Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• ; 4, Figure 1) [36][37]. The relevance of acridine in drug discovery galvanized Singh and co-workers [38] to develop a water-promoted three-component reaction involving aldehydes 5, cyclic 1,3-diketone 6 and ammonium acetate powered by microwave irradiation resulting in 4-arylacridinediones 7 in

• -fused tetrahydrodibenzoacridinones 9 using phenanthren-9-amine 8, aldehydes 5, and cyclic 1,3-diketones 6 as structural units in ethanol under microwave irradiation to result in the targeted products in excellent yields. A conventional heating used for the same protocol delivered the desired products in

• -ones 24 using substituted phenylenediamine 23, aldehydes 5 and cyclic 1,3-diketone such as tetronic acid 6c under microwave irradiation in aqueous conditions delivering the product in good yields (70–89%). The use of a non-polar solvent resulted in the formation of side products like benzimidazole

Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles

• Ramazan Koçak and
• Arif Daştan

Beilstein J. Org. Chem. 2021, 17, 719–729, doi:10.3762/bjoc.17.61

• unsubstituted pyrrole 10ac was synthesized by the reaction of pyrrole 10ab with 4 equivalents of KOH under microwave irradiation (Scheme 6). The reaction of 2-pyridylpyridazine 4b with Zn did not work at room temperature. Under reflux conditions compound 10ba was obtained, which contained the corresponding

Effective microwave-assisted approach to 1,2,3-triazolobenzodiazepinones via tandem Ugi reaction/catalyst-free intramolecular azide–alkyne cycloaddition

• Maryna O. Mazur,
• Oleksii S. Zhelavskyi,
• Eugene M. Zviagin,
• Svitlana V. Shishkina,
• Vladimir I. Musatov,
• Maksim A. Kolosov,
• Elena H. Shvets,
• Anna Yu. Andryushchenko and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2021, 17, 678–687, doi:10.3762/bjoc.17.57

• temperature conditions for the cyclization, performing a reaction under microwave irradiation in a sealed vial, and changed the solvent to less toxic (than benzene) toluene. That led to a decreasing reaction time to 1–1.5 hours (the reaction progress was monitored by TLC) with no impact on the product purity

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

Designed whole-cell-catalysis-assisted synthesis of 9,11-secosterols

• Marek Kõllo,
• Marje Kasari,
• Villu Kasari,
• Tõnis Pehk,
• Ivar Järving,
• Margus Lopp,
• Arvi Jõers and
• Tõnis Kanger

Beilstein J. Org. Chem. 2021, 17, 581–588, doi:10.3762/bjoc.17.52

• microwave irradiation, a mixture of monoacylated and diacylated products 3 and 4 in 52% and 33% yield, respectively, was isolated [28]. Enzymatic hydroxylation 3-Ketosteroid 9α-hydroxylase (KSH) from R. rhodochrous has been shown to oxidize C9 in several steroids [29]. This enzyme consists of two

• p-toluenesulfonic acid monohydrate (2.8 mg, 0,008 mmol, 0,01 equiv) in a beaker was subjected to continuous mode of microwave irradiation (800 W) at high power setting in a domestic microwave oven for 6 min. After this, the mixture was cooled to room temperature, and saturated aqueous NaHCO3 (5 mL

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• addition, another modification was made in order to increase the speed of the reaction of sodium halodifluoroacetate and alkenes. This was achieved by the use of microwave irradiation in THF solution, which allowed the reactions to be completed within 5 minutes [31]. An application of this method to

1,2,3-Triazoles as leaving groups in S_NAr–Arbuzov reactions: synthesis of C6-phosphonated purine derivatives

• Kārlis-Ēriks Kriķis,
• Irina Novosjolova,
• Anatoly Mishnev and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 193–202, doi:10.3762/bjoc.17.19

• development of this topic [8][9][10][11]. On the contrary, only a few examples can be found in the literature where a phosphorus-containing substituent is directly attached to the purine ring [12][13]. In 2008, an SNAr–Arbuzov reaction was developed for 6-chloropurine derivatives under microwave irradiation

