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

• electronic density provided by the nitrogen lone-pair, which plausibly stabilizes the cationic or radical species formed by the oxidant reagent during the aromatization process [46], as efficiently occurred with derivatives 9. Finally, in order to obtain the aromatic indole-based pentacycles 12, the

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

• strong single-electron oxidant, cerium(IV) ammonium nitrate, in methanol [38]. To record EPR spectra, a flow system was used, which allowed observation of radicals with lifetimes of about 10−2 s [39]. The EPR spectra of iminoxyl radicals are characterized by large values of the hyperfine splitting

• optimization of the reaction conditions Fe(ClO4)3 was chosen as the optimal oxidant for the synthesis of C–O cross-dehydrogenative coupling products 51 (Scheme 19). The extremely persistent diacetyliminoxyl radical (20) [44] was directly introduced into the reaction with pyrazolones 50 with the formation of

• using DTBP or aerial oxygen as an oxidant. Aliphatic, aromatic, and heteroaromatic amines 140, both primary and secondary, are applicable for this reaction. The reaction of TEMPO with β,γ- and γ,δ-unsaturated oximes 143 leads to substituted unsaturated isoxazolines 144 and cyclic nitrones 145

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

• quenching cycle, PC* acts as a reductant donating an electron to A. This generates the oxidized form of the photocatalyst, PC•+, and a reduced acceptor, A•−. Alternatively, in a reductive quenching cycle, PC* acts as an oxidant promoting an SET oxidation of the electron donor D. This leads to the reduced

• use of the strong oxidant Mes-Acr-Ph+ (OD3, E(PC+*/PC) ≈ 2 V) as organic photocatalyst leads to the oxidation/decarboxylation of the in situ-generated carboxylates (Eox ≈ 1.3 V). An organic disulfide cocatalyst, (PhS)2, activated by the reduced photocatalyst, was found to act as a co-base (PhS−) and a

• cyclic ethers 22.3. Mes-Acr-Me+ (OD2) is a strong enough oxidant (E(PC+*/PC) ≈ 2.1 V), allowing the oxidation of unactivated alkenes (1.2 ≤ Eox ≤ 1.9 V). In this transformation, the cocatalyst 22.2 acts as an H atom shuttle. This alkene radical cation-based strategy has been extended to various

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

• oxidant) as the selenium source under acidic conditions, and the substrate scope and limitations have not been clarified. Moreover, the syntheses of bis(2-arylimidazo[1,5-a]pyridin-3-yl) selenides and diselenides have recently been investigated using Cu-catalyzed reactions involving imidazo[1,5-a

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

• application in the synthesis of quinazolin-4-(3H)-ones by the one-pot reaction between alcohols and 2-aminobenzamide under an oxidative quenching, visible light irradiation using air or oxygen as oxidant (60–81% yields). The authors propose the generation of the superoxide radical anion with the MOF. The

Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties

• Liliia Moshniaha,
• Marika Żyła-Karwowska,
• Joanna Cybińska,
• Piotr J. Chmielewski,
• Ludovic Favereau and
• Marcin Stępień

Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81

• stoichiometric oxidant. The scope of such Pd(II)-induced couplings was further developed into tandem processes involving consecutive cyclization of substituents (dcTTEE) and oxygenation of pyrrolic α-positions to form lactams cNDA1O and cNMI1O. The mechanism of those transformations was subsequently explored

Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts

• David Schönbauer,
• Carlo Sambiagio,
• Timothy Noël and
• Michael Schnürch

Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74

• ], alkynation [17][18], or allylation [19]), this method has certain drawbacks, most importantly the frequent requirement of superstoichiometric amounts of an oxidant. Hence, alternative methods were investigated and photoredox catalysis proved to be a viable option [20][21][22]. By now, several different

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

• with AlCl3 reproducibly provided a pure terrylene [8]. Scholl reaction using a superacid catalyst in combination with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant provides a scalable preparation of quaterrylene [9], but unfortunately the low solubility prevents 1H NMR characterization

KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones

• Qiao Lin,
• Shiling Zhang and
• Bin Li

Beilstein J. Org. Chem. 2020, 16, 492–501, doi:10.3762/bjoc.16.44

• synthesis of β-nitrate ester carboxamides using tert-butyl nitrite as the nitro source and oxygen as the oxidant through the ring opening of 2-oxazolines [9] (Scheme 1a). Kappe reported a two-step continuous-flow synthesis of N-(2-aminoethyl)acylamides through ring opening/hydrogenation of oxazolines with

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• 2012, Collins and co-workers described a copper-catalyzed photocyclization to synthesize [5]helicene (Scheme 29) [43]. Using the in situ-formed [Cu(I)(dmp)(xantphos)]BF4 (25 mol %) in the presence of iodine and propylene oxide as the oxidant system under visible light irradiation, [5]helicene was

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• by the work of Yoon, Stephenson and MacMillan [11]. By selective excitation of an organic or organometallic dye by visible light a species is formed that can act as a single-electron oxidant and single-electron reductant. In this way reactive radical intermediates can be formed catalytically in situ

• , resulting in reactivity different from common two-electron pathways. Photoredox catalysis reactivity is very different from traditional redox reactions, and the same reactivity cannot be achieved by stoichiometric addition of both a reductant and an oxidant to a reaction mixture (as that would lead to a

• rapid redox reaction between the oxidant and the reducing agent instead of converting the substrate). Excitation of the photocatalyst, on the other hand, allows continuous formation of low concentrations of both oxidized and reduced radical forms of the substrate(s), and the excited catalysts (and/or

Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3’,2’-e]pyridines (BBZFPys)

• Ryo Takishima,
• Yuji Nishii,
• Tomoaki Hinoue,
• Yoshitane Imai and
• Masahiro Miura

Beilstein J. Org. Chem. 2020, 16, 325–336, doi:10.3762/bjoc.16.32

• unsymmetrically substituted pyridines 3a–c in high yields. We then examined the oxidative cyclization of these compounds under the standard conditions adopting Pd(TFA)2 (30 mol %, TFA = trifluoroacetate) and AgOAc (3.0 equiv) as catalyst and oxidant, respectively, in pivalic acid as solvent (Scheme 3). Since the

Copper-promoted/copper-catalyzed trifluoromethylselenolation reactions

• Clément Ghiazza and
• Anis Tlili

Beilstein J. Org. Chem. 2020, 16, 305–316, doi:10.3762/bjoc.16.30

• form C(sp)–SeCF3 bonds (Scheme 3) [18]. Therein, Dess–Martin periodinane (DMP) was used as the oxidant and potassium fluoride as the base, and the reactions were performed at room temperature in DMF as the solvent. The desired compounds were obtained in moderate to very good yields. Both electron

• and molecular oxygen as the oxidant, the substrates were successfully converted to the trifluoromethylselenylated analogs in good to very good yields. The substrate scope highlighted a broad functional group tolerance, including electron-withdrawing and -donating groups, heterocycles, and ferrocene

• already demonstrated its versatility in numerous processes. Nevertheless, its use in oxidative cross-coupling reactions requires stoichiometric amounts of the oxidant, which limits the attractiveness of the method in some cases. Finally, the newly developed electrophilic reagent TsSeCF3 also demonstrated

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• groundbreaking advancements were accomplished in this wonderful area of research, transforming a specific C–H bond effectively and selectively under favorable conditions (viz, room temperature, without external oxidant, cost-effective, sustainable, and environmentally friendly) still remains a highly challenging

• noteworthy renaissance not only because of the lower toxicity, stability, speed, and efficiency of the method, but also thanks to the easy generation of radical species and the formation of a long-lived triplet excited state under photoirradiation that can behave as a reductant as well as an oxidant [51][52

• metal catalysis, which include: (i) excellent regioselectivity of the targeted C–H bond formations thanks to favorable dissociation enthalpies and electronic properties as compared to other concurrent C–H bonds; (ii) avoidance of an extra oxidant because the reaction proceeds with overall redox

Synthesis of 4-(2-fluorophenyl)-7-methoxycoumarin: experimental and computational evidence for intramolecular and intermolecular C–F···H–C bonds

• Vuyisa Mzozoyana,
• Fanie R. van Heerden and
• Craig Grimmer

Beilstein J. Org. Chem. 2020, 16, 190–199, doi:10.3762/bjoc.16.22

• ], anti-oxidant [7], antibacterial [8], hepatoprotective, anticoagulant, antiviral and antithrombotic activities [9]. The variety of uses of these compounds resulted in an increase in demand for large quantities of coumarins. Due to an insufficient natural supply to meet this demand for these compounds

