Design, synthesis and structure of novel G-2 melamine-based dendrimers incorporating 4-(n-octyloxy)aniline as a peripheral unit

• Cristina Morar,
• Pedro Lameiras,
• Attila Bende,
• Gabriel Katona,
• Emese Gál and
• Mircea Darabantu

Beilstein J. Org. Chem. 2018, 14, 1704–1722, doi:10.3762/bjoc.14.145

• -displaced dendritic scaffolds (Figure 11): (i) (π–π) between the electron-poor N-atoms, adjacent to s-triazine rings, as π-acceptors, from one hand, and the π-enriched (hetero)cycles, s-triazines and 4-(n-octyloxy)phenylamino peripheral units, on the other hand, as π-donors. (ii) (π–H) of type (s-triazine

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• employed and found to be completely ineffective (<10% conversion, 56:42 dr), indicating that the hydrophobic calixarene platform was crucial. Aromatic aldehydes with different substitution patterns on the benzene ring were also tested as aldol acceptors and high yields (up to 95%), enantioselectivities (up

Synthesis of chiral 3-substituted 3-amino-2-oxindoles through enantioselective catalytic nucleophilic additions to isatin imines

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 1349–1369, doi:10.3762/bjoc.14.114

• maleimides 37 using β-isocupreidine as catalyst [61]. It must be noted that maleimides as Morita–Baylis–Hillman donors were challenging in these reactions since they are more usually employed as Michael acceptors. As shown in Scheme 13, a wide variety of chiral 3-amino-2-oxindoles 38 was synthesized in

• and organocatalysts. While isatins have been widely used as substrates in asymmetric Henry reactions, isatin imines have been less explored as aza-Henry acceptors in enantioselective reactions. Recently, several groups have developed enantioselective aza-Henry reactions of isatin imines catalyzed by

D–A–D-type orange-light emitting thermally activated delayed fluorescence (TADF) materials based on a fluorenone unit: simulation, photoluminescence and electroluminescence studies

• Lin Gan,
• Xianglong Li,
• Xinyi Cai,
• Kunkun Liu,
• Wei Li and
• Shi-Jian Su

Beilstein J. Org. Chem. 2018, 14, 672–681, doi:10.3762/bjoc.14.55

• donors (D) and electron acceptors (A) are introduced into the molecule to form an intramolecular charge transfer (ICT) state with a large twisting angle between the donor and the acceptor to achieve the separation of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO

Investigations towards the stereoselective organocatalyzed Michael addition of dimethyl malonate to a racemic nitroalkene: possible route to the 4-methylpregabalin core structure

• Denisa Vargová,
• Rastislav Baran and
• Radovan Šebesta

Beilstein J. Org. Chem. 2018, 14, 553–559, doi:10.3762/bjoc.14.42

• reactivity of the nitroalkene 6 compared with that of similar Michael acceptors is probably due to the higher steric hindrance near the β-carbon caused by branching of the alkyl chain. More relevant results in the Michael addition were obtained with more reactive, and likely less hindered, catalysts C5–C8

Addition of dithi(ol)anylium tetrafluoroborates to α,β-unsaturated ketones

• Yu-Chieh Huang,
• An Nguyen,
• Simone Gräßle,
• Sylvia Vanderheiden,
• Nicole Jung and
• Stefan Bräse

Beilstein J. Org. Chem. 2018, 14, 515–522, doi:10.3762/bjoc.14.37

• examples, we showed that it is possible to extend the presented procedure to the reaction of dithiolanylium TFB with other Michael acceptors as, e.g., α,β-unsaturated esters 12a or 12b (yielding 13a and 13b, Scheme 5). The reaction proceeded under similar conditions as shown in Table 1 (the reaction

• ketene dithioacetals or their synthetic equivalents to electrophiles can be overcome by the use of dithi(ol)anylium TFBs. Dithi(ol)anylium TFBs were used in combination with α,β-unsaturated ketones as Michael-type acceptors yielding ketene diothiolanes and ketene dithianes with various substitution

• use of possible Michael acceptors was identified so far as the conversion of dithi(ol)anylium TFBs with 3,3-disubstituted alk-2-en-1-ones did not occur. Previously reported procedure for the addition of ketene dithioacetals to α,β-unsaturated ketones [33] in comparison to our dithi(ol)anylium TFB

Synthetic and semi-synthetic approaches to unprotected N-glycan oxazolines

• Antony J. Fairbanks

Beilstein J. Org. Chem. 2018, 14, 416–429, doi:10.3762/bjoc.14.30

• Shoda [32] and co-workers reported that a disaccharide oxazoline (Scheme 1) was an effective donor substrate for two ENGase enzymes (Endo A and Endo M), both of which were capable of using it to glycosylate two GlcNAc acceptors, to produce trisaccharide products. Subsequently the ENGases in combination

Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)

• Thanh-Tuân Bui,
• Fabrice Goubard,
• Malika Ibrahim-Ouali,
• Didier Gigmes and
• Frédéric Dumur

Beilstein J. Org. Chem. 2018, 14, 282–308, doi:10.3762/bjoc.14.18

• investigated in organic electronics [31] as these materials are characterized by a remarkable electron mobility resulting from the presence of a vacant p-orbital on the boron atom [32][33]. Triarylboron compounds are also strong electron acceptors, justifying that numerous groups developed TADF emitters using

• triarylboron moieties as acceptors. As possible donors, diarylamines have often been proposed (carbazole, triphenylamine, carbazole/triphenylamine hybrids, 9,9-dimethyl-9,10-dihydroacridine), as exemplified in Figure 2 [34][35][36]. In B1 and B2, isolation of the two parts was obtained by linking the 10H

• -TADF white OLEDs with 16% EQE could be fabricated [30]. 4. Triazine–pyrimidine based emitters Among possible electron acceptors, another structure has been extensively regarded as an adequate electron acceptor for the design of blue TADF emitters and this structure is the triazine unit. When combined

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• delivered comparable and even higher yields of the products in longer reaction times but with lower catalyst loading (1 mol %). Both unactivated terminal alkenes and electron-deficient alkenes (Michael acceptors) were successfully hydrotrifluoromethylated under irradiation with 36 W blue LEDs in the

A Brønsted base-promoted diastereoselective dimerization of azlactones

• Danielle L. J. Pinheiro,
• Gabriel M. F. Batista,
• Pedro P. de Castro,
• Leonã S. Flores,
• Gustavo F. S. Andrade and
• Giovanni W. Amarante

Beilstein J. Org. Chem. 2017, 13, 2663–2670, doi:10.3762/bjoc.13.264

• and Mannich acceptors [20][21][22][23]. Enolate anions derived from azlactone are effective intermediates for the functionalization of α-amino acids. However, the acylation of the enolate ion by another azlactone has been less reported in the literature [24][25][26]. This transformation affords an

Electron-deficient pyridinium salts/thiourea cooperative catalyzed O-glycosylation via activation of O-glycosyl trichloroacetimidate donors

• Mukta Shaw,
• Yogesh Kumar,
• Rima Thakur and
• Amit Kumar

Beilstein J. Org. Chem. 2017, 13, 2385–2395, doi:10.3762/bjoc.13.236

• thiourea derivative as an hydrogen-bonding cocatalyst. This transformation occurs under mild reaction conditions with a wide range of O-glycosyl trichloroacetimidate donors and glycosyl acceptors to afford the corresponding O-glycosides in moderate to good yields with predictable selectivity. In addition

• system on glycosylation of 1α with several acceptors (Table 2). In all cases, reactions proceeded smoothly within 2–6 h and in good yields with moderate to good selectivity, as determined by the 1H and 13C NMR spectra. Glycosylation with less sterically hindered primary alcohols, e.g., allyl alcohol (2b

• alcohol, 1-adamantanemethanol (2i) produced the desired glucoside 5i in 75% yield and moderate selectivity (Table 2, entry 8). Further, reactions with hindered acceptors, for instance, 1-adamantanol (2j), (+)-menthol (2k), (–)-menthol (2l), cholesterol (2m) required longer reaction times with high

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• dicyanofumarates and maleates as highly functionalized electron-deficient dipolarophiles, dienophiles and Michael acceptors is summarized. The importance for the studies on reaction mechanisms of cycloadditions is demonstrated. Multistep reactions with 1,2-diamines and β-aminoalcohols leading to diverse five- and

• exploration in mechanistic studies of their reactions. Similar to TCNE, these compounds are also attractive Michael acceptors with numerous applications for multistep reactions leading to heterocyclic products. The chemistry of E-1 and Z-1 has not been reviewed, and the goal of the present survey is to

• with diethyl phosphite in boiling 1,2-dichloroethane leading to the dialkyl dicyanosuccinates 96 [7]. Charge-transfer (CT) complexes Dialkyl dicyanofumarates E-1, similar to tetracyanoethylene (TCNE), are well-known as one-electron acceptors. They react with metallocenes 99, such as manganocenes [73

Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective

• Yaroslav D. Boyko,
• Valentin S. Dorokhov,
• Alexey Yu. Sukhorukov and
• Sema L. Ioffe

Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220

• acceptors in organic synthesis [1][2][3][4][5]. Unlike the parent α-nitroalkenes, α-nitrosoalkenes are unstable species usually generated in situ, and their synthetic potential has been studied in significantly less detail [6][7]. Because of relatively short lifetimes of α-nitrosoalkenes, conjugate addition