• : DMSO-d6, 90 °C. Single-crystal X-ray analysis of diethyl (9-heptyl-2-(4-phenyl-1H-1,2,3-triazol-1-yl)-9H-purin-6-yl)phosphonate (4d). CCDC-2044976. Structural diversity and synthetic methods of purinylphosphonates. MWI = microwave irradiation; LG = leaving group. Synthetic routes for the formation of

An atom-economical addition of methyl azaarenes with aromatic aldehydes via benzylic C(sp³)–H bond functionalization under solvent- and catalyst-free conditions

• Divya Rohini Yennamaneni,
• Vasu Amrutham,
• Krishna Sai Gajula,
• Rammurthy Banothu,
• Murali Boosa and
• Narender Nama

Beilstein J. Org. Chem. 2020, 16, 3093–3103, doi:10.3762/bjoc.16.259

• times [30]. Rao et al. performed similar reactions without catalyst under microwave irradiation in the presence of water as a solvent [31], but when considering an industrial scale, there are numerous factors that serves as obstacles for the usage of microwave reactors, such as escalated heat loss

Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

• Alexander P. Molchanov,
• Mariia M. Efremova,
• Mariya A. Kryukova and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2020, 16, 2679–2686, doi:10.3762/bjoc.16.218

• that the Lewis acid-catalyzed reaction of diaziridines with donor–acceptor cyclopropanes and aziridines affords the perhydropyridazine or triazine derivatives, respectively, in good yields [31][32][33]. The use of microwave irradiation in organic synthesis complies with the principles of green

• chemistry and has attracted much interest. For 1,3-dipolar cycloaddition reactions microwave irradiation not only allows to reduce the reaction time and to increase yields, but in some cases also can affect the selectivity of the reaction [34][35][36]. The efficiency of microwave irradiation has been shown

• cycloaddition reaction of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes 1a–d (DABCH) with 1,3-diarylpropenones 2a–l at 110 °С under microwave irradiation using a microwave oven Discover SP in a 10 mL glass reactor. It was found that under these conditions the (3 + 2) cycloaddition products – perhydropyrazolopyrazoles

Synthesis and characterization of S,N-heterotetracenes

• Astrid Vogt,
• Florian Henne,
• Christoph Wetzel,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2020, 16, 2636–2644, doi:10.3762/bjoc.16.214

• 3-nitro-2,2’-bithiophene with triethyl phosphite under microwave irradiation and surprisingly obtained targeted heterotriacene H-DTP (vide supra) with only 11% yield [45]. This result prompted us to have a closer look on the applicability of the Cadogan reaction/cyclization in order to provide S,N

Synergy between supported ionic liquid-like phases and immobilized palladium N-heterocyclic carbene–phosphine complexes for the Negishi reaction under flow conditions

• Edgar Peris,
• Raúl Porcar,
• María Macia,
• Jesús Alcázar,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2020, 16, 1924–1935, doi:10.3762/bjoc.16.159

• of methylimidazolium units leading to a Pd(II)-SILLP system 11 with 0.56 mequiv of Pd/g of SILLP and 3.79 mequiv of IL-like units/g of SILLP (Scheme 4). This system was treated with either NaBH4 or EtOH under microwave irradiation to produce the corresponding PdNPs immobilized onto SILLPs (12a,b

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

• Dalel El-Marrouki,
• Sabrina Touchet,
• Abderrahmen Abdelli,
• Hédi M’Rabet,
• Mohamed Lotfi Efrit and
• Philippe C. Gros

Beilstein J. Org. Chem. 2020, 16, 1722–1731, doi:10.3762/bjoc.16.144

• as the main product, with the best yield being obtained in butanol (43%, Table 1, entry 11), however, with the formation of 6b occurring only in 10% yield. Switching to microwave irradiation formed exclusively 7b in 60% yield after 3 h (Table 1, entry 13). Note, that to check the effect of a shorter

Microwave-assisted efficient one-pot synthesis of N²-(tetrazol-5-yl)-6-aryl/heteroaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines

• Moustafa Sherief Moustafa,
• Ramadan Ahmed Mekheimer,
• Saleh Mohammed Al-Mousawi,
• Mohamed Abd-Elmonem,
• Hesham El-Zorba,
• Afaf Mohamed Abdel Hameed,
• Tahany Mahmoud Mohamed and
• Kamal Usef Sadek

