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

• source of hydrogen [21]. We thought that silane 1 could couple with silyl enol ethers in the presence of a photocatalyst affording fluoroalkylation products. Indeed, silyl enol ethers were found to be good acceptors of fluorinated radicals, and the resultant silyloxy-substituted radicals underwent single

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

• decomposition [69][70], these species are straightforward to synthesize and can be easily reduced (Ered ≈ −0.1 V to −0.3 V) [71][72]. This makes them valuable electron acceptors for photocatalytic strategies. The SET reduction results in the generation of an aryl radical upon the irreversible loss of N2 as the

• acceptors 18.2 to afford the desired ketone 18.3. Recently, the Melchiorre group reported a carbamoyl radical-mediated metallaphotoredox synthesis of arylamides (Scheme 19) [91]. In this protocol, excited-state 4CzIPN (OD6) oxidizes a 4-carbamoyl-1,4-dihydropyridine 19.1, which then fragments, releasing the

Copper-catalysed alkylation of heterocyclic acceptors with organometallic reagents

• Yafei Guo and
• Syuzanna R. Harutyunyan

Beilstein J. Org. Chem. 2020, 16, 1006–1021, doi:10.3762/bjoc.16.90

• the synthesis of complex molecules with single or multiple stereogenic centres over the past decades. Among the various acceptors employed in such reactions, those with a heterocyclic core are of particular importance because of the frequent occurrence of heterocyclic scaffolds in the structures of

• chiral natural products and bioactive molecules. Hence, this review focuses on the progress made over the past 20 years for heterocyclic acceptors. Keywords: conjugate addition; copper catalysis; heterocyclic Michael acceptor; organometallics; Introduction The copper-catalysed asymmetric addition of

• organometallic reagents to various acceptors is a useful strategy for C–C bond-forming reactions [1][2][3][4]. These important transformations have been thoroughly developed in the last few decades and were widely used in the synthesis of chiral natural products and bioactive molecules [5][6][7][8]. The majority

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

• -step electron transfer from the merocyanine to the metal cations, which acted as electron acceptors. Similarly, Malatesta et al. found that the thermal dark reaction of spironaphthoxazines in the presence of a suitable electron acceptor, such as 7,7,8,8-tetracyanoquinodimethane, gave the corresponding

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

• hydroacylation of Michael acceptors under irradiation with 80 W household bulbs [59]. 4-Cyanobenzaldehyde (53) exhibited the highest yield (86%) among 25 substituted benzaldehydes in the reaction between diethyl maleate (154) and octanal (155) (Scheme 36). During the optimization, different solvents, catalyst

• for the formation of the α,α-disubstituted aldehydes. Substrate scope for the photochemical addition of aldehydes to Michael acceptors. Proposed mechanism for the hydroacylation of Michael acceptors using 4-cyanobenzaldehyde (53) as the photoinitiator. Catalytic arylation of aromatic aldehydes by aryl

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• decade later, Molander et al. made use of the same disilane as a source of the nucleophile for additions to α,β-unsaturated alkenes and alkynes as Michael acceptors bearing sulfones, nitriles, cyano, amido, and carboxyl ester groups to form β-silylated alkanes and alkenes in good to moderate yields [55

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• imaging applications. This would definitively decrease the efficiency of electron back transfer. Nowadays, typical electron acceptors (AC) applied in such systems related to either iodonium salts or triazines also possess a high capability of electron back transfer resulting in a decrease of the overall

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

• Delphine Pichon,
• Jennifer Morvan,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2020, 16, 212–232, doi:10.3762/bjoc.16.24

• nucleophiles to electron-deficient alkenes (Michael acceptors) represents an efficient and attractive methodology for providing a wide range of relevant chiral molecules. In order to increase the attractiveness of this useful catalytic transformation, some Michael acceptors bearing challenging electron

• reagents to these challenging Michael acceptors, with excellent regio- and enantioselectivity. Furthermore, thanks to their easy derivatization, the resulting chiral conjugated products could be converted into various natural products. The aim of this tutorial review is to summarize recent advances

