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

• position indicates an inversely proportional relation between the strength of the −I effect exerted by substituents and the efficiency of the cyclization. Reaction of amine 15m (see Scheme 5) did not give the corresponding fluorenone, instead phenanthridine 10m was isolated in 36% yield. Most likely

• unsuccessful, fluorenone (3) was not formed under either of these conditions, suggesting the involvement of radicals in the cyclization reaction rather than an SEAr mechanism as proposed in Scheme 3. A more detailed investigation might be required to fully understand the mechanism of this oxidative benzylamine

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

• Robin Klintworth,
• Garreth L. Morgans,
• Stefania M. Scalzullo,
• Charles B. de Koning,
• Willem A. L. van Otterlo and
• Joseph P. Michael

Beilstein J. Org. Chem. 2021, 17, 2543–2552, doi:10.3762/bjoc.17.170

• well as tert-butyl as precursors for the silica gel-mediated cyclization reaction to form pyrrolizine products. The bromomethyl ketones required for the initial sulfide contraction were either purchased from commercial suppliers or prepared from the corresponding methyl ketones by reported procedures

• which characteristic 1H or 13C NMR spectroscopic signals could be observed, and suitable HRMS values could be measured; see Supporting Information File 1) to the optimized cyclization reaction conditions, since the contaminants did not inhibit pyrrolizine formation. Chromatographic purification of

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

• tetrahydroisoquinoline derivatives, 7,12-dihydro-6,12-methanodibenzo[c,f]-azocine-5-carboxylic acids by three component Petasis reaction with the use of aminoacetaldehyde acetals bearing substituted benzyl groups as the amine components followed by Pomeranz–Fritsch double cyclization reaction. By applying this method

• 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

• cyclization reaction was easily performed by treatment of 6a with 20% HCl for 24 h to give dihydromethanodibenzoazocine-5-carboxylic acid (7a, Scheme 5) in 72% yield by extraction of the neutralized reaction mixture. Compound 7a was obtained in two simple steps from 3a with an overall yield of 67%. Then the

Recent advances in the tandem annulation of 1,3-enynes to functionalized pyridine and pyrrole derivatives

• Yi Liu,
• Puying Luo,
• Yang Fu,
• Tianxin Hao,
• Xuan Liu,
• Qiuping Ding and
• Yiyuan Peng

Beilstein J. Org. Chem. 2021, 17, 2462–2476, doi:10.3762/bjoc.17.163

• ][28][29]. In industry, pyrrole mainly comes from the extraction of coal tar, the condensation reaction of furan and ammonia under high temperature, or the cascade cyclization reaction of acetylene, formaldehyde, and ammonia. In the laboratory, there are many efficient methods for the synthesis of

Enantioselective PCCP Brønsted acid-catalyzed aminalization of aldehydes

• Martin Kamlar,
• Robert Reiberger,
• Martin Nigríni,
• Ivana Císařová and
• Jan Veselý

Beilstein J. Org. Chem. 2021, 17, 2433–2440, doi:10.3762/bjoc.17.160

• Abstract Here we present an enantioselective aminalization of aldehydes catalyzed by Brønsted acids based on pentacarboxycyclopentadienes (PCCPs). The cyclization reaction using readily available anthranilamides as building blocks provides access to valuable 2,3-dihydroquinazolinones containing one

• averaged only around 50%. In addition, the role of an electron-donating methyl group on the aromatic ring was investigated. When p-tolualdehyde (1f) was used in the cyclization reaction with anthranilamide (1a), the corresponding aminal 3f was obtained in high yield (83%) and with good enantiomeric excess

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

• reported that the electron-withdrawing electronic effect at the aromatic ring promotes the cyclization reaction, whereas there is no cyclization in the absence of the withdrawing group (Scheme 29) [82]. Larock et al. had performed the mercuration of 4-hydroxy-2-alkyn-1-ones 90 with HgCl2 to get

• HgCl2-mediated cyclization reaction of tethered alkynedithioacetals 110 to provide six- and five-membered carbocyclic and heterocyclic derivatives 111 and 112, respectively. They had observed that the formation of five-membered rings (112a–c) was preferred when substitutents were present at the alkyne

• lactones had been synthesized from alkynoic acids via Hg(II)-salt-catalyzed cyclization reaction. For example, simple 4-pentynoic acid derivatives 137 afforded γ-methylene butyrolactones 139 in good yields via the formation of organomercural compounds 138 using catalytic mercuric oxide, mercuric acetate

Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• cyclization reaction of succinimide and glutarimide-derived hydroxylactams 7 (Scheme 3) [33]. This system was designed in a way that key experimental observations could be made to analyze whether a SN1 or SN2-type mechanism takes place. A strong dependence of the enantioselectivity on the counterion and

• . Based on this concept, the applicability of N-acyliminium chlorides in thiourea-catalyzed anion-binding reactions was further explored. In 2008, an intramolecular asymmetric Pictet–Spengler-type cyclization reaction with pyrrole derivatives 13 was reported. The authors were not only able to control the

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

• synthesized using the combination of hexafluoroisopropanol and triflimide as a catalyst [29]. One of the most effective C–C bond establishing reactions, which ensures an efficient synthetic way to a plenty of functionalized aryl compounds, is the Friedel–Crafts cyclization reaction [30][31][32][33][34

• , K2CO3, DMF, reflux, 2 h, 91%; (ii) PhMgBr, dry THF, 0 °C, 2 h, 86%; (iii) PCC, CH2Cl2, rt, 2 h, 80%; (iv) Me(Ph)3PBr, t-BuOK, NaH, dry THF, rt, 3 h, 85%. Plausible reaction mechanism for the cyclization reaction of alkene 4a. Screening of catalysts for intramolecular FCA of 1a.a Exploration of solvents

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

• activation In 2009, Liang et al. reported an efficient and highly regioselective route to construct substituted tetracyclic benz[a]anthracene derivatives 115 (Scheme 26) [60]. For this purpose, the authors developed an efficient palladium-catalyzed tandem C–H activation/bis-cyclization reaction of

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

• compounds 25 through the regioselective addition and cyclization reaction of 1,1-enediamines (EDAMs) 24 with p-methylbenzenesulfonyl azide in 1,4-dioxane as solvent at reflux was presented by Yan et al. Some substituted EDAMs (R1 = R2) were concluded to be treated with TsN3. In continuation, substituted

• EDAMs (R1 ≠ R2) were also applied to check the regioselectiveness of this addition and cyclization reaction. The methodology provides a simple, straightforward, and facile path to access fully decorated 1,2,3-triazoles 25 in moderate to good yield. Noticeably, this uncatalyzed addition and cyclization

• via intramolecular cyclization reaction of ketones 31, p-nitrophenyl azide (PNA, 32) and amino esters 33 has been described by Dehaen et al. The products were often obtained in good yield and in all cases with the retention of the configuration of the stereocenter. The reaction was carried out by

Heterogeneous photocatalytic cyanomethylarylation of alkenes with acetonitrile: synthesis of diverse nitrogenous heterocyclic compounds

• Guanglong Pan,
• Qian Yang,
• Wentao Wang,
• Yurong Tang and
• Yunfei Cai

Beilstein J. Org. Chem. 2021, 17, 1171–1180, doi:10.3762/bjoc.17.89

• recyclability, broad substrate scope, and high functional group tolerance (Scheme 1). Results and Discussion Our initial investigation focused on the CN-K photocatalyzed cascade alkyl radical addition/cyclization reaction of the N-arylallylamine 1a with tert-butyl N-hydroxyphthalimide (NHPI) ester (2a), a

• in 41% yield (Scheme 6c). Furthermore, the tricyclic indoline 14, a structural motif in diverse natural products [4], could be obtained in 60% yield through a reductive cyclization reaction (Scheme 6d). To investigate the mechanism of the cyanomethylarylation of alkenes, a series of control

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• were the only reaction products, meanwhile for aliphatic derivatives 24 (R = alkyl), trans- and cis-aziridines 22 were isolated in practically the same ratio as the anti/syn ratio of their precursors 24. This shows that the cyclization reaction is stereospecific (Scheme 8). Comparing both methodologies

• , indicating a mismatch between the chiral auxiliary and the stereocenter in this substrate. Concerning the oxidative cyclization reaction, pyridinium dichromate (PDC) provided low yields of expected lactam 77. Many oxidants were checked for this transformation to take place, and the Sarett reagent [CrO3·(C5H5

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

• generated as shown in Scheme 32. Silyl-Prins cyclization Extensive research efforts were made towards the synthesis of THP using the silyl-Prins cyclization reaction. In this reaction, an oxocarbenium ion is being trapped by allylsilanes, vinylsilanes, alkenyl methylsilanes, or propargylsilanes to produce a

• Sakurai macrocyclization/dimerization strategy to produce 150 in the presence of TMSOTf, as shown in Scheme 35 [70]. Hoye and Hu utilized camphor sulfonic acid (CSA) to construct a cis-2,6-disubstituted tetrahydropyran 153 via an intramolecular Sakurai cyclization reaction between the enal 151 and an

