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

• cyclization. From aldehyde 2l an acyl radical should subsequently be formed, for which cyclization reactions with heteroarenes and benzenoids are well documented [67][68]. Aldehyde 2l may also be further oxidized to give carboxylic acid B instead. With the oxidant of choice, aqueous TBHP, however, aldehyde 2l

Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides

• Pratibha Sharma,
• Raakhi Gupta and
• Raj K. Bansal

Beilstein J. Org. Chem. 2021, 17, 2585–2610, doi:10.3762/bjoc.17.173

• formation of HOMO raised dearomative aza-dienamine-type intermediates, which undergo direct aza-Michael addition to β-trifluoromethyl enones to afford N-functionalized heteroarenes 121 efficiently in moderate to excellent yields, albeit with low to fair enantioselectivity. However, asymmetric aza-Michael

• additions of these heteroarenes with crotonaldehyde yielded the adducts in moderate to good enantioselectivity under dual catalysis of chiral amines (Scheme 5) [69]. Conclusion The asymmetric aza-Michael reaction being a useful synthetic strategy for constructing C–N bonds to make a variety of nitrogen

• . Asymmetric synthesis of chiral N-functionalized heteroarenes. Asymmetric cascade aza-Michael−aldol reactions of α,β-unsaturated ketones with pyrroles. Intramolecular aza-Michael addition of conjugated ketones. Intramolecular enantioselective aza-Michael addition. Asymmetric aza-Michael addition of 4

α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• heteroarenes were much poorer, with pyrroles and thiophenes giving yields of ≈20% or less and benzofuran and benzothiophene failing to produce any product. Interestingly, a cyclopentanone-derived substrate (120) failed to yield the corresponding α-amino cyclohexanone 121 under the standard conditions used for

• original source). Tandem synthesis of functionalized α-amino cyclopentanones 119 from heteroarenes 115 and cyclobutanone-derived cyanohydrins 116. a) Pd-catalyzed C–H addition of 115 to the nitrile group of 116 produces intermediates 117 and 118. An α-iminol rearrangement with ring expansion subsequently

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• with aryl iodides to generate intermediate D, which then undergoes reductive elimination to generate the desired products (Scheme 23). In 2017, Evano’s group [55] established a photoinduced, copper-catalyzed C–C cross-coupling of aryl halides, and heteroarenes. The cyclization of N-allyl-o-iodoanilines

• between N-heteroarenes 69 and redox-active esters 68. In 2018, Gong and co-workers [43] used benzyltrifluoroborates 71 as a benzylic radical source for the visible-light-induced alkylation of imines 70. In the catalytic system, chiral ligands initiated benzylic radical formation and governed the

• and heteroarenes. Benzylic or α-amino C–H functionalization. α-Amino C–H functionalization of aromatic amines. C–H functionalization of aromatic amines. α-Amino-C–H and alkyl C–H functionalization reactions. Other copper-photocatalyzed reactions. Cross-coupling of oxime esters with phenols or amines

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

• , that Reissert dearomatizations of N-heteroarenes, especially of isoquinolines [36], and nucleophilic addition to 1-chloroisochromanes [38] have become benchmark reactions in the context of anion-binding catalysis. Besides reports of thiourea-catalyzed reactions with different nucleophiles [39][40], the

• extended to other N- and O-heteroarenes and various nucleophiles (Scheme 18b) [87][88][89][90][91]. Computational studies on the helical tetrakistriazole catalyst were additionally carried out, aiming at gaining insight into its interactions with the anion and cationic counterpart of the ionic substrate

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

• present in the natural product bismurrayafoline E (36) [105], an alkaloid found in the leaves of Murraya koeniggi (Scheme 13D) [106]. The oxidative formation of carbon–carbon bonds mediated by vanadium has been reported as a method for the aminomethylation of arenes and heteroarenes. The so far described

Free-radical cyclization approach to polyheterocycles containing pyrrole and pyridine rings

• Ivan P. Mosiagin,
• Olesya A. Tomashenko,
• Dar’ya V. Spiridonova,
• Mikhail S. Novikov,
• Sergey P. Tunik and
• Alexander F. Khlebnikov

Beilstein J. Org. Chem. 2021, 17, 1490–1498, doi:10.3762/bjoc.17.105

• in materials science, especially in post-silicon electronics [1][2][3][4]. Though the remarkable progress in the synthesis of the polycyclic heteroarenes during the last two decades, further development of the existing methodologies is still required for broadening of the scope of polycyclic

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

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

• with electron-rich as well as electron-poor arenes and heteroarenes. Subsequently, in order to prove the practicability of this approach, 1,2,3-triazoles were assembled by reaction of 157 with alkynes. In 2019, Bosque and Bach [41] reported that 3-acetoxyquinuclidine (q-OAc) could be utilized as an

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

• bond alkynylations of heteroarenes [9]. The 1,1-dichloro-1-alkenyl moiety is found in a number of pyrethroid insecticides including permethrin and marine natural products such as caracolamide A [10] (Figure 1). 1,1-Dichloro-1-alkenes 2 are commonly prepared from the corresponding aldehydes 1 in one

