1,2-Naphthoquinone-4-sulfonic acid salts in organic synthesis

• Ruan Carlos B. Ribeiro,
• Patricia G. Ferreira,
• Amanda de A. Borges,
• Luana da S. M. Forezi,
• Fernando de Carvalho da Silva and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 53–69, doi:10.3762/bjoc.18.5

• transformations. Organometallics are the most commonly used catalysts to promote C–C bond formation. In addition, other so-called classical reactions are also widely used, such as Friedel–Crafts alkylation and acylation, Wittig and Horner–Emmons reactions, carbonyl addition/substitution, α-alkylation, aldol

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

• Ilya A. P. Jourjine,
• Lukas Zeisel,
• Jürgen Krauß and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2668–2679, doi:10.3762/bjoc.17.181

• activated derivatives (intramolecular Friedel–Crafts acylation) [29][30][31] found wide application here. In a different approach, a total synthesis of dengibsin (1a) was accomplished by Wang and Snieckus in 15 steps by means of a directed remote metalation [32], using a benzamide residue as the directing

Synthesis of new substituted 7,12-dihydro-6,12-methanodibenzo[c,f]azocine-5-carboxylic acids containing a tetracyclic tetrahydroisoquinoline core structure

• Agnieszka Grajewska,
• Maria Chrzanowska and
• Wiktoria Adamska

Beilstein J. Org. Chem. 2021, 17, 2511–2519, doi:10.3762/bjoc.17.168

• the intramolecular Friedel–Crafts double cyclization reaction and N,N-dibenzylaminoacetaldehyde dialkyl acetals [12][14][15][16] in the Pomeranz–Fritsch-type double cyclization reaction. There is also one example of employing p-quinol acetates as substrates for the synthesis of these compounds [17

• ]. Recently, a methodology for the synthesis of dihydromethanodibenzoazocines based on a combination of Friedel–Crafts and Pictet–Spengler reactions was proposed by Moshkin et al. [18]. We have developed a convenient method for the preparation of C-1-substituted tetrahydroisoquinoline derivatives by using the

Efficient synthesis of polyfunctionalized carbazoles and pyrrolo[3,4-c]carbazoles via domino Diels–Alder reaction

• Ren-Jie Fang,
• Chen Yan,
• Jing Sun,
• Ying Han and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2021, 17, 2425–2432, doi:10.3762/bjoc.17.159

• scope of this domino Diels–Alder reaction, another kind of 3-vinylindoles was employed in the one-pot reaction. First, the 3-(indol-3-yl)-1,3-diphenylpropan-1-ones prepared through Friedel–Crafts alkylation of indole with chalcones, were oxidized by DDQ in acetonitrile to generate in situ the expected

Synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

• Andrey I. Puzanov,
• Dmitry S. Ryabukhin,
• Anna S. Zalivatskaya,
• Dmitriy N. Zakusilo,
• Darya S. Mikson,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2417–2424, doi:10.3762/bjoc.17.158

• bond of these oxadiazoles quantitatively resulted in E/Z-vinyl triflates. The reactions of the cationic intermediates have been studied by DFT calculations and the reaction mechanisms are discussed. Keywords: acetylene-oxadiazoles; Friedel–Crafts reaction; hydroarylation; superelectrophilic activation

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• derivative 127. The plausible mechanism for the formation of compound 127 proceeded consecutively with π-complex formation, Friedel–Crafts type addition, deprotonation, and finally protonation of alcohol for the elimination of water to get the final product [92]. A Hg(OTf)2-mediated cyclization was utilized

• exemplifying benzyl derivative 160 [106]. The reported methodology was an example of the Hg(OTf)2·(TMU)3 complex promoting a moderate and efficient procedure for arylalkyne cyclization to directly afford dihydronapthalene derivatives (Scheme 47). Later, Friedel–Crafts type reaction of alkynylfuran 162 and 164

A novel methodology for the efficient synthesis of 3-monohalooxindoles by acidolysis of 3-phosphate-substituted oxindoles with haloid acids

• Li Liu,
• Yue Li,
• Tiao Huang,
• Dulin Kong and
• Mingshu Wu

Beilstein J. Org. Chem. 2021, 17, 2321–2328, doi:10.3762/bjoc.17.150

• recently as precursors in Friedel–Crafts reactions of arenes [30][31] and cross-coupling reactions of arylboronic reagents [32]. However, the direct SN1 reaction of such isatin-derived 3-phosphate-substituted oxindoles by halide ions as nucleophiles has not been developed yet and remains an unsolved

Transition-metal-free intramolecular Friedel–Crafts reaction by alkene activation: A method for the synthesis of some novel xanthene derivatives

