Aqueous semisynthesis of C-glycoside glycamines from agarose

• Juliana C. Cunico Dallagnol,
• Alexandre Orsato,
• Diogo R. B. Ducatti,
• Miguel D. Noseda,
• Maria Eugênia R. Duarte and
• Alan G. Gonçalves

Beilstein J. Org. Chem. 2017, 13, 1222–1229, doi:10.3762/bjoc.13.121

• data retrieved from literature [25]. Overview of the hydrolysis–reductive amination procedure to produce primary glycamine 3 and byproducts. Overview of synthetic procedures, yields and specific rotation of glycamines 3, 7, 8, epi-8, 9 and 13. a) 0.1 M TFA, 80 °C; b) NaBH4; c) 2.0 M TFA, 110 °C; d

Sugar-based micro/mesoporous hypercross-linked polymers with in situ embedded silver nanoparticles for catalytic reduction

• Qing Yin,
• Qi Chen,
• Li-Can Lu and
• Bao-Hang Han

Beilstein J. Org. Chem. 2017, 13, 1212–1221, doi:10.3762/bjoc.13.120

• an excess amount of NaBH4 as the reducing reagent [45]. In our study, the process of the catalytic reaction was readily followed as the color of the solution turned from yellow to colorless. Both the reactants and products are easily monitored by UV–vis spectroscopy without any formation of

• absorption peak at 317 nm of observed for the neutral 4-NP solution, the absorption at 400 nm is attributed to the 4-nitrophenolate ion. The latter is generated through deprotonation of 4-NP (pKa = 7.15) upon the addition of NaBH4 [41]. As can be seen from Figure 5a, the absorption peak of the substrate

• of 4-NP at time t, and k is the first-order rate constant. Figure 5b shows the ct/c0 and ln(ct/c0) changes with time for the reduction of 4-NP in the presence of NaBH4 with the AgNPs/SugPOP-1 composite as catalyst. By the Beer–Lambert law we find that ct/c0 is proportional to At/A0. At/A0 was

Glyco-gold nanoparticles: synthesis and applications

• Federica Compostella,
• Olimpia Pitirollo,
• Alessandro Silvestri and
• Laura Polito

Beilstein J. Org. Chem. 2017, 13, 1008–1021, doi:10.3762/bjoc.13.100

• Penadès and co-workers [15] is a modified Brust–Shiffrin method [17], based on the in situ Au3+ reduction by means of NaBH4 in the presence of thiol-ending neoglycoconjugates. Following this approach, a rapid synthesis of AuNPs characterized by elevated glycan density on the NP surface and a 1–10 nm

• simply mixing at room temperature Au3+ salts and thio-glucoside as reducing and stabilizing agents, without the addition of NaBH4 [19]. The two-step synthetic procedure consists in the initial synthesis of AuNPs stabilized by temporary compounds (i.e., citrates, amines or phosphines), followed by the

Transition-metal-free one-pot synthesis of alkynyl selenides from terminal alkynes under aerobic and sustainable conditions

• Adrián A. Heredia and
• Alicia B. Peñéñory

Beilstein J. Org. Chem. 2017, 13, 910–918, doi:10.3762/bjoc.13.92

• the latter with K3PO4 generates the alkyl selenolate anion (RSe−) which reacts with another RSeCN molecule to give the corresponding diselenide R2Se2. Reduction of the latter diselenide by treatment with NaBH4 affords an alkyl selenolate anion, which reacts with styryl halide to give the desired

Fluorinated cyclohexanes: Synthesis of amine building blocks of the all-cis 2,3,5,6-tetrafluorocyclohexylamine motif

• Tetiana Bykova,
• Nawaf Al-Maharik,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2017, 13, 728–733, doi:10.3762/bjoc.13.72

• h, rt, 30%; c) Et3N·3HF (10 equiv), 4 days, 120 °C, 30%; d) NaBH4 (10 equiv)/NiCl2·6H2O (5 equiv), MeOH, 1 h, 0 °C, 18 h, rt, 50%; e) 10% Pd/C (10 mol %), H2, Et3N/CHOOH: molar ratio 1:37, THF, 18 h, rt, 78%. Reagents and conditions: a) Et3N·3HF (8 equiv), 18 h, 140 °C; b) Tf2O (4 equiv), pyridine

