Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

• Songeziwe Ntsimango,
• Kennedy J. Ngwira,
• Moira L. Bode and
• Charles B. de Koning

Beilstein J. Org. Chem. 2021, 17, 2340–2347, doi:10.3762/bjoc.17.152

• methoxy group as a leaving group have been documented [16]. Our previous research, as shown in Scheme 1, indicated that exposure of the oxime ether 7 to UV radiation resulted in the formation of the phenanthridine 8. Attempts to synthesize the related oxime ethers from biaryl compounds 13a, 13c and 13e

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

• chiral contact-ion pair can be formed, which is necessary for the transfer of the chiral information to the product. As a consequence, most of the reported methods embracing enantioselective anion-binding catalysis rely on the use of nonpolar solvents such as ethers or aromatic compounds. Pioneering work

• ][75][76][77][78]. Nevertheless, the activation of α-chloro ethers via anion abstraction continued to be a foundation for anion-binding catalyst evolution. In fact, Jacobsen's group further refined the design of their tetradentate N–H-bond donor catalyst 80 by covalently linking it into the more rigid

Photoredox catalysis in nickel-catalyzed C–H functionalization

• Lusina Mantry,
• Rajaram Maayuri,
• Vikash Kumar and
• Parthasarathy Gandeepan

Beilstein J. Org. Chem. 2021, 17, 2209–2259, doi:10.3762/bjoc.17.143

• arylation of cyclic and acyclic ethers 9 with aryl chlorides 8 under photoredox nickel catalysis (Scheme 5) [56]. Here, aryl chlorides 8 serve as cross-coupling partners and the chlorine radical source, which rapidly abstracts an α-oxy C(sp3)−H of the ethers to form the key α-oxyalkyl radical intermediate

• photocatalyst, substoichiometric 4,4′-dimethoxybenzophenone (DMBP) additives, and visible light (Scheme 6) [57]. A variety of cyclic and acyclic ethers 9 reacted with (hetero)aryl bromides 3 under the mild reaction conditions to give the desired products 10 in moderate to good yields, however, with longer

• the oxidative addition of the nickel(0) catalyst 6-VI to aryl bromide 3b. The photochemical nickel catalysis is not limited to an α-oxy C(sp3)‒H arylation of ethers. MacMillan and co-workers disclosed a method for the selective direct α-arylation of alcohols 18 using photoredox, HAT, and nickel triple

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

• -substituted amines 15, 18, and 20 [43]. Taking aniline as the pivotal moiety, it was coupled with isomeric bromoindoles 14 and 16 for the synthesis of the targeted products (Scheme 3b). Ethers Hongtao and co-workers also studied the electroluminescence properties of the 3,3’-bis(indolyl) ether derivatives 23

• ability of the products. Up to >80% inhibition of the amyloid-β peptide aggregates were achieved with these compounds, with the highest activity found for the 4-N-methylpiperidyl derivative. Ethers The synthesis of the bis(indol-6-yl) ether 175 was performed by Chai in 2017. Their protocol used a Cu(OAc)2

• indolyl amines through Buchwald–Hartwig cross coupling. Synthesis of 3,3’-bis(indolyl) ethers. C–H silylation of indoles. n-BuLi-mediated syntheses of bis(indol-3-yl)silanes. Acid-catalyzed syntheses of bis(indol-3-yl)silanes and mechanisms. B(C6F5)3 and Al(C6F5)3-catalyzed syntheses of bis(indol-3-yl

A study on selective transformation of norbornadiene into fluorinated cyclopentane-fused isoxazolines

• Zsanett Benke,
• Attila M. Remete and
• Loránd Kiss

Beilstein J. Org. Chem. 2021, 17, 2051–2066, doi:10.3762/bjoc.17.132

• the selectivity of olefin bonds during a CM reaction [38][39][40][41][42][43]. Investigations of various types of olefins in CM, such as substituted and functionalized styrenes, unsaturated tertiary alcohols, olefins with quaternary carbon centers, acrylates, allyl ethers or allyl acetates gave a

Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• alkyl enol ethers as the allylic counterpart [120]. In the field of C–H activation studies, not many examples have been described in the literature so far, especially towards the synthesis of biologically active compounds. However, an interesting example of a C(sp2)–H activation reaction promoted by Cr

Development of N-F fluorinating agents and their fluorinations: Historical perspective

