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

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• groups capable for the formation of additional hydrogen bonds, both as donors and acceptors. The majority of synthetic strategies starts from natural products and relies on application of chirons having the required configuration at the carbon atom bonded to nitrogen (e.g., serine, glutamic and

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• decrease of the O–H stretching frequency [71]. An alternative method is to determine the relaxed force constant [72]. In the following, the stretching frequency und the NBO analyses were calculated for different acceptors and water (Table 4). The silanol group is a better hydrogen bond acceptor than an

• hydrogen bonds [74]. X-ray structures of BIFOXSi(OH)2 (9, Figure 16) and BIFOXSiCl(OH) (8, Figure 17) with co-crystallized acetone indicate the bonding behavior of the silanediols to carbonyl acceptors. Chlorosilanol 8 binds one acetone with a bonding length of 2.16(0) Å (H3···O4) and 2.89(4) Å (O3–H···O4

Unexpected loss of stereoselectivity in glycosylation reactions during the synthesis of chondroitin sulfate oligosaccharides

• Teresa Mena-Barragán,
• José L. de Paz and
• Pedro M. Nieto

Beilstein J. Org. Chem. 2019, 15, 137–144, doi:10.3762/bjoc.15.14

• and D-glucuronic acid (GlcA) acceptors. These results, together with those obtained from experiments employing model monosaccharide building blocks, highlight the impact of the glycosyl acceptor structure on the stereoselectivity of glycosylation reactions. Our study provides useful data about the

• % of TMSOTf with respect to the donor, 0 ºC, CH2Cl2 as solvent). As mentioned before, it has been reported that cyclic protecting groups like 4,6-O-benzylidene acetals in GalNAc trichloroacetimidates lead to the formation of α/β mixtures in glycosylations involving GlcA acceptors [43][47]. However

• -acylated N-TFA-protected GalNAc donors and GlcA acceptors that is not due to the presence of the fluorous tail. We hypothesized that the substitution pattern of the GlcA acceptor was responsible for the displayed stereochemistry and some experiments with model monosaccharides were planned to confirm this

Mn-mediated sequential three-component domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction towards annulated imidazo[1,2-a]pyridines

• Olga A. Storozhenko,
• Alexey A. Festa,
• Delphine R. Bella Ndoutoume,
• Alexander V. Aksenov,
• Alexey V. Varlamov and
• Leonid G. Voskressensky

Beilstein J. Org. Chem. 2018, 14, 3078–3087, doi:10.3762/bjoc.14.287

• key intermediate of the domino sequence (Scheme 1, reaction 1). Taking into account the capability of 2-iminochromenes to perform as Michael acceptors [39][40][41], we envisioned the diversification of the substitution pattern at the chromene ring to be a realizable and an appealing target

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

• electronically excited state which significantly changes the distribution of electrons in the molecule. Thus, chemical properties such as reactivity, oxidation potential or reduction potential change drastically. With appropriate donors or acceptors, electron charge transfer is possible via this excited state

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov,
• Olesya V. Khoroshilova and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

• explored in organic synthesis for the construction of various molecules [1][2][3][4][5][6][7]. In particular, arylsulfonyl (ArSO2) allenes are usefull building blocks in miscellaneous transformations. For instance, addition of such allenes to Michael acceptors leading to terminal acetylenes has been

Synthesis of α-D-GalpN₃-(1-3)-D-GalpN₃: α- and 3-O-selectivity using 3,4-diol acceptors

• Emil Glibstrup and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2018, 14, 2805–2811, doi:10.3762/bjoc.14.258

• acceptors and donors are made from common building blocks, limiting protective manipulations, and in this context, unavoidable side reactions. Keywords: diastereoselectivity; glycosylation; regioselectivity; Introduction The disaccharide α-D-GalpNAc-(1-3)-β-D-GalpNAc is a widespread motif in glycobiology

• sugar [41][42][43] and none for the synthesis of the α-D-GalpNAc-(1-3)-D-GalpNAc motif or its precursors. We therefore set out to study this regioselective glycosylation in more detail and synthesized the necessary model donors and acceptors. Here, the simplicity of the approach showed its potential, as

• acceptors were obtained via Zemplén deprotection in 94% and 90% yield for the 6-O-TBDPS 9 and 6-O-Bn 10, respectively (Scheme 2). The acceptors could in turn be transformed into the corresponding donors in three simple steps by first benzylating the 3,4-diol (11 and 12), hydrolyzing the thiophenol using NBS

DABCO- and DBU-promoted one-pot reaction of N-sulfonyl ketimines with Morita–Baylis–Hillman carbonates: a sequential approach to (2-hydroxyaryl)nicotinate derivatives

• Soumitra Guin,
• Raman Gupta,
• Debashis Majee and
• Sampak Samanta

Beilstein J. Org. Chem. 2018, 14, 2771–2778, doi:10.3762/bjoc.14.254

• -unsaturated ketones (from alkyl ketones) as Michael acceptors to construct a diverse set of nicotinate derivatives were developed by Bohlman–Rahtz [39], Bagley [40][41] and other groups independently [42][43][44][45][46][47][48][49][50][51][52][53][54][55]. Similarly, the synthesis of functionalized

Non-native autoinducer analogs capable of modulating the SdiA quorum sensing receptor in Salmonella enterica serovar Typhimurium

• Matthew J. Styles and
• Helen E. Blackwell

Beilstein J. Org. Chem. 2018, 14, 2651–2664, doi:10.3762/bjoc.14.243

• ) [21][22]. C) The solid-state structure of the SdiA homodimer (PDB 4Y15; monomers shown in green and grey) bound to OOHL (cyan) [22]. D) Selected residues surrounding OOHL (cyan) in the SdiA ligand binding pocket (from PDB 4Y15 [22]): hydrogen bond acceptors/donors (orange), hydrophobic residues (grey

Coordination-driven self-assembly of discrete Ru₆–Pt₆ prismatic cages

• Aderonke Ajibola Adeyemo and
• Partha Sarathi Mukherjee

Beilstein J. Org. Chem. 2018, 14, 2242–2249, doi:10.3762/bjoc.14.199

• donors and transition metals as electron-deficient acceptors. Diverse functionalities embedded in these homometallic architectures have found useful applications in chemical sensing [24][25][26][27][28][29][30][31][32][33][34][35], catalysis [11][36][37][38][39][40][41][42][43][44][45][46], drug delivery

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• such a mild and selective oxidation. MacMillan and co-workers have recently developed a method for the bioconjugation of peptides by radical decarboxylation of the C-terminus of peptides and subsequent Giese-type addition to Michael acceptors. This is performed under blue light irradiation, using

• reactions using traditional chemistry and organophotoredox synthesis can offer some interesting options as well. Wu et al. reported the alkylation of unfunctionalised allylic and benzylic sp3 C–H bonds by reaction with Michael acceptors, using blue LEDs and acridinium salts (Scheme 12) [55]. The main

• advantage is the absence of strong bases like tert-butyllithium (t-BuLi). A very broad scope of Michael acceptors, allylic and benzylic substrates is reported, with an equally broad range of yields achieved (10–99%). Some selectivity is observed when asymmetric alkenes are used. The key to this selectivity