Design, synthesis and application of carbazole macrocycles in anion sensors

• Alo Rüütel,
• Ville Yrjänä,
• Sandip A. Kadam,
• Indrek Saar,
• Mihkel Ilisson,
• Astrid Darnell,
• Kristjan Haav,
• Tõiv Haljasorg,
• Lauri Toom,
• Johan Bobacka and
• Ivo Leito

Beilstein J. Org. Chem. 2020, 16, 1901–1914, doi:10.3762/bjoc.16.157

• reference [6]. It is worth noting that the described cleavage problem during nitration was specific to tert-butyl groups. We also studied the possibility of hexyl substituents instead of tert-butyl groups [25]. In this case, the nitration process yielded only the desired product. However, since this

On the hydrolysis of diethyl 2-(perfluorophenyl)malonate

• Ilya V. Taydakov and
• Mikhail A. Kiskin

Beilstein J. Org. Chem. 2020, 16, 1863–1868, doi:10.3762/bjoc.16.153

• of diethyl 2-(perfluorophenyl)malonate, acid-catalyzed reactions were also tested. Trifluoroacetic acid (TFA) is a common reagent for the catalytic cleavage of tert-butyl esters, but in the stoichiometric quantity it is also suitable for the cleavage of nonvolatile methyl or ethyl esters due to

Synthesis, docking study and biological evaluation of ᴅ-fructofuranosyl and ᴅ-tagatofuranosyl sulfones as potential inhibitors of the mycobacterial galactan synthesis targeting the galactofuranosyltransferase GlfT2

• Marek Baráth,
• Jana Jakubčinová,
• Zuzana Konyariková,
• Stanislav Kozmon,
• Katarína Mikušová and
• Maroš Bella

Beilstein J. Org. Chem. 2020, 16, 1853–1862, doi:10.3762/bjoc.16.152

• % and 54% yield, respectively. Moderate yields of 2-thio-ᴅ-tagatofuranosides 17 can be explained by cleavage of the benzyl protecting group [21] as well as further side reactions (Scheme 4). In order to increase the yield of 2-thio-ᴅ-tagatofuranosides 17, compound 12 was converted to the more reactive

• diacetate 18 under acetolysis conditions (Ac2O/BF3∙OEt2) [22]. However, besides the expected diacetate 18, 1,2,6-tri-O-acetate 19 was observed and isolated as a byproduct (Scheme 4). The cleavage of the O-benzyl ethers followed by acetylation of the liberated hydroxy groups under acidic conditions was

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

• reaction of CSI with epoxides in different solvents under mild conditions and compared the reaction mechanism with previously proposed mechanisms using theoretical calculations. Keshava Murthy and Dhar [41] postulated a mechanism involving a zwitterionic intermediate. C–O bond cleavage in this unstable and

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• the C–H cleavage step slightly, yet significantly absorbed light in the relevant blue region. This absorption was believed to trigger the overall catalytic cycle at room temperature as no product formation was observed in the dark. The mechanistic scenario thus foresees an initial pyridine-directed

Et₃N/DMSO-supported one-pot synthesis of highly fluorescent β-carboline-linked benzothiophenones via sulfur insertion and estimation of the photophysical properties

• Dharmender Singh,
• Vipin Kumar and
• Virender Singh

Beilstein J. Org. Chem. 2020, 16, 1740–1753, doi:10.3762/bjoc.16.146

• addition of the trisulfur radical anion to the double bond in 2-nitrochalcone (1bA) may yield the intermediate 7. The further abstraction of hydrogen in intermediate 7 may result in formation of intermediate 8. The cleavage of the S–S bond in 8 under basic conditions may generate sulfur anion 9. The

Synthesis of Streptococcus pneumoniae serotype 9V oligosaccharide antigens

• Sharavathi G. Parameswarappa,
• Claney L. Pereira and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2020, 16, 1693–1699, doi:10.3762/bjoc.16.140

• mannosamine was obtained from 33, that in turn was a product of the benzylation of 32. Cleavage of the benzylidene group in 33 yielded 34 that was selectively acetylated at the primary alcohol at low temperature to obtain 35 [30]. The subsequent removal of the benzyl groups using hydrogenation with Pd/C in an

A dynamic combinatorial library for biomimetic recognition of dipeptides in water

• Florian Klepel and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2020, 16, 1588–1595, doi:10.3762/bjoc.16.131

• SPPS. Thus one cysteine moiety is left deprotected and can be addressed selectively either by dimerization with another CFC(Acm) or with inversely substituted tripeptide (C(Acm)FC). These linear peptide dimers were subsequently cyclized by oxidative cleavage of the Acm groups to give a(CFC)2 and p(CFC