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

Photocatalytic trifluoromethoxylation of arenes and heteroarenes in continuous-flow

• Alexander V. Nyuchev,
• Ting Wan,
• Borja Cendón,
• Carlo Sambiagio,
• Job J. C. Struijs,
• Michelle Ho,
• Moisés Gulías,
• Ying Wang and
• Timothy Noël

Beilstein J. Org. Chem. 2020, 16, 1305–1312, doi:10.3762/bjoc.16.111

• , Road, North Chicago, Illinois 60064, United States of America 10.3762/bjoc.16.111 Abstract The first example of photocatalytic trifluoromethoxylation of arenes and heteroarenes under continuous-flow conditions is described. Application of continuous-flow microreactor technology allowed to reduce the

• methodologies [27][28][29][30][31], herein we report the first application of flow methods for the direct trifluoromethoxylation of arenes and heteroarenes. Results and Discussion Among the three reagents shown in Scheme 1B, we decided to use the “second” Ngai reagent (1, Scheme 1C) for our investigation, as

• conditions in hands, we proceeded to investigate the trifluoromethoxylation of different arenes and heteroarenes in acetonitrile. Solvent mixtures and lower concentrations had to be used in some cases due to solubility issues. As can be seen in Scheme 3, trifluoromethoxylation occurs preferentially at the

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• radical adds to the imine substrate 5.5, yielding the desired amine product 5.6. Finally, the same group developed a photochemical radical alkylation of heteroarenes with alkyl trifluoroborate salts (Scheme 6) [51]. In this reaction, the photoinduced oxidative fragmentation of the alkyl trifluoroborate

• visible-light irradiation. The key aryl radical was trapped with heteroarenes, such as 11.2, to give the arylation products 11.3. Recently, similar methodologies for aryl radical generations have been developed exploiting flow techniques [74] and different organophotocatalysts, such as a metal-free

• for the synthesis of the arylated heteroarenes 12.3 via an intermolecular process [79]. Alemán and co-workers used PHTH (OD16) for the synthesis of various heteroatom-containing bicycles 12.4 through a tethered electrophile approach [80]. For the second strategy, König and co-workers developed an

Copper-based fluorinated reagents for the synthesis of CF₂R-containing molecules (R ≠ F)

• Louise Ruyet and
• Tatiana Besset

Beilstein J. Org. Chem. 2020, 16, 1051–1065, doi:10.3762/bjoc.16.92

• )aryldiazonium salts, a panel of difluoromethylated arenes and heteroarenes was obtained (26 examples, up to 84% yield). Note that the transformation was also carried out starting from 4-methoxyaniline followed by the in situ formation of the corresponding diazonium salt. In the same vein, the authors used this

• organocopper derivative was then oxidized resulting in the formation of the desired products. Note that in 2018 the same group reported the copper-mediated oxidative difluoromethylation of heteroarenes under similar reaction conditions (TMSCF2H, CuCN, 9,10-phenanthrenequinone, t-BuOK in NMP) [46]. Not only

• oxazoles (17 examples, up to 87% yield) were difluoromethylated but a variety of other heteroarenes turned out to be suitable such as pyridine, imidazole, benzo[d]thiazole, benzo[b]thiophene, benzo[d]oxazole, thiazole and thiophene derivatives (Scheme 6). Copper-based CF2FG-containing reagents Besides the

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• reported a metal-free photoarylation of five-membered heteroarenes with aryldiazonium salts and meso-arylated porphyrin derivatives as photoredox catalyst [11]. Compounds such as furan, thiophene, and N-Boc-pyrrole derivatives were obtained by this methodology in 29–81% yields (Scheme 3). The key-step of

• , meta and para positions. Moreover, the methodology also showed effectiveness for heteroarenes such as pyridines and benzothiazoles. The authors also evaluated the use of NiTPP as a photoredox catalyst for other transformations involving both oxidative and reductive quenchings. The NiTPP-catalyzed

• ). For an oxidative quenching, the photoarylation of heteroarenes and alkynes with aryldiazonium salts, and the oxidative decarboxylative coupling between cinnamic acid and tetrahydrofuran also showed better results when NiTPP was used instead of eosin [32][33][34] (Scheme 10). Regarding protocols

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• ., formamide) and ethers through C–H activation using various five- and six-membered heteroarenes (e.g., benzothiazole) and employing benzaldehyde (8) as the photoinitiator [56]. This protocol was compatible with both C(sp3)–H activation (N-alkyl C–H bonds of amides or Cα–H bonds of ethers) and C(sp2)–H

• activation (carbonyl C–H bonds of formamides). Some of the amides or ethers found to be compatible with this method are shown in Scheme 26. A wide range of heteroarenes 114 was also found compatible with this method, including substituted benzothiazole substrates, substituted benzimidazoles, and thiazoles

Extension of the 5-alkynyluridine side chain via C–C-bond formation in modified organometallic nucleosides using the Nicholas reaction

