Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• pressure and ultrasound sonication (Scheme 40). Microwave irradiation proved to be the most efficient conditions with regard to reaction time and conversion. Moderate to high isolated yields (43–95%) were obtained depending on the carbodiimides, the elevated temperatures sometimes required led to the

Ultrasound-assisted Strecker synthesis of novel 2-(hetero)aryl-2-(arylamino)acetonitrile derivatives

• Emese Gal,
• Luiza Gaina,
• Hermina Petkes,
• Alexandra Pop,
• Castelia Cristea,
• Gabriel Barta,
• Dan Cristian Vodnar and
• Luminiţa Silaghi-Dumitrescu

Beilstein J. Org. Chem. 2020, 16, 2929–2936, doi:10.3762/bjoc.16.242

• heterocyclic compounds, the use of ultrasound irradiation became a powerful tool by proving to be superior in terms of reaction rates, yields, and the purity of the products as compared to traditional convective heating methods [2]. Sonochemical syntheses can be successfully performed in homogeneous media

• ] appeared improved under ultrasound-assisted conditions, which also enhanced the yields of the final α-aminonitrile derivatives. The Strecker reaction of cyclopropanone acetal substrates with sodium cyanide and several amines was also facilitated by sonication conditions which afforded cleaner N-alkylated α

• -nitrile pharmacophoric units. In this work we report the experimental procedure for the ultrasound-assisted addition of the TMSCN nucleophile to heterocyclic aldimines. The substrates tested were mostly represented by a series of phenothiazinyl aldimines, but the scope of the new synthetic procedure was

A new method for the synthesis of diamantane by hydroisomerization of binor-S on treatment with sulfuric acid

• Rishat I. Aminov and
• Ravil I. Khusnutdinov

Beilstein J. Org. Chem. 2020, 16, 2534–2539, doi:10.3762/bjoc.16.205

• mL/min)]. The sonication was carried out with an ultrasound generator IL10–0.63 (INLAB LTD) for 180 min at a frequency of 22 kHz with a submerged 15 mm diameter titanium horn, with output power 150 W. The reactions were carried out in a 100 × 35 mm glass reactor equipped with a jacket to maintain the

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

• yield (Scheme 42). 3.3 Preparation of tritellurasumanene derivatives On the other occasion, tritellurasumanene derivatives 162–165 have been prepared by Shao’s team starting from triphenylene skeletons by means of an ultrasound-assisted one-pot procedure (Scheme 43) [79][80]. As can be noted from Scheme

Natural dolomitic limestone-catalyzed synthesis of benzimidazoles, dihydropyrimidinones, and highly substituted pyridines under ultrasound irradiation

• Kumar Godugu,
• Venkata Divya Sri Yadala,
• Mohammad Khaja Mohinuddin Pinjari,
• Trivikram Reddy Gundala,
• Lakshmi Reddy Sanapareddy and
• Chinna Gangi Reddy Nallagondu

Beilstein J. Org. Chem. 2020, 16, 1881–1900, doi:10.3762/bjoc.16.156

• pyridines via C–N, C–C, and C–S bond formations in a mixture of ethanol and H2O under ultrasound irradiation. The catalyst is characterized by XRD, FTIR, Raman spectroscopy, SEM, and EDAX analysis. The main advantages of this methodology include the wide substrate scope, cleaner reaction profile, short

• : benzimidazoles; dihydropyrimidinones; highly substituted pyridines; natural dolomitic limestone; ultrasound irradiation; Introduction Nitrogen heterocycles are recognized as “privileged medicinal scaffolds” because these compounds are found in a wide variety of bioactive natural products and pharmaceuticals [1

• synthesis of 1-benzyl-2-phenyl-1H-benzo[d]imidazole (3a). At first, a control experiment was conducted by using model substrates, 1 and 2a, in H2O in the absence of catalyst under ultrasound irradiation for 60 min at 45–50 °C. It was found that the reaction did not proceed in the absence of a catalyst

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

• techniques have recently been shown to have interesting enhancements when coupled with ultrasonic irradiation [158]. Ultrasonic irradiation, from 20 kHz to 1 GHz, does not directly interact with molecular energy levels. However, the extreme conditions generated from an ultrasound wave expanding within a

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

Asymmetric synthesis of CF₂-functionalized aziridines by combined strong Brønsted acid catalysis