• 29 into isocomene failed (Scheme 12) [32]. Recently, Weinreb’s group used the advantage of nitrosoalkenes as Michael acceptors to accomplish total syntheses of several alkaloids, such as (+/−)-alstilobanines A and E, (+/−)-angustilodine [33] and (+/−)-myrioneurinol [34][35] (Figure 1). In the total

Regiodivergent condensation of 5-alkoxycarbonyl-1H-pyrrol-2,3-diones with cyclic ketazinones en route to spirocyclic scaffolds

• Alexey Yu. Dubovtsev,
• Maksim V. Dmitriev,
• Аndrey N. Maslivets and
• Michael Rubin

Beilstein J. Org. Chem. 2017, 13, 2179–2185, doi:10.3762/bjoc.13.218

• product of 1,2-addition of the C-nucleophile to the most reactive keto function and subsequent nucleophilic attack by the O-enolate on the conjugate C=C bond activated by two electron acceptors could become more preferable as compared to the alternative “normal” pathway, leading to adducts 10 and

Preactivation-based chemoselective glycosylations: A powerful strategy for oligosaccharide assembly

• Weizhun Yang,
• Bo Yang,
• Sherif Ramadan and
• Xuefei Huang

Beilstein J. Org. Chem. 2017, 13, 2094–2114, doi:10.3762/bjoc.13.207

• nucleophilically attacks the intermediate forming the desired glycosidic product [22][23][24]. With the preactivation protocol, the donor activation and acceptor glycosylation occur in two distinctive steps. As a result, a unique chemoselectivity can be achieved with preactivation. Glycosyl donors and acceptors

• , affording glycoside 22 in 86% yield (α:β = 27:73, Scheme 6). This glycosylation strategy can be applied to a variety of glycosyl acceptors, including oxygen, sulfur, carbon and nitrogen nucleophiles (Figure 1) [36]. Even the unreactive N-(trimethylsilyl)trimethylacetamide could be efficiently glycosylated

• uronic acid in an α-selective fashion. A variety of azido hemiacetal glucoside donor and uronic acid thioglycosyl acceptor pairs were screened under preactivation conditions. The anomeric leaving groups of the acceptors had significant impacts on the glycosylation outcomes (Scheme 11a). When donor 54 was

Main group mechanochemistry

• Agota A. Gečiauskaitė and
• Felipe García

Beilstein J. Org. Chem. 2017, 13, 2068–2077, doi:10.3762/bjoc.13.204

• methods (see Scheme 3).· Also noteworthy is the multistep solvent-free mechanochemical route to indium(III) complexes featuring aryl bis(imino)acenaphthene (Ar-BIAN) ligands [84]. Ar-BIAN ligands are versatile π-acceptors and have been widely employed for catalysis. These ligands are typically synthesised

Intramolecular glycosylation

• Xiao G. Jia and
• Alexei V. Demchenko

Beilstein J. Org. Chem. 2017, 13, 2028–2048, doi:10.3762/bjoc.13.201

• high α-selectivity (α/β = 8:1). Interestingly, when the donor and acceptor positions on the peptide were reversed, such as conjugate 39, glycosidation of this compound produced disaccharide 40 in 75% yield albeit the stereoselectivity was entirely lost (α/β = 1:1). Galactosyl acceptors also showed a

• dramatic effect of the relative position of the donor and acceptor on the peptide sequence. Intriguingly, the stereoselectivity outcome was reversed (1.8:1 and 9:1) in comparison to glucosyl acceptors. When a similar concept was applied to mannosyl acceptor low 2:1 stereoselectivity was obtained regardless

• acceptors together [56][82]. The templated synthesis also falls into the general molecular clamping method. High stereoselectivity could be achieved with both flexible and rigid linkers (L1 and L2, Scheme 13). However, the use of the rigid BPA template core appears to be the key to ensure the high

1,3-Dibromo-5,5-dimethylhydantoin as promoter for glycosylations using thioglycosides

• Fei-Fei Xu,
• Claney L. Pereira and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2017, 13, 1994–1998, doi:10.3762/bjoc.13.195

• investigated by using a variety of glycosyl donors 4–10 [34][35][36][37][38] containing C-2 participating groups to ensure 1,2-trans-glycoside formation (Table 2). Each glycosylating agent was reacted with D-glucose acceptors 2 (Table 2, entries 1–8) and 11 [39] (Table 2, entries 9–16) with a free hydroxy

Enzymatic synthesis of glycosides: from natural O- and N-glycosides to rare C- and S-glycosides