• Teruo Umemoto,
• Yuhao Yang and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

• -handle, their fluorinating power was low. They could fluorinate only reactive carbanions, but not aromatics, olefins, vinyl acetates, trimethylsilyl or alkyl enol ethers, and so on. Soon after (1986), Schwartz and co-worker reported the stereospecific synthesis of alkenyl fluorides with N-fluoro-N-tert

• , olefins, silyl enol ethers, vinyl acetates, sulfides and so on, under mild conditions with high selectivity and yields [29][30][31][32]. All these reactions could be carried out routinely using standard glassware in normal laboratory environments and without any specialist training. Some interesting

•  30). NFSI is a stable and non-hygroscopic crystalline solid with a mp of 114–116 °C. NFSI was shown to fluorinate a variety of nucleophiles. As seen in Scheme 31, trimethylsilyl enol ethers, enolate anions of ketones and esters, and aryl- and vinyllithiums were fluorinated with NFSI in moderate to

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• hampered the development of more general catalytic hydrofunctionalization methodologies until Widenhoefer’s work in 2001 [25]. Based on previous works that had demonstrated the addition of stabilized carbanions [26][27] and enol silyl ethers [28] to olefins under stoichiometric Pd catalysis, the authors

• hydroalkylation reactions of less activated substrates [31]. Later studies demonstrated that the true reason for the reaction success was not the putative in situ formation of silyl enol ethers but the HCl formation due to TMSCl hydrolysis. The HCl catalyzed the formation of the enolic form responsible for the

• also tolerable to functional groups, such as silyl ethers (52a), carbamates (52b), and heterocycles (52c), present in the olefin moiety. The initial mechanism proposed by the authors begins with the formation of Fe(III) hydride species (A), followed by hydrogen atom transfer to the olefin in a

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

• + 2]-cycloadduct 10b undergoes spontaneous elimination of MeOH, yielding the aromatized product 9d. A similar mechanistic scenario was observed and discussed previously for the reactions of trifluoroacetonitrile imines 7 with enol ethers used as dipolarophiles [27]. An additional experiment deserves a

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

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

• -pyrrolines 82 were formed as single diastereomers [101]. The whole process could be considered a [3 + 2] annulation, and aziridines were not observed as competing reaction products (see above Scheme 11). In addition, hindered imines, ethers, sulfonates, heteroaryl substituents, and conjugated imines were all

• (Scheme 33) [122]. The group of Prasad reported the diastereoselective synthesis of β-amino ketone derivatives from N-tert-butanesulfinyl imines and silyl enol ethers of aryl methyl ketone [123]. The synthetic interest in β-amino ketones was exemplified in the synthesis of alkaloid (+)-sedamine (125

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

• Jan Bartáček,
• Jan Svoboda,
• Martin Kocúrik,
• Jaroslav Pochobradský,
• Alexander Čegan,
• Miloš Sedlák and
• Jiří Váňa

Beilstein J. Org. Chem. 2021, 17, 1048–1085, doi:10.3762/bjoc.17.84

• %; 85% ee), but the reaction times were very short (Scheme 7) [41]. In 2011, the groups of Hayashi and Chujo studied Pd complexes of diphosphacrown ethers [42]. The macrocyclic Pd complex PdL5 in combination with AgSbF6 or AgOTf was tested for the addition reaction of various arylboronic acids to 2

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

• an oxocarbenium ion is generated from a masked aldehyde bearing a homoallylic alcohol moiety has been examined. In this context, the α-acetoxy ethers with different functionalities at C4 were examined in the presence of a variety of Lewis acids, and it was found that the α-acetoxy ether (R)-42

• 2,6 disubstituted 3,4-dimethylene-THP. Furman and co-workers’ THP synthesis from propargylsilane. THP synthesis from silyl enol ethers. Rychnovsky and co-workers’ strategy for THP synthesis from hydroxy-substituted silyl enol ethers. Li and co-workers’ germinal bissilyl Prins cyclization strategy to

Synthesis of bis(aryloxy)fluoromethanes using a heterodihalocarbene strategy

• Carl Recsei and
• Yaniv Barda

Beilstein J. Org. Chem. 2021, 17, 813–818, doi:10.3762/bjoc.17.70

• purposes. Recently, a proliferation of methods has allowed easy access to a particularly desired class of these compounds: singly fluorinated compounds such as fluoromethyl ethers [1]. Still missing from the chemist’s toolkit, however, are means to construct their more highly oxidized analogues

