Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• ) complex 123 as an endo-coordinated complex at the concave side. The complex 123a was prepared through the metalation of sumanene involving ligand exchange with a cyclopentadienyl (Cp) group of ferrocene by heating in the presence of Al powder and AlCl3 under solvent-free conditions followed by a counter

Mechanochemical green synthesis of hyper-crosslinked cyclodextrin polymers

• Alberto Rubin Pedrazzo,
• Fabrizio Caldera,
• Marco Zanetti,
• Silvia Lucia Appleton,
• Nilesh Kumar Dhakar and
• Francesco Trotta

Beilstein J. Org. Chem. 2020, 16, 1554–1563, doi:10.3762/bjoc.16.127

• present a new green synthesis of biodegradable polymers through a solvent-free procedure, displaying high potential of applications in various fields. After the synthesis, a significant amount of still reactive imidazoyl carbonyl groups within the NS structure were detected. These could be easily removed

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• formed after hydrogen atom abstraction from the allyl or benzyl position couple with the di-tert-butyliminoxyl radical forming the oxime ethers 21 and 22. 1,4-Cyclohexadiene is dehydrogenated to benzene instantly and exothermally at room temperature [45]. The solvent-free reaction of oxime radical 8 and

Suzuki–Miyaura cross coupling is not an informative reaction to demonstrate the performance of new solvents

• James Sherwood

Beilstein J. Org. Chem. 2020, 16, 1001–1005, doi:10.3762/bjoc.16.89

• from a green chemistry perspective if the water can be reused. To this end, micellar chemistry is appropriate for cross couplings [19]. Residual water also assists ‘solvent-free’ methods [20]. In summary, the Suzuki–Miyaura reaction is a fantastically versatile and industrially important reaction [21

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• -membered ring. As the thermal rearrangement was only feasible under solvent-free conditions, one may assume mechanism B, which involves the formation of phospholene oxide 1 dimers, and the second molecule only assists the rearrangement similarly to mechanism A. However, according to computations, in this

Reaction of indoles with aromatic fluoromethyl ketones: an efficient synthesis of trifluoromethyl(indolyl)phenylmethanols using K₂CO₃/n-Bu₄PBr in water

• Thanigaimalai Pillaiyar,
• Masoud Sedaghati and
• Gregor Schnakenburg

Beilstein J. Org. Chem. 2020, 16, 778–790, doi:10.3762/bjoc.16.71

• (TMG), also known as Barton's base, in excellent yields (Figure 2A) [24]. Recently, Liu and co-workers reported this reaction in the presence of cesium carbonate in acetonitrile (Figure 2B) [25]. Dinuclear zinc [26], cinchonidine catalysts, and solvent-free conditions [27] have been also utilized for

Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

• Faïma Lazreg,
• Marie Vasseur,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2020, 16, 482–491, doi:10.3762/bjoc.16.43

• : catalysis; copper; copper catalysis; N-heterocyclic carbene; solvent-free; sulfonylamidines; Introduction Amide derivatives represent a ubiquitous molecular construct in chemistry [1][2][3]. This structural motif favours rearrangements that lead to high reactivity and associated bioactivity [4][5]. Indeed

• reaction performed in air, using solvent-free conditions and in the absence of any additive. Results and Discussion [Cu(ICy)2]BF4 (1), [Cu(IPr)(ICy)]BF4 (2) and [Cu(IPr)(Pt-Bu3)]BF4 (3) were initially selected as optimum candidates [22]. This class of catalysts was expanded through the synthesis of the

• % conversion to the desired product was observed using the homoleptic cationic MIC (mesoionic carbene) complex 6 (Table 1, entry 6). For complexes 1–5, the conversion proved modest and ranged between 42 and 49% (Table 1, entries 1–5). Subsequently, solvent-free conditions were investigated (Table 1, entries 7

Oligomeric ricinoleic acid preparation promoted by an efficient and recoverable Brønsted acidic ionic liquid

• Fei You,
• Xing He,
• Song Gao,
• Hong-Ru Li and
• Liang-Nian He

Beilstein J. Org. Chem. 2020, 16, 351–361, doi:10.3762/bjoc.16.34

• oligomeric ricinoleic acid from ricinoleic acid under solvent-free conditions. The reaction parameters containing reaction temperature, vacuum degree, amount of catalyst and reaction time were optimized and it was found that the reaction under the conditions of 190 °C and 50 kPa with 15 wt % of the [HSO3

• undergo esterification, providing the oligomeric ricinoleic acid with different oligomerization degree. Conclusion To conclude, a highly efficient Brønsted acidic IL catalyst [HSO3-BDBU]H2PO4 was developed for the esterification of ricinoleic acid. The reaction performed well under solvent-free conditions