Beilstein J. Org. Chem. 2020, 16, 1706–1712, doi:10.3762/bjoc.16.142

• developed by reacting 5-amino-1,2,3,4-tetrazole with aromatic aldehydes and cyanamide in pyridine under controlled microwave heating with high yields. X-ray crystallography confirmed the structure of the obtained products. Keywords: microwave irradiation; N2-(tetrazol-5-yl)-6-aryl/heteroaryl-1,3,5-triazine

• favorable due to the high nucleophilicity of the exocyclic amino function attached to the electron-rich tetrazole ring [45]. In support of this assumption we stopped the reaction after 4 minutes of heating under microwave irradiation and inspected the prior formation of 9 via comparison with an authentic

• ://www.ccdc.cam.ac.uk CCDC1961565 for compound 4i. All reactions were monitored by TLC with 1:1 ethyl acetate/petroleum ether as eluent and were carried out until starting materials were completely consumed. After 7 min microwave irradiation was stopped and the reaction mixture was analyzed by TLC; after further

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• endotermic process is the rate-limiting step and long reaction times are generally associated to this. However, the reaction can be accelerated in conditions that facilitate the dissociation of CO ligands such as heating, microwave irradiation [37][38], visible light, or ultrasonication [39]. Alternatively

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

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

Activated carbon as catalyst support: precursors, preparation, modification and characterization

• Melanie Iwanow,
• Tobias Gärtner,
• Volker Sieber and
• Burkhard König

Beilstein J. Org. Chem. 2020, 16, 1188–1202, doi:10.3762/bjoc.16.104

• be produced by salt templating or ultrasonic spray pyrolysis as well as by microwave irradiation. The resulting activated carbon materials are characterized by a variety of techniques such as SEM, FTIR, nitrogen adsorption, Boehm titrations, adsorption of phenol, methylene blue and iodine, TPD, CHNS

• ]. Microwave irradiation is a promising alternative with some advantages. In contrast to conventional heating, which is based on the convection mechanism involving conduction and radiation, the sample can be heated uniformly and contactless by the heat generated from electromagnetic energy, resulting in

• surface areas by microwave-induced ZnCl2 activation within minutes. The porosity of the materials can be tailored by the carbon precursor to ZnCl2 ratio and the microwave irradiation time [104]. Foo et al. investigated the activated carbon preparation by microwave heating with K2CO3 activation from wood

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• product 2-[18F]FPhe 46 in 43% yield, whereas under microwave irradiation a 34% yield was obtained. Under the optimized conditions, the enantiomeric purity was reported to be ≥94% ee [46] (Scheme 10). 1.3. Photooxidative cyanation of fluorinated benzylamine A convenient, protecting group-free, and

Diversity-oriented synthesis of 17-spirosteroids

• Benjamin Laroche,
• Thomas Bouvarel,
• Martin Louis-Sylvestre and
• Bastien Nay

Beilstein J. Org. Chem. 2020, 16, 880–887, doi:10.3762/bjoc.16.79

• at 170 °C for 17-(4-penten-1-yloxy)steroids, for 1 h under microwave irradiation. The solvent was removed by evaporation, and the resulting crude material was purified by chromatography on silica gel (petroleum ether/EtOAc 99:1) to afford the spirocyclic diene. General procedure C for one-pot RCEYM

• /Diels–Alder reaction The enyne (1 mmol) was dissolved in dry toluene (c 0.03 M). The solution was placed in a sealed microwave tube containing a magnetic stirrer under argon. The Grubbs second generation catalyst (2 mol %) was added and the reaction mixture was stirred at 120 °C for 1 h under microwave

• irradiation. The microwave tube was opened and the dienophile (1.2 mmol) was added in one portion. The mixture was stirred at 150 °C for 35 min. The solvent was removed and the crude material was purified by chromatography on silica gel (petroleum ether/EtOAc 8:3) to afford the product. Structure of four 17