Photoredox-catalyzed silyldifluoromethylation of silyl enol ethers

• Vyacheslav I. Supranovich,
• Vitalij V. Levin and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2020, 16, 1550–1553, doi:10.3762/bjoc.16.126

• )trimethylsilane followed by a reduction of the primary products with sodium borohydride is described. An 18 W, 375 nm LED was used as the light source. The reaction is performed in the presence of a gold photocatalyst, which effects the generation of a (trimethylsilyl)difluoromethyl radical via cleavage of the

• carbon-based radical via cleavage of the carbon–bromine bond by a gold photocatalyst. Reaction of silyl enol ethers. Yields refer to isolated yields. aReaction time 24 h; b1.0 equiv of silane 1 was used; cketone was isolated. Reactions of (bromodifluoromethyl)trimethylsilane (1). Optimization studies

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

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

• Alessandra Del Tito,
• Havall Othman Abdulla,
• Davide Ravelli,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

• conditions finally afforded the desired phenanthridine 8.7 in 90% yield [69]. Carbon-based radicals could be likewise generated via a C–H hydrogen-atom transfer path. As an example, ethers were used as hydrogen donors and underwent a C–H cleavage step promoted by a photogenerated tert-butoxyl radical. The so

• preparation of phenanthridines with the intermediacy of imidoyl radicals. As an example, the process depicted in Scheme 10 involved a visible-light homolytic radical aromatic substitution (HAS) starting from trifluoroacetimidoyl chlorides 10.1a–e. Thus, the photocatalyzed cleavage of the C(sp2)–Cl bond in

• photocatalyzed reduction of acyloximes 14.1a,b offered a smooth entry to iminyl radicals (Scheme 14) [76]. The process took place at room temperature and involved the cleavage of a C–O bond, followed by a cyclization to give access to the benzo[c]phenanthridine alkaloids noravicine (14.2a) and nornitidine (14.2b

In silico rationalisation of selectivity and reactivity in Pd-catalysed C–H activation reactions

• Liwei Cao,
• Mikhail Kabeshov,
• Steven V. Ley and
• Alexei A. Lapkin

Beilstein J. Org. Chem. 2020, 16, 1465–1475, doi:10.3762/bjoc.16.122

• -addition, respectively [15]. Even though the mechanisms are inherently different, three most important aspects should be primarily taken into account when classifying and rationalising C–H activation reactions: the proximity of C–H bond to the transition metal; the energy of C–H bond cleavage within the

• feature of the proton abstraction (PA) mechanism [25] is that the formation of the metal–carbon bond (M–C) occurs simultaneously with the cleavage of the carbon–hydrogen (C–H) bond, while the hydrogen is being transferred to a basic centre, Scheme 1. Assuming the reaction proceeds through the formation of

The McKenna reaction – avoiding side reactions in phosphonate deprotection

• Katarzyna Justyna,
• Joanna Małolepsza,
• Damian Kusy,
• Waldemar Maniukiewicz and
• Katarzyna M. Błażewska

Beilstein J. Org. Chem. 2020, 16, 1436–1446, doi:10.3762/bjoc.16.119

• reagent of choice for phosphonate ester cleavage, compared with its more and less reactive analogs, iodotrimethylsilane (ITMS) [11][12] and chlorotrimethylsilane (CTMS) [13], respectively. While being one of the most popular methods for the deprotection of organophosphorus esters, the McKenna reaction may

• be accompanied by side reactions such as the cleavage of tert-butyl carboxyester, [14][15] or other ester groups [16], as well as the formation of decomposition products [17][18][19][20]. Instead of focusing only on the experiments that “did work”, we decided to follow an alternative strategy

• reaction with BTMS, and underwent exchange of the chlorine substituent for bromine. This reaction can be partially circumvented by using nonpolar solvents, amines and lower temperatures. Section 5: Cleavage of the tert-butyl carboxyester group BTMS is known for its chemoselectivity and cleaves phosphonate

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• , cyclopentanone, and three carbon ring-expanded 1,3-diones from vinyl spiro epoxides [14]. The reaction is initiated by the addition of a thiyl radical to the vinyl epoxide 24, followed by the epoxide fragmentation to the alkoxy radical 25. Then, the β-cleavage to form the carbon-centered radical 26, the final

• by the excitation with visible light, the homolytic cleavage of disulfide generates an arylthiyl radical (ArS•), which adds to diphenylacetylene to form a free-radical intermediate 28. Subsequently, this intermediate traps a molecule of singlet oxygen (1O2), and the thiyl radical is regenerated to

• give the four-membered ring intermediate 29. Finally, the rearrangement of the four-membered intermediate provides the diketone 30 as the product (Scheme 8). In 2017, Wang and co-workers reported an oxidative cleavage of aromatic alkenes at ambient temperature with visible-light irradiation, using

