also addressed.

Unsymmetrical difunctionalization of cyclooctadiene under continuous flow conditions: expanding the scope of ring opening metathesis polymerization

Functionalized cyclooctenes (FCOEs) are important monomers in ring-opening metathesis polymerization (ROMP). Herein, a new library of disubstituted FCOEs bearing adjacent heteroatoms were synthesized and applied in ROMP. To address the issues associated with the handling of the reactive thienyl chloride intermediate, a two-step continuous flow method has been developed to prepare 5-thio-6-chlorocyclooctene compounds from abundant cyclooctadiene starting materials. These newly synthesized FCOE monomers were subsequently polymerized through ROMP, giving rise to a range of functionalized polymers with high molecular weights. Furthermore, we demonstrated that the thermal properties of these polymers could be fine-tuned by changing the functional groups in the FCOE monomers. We expect that this functionalization-polymerization strategy will enable the preparation of a range of polymeric materials with complex structures.

Control of tandem isomerizations: flow-assisted reactions of o-lithiated aryl benzyl ethers

We report a flow microreactor platform for controlling tandem isomerizations of o-lithiated aryl benzyl ethers based on precise residence time control.

Indirect fabrication of versatile 3D microfluidic device by a rotating plate combined 3D printing system

Rapid on-demand sacrificial printing techniques using suitable combinations of resin and sacrificial materials would be desirable to fabricate versatile and functional microfluidic devices with complex designs and chemical resistance.

Integrated CO2 capture-fixation chemistry via interfacial ionic liquid catalyst in laminar gas/liquid flow

Simultaneous capture of carbon dioxide (CO₂) and its utilization with subsequent work-up would significantly enhance the competitiveness of CO₂-based sustainable chemistry over petroleum-based chemistry. Here we report an interfacial catalytic reaction platform for an integrated autonomous process of simultaneously capturing/fixing CO₂ in gas–liquid laminar flow with subsequently providing a work-up step. The continuous-flow microreactor has built-in silicon nanowires (SiNWs) with immobilized ionic liquid catalysts on tips of cone-shaped nanowire bundles. Because of the superamphiphobic SiNWs, a stable gas–liquid interface maintains between liquid flow of organoamines in upper part and gas flow of CO₂ in bottom part of channel. The intimate and direct contact of the binary reagents leads to enhanced mass transfer and facilitating reactions. The autonomous integrated platform produces and isolates 2-oxazolidinones and quinazolines-2,4(1H,3H)-diones with 81–97% yields under mild conditions. The platform would enable direct CO₂ utilization to produce high-valued specialty chemicals from flue gases without pre-separation and work-up steps.

Microfluidics is an attractive route for synthesis, but can suffer from poor reactivity with gaseous reagents. Here the authors report a microfluidic system catalysing an interfacial reaction between CO₂ and liquid phase reagents by modifying silicon nanowires with immobilized ionic liquid catalysts.

A facile hybrid 'flow and batch' access to substituted 3,4-dihydro-2H-benzo[b][1,4]oxazinones

We describe a simple flow chemistry approach to libraries of ethyl 3-oxo-2-(substituted-phenylamino)-3,4-dihydro-2H-benzo[b][1,4]oxazine-6-carboxylates (12a-l) and N-ethyl-3-oxo-2-(substituted-phenylamino)-3,4-dihydro-2H-benzo[b][1,4]oxazine-6-carboxamides (13a-l) in 38-87% yields. This scaffold is poorly described in the chemical literature. Screening against a panel of 11 cancer and one normal cell line showed that the amide linked library 13a-l was devoid of toxicity. Whereas the ester linked analogues 12b, 12c, 12g, 12j and 12l were highly cytotoxic with growth inhibition (GI₅₀) values from 0.34 to >50 μM across all cell lines, with the 2-OH-Ph substituted 12l analogue presenting with sub-micromolar potency against the A2780 (ovarian; 0.34 ± 0.04 μM), BEC-2 (glioblastoma; 0.35 ± 0.06 μM), MIA (pancreas; 0.91 ± 0.054 μM) and SMA (murine glioblastoma; 0.77 ± 0.029 μM) carcinoma cell lines. Interestingly, the U87 glioblastoma cell line showed inherent resistance to growth inhibition by all analogues (GI₅₀ 32 to >50 μM) while the A2780 cells were highly sensitive (GI₅₀ 3.8-0.34 μM), suggesting that the analogues developed herein may be valuable lead compounds for the development of ovarian carcinoma specific cytotoxic agents. The differences in amide versus ester cytotoxicity was consitent with esterase cleaveage to release the cytotoxic warhead.