Catalyst-free Conditions Research Articles

Fluorosulfonylvinylation of Unactivated C(sp3)-H via Electron Donor-Acceptor Photoactivation.

An electron donor-acceptor (EDA) complex photoactivation strategy for radical fluorosulfonylation is disclosed for the first time. Simply upon blue light irradiation, the FSO2 radical can be generated efficiently under catalyst-free, base-free, and additive-free conditions, which enables facile access to 6-keto alkenylsulfonyl fluorides from readily available propargyl alcohols and FSO2Cl. The 6-keto alkenylsulfonyl fluoride motif has been showcased as a versatile SuFEx hub with diverse follow-up derivatizations.

Photocatalytic Multi-Component Reactions: An Emerging Avenue

Abstract: In recent years, photocatalytic multi-component reactions have emerged as a cutting-edge innovation in the field of organic synthesis. These reactions allow the simultaneous transformation of multiple reactants, which not only saves time and resources but also provides access to a diverse range of complex molecules. The use of photocatalysts in these reactions provides several advantages, including mild reaction conditions, high selectivity, and high functional group tolerance. Moreover, the integration of renewable energy sources such as visible light as a driving force for these reactions further adds to their sustainability. This innovation has opened up new avenues for the synthesis of complex molecules and holds great promise for the development of sustainable and efficient chemical processes. This review gives a broad understanding of photocatalyzed multi- component reaction protocols developed with wide applications in synthetic organic chemistry. These green, efficient, and straightforward reactions utilize recyclable photocatalyst, solvent-free or catalyst-free conditions for the synthesis of compounds with biological significance in a costeffective fashion. They are easily purified due to the minimum or no by-product formation. The review is divided into sections based on the type of photocatalysts involved and covers literature up to 2022.

Microwave‐Assisted PEG‐400 Medaited Synthesis of 4,5‐dihydro‐1H‐benzo[g]indazole Derivatives: An Enaminone Approach

AbstractA simple, rapid and conceptually new efficient protocol for the synthesis of 4,5‐dihydro‐1H‐benzo[g]indazole derivatives from novel enaminones prepared via Blaise reaction under catalyst free conditions is reported involving polyethylene glycol (PEG‐400) as an efficient recyclable medium without using any organic co‐solvent or additive by Microwave irridation with 91–95 % yields without chromatography.

Selective Electroreductive Hydroboration of Olefins with B2pin2

Organoboron showed great potential in the synthesis of various high-value chemical compounds. Direct hydroboration of olefins has been witnessed over time as a mainstream method for the synthesis of organoboron compounds. In this work, an electroreductive anti-Markovnikov hydroboration approach of olefins with readily available B2pin2 to synthesize valuable organoboron compounds with high chemo- and regioselectivities under metal catalyst-free conditions was reported. This protocol exhibited broad substrate scope and good functional-group tolerance on styrenes and heteroaromatic olefins, providing synthetically useful alkylborons with high efficiency and even various deuterium borylation products with good D-incorporation when CD3CN was employed as solvent. Furthermore, gram-scale reactions and extensive functional derivatization further highlighted the potential of this method.

A route to high-solid coatings: Hydrophobic polyurethane triazoles via bulk polymerization of azide-alkyne cycloaddition

In the present study, we showcase a series bulk polymerized siloxane-decorated polyurethane triazole coatings (Si-PUTs) achieved via azide-alkyne cycloaddition with excellent surface hydrophobicity and anti-corrosion properties. A simple functional modification converts aminopropyl trimethoxy silane to a dialkyne terminated monomer under mild conditions. Concurrently, a series of azide-terminated urethane monomers were synthesized by reacting azidoethanol with three common diisocyanates. Structural elucidation of the monomers was accomplished by FT-IR, 1H and 13C NMR along with ESI-MS. The azide-/alkyne- terminated monomer pairs undergo cycloaddition in absence of solvent and catalyst-free conditions to yield highly crosslinked siloxane-decorated polyurethane (Si-PUT) matrices post curing. FTIR and XPS analysis confirmed the successful formation of these Si-PUTs while the cure kinetics and reaction order was investigated by real-time FTIR. The physico-chemical properties of the polymers achieved were comprehensively assessed prior to evaluating their performance and feasibility as corrosion resistive coatings. The high contact angles in excess of 110°, transparency >85 % in the visible region, low Icorr, high polarization resistance, and corrosion rates in the order of 10−4 mm/year, all underscores the promise of Si-PUTs as excellent corrosion protection coatings. The encouraging results and ease of application demonstrate the potential to formulate environment friendly and multifunctional high-solid protective coatings.