Synthesis of new fluorescent molecules having an aggregation-induced emission property derived from 4-fluoroisoxazoles

• Kazuyuki Sato,
• Akira Kawasaki,
• Yukiko Karuo,
• Atsushi Tarui,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2020, 16, 1411–1417, doi:10.3762/bjoc.16.117

• diketone (Scheme 5). As an alternative method to synthesize F-BKIs 9, we turned our attention to the ring-opening reaction of isoxazoles. The reductive cleavage of the N–O bond in isoxazoles can be achieved by transition metals or their complexes to give the corresponding enaminoketones [35][37

• in the aggregated state and exhibited a redshift in the emission intensity. We also achieved the first synthesis of α-fluorinated boron ketoiminates (F-BKIs) by the reductive cleavage of the N–O bond in 4-fluorinated isoxazoles and demonstrated that F-BKIs exhibited AIE property similarly to their

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• second displacement was an intramolecular SN2 process performed under mild basic conditions, affording the desired thietane 116 in 92% yield. After deprotection, oxidative cleavage, and reduction, a thietanose 117 was obtained in 63% overall yield. The thietanose 117 was further applied to synthesize a

• cleavage and aromatization to give substituted pyridines 255 [75] (Scheme 49). In 1989, Kanaoka and co-workers further studied the photo [2 + 2] cycloadditions of thiobarbiturates 256–258, whose skeletons consisted of a combination of a thioamide and an amide or a thioamide (two-imides system), and olefins

• were obtained via a ring cleavage of the thietanes, that had formed in the [2 + 2] photocycloaddition of the thiocarbonyl moiety and the olefin. However, the reaction of 1,3,3-trimethylindoline-2-thione (300) and isobutene (215c) afforded the corresponding spiroindoline-thietane derivative 301 [80

Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration–oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles

• Lívia Dikošová,
• Júlia Laceková,
• Ondrej Záborský and
• Róbert Fischer

Beilstein J. Org. Chem. 2020, 16, 1313–1319, doi:10.3762/bjoc.16.112

• readily obtained through the reductive cleavage of benzoylated isoxazolidines, employing the Lewis acid-catalyzed SN reaction with triethylsilane as the hydride source (Scheme 1). For this reason, the benzoates 6a and 6b were readily prepared from the corresponding 2,3-dihydroisoxazoles 5a and 5b

• showed the applicability of the reductive cleavage of anomeric isoxazolidinyl carboxylates in the synthesis of the respective 5-unsubstituted 4-hydroxyisoxazolidines, this pioneering approach mainly suffered from a large number of synthetic steps starting from 2,3-dihydroisoxazoles, leading to the target

• 8b resulted only in a reductive cleavage of the N–O bond. A successful debenzylation was achieved in a two-step procedure using 2,2,2-trichloroethyl chloroformate (TrocCl). However, the protection of the hydroxy group was required first (for the reaction of 8b with benzoyl chloride, see Supporting

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

• reactions of oxime radicals. These reactions are classified into cyclizations involving C–H bond cleavage and cyclizations involving a double C=C bond cleavage. Keywords: iminoxyl radicals; isoxazolines; oxidative cyclization; oxime radicals; oximes; Introduction Free radicals in which an unpaired

• abstraction with cleavage of the C–H bond [12][13][14][15][16][17][18] and in the processes of functionalization of С=С double bonds [19][20]. Amidoxyl radicals (Figure 1, III) are applied in the functionalization of the double bonds [21][22][23][24][25][26] and in mild oxidations [27]. In contrast to the

• hardly achievable or not achievable by non-radical methods. In this review only works in which the participation of iminoxyl radicals was confirmed or assumed are discussed. Oxidative cyclization with the cleavage of the C–H bond In one of the first works in this area oximes with activated C–H bond in

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

• heteroarene 6.3. Other reductive fragmentations Another organophotocatalytic strategy for accessing C(sp3) radicals relies on the reductive homolytic cleavage of easily reducible functional groups. In this case, the substrates can act as acceptors in SET reductions, and the alkyl radical is obtained after the

• cleavage of various benzyl halides 7.1 (I, Br, Cl). The radical is then intercepted by an H atom donor (Hantzsch ester), which delivers the corresponding toluene derivative 7.2. Other organic dyes can promote the reductive fragmentation of alkyl halides. For instance, König and Zeitler demonstrated that a

• Photocatalytic hydrogen atom transfer (HAT) represents a valuable strategy for accessing C(sp3) radicals. This method allows the direct cleavage of a C–H bond and the consequent generation of alkyl radicals without relying on the presence of redox-active functional groups. This results in a superior atom economy

A smart deoxyribozyme-based fluorescent sensor for in vitro detection of androgen receptor mRNA