• (Michael acceptors) is one of the most relevant and versatile methods to achieve this goal [1][2][3][4]. Among the plethora of metals studied, copper-based catalytic systems proved to be highly efficient for the conjugate addition of various organometallic reagents, such as diorganozinc, triorganoaluminium

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

• activity of a molecule. Oxygen and nitrogen have been proven to be good hydrogen-bond acceptors which form strong intermolecular and intramolecular hydrogen bonds, however, fluorine is still denied hydrogen-bond acceptor status by some scientists. There is evidence of the existence of C–F···H interaction

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• (in ortho-position to the key south ring methoxy group) has been replaced by a synthetically more accessible hydroxy group (delivered via demethylation of a trimethoxy precursor through BBr3). The hydroxy and amino groups have similar size and polarity, and can both act as H-bond donors or acceptors

Halogen-bonding-induced diverse aggregation of 4,5-diiodo-1,2,3-triazolium salts with different anions

• Xingyu Xu,
• Shiqing Huang,
• Zengyu Zhang,
• Lei Cao and
• Xiaoyu Yan

Beilstein J. Org. Chem. 2020, 16, 78–87, doi:10.3762/bjoc.16.10

• ], diiodoacetylene [15] and iodo/bromoethynyl moieties [16] have revealed that the XB-donors interacting with XB-acceptors (a nucleophilic region) are in approximately linear orientation. Besides, linearity, tunability and hydrophobicity (features of the XB ) are widely applied in crystal engineering, supramolecular

• halogen acceptors was also investigated. Diffusion of ether into the mixture of 4,4'-bipyridine (bpy) and 2-BF4 in dichloromethane leads to the crystallization of 2-BF4·0.5bpy (Figure 8). It crystallizes in the monoclinic space group P21/c. The acceptor 4,4'-bipyridine provides a complementary link for 1D

SnCl₄-catalyzed solvent-free acetolysis of 2,7-anhydrosialic acid derivatives

• Kesatebrhan Haile Asressu and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2019, 15, 2990–2999, doi:10.3762/bjoc.15.295

• synthetic applications of 2,7-anhydro-Neu5Ac are available in the literature. Previously, we successfully constructed the fucosyl α(1→4) to Neu5Ac linkage of ganglioside HPG-7 using 2,7-anhydro-Neu5Ac derivatives as acceptors [6]. For utilization as selective sialidase inhibitors, Chen’s and Juge’s groups

Regioselectivity of glycosylation reactions of galactose acceptors: an experimental and theoretical study

• Enrique A. Del Vigo,
• Carlos A. Stortz and
• Carla Marino

Beilstein J. Org. Chem. 2019, 15, 2982–2989, doi:10.3762/bjoc.15.294

• analyzed the relative reactivity of the OH-3 and OH-4 groups of 2,6-diprotected methyl α- and β-galactopyranoside derivatives in glycosylation reactions. The glycosyl acceptors were efficiently prepared by simple methodologies, and glycosyl donors with different reactivities were assessed. High

• some of the acceptors. However, the Galp-(β1→3)-Galp linkage could be regioselectively installed by using some of the acceptors assayed herein. Keywords: Fukui indexes; galactopyranosyl acceptors; galactose donors; molecular modeling; regioselectivity; Introduction Given the importance of

• . Regioselectivity responds to multiple steric and electronic factors present in both the glycosyl donor and acceptor, and they are characteristic for each particular sugar. Although relative reactivity values have been established for glycosyl donors, it has not been possible to do the same for glycosyl acceptors

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

• diastereoselective Michael addition reactions [103][104]. The glycine–nickel complex 184 was deprotonated using a radical anion generated from the electrochemical reduction of azobenzene. The anionic Ni complex 185 acted as a good C-nucleophile towards Michael acceptors 186 resulting in diastereoisomeric mixtures of

1,5-Phosphonium betaines from N-triflylpropiolamides, triphenylphosphane, and active methylene compounds