• ]. Similar to Prins cyclization of allylsilanes, Dobbs and co-workers recently utilized the corresponding vinylsilane as an alternative for the synthesis of cis-2,6-dihydropyran [89][90]. The synthesis involves tandem addition of vinylsilane, followed by silyl-Prins cyclization reaction. For example, 4

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• over the last five years. Cyclization reactions In the pharmaceutical industry, retail drugs with a heterocyclic composition have exceeded 60% of the market volume. Hence, cyclization reaction innovation seems to be a requisite for pharmaceutical industry and human health. As an outstanding way, free

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

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

• cyclopropane formation did not require Et3B (Scheme 25). The work was extended to include boron-free, diastereoselective versions incorporating N-acylimidazolidinone chiral auxiliaries (Scheme 26). Cyclization reaction of phenylacetonitrile and 1,2-dibromo-1,1-difluoroethane: Kagabu et al. showed that the

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• date, and their accessibility creates exciting synthetic opportunities. Here we present two examples of possible further transformations of the products obtained over the course of this research directed towards novel, attractive molecules. Compound 3b underwent a cyclization reaction in the presence

Synthesis of aryl 2-bromo-2-chloro-1,1-difluoroethyl ethers through the base-mediated reaction between phenols and halothane

• Yukiko Karuo,
• Ayaka Kametani,
• Atsushi Tarui,
• Kazuyuki Sato,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2021, 17, 89–96, doi:10.3762/bjoc.17.9

• the further application of compound 2o in a cyclization reaction. Upon the treatment of 2o with zinc and chlorotrimethylsilane (TMSCl), the intramolecular 1,4-addition reaction of 2o proceeded to give the 2,2-gem-difluorochromane 3 in low yield (Scheme 3). Next, we moved on consideration of the

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• positive charge of the allyl system by conjugation, affecting the following cyclization reaction. Meanwhile, the 2-substitued analogue VII does not present a conjugated system, and the total allyl charge cannot be stabilized, maintaining a positive value (+0.115). As a result, VII seems to be much more

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• 472 nm. If the state SelfSORT-II was generated in the presence of substrate 37 a cyclization to product 38 was seen (45% yield). In contrast, the silver(I) ions in [Ag(35)]+ (state: SelfSORT-I) were not able to act as a catalyst for the cyclization reaction. The double self-sorting along with ON/OFF

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

• formed during the cyclization reaction of 16 compared to phenyl nitrene [42]. Besides H-SN4 13, which is formed by insertion of the nitrene N-atom into the C3–H σ-bond of the thienothiophene in 16 and simultaneous migration of the H-atom to the nitrogen, mostly undefined black oligomeric or polymeric

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

Synthesis of 3(2)-phosphonylated thiazolo[3,2-a]oxopyrimidines

• Ksenia I. Kaskevich,
• Anastasia A. Babushkina,
• Vladislav V. Gurzhiy,
• Dmitrij M. Egorov,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2020, 16, 1947–1954, doi:10.3762/bjoc.16.161

• [3,2-a]pyrimidine-7-one [16]. A similar reaction outcome was observed when chloroethynylphosphonates 2a–c were reacted with unsubstituted 2-thiouracil (1d). The cyclization reaction also proceeded predominantly through the N1 atom to form the corresponding 3-phosphonylated thiazolo[3,2-a]-7

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

• Clément Q. Fontenelle,
• Thibault Thierry,
• Romain Laporte,
• Emmanuel Pfund and
• Thierry Lequeux

Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160

• between fluorine and bromine limited the intermolecular ring-opening reaction by bromide in favor of a faster intramolecular reaction involving the ester group leading to 14. Indeed, a competitive cyclization reaction occurred forming 14 with HBr/AcOH and confirmed when the reaction was performed in the

One-pot synthesis of oxazolidinones and five-membered cyclic carbonates from epoxides and chlorosulfonyl isocyanate: theoretical evidence for an asynchronous concerted pathway

• Esra Demir,
• Ozlem Sari,
• Yasin Çetinkaya,
• Ufuk Atmaca,
• Safiye Sağ Erdem and
• Murat Çelik

Beilstein J. Org. Chem. 2020, 16, 1805–1819, doi:10.3762/bjoc.16.148

• performed. Formation of oxazolidinone 9f There are two possible channels for the cyclization reaction of epoxide 7f with CSI to form oxazolidinone intermediates 10 and 11 as shown in Figure 1. In both transition states it is found that the ring-opening reaction of the epoxide, a nucleophilic attack of N4