Efficient method for propargylation of aldehydes promoted by allenylboron compounds under microwave irradiation

• Jucleiton J. R. Freitas,
• Queila P. S. B. Freitas,
• Silvia R. C. P. Andrade,
• Juliano C. R. Freitas,
• Roberta A. Oliveira and
• Paulo H. Menezes

Beilstein J. Org. Chem. 2020, 16, 168–174, doi:10.3762/bjoc.16.19

• time and the possibility to perform solvent-free reactions [30]. However, the relative “greenness” of microwave-assisted reactions is still a point of discussion. For example, the question about the energy efficiency of microwave vs conventionally heated reactions must, in general, be evaluated with

• great care on a case-by-case basis. Even so, the search for safer alternatives to current synthetic methodologies avoiding the use of moisture/air-sensitive organometallics and, more important, the development of solvent-free protocols are in accordance with the concept of environmental impact factor (E

• factor) [31]. Within this context, the development of solvent-free methods is highly desirable since the difficult for solvent recycling in academic laboratories and chemical manufacturing plants is universal. In addition, a reliable method for the propargylation reaction which could involve the use of

Microwave-assisted synthesis of 2-substituted 4,5,6,7-tetrahydro-1,3-thiazepines from 4-aminobutanol

• María C. Mollo,
• Natalia B. Kilimciler,
• Juan A. Bisceglia and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2020, 16, 32–38, doi:10.3762/bjoc.16.5

• alcohols promoted by trimethylsilyl polyphosphate (PPSE) in solvent-free conditions allowed for the synthesis of several hitherto unreported seven-membered iminothioethers bearing 2-aryl, alkenyl, aralkyl and alkyl substituents. The cyclodehydration reaction is likely to involve an SN2-type displacement

• % yield). Based on our previous experience on related heterocycles, the cyclization was performed with PPSE under solvent-free conditions (8 min, 90 °C), delivering 73% of compound 4a as the only product. As already mentioned, Wipf et al. had previously reported that cyclization of N

SnCl₄-catalyzed solvent-free acetolysis of 2,7-anhydrosialic acid derivatives

• Kesatebrhan Haile Asressu and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2019, 15, 2990–2999, doi:10.3762/bjoc.15.295

• order to access glycans in a pure form. In line with this, various C-5-substituted 2,7-anhydrosialic acid derivatives bearing both electron-donating and -withdrawing protecting groups were synthesized and subjected to different Lewis acid-catalyzed solvent-free ring-opening reactions at room temperature

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• reaction was carried out without any solvent (Table 5, entry 8). Again, catalyst C6 (10 mol %) decreased the yield under solvent-free conditions from 95 to 73% (Table 5, entries 8 vs 9). The Ireland–Claisen rearrangement of cinnamyl isobutyrate (1d) gave under solvent-free conditions only 17% of the acid

• hand, catalyst-free Ireland–Claisen rearrangements proceed well in green solvents such as CpOMe or under solvent-free conditions. NMR kinetic measurements supported the notion that thiourea and squaramide organocatalysts bind strongly to the starting silyl ketene acetals and prevent the Ireland–Claisen

• in TS (black); hydrogen-bond distances (black). a) Rate of product formation; b) reaction profile without catalyst determined by 1H NMR. Ireland–Claisen rearrangement of allyl esters 1a–c. Ireland–Claisen rearrangement of 1c mediated by tertiary amines. Solvent-free Ireland–Claisen rearrangement of

One-pot synthesis of substituted pyrrolo[3,4-b]pyridine-4,5-diones based on the reaction of N-(1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-oxo-2-arylethyl)acetamide with amines

• Valeriya G. Melekhina,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Vitaly S. Mityanov,
• Artem N. Fakhrutdinov,
• Arkady A. Dudinov,
• Vasily A. Migulin,
• Yulia V. Nelyubina,
• Elizaveta K. Melnikova and
• Michail M. Krayushkin

Beilstein J. Org. Chem. 2019, 15, 2840–2846, doi:10.3762/bjoc.15.277

• -one (4), arylglyoxals 5, and acetamide (6) using SnCl2–SiO2 nanoparticles as heterogeneous catalyst under solvent-free conditions [10]. However, as we found out, the use of a catalyst was unnecessary for this transformation. In turn, refluxing the reaction mixture in acetonitrile was sufficient for

A new approach to silicon rhodamines by Suzuki–Miyaura coupling – scope and limitations

• Thines Kanagasundaram,
• Antje Timmermann,
• Carsten S. Kramer and
• Klaus Kopka