• Ekaterina A. Bryushkova,
• Erik R. Gandalipov and
• Julia V. Nuzhina

Beilstein J. Org. Chem. 2020, 16, 1135–1141, doi:10.3762/bjoc.16.100

• diagnosis. Keywords: androgen receptor; 10–23 deoxyribozyme; nucleic acid sensor; malachite green aptamer; RNA cleavage; Introduction The fast and precise diagnostics of diseases are one of the key factors that allow choosing the most effective method of treatment. Disease markers can be found at a few

• assembling was evaluated using agarose gel electrophoresis (Figure 1E). The single band proved that in the chosen conditions there was a complete hybridization of all 5 strands into an integrated SDFS complex. After hybridization between SDFS and 60-AR_RNA we expected to see a specific cleavage of target

• -nt fragment has steric and thermodynamic benefits to interact with MGA compared to 60-AR_RNA, or especially full-length AR mRNA. Due to the close proximity of “GU” cleavage sites in the selected 60-AR_RNA fragment, we decided to use asymmetric Dz1 design with an extremely short left RNA-binding part

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• . Thus, a three-component condensation of a series of fluorinated benzaldehydes 50a–h, N-acetyl- or N-benzoylglycine 51a or 51b, respectively, and an excess of acetic anhydride in the presence of sodium acetate afforded the oxazolones 52a–h. The subsequent reductive ring cleavage of 52a–h without

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

• energies, as for example the thiaporphyrins that absorb beyond 650 nm [8][28]. Derksen and co-workers studied bond-cleavage reactions that can occur in biological microenvironments, using a light source with wavelengths frequently employed in photomedicine (650–850 nm) and thiophene-containing porphyrins

• platform for dual catalysis due to their ability to promote both metallocatalysis and photocatalysis in a one-pot system [36][37][38][39]. Martin and co-workers carried out the C–O bond cleavage of alcohols using a cobalt porphyrin under visible light irradiation and a carbon monoxide atmosphere (Scheme 11

• ) [36]. The authors hypothesized that the C–O bond cleavage could be achieved via cobalt-mediated alcohol carbonylation followed by radical decarboxylation of the alkoxycarbonyl intermediate. In a proof-of-concept study, they proceeded with the carbonylation of 1-phenylethanol using Co(II) tetrakis(4

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

• Phil M. Pithan,
• Sören Steup and
• Heiko Ihmels

Beilstein J. Org. Chem. 2020, 16, 904–916, doi:10.3762/bjoc.16.82

• photoreaction [12][15][16]. The photochromism is based on a reversible electrocyclic reaction that proceeds through the UV light-induced cleavage of the C2’–O bond of the closed, colorless form to give the colored, metastable merocyanine form, whereas the back reaction can be initiated thermally or by the

Synthesis of new asparagine-based glycopeptides for future scanning tunneling microscopy investigations

• Laura Sršan and
• Thomas Ziegler

Beilstein J. Org. Chem. 2020, 16, 888–894, doi:10.3762/bjoc.16.80

• significantly higher yield than HBTU. The Fmoc cleavage of the compounds 3–5 was performed with piperidine in DMF (20 vol %) [36]. The reaction products were not isolated and purified but instead immediately used for the succeeding peptide coupling step to give the dipeptides 4 and 5 from the glycosylated

• showed that the use of HATU reduced the reaction times but did not always result in higher yields, as anticipated from the literature. A simple cleavage protocol that did not necessitate any further purification step allowed for the preparation of the unprotected glycopeptides in solution. The

• investigation of the self assembly of such glycopeptides on metal surfaces will be performed via pMS and STM in further studies. Description of the starting materials 1a–f and 2a–f. Peptide coupling reactions, including the previous Fmoc cleavage. Cleavage of the fully protected peptides 6 and 7. Yields of the

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

• household 23 W compact fluorescent light (CFL) bulb at ambient temperature [55]. A base, 2,6-lutidine, was used to neutralize traces of HX (X = halogen), which formed by the homolytic cleavage of the C–X bond of the haloalkanes 93 (Scheme 24). Among the aldehydes tested, benzaldehyde (8) and 4

• -anisaldehyde (98), which possessed a relatively long lifetime and an energetic value sufficient for C–X bond cleavage. The participation of the triplet state 4-anisaldehyde (98) in the reaction mechanism was also confirmed by the complete inhibition of the ATRA reaction in the presence of oxygen, a triplet

• homolytic cleavage of the C–S bond, providing the sulfonyl radical 186. The sulfonyl radical 186 can then approach anti to the oxazolidinone moiety in 180, generating a β-sulfonyl radical 187, which, once trapped by another sulfonyl cyanide molecule 181, affords the desired product 182, and the sulfonyl