• , 1 h, 0 °C, 3 h, rt, 40% (10b), 15% (10c); c) Et3N·3HF (10 equiv), 4 days, 120 °C, 51% (11b), 31% (11c); d) NaBH4 (10 equiv)/NiCl2·6H2O (5 equiv), MeOH, 1 h, 0 °C, 18 h, rt, 65% (5b), 23% (5c). Reagents and conditions: a) terephthaloyl chloride (1 equiv), Et3N (4 equiv), DMAP (20 mol %), DCM, 18 h

Transition-metal-catalyzed synthesis of phenols and aryl thiols

• Yajun Liu,
• Shasha Liu and
• Yan Xiao

Beilstein J. Org. Chem. 2017, 13, 589–611, doi:10.3762/bjoc.13.58

• with aryl iodides at 90 °C in the presence of CuI as catalyst to afford biaryl disulfides and polysulfides, which could be further converted to aryl thiols through a followed reduction using NaBH4 or PPh3 (Scheme 59) [103]. A wide range of functional groups including methoxy, hydroxy, acyl, carboxy

Brønsted acid-mediated cyclization–dehydrosulfonylation/reduction sequences: An easy access to pyrazinoisoquinolines and pyridopyrazines

• Ramana Sreenivasa Rao and
• Chinnasamy Ramaraj Ramanathan

Beilstein J. Org. Chem. 2017, 13, 428–440, doi:10.3762/bjoc.13.46

• this methodology for the synthesis of 1-arylethylpiperazine-2,6-diones intrigued us to examine them in 6-exo-trig cyclization using TfOH followed by reduction with NaBH4/MeOH to accomplish the synthesis of tetrahydropyrazinoisoquinoline. Surprisingly, the reaction of 7a furnished a mixture of ene

• -diamide 9a and substituted pyrazinone 10a in 90:10 ratio. Generally, the syntheses of these types of units are very limited in the literature [31]. Under controlled experimental conditions, in the absence of NaBH4/MeOH, the ene-diamide 9a was successfully generated in 90% yield using 4 equivalents of TfOH

• the potassium salt of N-benzyliminodiacetic acid in THF at reflux to furnish the expected imides 8a–c, 8h, and 8i in good yields (Scheme 6). The imide 8h was subjected to the cyclization reaction conditions using 6 equivalents of TfOH under neat conditions at 70 °C followed by reduction using NaBH4

The reductive decyanation reaction: an overview and recent developments

• Jean-Marc R. Mattalia

Beilstein J. Org. Chem. 2017, 13, 267–284, doi:10.3762/bjoc.13.30

• hydride donors (Scheme 6). Alternatively, secondary amines could involve an elimination of HCN and reduction of the formed imine. NaBH4 [45][46][47][48][49][50][51] or NaBH3CN [47][52][53][54][55][56][57][58][59] are widely used hydride donors and, less frequently, BH3 [60][61], AgBF4/Zn(BH4)2 [62][63][64

• treatment with NaBH4 in 2-propanol by using both basic and nucleophilic properties of the hydride ion. The proposed mechanism involves a double-bond isomerization to the α-aminonitrile intermediate which is then reduced by the hydride ion in a classical way (Scheme 7). Interestingly, deuterium-labelling

• phenanthroquinolizidines (13, n = 2). Anticancer activities of these 18 compounds were evaluated against three human cancer cell lines. BH3·THF containing NaBH4 has been used for the reduction of diimines [72][73] and was studied in-depth by Zhang and co-workers in the reductive decyanation reaction. In their work, the

First DMAP-mediated direct conversion of Morita–Baylis–Hillman alcohols into γ-ketoallylphosphonates: Synthesis of γ-aminoallylphosphonates

• Marwa Ayadi,
• Haitham Elleuch,
• Emmanuel Vrancken and
• Farhat Rezgui

Beilstein J. