Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• due to the formation of dehydropolyazulene via oxidative aromatization. In 2003, Lai and co-workers [20] synthesized 1,3-polyazulene 5 from azulene in two steps as shown in Scheme 3. First, azulene (1) was dibrominated at the 1,3-positions by treatment with N-bromosuccinimide (NBS) and the consequent

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• products 24. Next, the key step was introducing chlorine, bromine, or iodine substituents by halodesilylation of 24. With the halogenated products 25 in hands, the authors employed DDQ in the oxidation/aromatization step, to obtain the di- and tetrahaloanthracenes 26 in good yields (61–85%) [39]. This

• formation, and further decarboxylative aromatization. The authors used several diphenyl carboxylic acids bearing electron-donating and electron-withdrawing groups on the aromatic rings to produce the corresponding substituted anthracenes, such as compounds 33a–f, in good yields [41]. Recently, Kim and co

• , the authors added previously prepared triarylmethanes 52 to the reaction mixture under air atmosphere, and then under oxygen atmosphere. Therefore, an efficient Bi(OTf)3/O2 system promoted the oxidation/aromatization step, providing the 9,10-disubstituted 2,3,6,7-tetraalkoxyanthracenes 53 in good

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

• Pezhman Shiri,
• Ali Mohammad Amani and
• Thomas Mayer-Gall

Beilstein J. Org. Chem. 2021, 17, 1600–1628, doi:10.3762/bjoc.17.114

• tandem reaction proceeds via formation of a Schiff-base 39 and subsequently 1,3-dipolar cycloaddition to produce the intermediate 42. Then, the intermediate 42 affords the final product 43 via an oxidative aromatization process in the presence of air or iodine (Scheme 15). To propose a precise mechanism

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• reaction time (up to 6 d) was required to complete these experiments, and the yield of the isolated products dropped significantly (to 41 and 64%, respectively). In analogy to the tricyclic pyrazole derivative 9a, the expected products 9b–h formed after spontaneous aromatization of the initial [3 + 2

Cascade intramolecular Prins/Friedel–Crafts cyclization for the synthesis of 4-aryltetralin-2-ols and 5-aryltetrahydro-5H-benzo[7]annulen-7-ols

• Jie Zheng,
• Shuyu Meng and
• Quanrui Wang

Beilstein J. Org. Chem. 2021, 17, 1481–1489, doi:10.3762/bjoc.17.104

• alkynyl-Prins cyclization, Friedel–Crafts alkenylation, and dehydration/aromatization reaction between 1-aryl-3-hexyne-2,6-diol derivatives and aldehydes, that led to the formation of 1,4-dihydro-2H-benzo[f]isochromenes [16]. The Prins reaction-induced cyclization, inter alia, became a versatile tool for

Iodine-catalyzed electrophilic substitution of indoles: Synthesis of (un)symmetrical diindolylmethanes with a quaternary carbon center

• Thanigaimalai Pillaiyar,
• Masoud Sedaghati,
• Andhika B. Mahardhika,
• Lukas L. Wendt and
• Christa E. Müller

Beilstein J. Org. Chem. 2021, 17, 1464–1475, doi:10.3762/bjoc.17.102

• undergoes a C3-selective Friedel−Crafts reaction with 2a to deliver intermediate D, and the catalyst I2 is regenerated by the reaction of HOI and I− (see C to D in box highlighted by dashed line). The intermediate D is stabilized by aromatization yielding product 3a and H2O. Conclusion The described novel

Design, synthesis and photophysical properties of novel star-shaped truxene-based heterocycles utilizing ring-closing metathesis, Clauson–Kaas, Van Leusen and Ullmann-type reactions as key tools

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2021, 17, 1374–1384, doi:10.3762/bjoc.17.96

• required C3-symmetric tripyrroltruxene 6 by means of RCM in the presence of Grubbs′ first generation catalyst (G-I, 9) followed by self-aromatization without the involvement of any oxidizing agent. Compound 3 was produced from the hexabutylated truxene system 2 involving nitration, reduction and N

Icilio Guareschi and his amazing “1897 reaction”

• Gian Cesare Tron,
• Alberto Minassi,
• Giovanni Sorba,
• Mara Fausone and
• Giovanni Appendino

Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93

• reactive intermediate capable of transferring a phosphate group to ATP. The Guareschi “1897 reaction” shows a basically different strategy to generate reductive power, associated to aromatization of a prearomatic substrate. The chemiosmotic generation of energy is as universal as the genetic code, and the

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

• -phenanthrolines and affords intermediate C. A subsequent cyclization D and aromatization E with loss of HCN yield the desired products 64. The lower yields in case of aliphatic isocyanides were reasoned with its low nucleophilicity losing the competition with aryledenemalononitrile A in the reaction with

• derivative 99, followed by aromatization under the described conditions. The preliminary in vitro antitumor studies of the compounds displayed low to moderate activity. Scheme 37 depicts the mechanism wherein an initial in situ generation of α,β-unsaturated intermediate A occur due to the Knoevenagel

• aldehyde and malononitriles undergoes Knoevenagel condensation resulting in alrylidene intermediate B. This is followed by Michael addition of imine A on the activated alrylidene intermediate B and subsequent intramolecular cyclization C and aromatization D affords the target molecules 123 (Scheme 46). N

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

• by the two attached fluorine atoms. The nucleophilic attack of the nitrile, followed by cyclization and aromatization could then give the pyrrole derivatives 142. Later, Xiao et al. performed another ring-opening reaction of gem-difluorocyclopropyl ketones 143, this time mediated by BX3 (X = F, Cl

Facile preparation and conversion of 4,4,4-trifluorobut-2-yn-1-ones to aromatic and heteroaromatic compounds

• Takashi Yamazaki,
• Yoh Nakajima,
• Minato Iida and
• Tomoko Kawasaki-Takasuka

Beilstein J. Org. Chem. 2021, 17, 132–138, doi:10.3762/bjoc.17.14

• cyclization/aromatization reactions allowed us to explore a brief scope and limitation of the present reaction by using four representative types of crude ynones 2 starting from the conjugate addition step either with acetylacetone or ethyl acetoacetate (Table 4). In all instances, the desired products 4 were

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• % yield (Scheme 6B). This adduct 92a underwent decarboxylation to afford 92b in 72% yield [42]. Exposure of freshly prepared 92b to triazabicyclodecene [45] led to a ring-expansion/aromatization/aldol cascade producing 93, which was reduced with Et3SiH/TFA smoothly to give indane 94 in 68% yield over two

Three-component reactions of aromatic amines, 1,3-dicarbonyl compounds, and α-bromoacetaldehyde acetal to access N-(hetero)aryl-4,5-unsubstituted pyrroles

• Wenbo Huang,
• Kaimei Wang,
• Ping Liu,
• Minghao Li,
• Shaoyong Ke and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2920–2928, doi:10.3762/bjoc.16.241

• enamine intermediate I to generate another intermediate III. Subsequently, III underwent an intramolecular electrophilic substitution to form the intermediate IV. Finally, IV underwent an elimination of HBr and a spontaneous aromatization to afford the pyrrole product 4a [48][49]. Apart from the pyrrole

• aromatization to produce 5a. KI may play a key role in the last step, and we suspected that it can promote the removal of bromide. Although 5a can theoretically be synthesized through a three-component reaction of 1b, 2a, and an appropriate aldehyde, for example, acetaldehyde [50][51] owing to the insufficient

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

• accessible compound, namely norbornadiene (10) by involving oxidative aromatization in the presence of DDQ via an intermediate 17, as displayed in Scheme 2. As can be seen from an inspection of Scheme 2, they first performed a single step cyclotrimerization of 10 using n-BuLi and t-BuOK in 1,2-dibromoethane

• hexahydrosumanene 17 which on subsequent aromatization using DDQ furnished the desired molecule sumanene (2) in good yield. To their surprise, tandem metathesis for achieving compound 17 from 13 (anti) was fruitless may be because of the endothermic reaction by 37.4 kcal/mol as compared to the exothermic (51.4 kcal

• -symmetric hexahydrotrimethylsumanene 27, which was then converted into the desired compound by aromatization with DDQ. Alternatively, when they used the more active G-II catalyst instead of the G-I and then the G-II catalyst under similar reaction conditions, they directly observed the formation of compound