• Vito A. Fiore,
• Chiara Freisler and
• Gerhard Maas

Beilstein J. Org. Chem. 2019, 15, 2603–2611, doi:10.3762/bjoc.15.253

• the reaction course, because analogous three-component reactions using propiolic acid esters as Michael acceptors are known to furnish another type of betaines in which the ester group (COOR) is retained. Questions on some mechanistic details, in particular at which stage of the reaction sequence the

Small anion-assisted electrochemical potential splitting in a new series of bistriarylamine derivatives: organic mixed valency across a urea bridge and zwitterionization

• Keishiro Tahara,
• Tetsufumi Nakakita,
• Alyona A. Starikova,
• Takashi Ikeda,
• Masaaki Abe and
• Jun-ichi Kikuchi

Beilstein J. Org. Chem. 2019, 15, 2277–2286, doi:10.3762/bjoc.15.220

• promising trigger to directly change the charge distributions of molecules and assemblies, potentially allowing tuning of the strength of non-covalent interactions, including hydrogen bonds (H-bonds) [23][24][25][26]. In this context, a number of redox-active compounds bearing H-bond donors and acceptors

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• efficient hydrogen-bond acceptors for the secondary dialkylammonium (in acid circumstances) or as binding units for NDI by the π-donor/π-acceptor interaction, which is signalled by a color change. 4.2. pH-sensitive double-lasso molecular machine The synthesis of various rotaxane molecular machines and

Fluorinated azobenzenes as supramolecular halogen-bonding building blocks

• Esther Nieland,
• Oliver Weingart and
• Bernd M. Schmidt

Beilstein J. Org. Chem. 2019, 15, 2013–2019, doi:10.3762/bjoc.15.197

• building blocks both in solution and in the solid state in combination with neutral halogen bonding acceptors, such as lutidines. Therefore, we investigate the photochemistry of a series of azobenzene photoswitches. Upon introduction of iodoethynyl groups, the halogen bonding donor properties are

• ) and E-4,4’-di(iodoethynyl)perfluoroazobenzene (A3) halogen bond donors can be combined with rigid u-shaped anthracene building blocks, bearing two 3,5-lutidine acceptors in 1 and 8 positions, to form self-assembled boxes of 25–30 Å length in solution and in the solid state [35]. We chose azobenzene

• , connected by C–H···F contacts. The azobenzenes A2 interact by lamellar 2D π-stacking, anthracene U1 interact predominantly by C–H···π interactions as both the solubilizing mesitylene group and the two perpendicular lutidine acceptors effectively prevent stacking of the anthracenes body (Supporting

Isolation and characterisation of irinans, androstane-type withanolides from Physalis peruviana L.

• Annika Stein,
• Dave Compera,
• Bianka Karge,
• Mark Brönstrup and
• Jakob Franke

Beilstein J. Org. Chem. 2019, 15, 2003–2012, doi:10.3762/bjoc.15.196

• (Table 1). Both showed two multiplets in the olefinic region, which are highly characteristic for withanolides with A-ring Michael acceptors. However, compared to other withanolides, several signals were missing. Typically, withanolides show five singlets for methyl groups in the aliphatic region, as

Vicinal difunctionalization of alkenes by four-component radical cascade reaction of xanthogenates, alkenes, CO, and sulfonyl oxime ethers

• Shuhei Sumino,
• Takahide Fukuyama,
• Mika Sasano,
• Ilhyong Ryu,
• Antoine Jacquet,
• Frédéric Robert and
• Yannick Landais

Beilstein J. Org. Chem. 2019, 15, 1822–1828, doi:10.3762/bjoc.15.176

• /acceptor type C1 synthons [6][7][8][9][10][11][12][13][14][15]. In this context, sulfonyl oxime ethers are powerful acceptors of type C1 synthon [8][16][17], which terminates the multicomponent reaction by a β-scission of RSO2 radicals [18][19][20]. Recently, one of us reported on a three-component radical

Molecular basis for the plasticity of aromatic prenyltransferases in hapalindole biosynthesis

• Takayoshi Awakawa and
• Ikuro Abe

Beilstein J. Org. Chem. 2019, 15, 1545–1551, doi:10.3762/bjoc.15.157

• ; prenyltransferase; Introduction Aromatic prenyltransferases (PTases) catalyze Friedel–Crafts reactions between aromatic prenyl acceptors and isoprenoid diphosphate prenyl donors to construct C–C, C–O, or C–N bonds, which enrich the structural diversity of aromatic natural products [1][2]. Their reactions are