• Xing-Fa Tan,
• Fa-Guang Zhang and
• Jun-An Ma

Beilstein J. Org. Chem. 2020, 16, 638–644, doi:10.3762/bjoc.16.60

• corresponding CF2-functionalized aziridine 4 was dissolved in isopropanol (0.05–0.2 mL/mg) with the help of ultrasound, followed by filtration, and the obtained solution was concentrated to give 4 with increased ee and dr values. a0.006 mmol of COOH-BA was employed. bThe reaction was operated at 45 °C for 24 h

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• heterogeneous nanocatalyst in “click” reactions for the multicomponent synthesis of triazole products in water with ultrasound irradiation and 0.017 mol % catalyst loading. As such, a series of aryl/alkyl-substituted oxiranes was treated with sodium azide and nonactivated terminal alkynes, giving 1,2,3-triazole

Ultrasonic-assisted unusual four-component synthesis of 7-azolylamino-4,5,6,7-tetrahydroazolo[1,5-a]pyrimidines

• Yana I. Sakhno,
• Maryna V. Murlykina,
• Oleksandr I. Zbruyev,
• Anton V. Kozyryev,
• Svetlana V. Shishkina,
• Dmytro Sysoiev,
• Vladimir I. Musatov,
• Sergey M. Desenko and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2020, 16, 281–289, doi:10.3762/bjoc.16.27

• reactions involving pyruvic acids (pyruvates) and different α-aminoazoles. Synthesis of 4-arylamino-substituted tetrahydroquinolines. Ultrasound-assisted multicomponent reactions of 3-amino-1,2,4-triazole or 5-amino-1H-pyrazole-4-carbonitrile, aldehydes, and pyruvic acid/ethyl pyruvate. Synthesis of 3-cyano

Mono- and bithiophene-substituted diarylethene photoswitches with emissive open or closed forms

• A. Lennart Schleper,
• Mariano L. Bossi,
• Vladimir N. Belov and
• Stefan W. Hell

Beilstein J. Org. Chem. 2019, 15, 2344–2354, doi:10.3762/bjoc.15.227

• ligands. The reaction with pinacolborane (HB(pin)) gave ester 9 in 97% yield [11]. Another ester (10) was synthesized by bromination of 3-thiopheneacetic acid with NBS (applying an ultrasound bath) followed by esterification of the crude product with methanol in the presence of sulfuric acid [12]. Other

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• , dioxane, acetonitrile, etc. Because the reaction rate is slow at room temperature, it needs activation by heating or other non-traditional methods such as ultrasound, microwave, IR irradiation and photochemical irradiation, as it will be exemplified below. In terms of reactants, the reaction seems to work

• 40 (Scheme 13). An alternative setup of Biginelli-3CR with steroids was reported by Boruah and co-workers [43] using ultrasound assistance instead of microwave irradiation or thermal heating. In this case, the reaction between cholestanic ketone 43, an alkyl or arylaldehyde, and urea or thiourea

• could be conducted under ultrasound irradiation using sodium ethoxide as catalyst, thus generating steroid ring A-fused 3,4-dihydropyrimidinones and 3,4-dihydropyrimidinthiones 44 in very good yields. Mohamed et al. [44] reported a 4CR for the synthesis of pyridopyrimidines fused to ring D of

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

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

• mixing [22][23], ultrasound [24], etc. as alternative energy sources to replace common laboratory techniques [25]. Among them, especially mechanochemical synthesis [26][27][28][29] has gained popularity due to its advantage over conventional solution-based methods [30]. The process is highly beneficial

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation

• Łukasz Gułajski,
• Andrzej Tracz,
• Katarzyna Urbaniak,
• Stefan J. Czarnocki,
• Michał Bieniek and
• Tomasz K. Olszewski

Beilstein J. Org. Chem. 2019, 15, 160–166, doi:10.3762/bjoc.15.16

• -heterocyclic carbene (NHC) ligand were revealed. The presented methodology allows for preparation of a variety of polar and non-polar metathesis products under environmentally friendly conditions. Keywords: catalysis; green chemistry; microwave; N-heterocyclic carbene; olefin metathesis; ruthenium; ultrasound

• research on synthesis of catalysts for olefin metathesis and to expand the utility of ammonium-tagged ruthenium-based catalysts [69][70][71][72][73][74][75][76], herein we present the use of such catalysts for olefin metathesis in aqueous media promoted by microwave and ultrasound irradiation. Results and