Synthesis of 6,13-difluoropentacene

• Matthias W. Tripp and
• Ulrich Koert

Beilstein J. Org. Chem. 2020, 16, 2136–2140, doi:10.3762/bjoc.16.181

• 14 then rapidly decomposes to 6,13-pentacenequinone (15) after elimination of HF. The final aromatization of diol 13 to the target molecule 5 proceeded smoothly in 74% yield using SnCl2 in 1,4-dioxane and aqueous HCl [11][12]. F2PEN 5 can be stored under inertgas atmosphere at −20 °C for a month

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• converted in two steps into cyclohexadienyl ketone 5-Ch by intentional hydrolysis followed by dehydrogenating aromatization leading to biphenyl-2-yl trifluoromethyl ketone 6. The latter product was more effectively prepared in a one-pot cycloaddition/hydrolysis/aromatization sequence. 1H NMR spectra of

• -(1-phenylvinyl)indene 12 through an intramolecular iminium ion-induced 1,5-cyclization. The same cyclization type together with oxidative aromatization converts dihydronaphthalenes 16 into benzo[a]fluorenes 13. The stereochemistry of 12d can be explained by a stereoselective formation of trans-3,4

Regiodivergent synthesis of functionalized pyrimidines and imidazoles through phenacyl azides in deep eutectic solvents

• Paola Vitale,
• Luciana Cicco,
• Ilaria Cellamare,
• Filippo M. Perna,
• Antonio Salomone and
• Vito Capriati

Beilstein J. Org. Chem. 2020, 16, 1915–1923, doi:10.3762/bjoc.16.158

• intramolecular nucleophilic attack to the terminal imino group of 9a, provides cyclized adduct 10a, and finally pyrimidine derivative 7a by aromatization/elimination of NH3. To the best of our knowledge, this is the first one-pot synthesis of functionalized pyrimidines using phenacyl azides as the sole starting

One-pot and metal-free synthesis of 3-arylated-4-nitrophenols via polyfunctionalized cyclohexanones from β-nitrostyrenes

• Haruyasu Asahara,
• Minami Hiraishi and
• Nagatoshi Nishiwaki

Beilstein J. Org. Chem. 2020, 16, 1830–1836, doi:10.3762/bjoc.16.150

• -nitrocyclohexanones. When the reaction was conducted in the presence of water, the cyclohexenes were efficiently hydrolyzed into cyclohexanones. Subsequent aromatization by heating the cyclohexanone with a catalytic amount of iodine in dimethyl sulfoxide gave 3-arylated-4-nitrophenols. The reaction of nitrostyrenes

• trimethylsiloxy group of the diene can be converted to a phenolic hydroxy group by hydrolysis) [20], followed by the oxidation and aromatization of the obtained cyclohexanone 4 (Scheme 1). Results and Discussion Heating an acetonitrile solution of nitrostyrene 1a with Danishefsky’s diene (2) at 60 °C for 18 h

• (Scheme 2). Cyclohexanone 4a has acidic hydrogen atoms that can facilitate the aromatization by modification, e.g., by iodination. In order to obtain further insights into this possibility, 4a was heated with deuterium oxide, but no change was observed. In contrast, the signals assigned to the protons in

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

• process, leading respectively to an indole 6 (after dehydration and aromatization) or an indolone 7. The reaction was first investigated by mixing the diketone 5b as the Michael acceptor and benzylamine under various conditions (Table 1). We first investigated the reactivity in the presence of a set of

• , leading to an intermediate enol that, after a keto–enol equilibrium and aromatization, gives the indolone 7. For the indole 6 and the cinnoline 8, the synthesis starts with the protonation of the oxygen atom of the conjugated carbonyl group of the 1,4-diketone, followed by an imine formation between the

• , the recovery of the proton catalyst, and atmospheric oxygen aromatization, leading to the indole 6 or the cinnoline 8. Conclusion In summary, we have successfully developed a straightforward and metal-free strategy for the synthesis of nitrogen-containing heterocyclic moieties of biological interest

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

• Alessandra Del Tito,
• Havall Othman Abdulla,
• Davide Ravelli,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