• aldehydes were present, and that unreacted phenol comprised a further 26% of the mass balance. Thus, the reactivity of fluorobromocarbene in this case mirrored the tendency of difluorocarbene to react with phenoxides to form dihalomethyl phenyl ethers, rather than forming aldehydes as with dichlorocarbene

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

• trifluoromethylation (Scheme 25). A variety of olefins, such as ene carbamates, styrene, aliphatic olefins, vinyl ethers, and acrylates are compatible in this approach, affording corresponding β-(trifluoromethyl)alkynes with good to excellent yield. The bifunctionalization was achieved by an EDA-complex-initiated

• , cyanides, esters, ethers, halides, and heterocycles, and various α-aminoketones (32 examples) can be yielded in 90% isolated yield. According to the author, the EDA complex had a six-membered-ring transient state, and the imine also acted as an organic base (abstracting proton from α-keto acid), proving

• effects of phenol, a variety of phenols, including electron-donor and electron-withdrawing groups, were been converted into corresponding 2-iodovinyl phenyl ethers in moderate to excellent yield with high regio- and stereoselectivities. According to the analysis of the mechanism (Scheme 60), a molecule of

β-Lactamase inhibition profile of new amidine-substituted diazabicyclooctanes

• Zafar Iqbal,
• Lijuan Zhai,
• Yuanyu Gao,
• Dong Tang,
• Xueqin Ma,
• Jinbo Ji,
• Jian Sun,
• Jingwen Ji,
• Yuanbai Liu,
• Rui Jiang,
• Yangxiu Mu,
• Lili He,
• Haikang Yang and
• Zhixiang Yang

Beilstein J. Org. Chem. 2021, 17, 711–718, doi:10.3762/bjoc.17.60

• -dimethylaminopyridine (DMAP) as the base. Then, the palladium-catalyzed hydrogenation of compounds B1–21 in THF or EtOAc led to the hydroxy derivatives C1–21. It has been observed that a catalytic amount of triethylamine (TEA) in EtOAc enhances the rate of the hydrogenolysis of benzyl ethers. Compounds C1–21 were then

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• theoretically possible isomeric methanofullerenes C60. Structures of monophenyldiazomethanes 28–30. Structures of diphenyldiazomethanes 31–34. Conjugates of benzocrown ethers with phenylmethanofullerenes 35–39. Structures of para-phenylenebis(phenylfulleroid) 40 and meta-phenylenebis(phenylfulleroid) 41

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

• ethers and N-methyl-2-pyrrolidone (NMP) and has a melting point around 240 °C [152]. Most methods for PS recycling are not economically advantageous [153]. Mechanical recycling, based on pelletizing and moulding, produces low-grade plastics with poor mechanical strength and low market value. Solid PS

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

• variety of α-(trifluoromethyl) silyl ethers 41b was converted into the corresponding indanes 43 in low to high yields [62]. The trans-isomers were generally obtained as the major product (Scheme 10). Bis[α-(trifluoromethyl)]-substituted carbenium ions: More destabilized bis(trifluoromethyl)-substituted

• , Vasilyev and Khoroshilova investigated the superacid-promoted activation of α-(trifluoromethyl) silyl ethers exhibiting a thiophene core [73]. At 0 °C, thiophenes 72-Cl and 72-Br undergo electrophilic dimerization, affording a mixture of 73-Cl and 73-Br (Scheme 20). When the reaction was cooled to −60 °C

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

• , and alkenyl (pinacol) boranes 16 were transformed into the corresponding difluorocyclopropanes in 93–99% yields. Highly sensitive substrates such as trimethylsilylenol ethers 20 can also be used in this method in order to prepare the difluorocyclopropanes 21 with good yields (Scheme 10) [29][30]. In

• hydrogenolysis of benzyl ethers (H2, Pd) [72], DIBAL-H reduction of esters to form alcohols [73], oxidative cleavage of vinyl groups to form carboxylic acids (KMnO4) [74], and the conversion of the acids into amines using the Curtius rearrangement (SOCl2, followed by Me3SiN3, thermolysis, and acid hydrolysis of