• , the cross metathesis (CM) between alcohol 8 and the electron-deficient cross partner methyl acrylate (10, Table 1). All reactions were run at 36 °C in D2O promoted either by microwave (µW) or ultrasound (US) irradiation, and for comparison purposes also with standard magnetic stirring. In the case of

Synthesis of mono-functionalized S-diazocines via intramolecular Baeyer–Mills reactions

• Miriam Schehr,
• Daniel Hugenbusch,
• Tobias Moje,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2018, 14, 2799–2804, doi:10.3762/bjoc.14.257

• the synthesis of a diazocine where the –CH2–CH2– bridge is replaced by a –CH2–S– bridge (S-diazocine) using an ultrasound-supported reductive azocoupling with lead [17]. In this reaction a small amount of S-diazocine is directly formed and a larger fraction of the azoxy compound is obtained, which can

Molecular iodine-catalyzed one-pot multicomponent synthesis of 5-amino-4-(arylselanyl)-1H-pyrazoles

• Camila S. Pires,
• Daniela H. de Oliveira,
• Maria R. B. Pontel,
• Jean C. Kazmierczak,
• Roberta Cargnelutti,
• Diego Alves,
• Raquel G. Jacob and
• Ricardo F. Schumacher

Beilstein J. Org. Chem. 2018, 14, 2789–2798, doi:10.3762/bjoc.14.256

• reaction conditions. During the experiments different parameters were evaluated such as temperature, reaction time, solvent, reagent amount and heating method (conventional heating or ultrasound, Table 1). In a first experiment, benzoylacetonitrile (1a, 0.5 mmol), phenylhydrazine (2a, 0.5 mmol) and

Synthesis and supramolecular self-assembly of glutamic acid-based squaramides

• Juan V. Alegre-Requena,
• Marleen Häring,
• Isaac G. Sonsona,
• Alex Abramov,
• Eugenia Marqués-López,
• Raquel P. Herrera and
• David Díaz Díaz

Beilstein J. Org. Chem. 2018, 14, 2065–2073, doi:10.3762/bjoc.14.180

• this work all gels were prepared via heating–cooling, we observed that the application of ultrasound [41] facilitated the formation of some gels by decreasing significantly the gelation time, especially after the gels were thermally destroyed for the first time (data not shown). This is in good

• agreement with our previous observations made with a different squaramide, where we hypothesized that ultrasound could help to preserve only the thermodynamically more stable aggregates through a self-sorting mechanism, thus providing a more robust starting platform for rebuilding the gel network [21]. At

Mechanochemistry of nucleosides, nucleotides and related materials

• Olga Eguaogie,
• Joseph S. Vyle,
• Patrick F. Conlon,
• Manuela A. Gîlea and
• Yipei Liang

Beilstein J. Org. Chem. 2018, 14, 955–970, doi:10.3762/bjoc.14.81

• nucleoside or nucleotide substrate which would be disfavoured in solution. Although bond disruption via ultrasound-induced cavitation can be considered within the purview of mechanochemistry [33][34], this review will be restricted to the delivery of mechanochemical energy on a macroscopic scale by vibration

• al. compared the amount of energy required to effect permanganate-mediated oxidative self-coupling of p-toluidine using different energy inputs. Ball milling was significantly more efficient (up to an order of magnitude) than conventional heating, microwave or ultrasound inputs [36]. The reduction in

On the design principles of peptide–drug conjugates for targeted drug delivery to the malignant tumor site

• Eirinaios I. Vrettos,
• Gábor Mező and
• Andreas G. Tzakos

Beilstein J. Org. Chem. 2018, 14, 930–954, doi:10.3762/bjoc.14.80

• bioconjugate in the tumor microenvironment. Such linkers are rationally designed to be cleaved when they sense specific stimuli in the environment of cancerous cells (slightly acidic pH, enhanced levels of reducing agents and/or enzymes) or external stimuli (ultrasound, temperature, irradiation). Specifically

• to cross it through various mechanisms [138] or novel techniques able to disrupt its dense structure like ultrasound-mediated drug delivery [139][140]. The design principles on the synthesis of the specific conjugate, ANG1005, were the following: the peptide angiopep-2 is able to cross the BBB via

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• , Samant et al. reported an ultrasound-promoted condensation catalysed by sulfamic acid [44]. As shown in Table 1, entries 39 and 40, both dichloroethane (DCE) and solvent-free conditions were tested. The catalyst worked at low temperature (28–30 °C) and the products were formed in short reaction times in