Beilstein J. Org. Chem. 2019, 15, 2569–2576, doi:10.3762/bjoc.15.250

• observation than cyanine-based fluorophores [24]. Different synthetic approaches were established to form the silicon rhodamine framework 1 (Scheme 1). While the group of Wu used a copper(II) bromide-catalyzed solvent-free condensation of a diarylsilane 2 with various benzaldehydes 3 [25], Sparr and Fischer

Probing of local polarity in poly(methyl methacrylate) with the charge transfer transition in Nile red

• Aydan Yadigarli,
• Qimeng Song,
• Sergey I. Druzhinin and
• Holger Schönherr

Beilstein J. Org. Chem. 2019, 15, 2552–2562, doi:10.3762/bjoc.15.248

• techniques, and (ii) different theoretical models of solvatochromic effects were employed, some of them take inductive solute–solvent interactions and solute polarizability into account, others neglect them, and (iii) different definitions of the molecular dipole moment in solvent-free conditions in vacuum

In water multicomponent synthesis of low-molecular-mass 4,7-dihydrotetrazolo[1,5-a]pyrimidines

• Irina G. Tkachenko,
• Sergey A. Komykhov,
• Vladimir I. Musatov,
• Svitlana V. Shishkina,
• Viktoriya V. Dyakonenko,
• Vladimir N. Shvets,
• Mikhail V. Diachkov,
• Valentyn A. Chebanov and
• Sergey M. Desenko

Beilstein J. Org. Chem. 2019, 15, 2390–2397, doi:10.3762/bjoc.15.231

• dihydrotetrazolopyrimidines one may concern carrying out these reactions under solvent-free conditions [15][16][17] or using water as a “green solvent” [18]. Results and Discussion Synthesis Due to the small number of reports available for dihydroazolopyrimidines with aliphatic substituents, we aimed by this work to

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• catalytic activity exhibited by Cu(0) NPs Chenglong et al. have reported an efficient, three-component one-pot reaction for the synthesis of imidazo[1,2-a]pyridines [111]. The protocol enjoyed a solvent-free domino reaction between compounds 3, 1 and 2 under nitrogen atmosphere at 120 °C (Scheme 15

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• carried out a large-scale one-pot solvent-free synthesis of amides 6a,b starting from propargyl alcohols 7a,b at room temperature (Scheme 4). At the first step, alcohols 7a,b in the reaction with PCl3 were transformed into the corresponding allenes 1a,h. Then, the addition of Brønsted acid (TfOH or H2SO4

• cations A, B, and F–H. Large-scale one-pot solvent-free synthesis of amides 6a,b from the corresponding propargylic alcohols. AlCl3-promoted hydroarylation of allene 1b by benzene leading to alkene Z-11n. Reaction of allene 1a with benzene under the action of AlCl3 followed by quenching of the reaction

Reaction of oxiranes with cyclodextrins under high-energy ball-milling conditions

• László Jicsinszky,
• Federica Calsolaro,
• Katia Martina,
• Fabio Bucciol,
• Maela Manzoli and
• Giancarlo Cravotto

Beilstein J. Org. Chem. 2019, 15, 1448–1459, doi:10.3762/bjoc.15.145

• substitution, which results in products having some DS-dependent solubilisation properties [8][9][10][11]. In solvent-free conditions, although the nature of the reaction means that they are not absolutely water free, not only the PG formation can be optimised but also the reagent use. As previously

Mechanochemical Friedel–Crafts acylations

• Mateja Đud,
• Anamarija Briš,
• Iva Jušinski,
• Davor Gracin and
• Davor Margetić

Beilstein J. Org. Chem. 2019, 15, 1313–1320, doi:10.3762/bjoc.15.130

• friendly, solvent-free mechanochemical reaction conditions of this industrially important reaction were developed. Reaction parameters such as FC catalyst, time, ratio of reagents and milling support were studied to establish the optimal reaction conditions. The scope of the reaction was explored by

• method in the synthesis of covalent triazine frameworks. Herein, we report related results on solvent-free FC acylation reactions conducted in a ball mill, which is the continuation of our program in organic mechanosynthesis [20][21][22][23][24]. Results and Discussion Mechanochemical FCR of pyrene (1

Mechanochemical synthesis of hyper-crosslinked polymers: influences on their pore structure and adsorption behaviour for organic vapors

• Sven Grätz,
• Sebastian Zink,
• Hanna Kraffczyk,
• Marcus Rose and
• Lars Borchardt