Synthesis of 3-alkenylindoles through regioselective C–H alkenylation of indoles by a ruthenium nanocatalyst

• Abhijit Paul,
• Debnath Chatterjee,
• Srirupa Banerjee and
• Somnath Yadav

Beilstein J. Org. Chem. 2020, 16, 140–148, doi:10.3762/bjoc.16.16

• -withdrawing groups, using Pd(OAc)2 as catalyst and Cu(OAc)2 as oxidant [25]. Since then, several variants of the reaction involving Pd catalysis and various oxidants have been reported for the synthesis of 3-alkenylindoles. For example, Chen et al. and Huang et al. independently reported the C3 alkenylation

• of indoles using Pd(OAc)2 and Pd(II)/polyoxometallate, respectively, as a catalyst and molecular oxygen as the oxidant [26][27]. Verma and co-workers used the reaction between indoles and alkenes in the presence of a Pd(OAc)2 catalyst, a Cu(OAc)2 oxidant, and a 2-(1-benzotriazolyl)pyridine ligand [28

• ]. Noël and co-workers reported the C3–H olefination of indoles using Pd(OAc)2 as a catalyst and molecular oxygen as the oxidant under continuous flow conditions [29]. Jia et al. reported the synthesis of 3-alkenylindoles using Pd(OAc)2 as the catalyst and MnO2 as the oxidant under ball milling conditions

Synthesis and optoelectronic properties of benzoquinone-based donor–acceptor compounds

• Daniel R. Sutherland,
• Nidhi Sharma,
• Georgina M. Rosair,
• Ifor D. W. Samuel,
• Ai-Lan Lee and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2019, 15, 2914–2921, doi:10.3762/bjoc.15.285

• temperature, it is also carried out in benign acetone as solvent and does not require any additional oxidant. It circumvents the additional prefunctionalization of the BQ step usually required for Pd cross-couplings [15], while also showing greater functional group tolerance than radical-based methods [16][17

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• developed an electrochemical approach for a Sharpless asymmetric dihydrohydroxylation of alkenes using an osmium complex [63]. In this protocol, the traditional chemical oxidant was replaced by an anode that regenerates [FeCN)6]3− via an Os(VIII) to Os(VI) interconversion. Similarly, Torri and co-workers

• oxidant required for this process was initially generated through anodic oxidation of aqueous Na2CO3 in an undivided cell under constant current electrolysis. A catalytic amount of chiral iminium salt 103 and olefinic substrate 71' were added to the same reaction mixture, and chiral epoxides 73' were

• obtained via oxidation by electrogenerated CO42− [73]. Moreover, they showed that electrogenerated persulfate generated in situ via a similar anodic oxidation of H2SO4 could act as an even better oxidant in presence of catalyst 103 to achieve the epoxidation of 71'c with higher ee values (Scheme 36). In

Formation of alkyne-bridged ferrocenophanes using ring-closing alkyne metathesis on 1,1’-diacetylenic ferrocenes

• Celine Bittner,
• Dirk Bockfeld and
• Matthias Tamm

Beilstein J. Org. Chem. 2019, 15, 2534–2543, doi:10.3762/bjoc.15.246

• behaviour can be ascribed to the fact that Ag(SbF6) acts as a stronger oxidant in DCM compared to THF solution [98]. Well-defined catalysts for alkyne metathesis. Examples for a ferrrocenic thiacrown ether complexing palladium (IV), and a dicationic ferrocenophane (V) featuring a diyne bridge for ion

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• (H2O2/NaOH) proceeded with the low yield (32%). Application of m-chloroperbenzoic acid (mCPBA) as an oxidant, similarly to Knochels findings [19], gave the higher yield (56%) of (((1R,2R,3R,4R,5R)-4-hydroxypinan-3-yl)methyl)diphenylphosphine oxide (22). Next, phosphine oxide 22 was reduced to the

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

• Eric W. Webb,
• Jonathan P. Moerdyk,
• Kyndra B. Sluiter,
• Benjamin J. Pollock,
• Amy L. Speelman,
• Eugene J. Lynch,
• William F. Polik and
• Jason G. Gillmore

Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240

• 2b. The addition of benzoquinone (a chemical oxidant) to the electrochemically reduced solution under argon gave similar results, consistent with our hypothesis. When the yellow solution remained open to the atmosphere during electrolysis, the initially yellow solution turned green at first

• reduction potential between PSHD and QSHD for eLW was much less. For 5b Eored was 28 mV more positive than 2b indicating that 5b is a slightly better oxidant than the parent PSHD. But Eored of eLW 5a was surprisingly shifted 10 mV more negative than PSHD LW 2a, meaning it was actually harder to oxidize

• chemical oxidant (benzoquinone) added to complete the reduction of the dianion to the LW isomer. NMR spectroscopy was performed on samples 5 mm NMR tubes (Wilmad) made of clear quartz (photolyzed samples) or amber pyrex (dark samples) on a Varian Mercury or Bruker AvanceIII 400 MHz NMR. 1H NMR experiments

Combining the Ugi-azide multicomponent reaction and rhodium(III)-catalyzed annulation for the synthesis of tetrazole-isoquinolone/pyridone hybrids

• Gerardo M. Ojeda,
• Prabhat Ranjan,
• Pavel Fedoseev,
• Lisandra Amable,
• Upendra K. Sharma,
• Daniel G. Rivera and
• Erik V. Van der Eycken

Beilstein J. Org. Chem. 2019, 15, 2447–2457, doi:10.3762/bjoc.15.237

• the relatively cheap complex (p-cymene)ruthenium(II) chloride dimer, in the presence of copper(II) acetate as oxidant under conventional heating. Despite all effort put in this attempt, the isolated yields were in the range of 14–62%, with the highest yield achieved after 24 h of reaction using 10 mol

• efficiently. The use of the nonhygroscopic and cheaper sodium acetate decreased the yield (Table 1, entry 5), whereas the absence of the acetate salt additive led to a very low reaction yield (Table 1, entry 6). Neither removal of the oxidant (Table 1, entry 7) nor further modification of the reaction

Current understanding and biotechnological application of the bacterial diterpene synthase CotB2

• Ronja Driller,
• Daniel Garbe,
• Norbert Mehlmer,
• Monika Fuchs,
• Keren Raz,
• Dan Thomas Major,
• Thomas Brück and
• Bernhard Loll

Beilstein J. Org. Chem. 2019, 15, 2355–2368, doi:10.3762/bjoc.15.228

• [1][2][3]. Sesqui- and diterpenes are a diverse class of secondary metabolites derived predominantly from plants, marine invertebrates, fungi and some prokaryotes [4][5][6][7][8]. Properties of these natural products include antitumor, anti-oxidant, anti-inflammatory, antiviral, antimalarial

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

• fluoride source and PhI(OPiv)2 as a hypervalent iodine oxidant (Scheme 8). Very recently, they [44] optimized this transformation and achieved the benzylic C–H radiofluorination with no-carrier-added Ag[18F]F. This method was applied to the radiolabeling of diversely substituted 8-methylquinoline

• –H fluorination of benzaldehydes. Notably, these transformations were achieved with orthanilic acids as new transient directing groups (TDGs) in DCE in the presence of air (Scheme 23). This approach employed 1-fluoro-2,4,6-trimethylpyridinium salts as a bystanding F+ oxidant or an electrophilic

• catalyst, AgF as fluoride source, NMO as oxidant, and DMF as solvent, they achieved the selective mono- or difluorination in high yields (Scheme 34). Notably, pyridine as an additive could prevent the decomposition of an amide substrate in a long-time reaction. Meanwhile, the group of Sanford [79

Characterization of two new degradation products of atorvastatin calcium formed upon treatment with strong acids

• Jürgen Krauß,
• Monika Klimt,
• Markus Luber,
• Peter Mayer and
• Franz Bracher

Beilstein J. Org. Chem. 2019, 15, 2085–2091, doi:10.3762/bjoc.15.206

• experiments” the drug is submitted to more drastic conditions (e.g., strong acid or base, strong oxidant, very high temperature), and potential degradation products can be identified in very short time [2][3]. However, forced degradation experiments are highly artificial in nature, and thus one has to keep in