• Renata Kaczmarek,
• Dariusz Korczyński,
• James R. Green and
• Roman Dembinski

Beilstein J. Org. Chem. 2020, 16, 1–8, doi:10.3762/bjoc.16.1

• diverse products via formation of C–C bonds. Nucleophiles as diverse as electron-rich arenes or heteroarenes [41][42], alkenes [43], allylmetalloids [44][45][46], enol derivatives [47][48], and organometallics [49] are suitable for the Nicholas reaction. Allenic byproducts are rarely seen, and

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• ) as an additive (Scheme 78). Mechanistic studies revealed that this reaction probably proceeds through a radical pathway. Copper-catalyzed trifluoromethylation of arenes and heteroarenes: In 2013, Xi et al. [142] reported a CuCl-catalyzed direct trifluoromethylation of sp2 C–H bonds with Togni reagent

• heteroarenes with the CF3 radical through a Cu(I/II) catalytic cycle. In 2013, the Szabó [143] and Wang group [144] described the copper-mediated C–H trifluoromethylation of quinones with Togni’s reagent. Szabó utilized a stoichiometric amount of CuCN combined with catalytic bis(pinacolato)diboron, whereas

Regioselective Pd-catalyzed direct C1- and C2-arylations of lilolidine for the access to 5,6-dihydropyrrolo[3,2,1-ij]quinoline derivatives

• Hai-Yun Huang,
• Haoran Li,
• Thierry Roisnel,
• Jean-François Soulé and
• Henri Doucet

Beilstein J. Org. Chem. 2019, 15, 2069–2075, doi:10.3762/bjoc.15.204

• functionalization of heteroarenes such as thiophenes, furans, pyrroles and indoles [14][15], this methodology has been widely applied for the preparation of new aryl-substituted heteroarenes [16][17][18][19][20][21]. Several results dealing with the C–H bond functionalization of indoles have been reported allowing

Reactions of 2-carbonyl- and 2-hydroxy(or methoxy)alkyl-substituted benzimidazoles with arenes in the superacid CF₃SO₃H. NMR and DFT studies of dicationic electrophilic species

• Dmitry S. Ryabukhin,
• Alexey N. Turdakov,
• Natalia S. Soldatova,
• Mikhail O. Kompanets,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1962–1973, doi:10.3762/bjoc.15.191

• ][20][21][22][23]. These carbonyl-substituted heteroarenes possess basic sites (nitrogen or oxygen atoms of the heterocyclic system), which are fully protonated in acid, so that upon subsequent protonation of the carbonyl oxygen, more reactive dicationic electrophiles can be generated. Previously

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• high level of functional group compatibility, intramolecular alkylations, inter and intramolecular C–H bond activation and regio/stereoselective homocoupling of alkynes [71][72][73]. Group of Cho and Chang have unprecedentedly reported a Rh catalytic system for facile addition of heteroarenes to both

Metal-free C–H mercaptalization of benzothiazoles and benzoxazoles using 1,3-propanedithiol as thiol source

• Yan Xiao,
• Bing Jing,
• Xiaoxia Liu,
• Hongyu Xue and
• Yajun Liu

Beilstein J. Org. Chem. 2019, 15, 279–284, doi:10.3762/bjoc.15.24

• potassium hydroxide and DMSO. This novel protocol is featured by direct C–H mercaptalization of heteroarenes and a simple reaction system. Keywords: benzothiazole; benzoxazole; C–H functionalization; mercaptalization; 1,3-propanedithiol; Introduction Both 2-mercaptobenzothiazoles and 2

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• through the addition of radical 99 to the quinones 94. Finally, the intermediate 100 occurres reoxidation with Ag(II) to provide the final product 95 along with regenerated Ag(I). In 2015, Duan et al. developed a Ag(I)-catalyzed oxidative ring-opening of cyclopropanols 91 with heteroarenes 101 or 103 for

• the synthesis of carbonyl-containing alkyl-substituted heteroarenes 102 or 104 under mild conditions in moderate to good yields with good functional group tolerance (Scheme 22) [100]. This reaction went through a selective C(sp3)–C(sp3) bond cleavage, C–H activation and C(sp3)–C(sp2) bond formation

• cyclopropanols and vinyl azides. Ag(I)-catalyzed oxidative ring-opening of cyclopropanols with quinones. Ag(I)-catalyzed oxidative ring-opening of cyclopropanols with heteroarenes. Cu(I)-catalyzed oxidative ring-opening/trifluoromethylation of cyclopropanols. Cu(I)-catalyzed oxidative ring-opening and

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• . Parallel to this, 4CzIPN was also used as an organoredox catalyst for the alkylation of heteroarenes [85], the oxidation of silicates [86], the alkylation of imines [87], the α-arylation/heteroarylation of 2-trifluoroboratochromanones [88]. In these different situations, comparisons with reference

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• ]. Direct C(sp2)–H bond carboxylation As described above, C–H carboxylations with CO2, particularly C(sp2)–H carboxylation reactions, have attracted much research interest. As a consequence, Nolan [57] and Hou [58] independently reported Cu-catalyzed carboxylations using heteroarenes as substrates, which