Direct and safe one-pot synthesis of functionalized dimethyl 1-aryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-1-phosphonates

A visible-light-induced direct and safe synthesis of functionalized dimethyl 1-aryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-1-phosphonates is realized from dimethyl (aryl(2-tosylhydrazono)methyl)phosphonates and pyridinium 1,4-zwitterionic thiolates with cesium carbonate as base in dichloromethane. The reaction involves the carbene generation from dimethyl (aryl(2-tosylhydrazono)methyl)phosphonates in the presence of cesium carbonate as base and the [1+5] annulation of the carbenes with pyridinium 1,4-zwitterionic thiolates to synthesize functionalized 1,9a-dihydropyrido[2,1-c][1,4]thiazine derivatives. The method avoids preparing, storing, and using potentially dangerous phosphoryl diazo compounds and features simple, convenient, catalyst-free, and mild reaction conditions.

The Synthesis of Amides from Benzoic Acids and Dicarbodiimides Under Catalyst-Free Conditions

Abstract: Amides are a critical class of widely distributed heterocycles in nature. The preparation of amides from benzoic acids and dicarbodiimides under catalyst-free conditions was reported. Various products were obtained in good to high yields. The model reaction could be scaled up to the gram-scale level. A reaction mechanism was proposed based on control experiments and relevant literatures.

A novel, simple, and facile synthesis of 3-(3-benzyl-2,3-dihydrobenzo[d]thiazol-2-yl)benzo[d]oxazole-2(3H)-thione derivatives

Novel 3-(3-benzyl-2,3-dihydrobenzo[ d]thiazol-2-yl)benzo[ d]oxazole-2(3 H)-thione derivatives are efficiently synthesized in excellent yields by reactions of benzothiazoles, benzyl bromides, and 2-mercaptobenzoxazole in acetone under catalyst-free conditions in the presence of triethylamine. The structures of the products are confirmed by nuclear magnetic resonance spectroscopy, infrared spectroscopy, electron ionization mass spectrometry, and elemental analyses.

Developments of pyridodipyrimidine heterocycles and their biological activities.

The entitled review aimed to assemble and highlight the synthetic approaches and biological aspects of heterocycles with pyridodipyrimidine motifs. The recent synthetic approaches were categorized according to the accomplishments of the approaches under catalyst or catalyst-free conditions. The topic involved the synthesis of substituted tricyclic systems and spirocyclic systems. The present study offered an overview of the recent literature in addition to a scope of the preceding literature. The proposed mechanisms of the varied target products were discussed. Pyridodipyrimidine displayed potential and privileged cytotoxic, antioxidant, and antimicrobial performances. The competitions, challenges, and prospects are also deliberated.

Catalyst free one pot three components synthesis of 2-iminothiazoles from nitroepoxides and thiourea

Nitroepoxides were introduced as efficient substrates for the one-pot three-component synthesis of 2-iminothiazoles under catalyst-free conditions. Reaction of amines, isothiocyanates, and nitroepoxides in THF at 10–15 °C afforded corresponding 2-iminothiazoles in high to excellent yields. The reaction proceeds via the in situ formation of thiourea from an amine and an isothiocyanate, followed by nitroepoxide ring opening with the sulfur of thiourea, cyclization reaction, and dehydration cascade. The structures of products were confirmed by IR, NMR, HRMS analyses and X-ray crystallography.

Synthesis of 3-Thiocyanobenzothiophene via Difunctionalization of Active Alkyne Promoted by Electrochemical-Oxidation.

A novel and green method for the synthesis of 3-thiocyanatobenzothiophenes via electrochemical-oxidation promoted difunctionalization of active alkyne has been developed. In this protocol, inexpensive and easily available potassium thiocyanate was chosen as the thiocyanation reagent, 2-alkynylthioanisoles as the substrates, a variety of 3-thiocyanatobenzothiophenes were obtained in moderate to good yields under oxidant- and catalyst-free conditions. Moreover, the continuous flow system has good applicability for this transformation, the use of continuous flow system has overcome the disadvantage of low efficiency in traditional electrochemical amplification, and realized the stable and excellent yields of target products in the scale-up reactions.