• Tülay Yıldız,
• İrem Baştaş and
• Hatice Başpınar Küçük

Beilstein J. Org. Chem. 2021, 17, 2203–2208, doi:10.3762/bjoc.17.142

• significance were synthesized by developing a new synthesis method. In order to obtain xanthene derivatives, the original alkene compounds to be used as the starting materials were synthesized in four steps using appropriate reactions. A cyclization reaction by intramolecular Friedel–Crafts alkylation was

• carried out in order to synthesize the desired xanthene derivatives using the alkenes as starting compounds. The intramolecular Friedel–Crafts reaction was catalyzed by trifluoroacetic acid (TFA) and provided some novel substituted 9-methyl-9-arylxanthenes with good yields at room temperature within 6–24

• hours. As a result, an alkene compound was used for activation with TFA in the synthesis of xanthene through intramolecular Friedel–Crafts alkylation for the first time. Keywords: alkene activation; intramolecular Friedel–Crafts alkylation; trifluoroacetic acid; xanthene; Introduction The interest in

Facile and innovative catalytic protocol for intramolecular Friedel–Crafts cyclization of Morita–Baylis–Hillman adducts: Synergistic combination of chiral (salen)chromium(III)/BF₃·OEt₂ catalysis

• Karthikeyan Soundararajan,
• Helen Ratna Monica Jeyarajan,
• Raju Subimol Kamarajapurathu and
• Karthik Krishna Kumar Ayyanoth

Beilstein J. Org. Chem. 2021, 17, 2186–2193, doi:10.3762/bjoc.17.140

• .17.140 Abstract The chiral (salen)Cr(III)/BF3·OEt2 catalytic combination was found to be an effective catalyst for intramolecular Friedel–Crafts cyclization of electron-deficient Morita–Baylis–Hillman adducts. In presence of mild reaction conditions the chiral (salen)Cr(III)/BF3·OEt2 complex affords 2

• -substituted-1H-indenes from unique substrates of Morita–Baylis–Hillman adducts via an easy operating practical procedure. Keywords: boron trifluoride etherate; chiral (salen)chromium(III); intramolecular Friedel–Crafts cyclization; Morita–Baylis–Hillman adducts; substituted-1H-indenes; Introduction

• Reactions associated with carbon–carbon bond formations are explored for their synthetic utility in extending the carbon framework in organic molecules [1][2][3]. Among the known C–C bond forming methodologies the Friedel–Crafts reaction is the most utilized methodology. As a result of its broad scope of

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• )silane 38 that involved n-BuLi as the base [58]. The strategy was later adopted by Ohshita in 2004 (40a, Scheme 6) [59]. Between 2016 and 2018, some acid-catalyzed syntheses of bis(indol-3-yl)silanes appeared [60][61][62][63]. Chen and co-workers demonstrated a Brønsted acid-catalyzed Friedel–Crafts

• the similar mechanisms. First, the Brønsted or Lewis acid coordinates with silane 51 leading to a solvent-stabilized electron-deficient silane complex 57, where N-protected indole attacks in a Friedel–Crafts fashion to give the 3-silylindoles 60 along with molecular hydrogen (Scheme 7b and Scheme 7d

• Friedel–Crafts fashion (Scheme 10a) gave 82 with moderate to good product yields, respectively [69][70]. A similar work by Janosik involved strongly basic conditions at low temperature with bis(phenylsulfonyl)sulfide (83) as the sulfur donor (Scheme 10b) [73][74]. Disulfides are also important reagents

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

• years (2008–2020) and focuses on direct and indirect methods to construct anthracene and anthraquinone frameworks. Keywords: anthracenes; anthraquinones; Friedel–Crafts cyclization; intramolecular cyclization; metal-catalyzed; Introduction Anthracene is an important aromatic hydrocarbon consisting of

• has been reported over the years. The most familiar methods to obtain substituted anthracenes include Friedel–Crafts reactions [17], Elbs reaction [18], aromatic cyclodehydration [19][20], Bradsher-type reactions from diarylmethanes [21][22][23], and, more recently, metal-catalyzed reactions with

• efficiently cyclized [42]. Friedel–Crafts alkylation of arenes with aromatic aldehydes The Lewis acid-catalyzed Friedel–Crafts alkylation of electron-rich arenes with aromatic aldehydes has proven an efficient and often direct method to prepare anthracene derivatives. Kodomari and co-workers disclosed a

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

• affording intermediary benzyl carbenium ions, which are then trapped by a variety of electron-rich aromatics via Friedel–Crafts alkylation. This cascade Prins/Friedel–Crafts cyclization protocol paves an expedient path to medicinally useful 4-aryltetralin-2-ol and 5-aryltetrahydro-5H-benzo[7]annulen-7-ol