Efficient synthesis of piperazinyl amides of 18β-glycyrrhetinic acid

• Dong Cai,
• ZhiHua Zhang,
• Yufan Meng,
• KaiLi Zhu,
• LiYi Chen,
• ChangXiang Yu,
• ChangWei Yu,
• ZiYi Fu,
• DianShen Yang and
• YiXia Gong

Beilstein J. Org. Chem. 2020, 16, 798–808, doi:10.3762/bjoc.16.73

• yields (<19%) of the desired compound 8 were obtained after a longer reaction time (Table 2, entries 1–4). A further investigation of the reaction using microwave irradiation to heat at reflux temperature also failed to produce the target product (Table 2, entry 2). The intermediate 6 exhibited very low

Synthesis of C₇₀-fragment buckybowls bearing alkoxy substituents

• Yumi Yakiyama,
• Shota Hishikawa and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2020, 16, 681–690, doi:10.3762/bjoc.16.66

• using 20 mol % of Pd(PPh3)2Cl2 and 150 mol % DBU in DMF at 150 °C under microwave irradiation conditions to afford the desired dimethoxy derivative 5a in 75% yield. In contrast, when the reaction of 4b was performed, not only the desired product 5b but also the unexpected regioisomer 5c was obtained

• . The temperature dependency of the product ratio between 5b and 5c was investigated and the results are shown in Table 1. The cyclization did not proceed under 140 °C, and at 140 °C the total yield is low (41% after 40 min microwave irradiation) but the ratio of 5b was the highest (5b/5c = 10:1). The

Microwave-assisted efficient and facile synthesis of tetramic acid derivatives via a one-pot post-Ugi cascade reaction

• Yong Li,
• Zheng Huang,
• Jia Xu,
• Yong Ding,
• Dian-Yong Tang,
• Jie Lei,
• Hong-yu Li,
• Zhong-Zhu Chen and
• Zhi-Gang Xu

Beilstein J. Org. Chem. 2020, 16, 663–669, doi:10.3762/bjoc.16.63

• developed through an Ugi/Dieckmann cyclization strategy with DBU. This two-step one-pot procedure afforded the targeted tetramic acid analogues in good yields. With commercially available Ugi starting materials, microwave irradiation, a simple operation, excellent yields, and a broad scope, this reaction

• investigated the effect of different inorganic and organic bases (Table 1). It was interesting to note that all of the bases tested in the study afforded the desired enol tetramic acid derivative 7a after the reaction was heated under the microwave irradiation conditions. The ketone compound 6a could be the

•  1, entries 9–12. DMF was superior to other solvents with the highest yield. Then the microwave irradiation temperature was varied: at 80 °C for 10 min, a large fraction of the Ugi adduct 5a was still present in the product mixture (LC–MS determination); at 120 °C, the desired compound 7a was

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

• , trimethylsilylacetylene (TMSA) was selected for coupling with aryl iodides in the presence of a catalytic amount of Pd–Cu/C and PPh3 using Et2NH as a base in methanol at 120 °C under microwave irradiation for 20 min. In the next step, the azide derivative was added to the reaction mixture. Finally, the reaction mixture

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

• such interactions can be tuned, for example, by application of a condition-based divergence strategy [25], which is based on the variation of solvents, catalysts, and activation methods [16][26][27][28][29]. Thus, using nonclassical activation methods such as ultrasonication and microwave irradiation

• applying different temperatures in the range of 0–110 °C (both with the help of conventional heating and microwave irradiation) and by using different solvents and catalysts, such as HOAc, DMSO, primary alcohols with and without the presence of HCl, Yb(OTf)3, or Et3N. In all these cases, mixtures of

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• following the reported method [48] employing copper catalysis, and tested on our starting material upon variation of copper salts, solvents and temperature, resulting in the neat reaction under CuI catalysis being optimal when carried out for 2 h at 100 °C under microwave irradiation (see Supporting

• mixture was heated under microwave irradiation to 100 °C for 2 h. Then, EtOAc was added and the organic phase was washed with 5% NH4OH (3 × 20 mL) and brine. The organic phase was dried with Na2SO4 and concentrated under reduced pressure. The crude product was purified by flash chromatography using the