• (DMATS)-type [6][7], and the membrane-bound type PTases [8][9]. Some of them exhibit broad substrate specificities and accept various aromatic compounds as prenyl acceptors. For example, NphB (also called Orf-2), the first reported ABBA-type PTase in naphtherpin biosynthesis, accepts several aromatic

• compounds, including dihydroxynaphthalenes, flavonoids, and resorcinols as prenyl acceptors, and C10 geranyl diphosphate (GPP) as a prenyl donor, to generate a variety of O- or C-prenylated aromatic compounds [4][10]. Some PTases accept multiple lengths of isoprenoid diphosphates, as exemplified by the ABBA

2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes

• Li-Li Wang,
• Yi-Kuan Tu,
• Huan Yao and
• Wei Jiang

Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146

• hydrogen bonds to recognize guests with hydrogen-bonding acceptors. Precious metal chloride complexes were found to be complexed by 1. Obvious chemical shifts in the 1H NMR spectra (Figure 3) were observed for H6 and amide NH protons when adding one equivalent of the tetrabutylammonium (TBA+) salt of AuCl4

Synthesis of non-racemic 4-nitro-2-sulfonylbutan-1-ones via Ni(II)-catalyzed asymmetric Michael reaction of β-ketosulfones

• Alexander N. Reznikov,
• Anastasiya E. Sibiryakova,
• Marat R. Baimuratov,
• Eugene V. Golovin,
• Victor B. Rybakov and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2019, 15, 1289–1297, doi:10.3762/bjoc.15.127

• acceptors and aldehydes [27][28][29][30][31][32], ketones [33], α-cyano esters [34][35], β-keto esters [35], β-keto acids [36], thiomalonates [37], nitroalkanes [38], oxindoles [39] and thiols [40] as Michael donors. There are only few examples of the use of sulfones as Michael donors in asymmetric addition

Halogen bonding and host–guest chemistry between N-alkylammonium resorcinarene halides, diiodoperfluorobutane and neutral guests

• Fangfang Pan,
• Mohadeseh Dashti,
• Michael R. Reynolds,
• Kari Rissanen,
• John F. Trant and
• Ngong Kodiah Beyeh

Beilstein J. Org. Chem. 2019, 15, 947–954, doi:10.3762/bjoc.15.91

• halogen bond acceptors [29][30][31][32][33][34]. We have previously shown that N-alkylammonium resorcinarene bromides (NARBrs) can form various halogen-bonded assemblies with the classical organic halogen bond donor 1,4-diiodooctafluorobutane (DIOFB) depending on the solvent, the presence of potential

• anisotropy influence from the host’s aromatic rings, increasing the shielding. Conclusion In conclusion, we present XB assemblies between Hex-NARBr and Cy-NARCl as tetravalent XB acceptors, a divalent XB donor DIOFB, and small organic guest solvents (MeOH, MeCN and water). In the assemblies, both XB and HB

Strong hyperconjugative interactions limit solvent and substituent influence on conformational equilibrium: the case of cis-2-halocyclohexylamines

• Camila B. Francisco,
• Cleverton S. Fernandes,
• Ulisses Z. de Melo,
• Roberto Rittner,
• Gisele F. Gauze and
• Ernani A. Basso

Beilstein J. Org. Chem. 2019, 15, 818–829, doi:10.3762/bjoc.15.79

• electron-density acceptors, and their presence in a system suggests the possibility of these interactions [17][21]. Although there have been several works on the conformational preference of 1,2-disubstituted cyclohexanes [4][11][12][13][14][20][22][23][24][25][26][27][28][29], cis-2-halocyclohexylamines

• no contribution for the PC’s, confirming that the rotational preference has no influence on the hyperconjugation. Analyzing the bonds pointed by the PCA as electron density donors (bonding orbitals) or acceptors (antibonding orbitals) in Figure 7, it is clear that the most significant interactions