• derivatives. Keywords: 4-aryltetralin-2-ol; 5-aryl-benzo[7]annulen-7-ol; cascade reaction; Prins/Friedel–Crafts; Introduction 2,4-Disubstituted tetralins (Figure 1, 1), especially 2-functionalized tetralins are privileged building blocks for medicinal chemistry applications which are known to exhibit a wide

• to 2,4-disubstituted tetralin compounds and thus facilitate their biological investigations. The cascade Prins/Friedel–Crafts reaction to form multiple chemical bonds in one operation has emerged as an atom-economic and straightforward strategy for the construction of oxygen-containing heterocycles

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

• and efficient synthetic protocol provides a convenient access to a wide range of unsymmetrical trifluoromethylated 3,3'-diindolylmethanes via I2-catalyzed Friedel–Crafts alkylation reaction of trifluoromethylated (indol-3-yl)-1-phenylethan-1-ols with substituted indoles. The method was also extended

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• subsequent trapping of the carbocation with the bromide ion led to all-cis-2,4,6-trisubstituted tetrahydropyran 297 (Scheme 69). Lalli and van de Weghe reported a chiral BINOL-derived bisphosphoric acid- and CuCl-catalyzed enantioselective tandem Prins–Friedel–Crafts cyclization between homoallylic alcohol

• ion, which was followed by a completely diastereoselective Friedel–Crafts reaction (Scheme 70). List and co-workers devised a strategy employing highly acidic confined iminoimidodiphosphate (iIDP) Brønsted acids 308 that catalyzed asymmetric Prins cyclizations of both aliphatic and aromatic aldehydes

Unexpected rearrangements and a novel synthesis of 1,1-dichloro-1-alkenones from 1,1,1-trifluoroalkanones with aluminium trichloride

• Beatrice Lansbergen,
• Catherine S. Meister and
• Michael C. McLeod

Beilstein J. Org. Chem. 2021, 17, 404–409, doi:10.3762/bjoc.17.36

• trichloride; dichloroalkenes; Friedel–Crafts alkylation; rearrangement; trifluoroalkanes; Introduction 1,1-Dichloro-1-alkenes are valuable synthetic intermediates and have been employed in Pd-mediated cross couplings of one or both chlorine atoms [1][2][3][4][5][6][7], carbonylation reactions [8], and C–H

• ) equivalents of AlCl3, a further two products were obtained, whose structures were elucidated as the 8,9-dihydrobenzo[7]annulen-9-ones 9 and 10 (Scheme 4). Presumably, these bicyclic compounds arise via an intramolecular Friedel–Crafts alkylation of 6b, promoted by the ortho/para-directing nature of the

Helicene synthesis by Brønsted acid-catalyzed cycloaromatization in HFIP [(CF₃)₂CHOH]

• Takeshi Fujita,
• Noriaki Shoji,
• Nao Yoshikawa and
• Junji Ichikawa

Beilstein J. Org. Chem. 2021, 17, 396–403, doi:10.3762/bjoc.17.35

• derivatives readily underwent intramolecular Friedel–Crafts-type C–C bond formation followed by dehydration or alcohol elimination, leading to the construction of benzene rings in the biaryl systems (Scheme 2) [20][21]. The reaction proceeded via oxocarbenium ion intermediates stabilized by HFIP. This method

• preparation of cyclization precursors. As described above, the tandem cycloaromatization of the obtained precursors proceeded via Friedel–Crafts-type bond formation followed by elimination, which enabled a rapid and efficient synthesis of helicenes, such as higher-order helicenes, double helical helicenes

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• ethers 41b upon the reaction in a dichloromethane solution of sulfuric acid or triflic acid [60][61]. The authors also reported that indenes 42 could undergo a subsequent Friedel–Crafts alkylation when 41b was reacted in the presence of an external aromatic partner Ar’H in pure triflic acid. Thus, a

• produced from the activation of 61 with Ga(OTf)3 and reacts with 62 in a Friedel–Crafts reaction to afford 63 (Scheme 18). Further control experiments showed that derivatives 63 were not stable at 80 °C under the reaction conditions and isomerized to furnish 64. Based on these observations, the authors

• proposed that upon heating, Ga(OTf)3 reacts with 63 to release an indolium ion 65 and forms an organogallium species 67 via intermediate 66, which, after protodemetallation, releases indole 62 and regenerates the catalyst. The retro-Friedel–Crafts reaction at 80 °C at the indole C3-position thus allows the

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

• mediated by strong acids led to the cleavage of the proximal bond by the generation of fluorine-stabilized carbocations (SN1 mechanism) [114]. The Friedel–Crafts reaction of 2,2-difluorocyclopropanecarbonyl chloride (148) with arenes 149a–c was accompanied by a proximal bond scission promoted by the strong