• alcohols, ethers, esters, and amines (121, Scheme 53) [103]. They proposed that an initial tin–lithium exchange was followed by a β-elimination of LiF to form the intermediate cyclopropenes 119. The ring opening of the latter then generated the vinylcarbenes 120. The carbenes 120 could then insert into the

Novel library synthesis of 3,4-disubstituted pyridin-2(1H)-ones via cleavage of pyridine-2-oxy-7-azabenzotriazole ethers under ionic hydrogenation conditions at room temperature

• Romain Pierre,
• Anne Brethon,
• Sylvain A. Jacques,
• Aurélie Blond,
• Sandrine Chambon,
• Sandrine Talano,
• Catherine Raffin,
• Branislav Musicki,
• Claire Bouix-Peter,
• Loic Tomas,
• Gilles Ouvry,
• Rémy Morgentin,
• Laurent F. Hennequin and
• Craig S. Harris

Beilstein J. Org. Chem. 2021, 17, 156–165, doi:10.3762/bjoc.17.16

• pyridine ring toward SNAr with the −OAt anion in an intermolecular or intramolecular fashion (Scheme 3). We saw this observation as having the potential to solve our hydrolysis issues and decided to explore it further. Inspection of the literature revealed that activated ethers (e.g., OBt) have been

• excess of POCl3 and heating the reaction mixtures to 60 °C over 4 h [17]. In turn, the C-2–Cl intermediates were transformed to their C-2–OBt ethers using an excess of HOBt·H2O in refluxing DCM to facilitate the final hydrolysis step to the desired pyridine-2-(1H)-one products 24h,i. The low yield

• (I). Formation of C2–OAt ether 15 using HATU. Reagents and condtions: (a) HATU, DIPEA, DCM, rt, 16 h, ((14) 5%, (15) 95% conversion by UV-LC–MS), 58% isolated yield (15). Proposed mechanistic pathways for the transformation of Py–OAt ethers 17 to the pyridin-2H-one 1 motif. Failure to exploit logical

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• with various macrocyclic hosts as well as on the role of macrocyclic-hosts-assisted hybrid materials in energy transfer. To keep the clarity of this review, the macrocycles are categorized into the most commonly used supramolecular hosts, including crown ethers, cyclodextrins, cucurbiturils

• supramolecular hosts (Figure 1); crown ethers (CEs), cyclodextrins (CDs), cucurbiturils (CBs), calixarenes (CAs), and pillararenes (PAs) for various photocatalytic reactions. However, biomolecules and other supramolecular-host-related photocatalytic reactions are not included in this minireview. Generally, a

• can easily gain information on host–guest interactions in supramolecular systems as well as the photocatalytic reaction efficiency. Review Macrocycle-promoted photocatalysis Photocatalysis based on crown ethers and crown ether derivatives CEs are a class of macrocycles that consist of a ring with a

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

• and highly functionalized aryl 2-bromo-2-chloro-1,1-difluoroethyl ethers has been developed. This approach exhibits a broad reaction scope, a simple operation and without the need of any expensive transition-metal catalyst, highly toxic or corrosive reagents. Notably, we demonstrate the potential

• utility of halothane for the synthesis of aryl gem-difluoroalkyl ethers containing the bromochloromethyl group. Keywords: aryl 1,1-difluoroethyl ether; 1,1-difluoroethene; fluorine compound; halothane; phenol; Introduction Molecules containing fluoroalkyl groups are of interest in pharmaceutical and

• demonstrated the synthesis of aryl fluoroalkyl ethers as shown in Scheme 1 [32][33][34]. For example, the reactions of phenols with “gem-difluorocarbene precursors (route (a))” or “bromodifluoroalkyl compounds (route (b))” have been typically used to obtain a variety of aryl gem-difluoromethyl ethers

Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

• Daria I. Tonkoglazova,
• Anna V. Gulevskaya,
• Konstantin A. Chistyakov and
• Olga I. Askalepova

Beilstein J. Org. Chem. 2021, 17, 11–21, doi:10.3762/bjoc.17.2

• ethers of 3,6-diacetylcarbazole with p-benzoquinone (Scheme 1B) [49], the double Buchwald–Hartwig amination of 4,4'-biphenanthrene derivatives (Scheme 1C) [45] and a enantioselective Fischer indolization–oxidation protocol (Scheme 1D) [43]. Each method is not without drawbacks such as hardly available