Photoinduced Electron Donor-Acceptor Complex-Mediated Radical Cascade Involving N-(Acyloxy)phthalimides: Synthesis of Tetrahydroquinolines.

We conceptualized a novel disconnection approach for the synthesis of fused tetrahydroquinolines that exploits a visible light-mediated radical (4 + 2) annulation between alkyl N-(acyloxy)phthalimides and N-substituted maleimides in the presence of DIPEA as an additive. The reaction proceeds through the formation of a photoactivated electron donor-acceptor complex between alkyl NHPI esters and DIPEA, and the final tetrahydroquinolines were obtained in a complete regioselective fashion. The methodology features a broad scope and good functional group tolerance and operates under metal- and catalyst-free reaction conditions. Detailed mechanistic investigations including density functional theory studies provide insight into the reaction pathway.

Catalyst-free, highly sensitive and adjustable photo-responsive azobenzene liquid crystal elastomers based on dynamic multiple hydrogen bond

Photo-responsive liquid crystal elastomers (LCEs) containing azobenzene components have received great attention and are in great demand gap for the development of smart materials. Herein, we have prepared a novel azobenzene photo-responsive liquid crystal elastomer (HAzo-LCEs) through simultaneously introducing azobenzene molecules and 2-ureido-4-pyrimidone (UPy) units into main chain of polyurethane molecule. Utilizing polyurethane system into this HAzo-LCEs has a trade-off between the exceptional mechanical performance and quick response. Especially, the transformation of photo-responsive HAzo-LCEs from polydomain to monodomain liquid crystal structures has been achieved under the catalyst-free and low temperature conditions by exploiting the dynamic nature of multiple hydrogen bond between UPy units. This synthetic method breaks the dilemma that the conventional photo-responsive LCEs require the preparation of monodomain liquid crystal structures at high temperatures or with the help of a large number of catalysts. Importantly, the HAzo-LCEs sample can bend rapidly in response to the UV light, and the maximum bending angle of the sample could reach 144°. Intriguingly, the blended HAzo-LCEs sample can rapidly straighten and finally extended under green light, showing the high sensitivity and flexible adjustability. It is valuable to integrating the high sensitivity, flexible adjustability and complete reversibility into one photo-responsive elastomers of this HAzo-LCEs. Furthermore, the multiple hydrogen bonds from UPy units allows the HAzo-LCEs to regulate its dynamics and stability by increasing the number and binding sites through the advantages of adjustable strength, high selectivity and abundant formation modes, providing great design and application scope for photo-responsive liquid crystal elastomers. This design route of non-toxic PU-based HAzo-LCEs provides a novel approach to broaden photo-responsive LCEs application in sensor and actuator.

Catalyst-Free Electrochemical Sulfonylation of Organoboronic Acids

A simple and efficient electrochemical sulfonylation of organoboronic acids with sodium arylsulfinate salts has been reported for the first time. A variety of aryl, heteroaryl, and alkenylsulfones were obtained in good to excellent yields via a simple electrochemical sulfonylation of various arylboronic acids, heterocyclic boronic acids, or alkenylboronic acids with sodium arylsulfinate at room temperature in 5 h under the catalyst-free and additive-free conditions. A plausible mechanism has been proposed based on various radical-trapping and CV control experiments.

Recent Developments on Synthesis of Organofluorine Compounds Using Green Approaches