• Jihen Ati,
• Pierre Lafite and
• Richard Daniellou

Beilstein J. Org. Chem. 2017, 13, 1857–1865, doi:10.3762/bjoc.13.180

• -glycosylation, although their endogenous role is not to generate S-glycosides. Brazier-Hicks and colleagues have screened many A. thaliana Family 1 GTs with three acceptors, to identify O-GT, N-GT and S-GT enzymatic activities [29]. Among the 99 enzymes tested, 17 were able to use 4-chlorothiophenol as the

• acceptor. UGT74B1, involved in glucosinolate biosynthesis (see supra), was one of these 17 enzymes. Other studies have identified S-GT activities when assaying the catalytic promiscuity of O-GT with a wide range of aglycone acceptors (Figure 3). OleD from Streptomyces antibioticus has been the first

• reported O-GT to catalyse S-glycosylation on thiol acceptors [30]. Genetic engineering of this enzyme has also led to S-GT activities on several thiols. UGT73AE1 from Carthamus tinctorius was able to transfer glucose on a wide range of acceptors, including a S-containing compound, dichlorothiophenol [31

Conformational impact of structural modifications in 2-fluorocyclohexanone

• Francisco A. Martins,
• Josué M. Silla and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2017, 13, 1781–1787, doi:10.3762/bjoc.13.172

• , the π*C=Y orbitals (Y = O, S and N) are better electron acceptors than the π*C=C in electron delocalization processes. These highlight the role of electrostatic and hyperconjugative effects on the conformational isomerism of the studied compounds. Two particularly clear trends are related to the NH

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

• Johannes Schörgenhumer,
• Maximilian Tiffner and
• Mario Waser

Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170

• -oxygenation reactions above, also the introduction of a nitrogen-based functionality alpha to a carbonyl group can be achieved by several complementary strategies. One powerful option is to carry out Michael addition-initiated aziridination reactions of α,β-unsaturated carbonyl acceptors [18][138][139][140

Oxidative dehydrogenation of C–C and C–N bonds: A convenient approach to access diverse (dihydro)heteroaromatic compounds

• Santanu Hati,
• Ulrike Holzgrabe and
• Subhabrata Sen

Beilstein J. Org. Chem. 2017, 13, 1670–1692, doi:10.3762/bjoc.13.162

• acceptor) or via oxidative dehydrogenation in the presence of appropriate oxidants. In absence of hydrogen acceptors, post dehydrogenation the hydrogen is released as H2↑. Catalysts such as iridium pincer complexes, CuAl2O3, hydroxyapatite bound palladium and ruthenium hydride complexes have been harnessed

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• position which could provide under the right conditions, regioselectively and stereoselectively 1,2-cis glycosides of a wide variety. The substrate scope is broad and even includes glycosyl phosphates and esters in addition to a host of alcohol acceptors (Scheme 8). Certainly the most important application

• donors screened in the study. The preparation of the phenyl galactothioside is shown in Scheme 15. The chemistry can be described as straightforward, however, the use of thiophenol is required which is highly toxic and odorous. 3.3.2 Regioselective glycosylation of unprotected acceptors: Another

• field. It is driven by the appeal of waste reduction in chemical synthesis that the use of stoichiometric amounts of reagents, unfortunately cause. Typical transition metals employed for promoting the glycosylation of protected acceptors using protected donors include Pd, Ni, Au, Rh, Ru, and Ti [61]. In

Membrane properties of hydroxycholesterols related to the brain cholesterol metabolism

• Malte Hilsch,
• Ivan Haralampiev,
• Peter Müller,
• Daniel Huster and
• Holger A. Scheidt

Beilstein J. Org. Chem. 2017, 13, 720–727, doi:10.3762/bjoc.13.71

• of sterols to and from membranes, this can be principally realized via vesicular traffic or via monomeric transfer. The latter mechanism requires the presence of donors and acceptors, respectively, due to the low water solubility of sterols. Nevertheless, the import and export of cholesterol is

• rather slow [34], wherefore membrane proteins have been proposed to facilitate these processes. One putative function of those proteins could be to relieve the presentation of cholesterol molecules on the membrane surface for a better binding to extracellular acceptors (see [35]). It can be hypothesized

Derivatives of the triaminoguanidinium ion, 5. Acylation of triaminoguanidines leading to symmetrical tris(acylamino)guanidines and mesoionic 1,2,4-triazolium-3-aminides

• Jan Szabo,
• Julian Greiner and
• Gerhard Maas

Beilstein J. Org. Chem. 2017, 13, 579–588, doi:10.3762/bjoc.13.57

• are present in the triclinic unit cell, being associated by two N–H···N hydrogen bonds in which benzylamino NH bonds act as donors and aminide nitrogen atoms as acceptors. As expected, the triazolium-aminide moiety in 7a is planar. The comparison of the bond lengths in this moiety with those in nitron