• intermediate allylic cation which was the electrophile in a Friedel–Crafts reaction with 159. The subsequent desilylation of the Friedel–Crafts product gave an α-fluorinated ketone intermediate which then reacted with a second equivalent of 159 in a (Z)-stereoselective, chelation-controlled process. Fu et al

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• nowadays a growing interest in the forging of Ar–Ar bonds under transition-metal-free conditions [24][25]. Apart the most common pathways, e.g., the Friedel–Crafts functionalization [26] or nucleophilic aromatic substitution [27], alternative approaches have emerged that make use of photogenerated

Activation of pentafluoropropane isomers at a nanoscopic aluminum chlorofluoride: hydrodefluorination versus dehydrofluorination

• Maëva-Charlotte Kervarec,
• Thomas Braun,
• Mike Ahrens and
• Erhard Kemnitz

Beilstein J. Org. Chem. 2020, 16, 2623–2635, doi:10.3762/bjoc.16.213

• such as hydrodefluorinations and dehydrofluorinations were observed, followed by hydroarylation and Friedel–Crafts-type reactions under mild conditions. Keywords: aluminum fluoride; C–F bond activation; dehydrofluorination; hydrodefluorination; hydrofluorocarbons; Introduction Hydrofluorocarbons

• HSiEt3 as a hydrogen source to produce, in the presence of benzene as the solvent, Friedel–Crafts products as main compounds [47]. In contrast, the hydrodefluorination products were generated in the absence of benzene. Thermodynamically, the generation of strong H–F, Al–F, or Si–F bonds can enforce an

• Friedel–Crafts products (Scheme 1) [16]. The activation of fluoropentane was achieved using a modified ACF, loaded with germane or silane [39]. When silane was immobilized at the surface of ACF in the presence of benzene, Friedel–Crafts products were again generated. In comparison, when ACF was loaded

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

• achieve this goal, they commenced with the two-fold Friedel–Crafts alkylation reaction of sumanene (2) with 2,5-dichloro-2,5-dimethylhexane (50) involving AlCl3 to generate compound 51 which on subsequent oxidation provided triketosumanene 52 (Scheme 11). Finally, compound 52 was reacted with ethylene

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

• Matthias W. Tripp Ulrich Koert Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35034 Marburg, Germany 10.3762/bjoc.16.181 Abstract 6,13-Difluoropentacene was synthesized from 1,4-difluorobenzene. Friedel–Crafts annulation of the latter with phthalic anhydride and

• subsequent reduction of the anthraquinone gave 1,4-difluoroanthracene. After ortho-lithiation and reaction with phthalic anhydride a carboxylic acid was obtained whose Friedel–Crafts acylation and subsequent reductive removal of the oxygen-functionalities resulted in the formation of the target compound. The

• HOMO–LUMO gap of 6,13-difluoropentacene was determined via UV–vis spectroscopy and compared to other fluorinated pentacenes. Keywords: fluorinated acenes; Friedel–Crafts reaction; ortho-lithiation; synthesis; Introduction Pentacenes are a prototype in the field of organic semiconductors due to their

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

• advantages of this protocol. Keywords: C–C-bond formation; C3-funtionalization of indole; diindolylmethane; Friedel–Crafts reaction; indole; indole-3-carbinol; large-scale synthesis; recyclability; Introduction (1H-Indol-3-yl)methanols have emerged as versatile pre-electrophiles for C–C functionalization

• at the position 3 of indoles [1][2][3][4]. Friedel–Crafts alkylation of (1H-indol-3-yl)methanols with indoles has proven to be a powerful strategy for the preparation of biologically important 3,3′-diindolylmethanes (DIMs) [5][6][7][8][9][10][11][12][13][14]. Additionally, (1H-indol-3-yl)methanols

• be synthesized by Friedel–Crafts hydroxyalkylation reactions of indoles with trifluoromethyl ketones in the presence of either Lewis/Bronsted acid catalysts. Bandini et al. reported the trifluoromethyl hydroxyalkylation of indoles catalyzed by an organic base 2-tert-butyl-1,1,3,3-tetramethylguanidine

Direct borylation of terrylene and quaterrylene

• Haruka Kano,
• Keiji Uehara,
• Kyohei Matsuo,
• Hironobu Hayashi,
• Hiroko Yamada and
• Naoki Aratani

Beilstein J. Org. Chem. 2020, 16, 621–627, doi:10.3762/bjoc.16.58

• photovoltaic components, the scalable synthesis of pure soluble compounds is essential. Recently, facile preparation methods of terrylene [8] and quaterrylene [9] were reported, after 50 years from the first reports, respectively [10][11]. Friedel–Crafts ring condensation reaction of 3-(1-naphthyl)perylene