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• -aminopyrazole 16 and 4-hydroxycoumarin (50) with isatin 54 under ultrasound irradiation in water (Scheme 11). Solvent and catalytic screening for the reaction have shown that water in presence of p-TSA at 60 °C on heating for 6 hours provide best results with excellent yields. Recently, Wang et al. [57] also

• conventional heating conditions (24 hours). A three-component reaction of 5-aminopyrazole 16, arylaldehydes 47 and indandione 58 under ultrasonic irradiation in ethanol was developed by Nikpassand et al. [66] to synthesize pyrazolo[3,4-b]pyridine derivatives 78 (Scheme 19). Ultrasound-mediated reactions

• reported a similar reaction of 5-aminopyrazole 16, arylaldehyde 47 with ethyl cyanoacetate (94) under ultrasound irradiation in presence of p-TSA in water for the synthesis of 3-methyl-6-oxo-4-aryl-4,5,6,7-tetrahydro-4H-pyrazolo[3,4-b]pyridine-5-carbonitrile derivatives 95 (Scheme 27). All the synthesized

Halogen-containing thiazole orange analogues – new fluorogenic DNA stains

• Aleksey A. Vasilev,
• Meglena I. Kandinska,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• David Sucunza,
• Juan J. Vaquero,
• Obis D. Castaño,
• Stanislav Baluschev and
• Silvia E. Angelova

Beilstein J. Org. Chem. 2017, 13, 2902–2914, doi:10.3762/bjoc.13.283

• TO-7Cl. The condensation of 2-methylbenzothiazolium salt 2a and 4,7-dichloroquinolinium methyl sulfate 4a was conducted in water, methanol or ethanol by stirring the reaction mixture at room temperature or by ultrasound irradiation for not more than 40 minutes. Prolonged sonication causes heating of

• the samples in the ultrasonic bath and this makes external cooling difficult. In addition, the ultrasound irradiation promotes side reactions and thus leads to slightly lower reaction yields when compared to the room temperature conditions. It is well known that water is one of the most useful green

• ether (10 mL) and dried in a vacuum desiccator. The dye was purified by three recrystallizations from methanol. Yield from reaction at room temperature (Procedure A1): 43% yield from reaction with ultrasound (Procedure A2) 41%; mp 281–283 °C; 1H NMR (500 MHz, DMSO-d6) δ 4.01 (s, 3H, NCH3), 4.11 (s, 3H

Synthesis, effect of substituents on the regiochemistry and equilibrium studies of tetrazolo[1,5-a]pyrimidine/2-azidopyrimidines

• Elisandra Scapin,
• Paulo R. S. Salbego,
• Caroline R. Bender,
• Alexandre R. Meyer,
• Anderson B. Pagliari,
• Tainára Orlando,
• Geórgia C. Zimmer,
• Clarissa P. Frizzo,
• Helio G. Bonacorso,
• Nilo Zanatta and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 2396–2407, doi:10.3762/bjoc.13.237

• using ultrasound irradiation promoted shorter reaction times, high regioselectivity, and excellent yields, when compared with conventional thermal heating [30]. Presently, we demonstrate an eco-friendly synthesis of 5- and 7-substituted tetrazolo[1,5-a]pyrimidine isomers, in good to excellent yields

Solvent-free copper-catalyzed click chemistry for the synthesis of N-heterocyclic hybrids based on quinoline and 1,2,3-triazole

• Martina Tireli,
• Silvija Maračić,
• Stipe Lukin,
• Marina Juribašić Kulcsár,
• Dijana Žilić,
• Mario Cetina,
• Ivan Halasz,
• Silvana Raić-Malić and
• Krunoslav Užarević

Beilstein J. Org. Chem. 2017, 13, 2352–2363, doi:10.3762/bjoc.13.232

• , there is a persistent incentive to find greener alternatives, which would reduce time and energy requirements as well as waste generated by these reactions. Among other non-conventional approaches such as microwave and ultrasound irradiation [7][12][13], mechanochemistry has emerged as a viable approach

Mechanochemical synthesis of small organic molecules

• Tapas Kumar Achar,
• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2017, 13, 1907–1931, doi:10.3762/bjoc.13.186

• /energy, etc. Non-conventional energy sources for chemical reactions such as microwave, mechanical mixing, visible-light and ultrasound are becoming surge of interest to the chemist as alternative energy sources in laboratories [7]. By imposing these techniques innumerable chemical transformations have