Abstract: The synthesis of organofluorine compounds plays a vital role in the field of pharmaceuticals, agrochemicals, and materials since the fluorine-containing compounds have shown improved biological and physicochemical properties. Significant research has been directed towards synthesizing organofluorine compounds because organofluorine compounds have been displayed in several biological activities, including anticancer, antitumor, antihypertensive, antidepressant, anti-HIV and treatment of stroke. Due to several pharmaceutical applications of organofluorine compounds, numerous conventional as well as green synthetic methodologies have been developed for the synthesis of fluorine-containing compounds. However, particularly, the synthesis of organofluorine compounds using green approaches has been continuously attracting research interest since green approaches have several advantages, including the use of inexpensive and nontoxic reagents, catalytic, highly efficient, short reaction time, energy efficient, high reaction yields, and environmentally benign over the conventional methods. Among the green tools, the use of microwave-assisted synthesis, water, and ionic liquids as green solvent/reaction media, organocatalysts, photocatalysts, and solvent-free and catalyst-free reaction conditions have been exploited in the past decades for the synthesis of organofluorine compounds. In this review, we highlighted the recent developments in various green methods for the synthesis of organofluorine compounds via electrophilic fluorination for synthesis of various fluorohydrins, fluorinated acyclic & cyclic β -ketoesters, 1,3-dicarbonyl compounds, cyclic and acyclic ketones, α - cyanoesters, α-aryl-tetralones, α-amino acids, flavanones, and several fluorinated heterocycles such as fluorinated pyridine, pyrimidine, pyrrole, pyrazolone, benzofuran, indole, flavanone, and coumarin derivatives. In addition, some green methodologies have been highlighted for the synthesis of biologically active fluorinated compounds, including HIV-1 integrase inhibitors, 20-deoxy-20-fluorocamptothecin, fluorinated estrone, sclareolide, BMS- 204352 (MaxiPost), fluorinated naproxen and fluoxetine.

#NextGenOrgChem Special Collection: Supporting Young Researchers

Guest Editor Prof. Stefano Protti introduces the #NextGenOrgChem special collection, which includes original research papers, reviews and concept articles by young organic chemists (post-doctoral and early-career researchers) nominated by the EurJOC advisory and editorial board members. The Seehotel Waldstätterhof in Brunnen (Ingenbohl, Switzerland), where every year the traditional Bürgenstock Conference is held, faces the lake of Lucerne. If distracted participants of the congress thought of leaning out towards its surrounding crush barriers, they would catch sight of tens of ducks’ nests, at a safe distance from one another, lying all along the sand stripe rimming the water. While heading back towards the hotel, the casual visitor might even find that double imprinting of a protected nest facing the limitless watery space as a natural choice. Well, supervisors are not ducks, this must be said, although they are often as greedy as geese, feeding on asterisks and funding. Yet it would be nice if in the eternal struggle to get free from their mentors, they remembered not to make the same mistakes, really trying their best to lead a postdoc on, crossing the thin line that divides the you work for me status, from the you work with me one, avoiding to fall into the tempting territorial marking, leaving them free to develop insights and work on reviews parallel to, and not instead of, their commitments as post-doc. Not guiding them into the world, but showing it to them, with a hand's gesture. As with the horizon of a lake. From there on, staying afloat it is also on them. In line the European Journal of Organic Chemistry's efforts of offering early career researchers a platform to present their work, the #NextGenOrgChem virtual collection showcases a set of contributions (both Research Articles and Reviews) from both advanced postdocs and young group leaders nominated by the EurJOC editorial and advisory board members. The manuscripts collected in the present special collection (more than 30 contributions among reviews and research papers) aim to provide a bright and colourful portrait of the incoming generation of chemists. Contributions to this collection include the optimization of synthetic strategies (in several cases the use of biocatalytic, electrochemical or photocatalytic approaches has been proposed), the design of innovative bioactive compounds and materials, as well as computational and experimental investigations on reaction mechanisms. The design and the synthesis of molecular switches and probes is likewise covered. The EurJOC editorial team and I thank all the participants that accepted our invitation, as well as the members of the International Advisory Board. Surf's up, guys. The opinions expressed in this publication are the view of the author and do not necessarily reflect the opinions or views of the European Journal of Organic Chemistry, the Publisher, Chemistry Europe, or the affiliated editors. This work has been made possible thanks to the commitment of the entire EurJOC editorial team and in particular Charlotte Gers-Panther (currently Editor-in-Chief of ChemCatChem), Leana Travaglini (Deputy Editor) and Anne Nijs (Editor-in-Chief). As the guest editor, my acknowledgment goes to the PhotoGreen Lab staff (mentors and students). I would also like to thank Dr. Rossana Quarteroni (University of Pavia) and Dr. Federica Rizzi (Wiley-VCH) who helped me to polish this text. Stefano Protti (Ph.D. in Chemistry, 2007, prof. A. Albini as the supervisor) is Associate Professor at the University of Pavia since 2018. His research is mainly focused on the design and the optimization of visible light mediated synthetic protocols under metal- and (photo)catalyst-free conditions. He is currently editor of the Specialist Periodical Reports in Photochemistry (Royal Society of Chemistry), associate editor of Photochemical and Photobiological Sciences and member of the International Advisory Board of the European Journal of Organic Chemistry.

Solar radiation-assisted one-pot synthesis of 3-alkylated indoles under catalyst-free conditions

Solar radiation-assisted green approach was developed for the chemoselective synthesis of 3-alkylated indoles via Yonemitsu-type condensation under catalyst-free conditions. The desired products were formed by one-pot three-component reaction of indole, aromatic aldehydes, and β-dicarbonyl compounds in polyethylene glycol-400 (PEG-400). The scope and generality of the presented approach were extended by various aromatic aldehydes and CH activated compounds. Using non-volatile solvent and renewable energy resources, absence of any catalyst, energy conservation, and the selective production of heterodimer product instead of homodimer adducts such as bisindole or xanthine, increase the economic and environmental effectiveness of the present protocol.

Surface analysis and thermal behavior of the functionalized cellulose by glutaric anhydride through a solvent-free and catalyst-free process

According to the 12 principles of green chemistry, surface functionalization was performed using glutaric anhydride under solvent-free and catalyst-free conditions. FTIR spectra and DS analyses demonstrated the functionalization of HCl-hydrolyzed cellulose. The influence of two parameters, i.e., the glutaric anhydride concentration and the reaction time, on the functionalization of HCl-hydrolyzed cellulose was investigated. Protocol efficiency was studied by a degree of substitution (DS). It was found that higher concentrations of glutaric anhydride cause an enhancement of DS to 0.75 and 0.87 for GA3–12 and GA9–12, respectively. In addition, the longer reaction time increased zeta potential from −12.2 ± 1.7 for G9–6 to −34.57 ± 2.2 for GA9–12. Morphology analysis by SEM showed a decrease in fiber length for the functionalized cellulose. DSC profiles confirmed dehydration at a range of 17 to 134 °C. A glass transition was revealed at −30 to −20 °C for all studied samples. The fusion, the depolymerization of cellulose chains, the cleavage of glycosidic linkages, and the decomposition of the crystalline parts of cellulose occur at 195 to 374 °C. Therefore, an efficient and greener process was developed to functionalize the HCl-hydrolyzed cellulose by glutaric anhydride, a safe and non-toxic anhydride, in the absence of the solvent and catalyst.

Photoinduced Synthesis of Functionalized Oxacyclic Spirooxindoles Via Ring Expansion

A versatile photochemical ring-expansion protocol for the synthesis of oxacyclic spirooxindoles under catalyst-free conditions is described. The reaction is enabled by the use of unstrained O-containing heterocycles with 3-diazoindolin-2-ones under visible-light irradiation. Several synthetic advantages for this method are exhibited, including mild conditions, good functional group tolerance, operational simplicity, and scalability. Mechanistic studies indicate that the transformation may proceed through the formation of oxonium ylide intermediate followed by an ionic cyclization.

Triazolato Pd(II) and Pt(II) complexes of 2,6-bis(1-ethylbenzimidazol-2′-yl)pyridine formed via catalyst-free [3 + 2] click reactions

At the ambient temperature and under catalyst-free conditions, reactions between [MN3(LET)]PF6 (M = Pd(II) and Pt(II); LET = 2,6-bis(1-ethylbenzimidazol-2′-yl)pyridine) and substituted alkynes (dimethyl acetylene-dicarboxylate and 4,4,4-trifluoro-2‑butynoic acid ethyl ester) afforded the corresponding triazolate complexes. These reactions produced a mixture of triazolate bound isomers. The N1 triazolate isomer of the Pt(II) complexes, which first appeared in the [3 + 2] coupling, eventually isomerized to the N2-analogue during the incubation in DMSO. The reactions of [MN3(LET)]PF6 with asymmetric alkyne, 4,4,4-trifluoro-2‑butynoic acid ethyl ester, produced a mixture of the three anticipated triazolate isomers, according to 19F NMR spectroscopy. The stability of the triazolate complexes was investigated, along with the cycloaddition reaction's mechanism and the nature of the intermediates, using NMR spectroscopy.