• ., the 2-thienyl derivative 13.2) afforded vinyl radical 13.5·. The final intramolecular cyclization of 13.5· and re-aromatization smoothly yielded the desired polyheteroaromatic derivative (see the case of 13.6; 84% yield). Interestingly, all the obtained scaffolds bear two heteroatoms in close

Recent synthesis of thietanes

• Jiaxi Xu

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

• cleavage and aromatization to give substituted pyridines 255 [75] (Scheme 49). In 1989, Kanaoka and co-workers further studied the photo [2 + 2] cycloadditions of thiobarbiturates 256–258, whose skeletons consisted of a combination of a thioamide and an amide or a thioamide (two-imides system), and olefins

Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole

• Carlos H. Escalante,
• Eder I. Martínez-Mora,
• Carlos Espinoza-Hicks,
• Alejandro A. Camacho-Dávila,
• Fernando R. Ramos-Morales,
• Francisco Delgado and
• Joaquín Tamariz

Beilstein J. Org. Chem. 2020, 16, 1320–1334, doi:10.3762/bjoc.16.113

• aromatization of the polycyclic intermediates provides the corresponding polycyclic pyrrolo-isoindoles and isoindolo-pyrrolo-indoles. A theoretical study on the stereoselective Diels–Alder reactions, carried out by calculating the endo/exo transition states, revealed the assistance of non-covalent interactions

• -polycyclic structures [42], we herein combined both approaches shown in Scheme 1 to design the construction of pentacycles 11, after carrying out an uncommon but highly diastereoselective Diels–Alder cycloaddition followed by a coupling reaction. This route also allowed out the aromatization of the B ring to

• ]indole-1,3-diones 9 were submitted to aromatization to generate the corresponding tetrahydropyrrolo[3,4-e]indole-1,3-diones 21 (Table 4). When 9e was treated with manganese oxide [32] at 25 or 100 °C for 24 h, no reaction occurred and the starting material was recovered (Table 4, entries 1 and 2

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

• one aryl group in the β-position (R3 = H, R2 = Ar) and further processing of the reaction mixture with atmospheric oxygen, an aromatization occurs with the formation of isoxazoles (64a,b 55–95%). Presumably, the reaction of TEMPO with oxime 62 affords the iminoxyl radical 65 (Scheme 24). 1,5-HAT in

• intermediate, 4,5-dihydro-1,2,4-oxadiazole. An example of such intermediate 74 is shown in Scheme 27. Oxidative aromatization of 74 leads to 1,2,4-oxadiazole 72a (Scheme 26). The second pathway, hydrogen abstraction followed by β-scission presumably leads to iminyl radical, which forms the observed

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

• porosity of the carbon spheres is induced by either aromatization of carbon around an in situ template, in situ chemical activation or gasification of carbon [96]. Xu et al. found that the morphology of the porous carbon materials prepared from propiolate salts with USP are dependent on the choice of

Synthesis and anticancer activity of bis(2-arylimidazo[1,2-a]pyridin-3-yl) selenides and diselenides: the copper-catalyzed tandem C–H selenation of 2-arylimidazo[1,2-a]pyridine with selenium

• Mio Matsumura,
• Tsutomu Takahashi,
• Hikari Yamauchi,
• Shunsuke Sakuma,
• Yukako Hayashi,
• Tadashi Hyodo,
• Tohru Obata,
• Kentaro Yamaguchi,
• Yasuyuki Fujiwara and
• Shuji Yasuike

Beilstein J. Org. Chem. 2020, 16, 1075–1083, doi:10.3762/bjoc.16.94

• the diselenide 2. On the other hand, in the presence of excess imidazopyridine, the oxidative addition of imidazopyridine 1 to B, followed by the aromatization of C leads to the intermediate D. The intermediate D undergoes a reductive elimination to give the selenide 3, with the generation of Cu(I

• -position to form the intermediate C and the selenide anion F. The intermediate C undergoes a reductive elimination and aromatization to give the selenide 3 and Cu(I). Moreover, the Cu-mediated electrophilic addition of 3 and selenium affords G, which aromatizes to form E and then probably undergoes a