Beilstein J. Org. Chem. 2019, 15, 1154–1161, doi:10.3762/bjoc.15.112

• Universität Darmstadt, Darmstadt, Germany 10.3762/bjoc.15.112 Abstract This study elucidates a mechanochemical polymerization reaction towards a hyper-crosslinked polymer as an alternative to conventional solvent-based procedures. The swift and solvent-free Friedel–Crafts alkylation reaction yields a porous

• sorption experiments with benzene and cyclohexane. Keywords: hyper-crosslinked polymers; mechanochemistry; microporous; solvent-free; vapor sorption; Introduction The widespread use of microporous materials in areas like gas storage, gas separation, and catalysis has led to the development of a wide

• synthesis of several porous materials [21][22][23][24][25][26][27][28][29] and polymers [30][31][32][33][34][35][36][37][38][39][40][41][42]. In this contribution, we employed mechanochemistry for a protocol for the solvent-free crosslinking of HCP (Figure 1). This is supported by an investigation of

Mechanochemical synthesis of poly(trimethylene carbonate)s: an example of rate acceleration

• Sora Park and
• Jeung Gon Kim

Beilstein J. Org. Chem. 2019, 15, 963–970, doi:10.3762/bjoc.15.93

• can now be obtained through green mechanochemical synthesis. In addition to the general merits of mechanochemistry, such as being solvent-free and resulting in high conversions, we herein explore rate acceleration under ball-milling conditions while the conventional solution-state synthesis suffer

• from low reactivity. The solvent-free mechanochemical polymerization of trimethylene carbonate using the organocatalysts 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) are examined herein. The polymerizations under ball-milling conditions exhibited significant

• synthesis of poly(azomethine) and poly(phenylene) [11][12]. Our group also contributed to this area by developing a ball-milling promoted high-molecular weight poly(lactic acid) synthesis [13][14] and a solvent-free post-polymerization modification of functional polystyrenes [15]. The Friščić team also

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• ; mechanochemistry; self-assembly; solvent-free; supramolecular; Introduction In living systems an important aspect is to create complex functional molecules from simpler units by following biomolecular mechanisms [1]. The biological assemblies for living beings are developed from processes of spontaneous self

• as the solvent-free condition may make traditional workup superfluous [31][32]. Also, mechanochemical methods have high impact in ecology and economy as they save time [33]. Mechanochemical syntheses benefit from high to quantitative conversions, minimized steps for purification and diminished

• ) and ethylenediamine (5). Subsequently, to the same pot appropriate metals were added to obtain the respective complexes 7 [55]. In 2002, Otera and co-workers reported the formation of some supramolecular self-assembled structures which was found to be faster under solvent-free mechanochemical

Synthesis of acylglycerol derivatives by mechanochemistry

• Karen J. Ardila-Fierro,
• Andrij Pich,
• Marc Spehr,
• José G. Hernández and
• Carsten Bolm

Beilstein J. Org. Chem. 2019, 15, 811–817, doi:10.3762/bjoc.15.78

• nucleophiles [36]. Moreover, salen complexes endure mechanochemical conditions, as proven during their preparation in ball mills [37]. In addition, various related Jacobsen salen complexes have shown catalytic activity under solvent-free conditions [38]. Collectively, these precedents made this synthetic route

• targeted the mechanosynthesis of the DAGs by reacting MAG 4a and fatty acids 3 in the ball mill. Such esterifications required the activation of 3 with N,N’-dicyclohexylcarbodiimide (DCC), thereby complementing other recently developed solvent-free carboxylic acid activations towards amidation or

• of solvent-free ester formation between monoacylglycerols and fatty acids to afford DAGs. Moreover, the synthesis of conjugated DAGs 10 represents a step forward towards the establishment of mechanochemical conjugation reactions for linking fluorescent materials to lipids at the proof-of-concept

Hoveyda–Grubbs catalysts with an N→Ru coordinate bond in a six-membered ring. Synthesis of stable, industrially scalable, highly efficient ruthenium metathesis catalysts and 2-vinylbenzylamine ligands as their precursors

• Kirill B. Polyanskii,
• Kseniia A. Alekseeva,
• Pavel V. Raspertov,
• Pavel A. Kumandin,
• Eugeniya V. Nikitina,
• Atash V. Gurbanov and
• Fedor I. Zubkov

Beilstein J. Org. Chem. 2019, 15, 769–779, doi:10.3762/bjoc.15.73

• styrenes 5 with a cyclic tertiary amino group from 1,2,3,4-tetrahydroisoquinoline (Scheme 2). In this case, the initial isoquinoline was reduced in the presence of formic acid and then converted into the desired products 5 by a one-pot solvent-free reaction under the action of the corresponding dihalide in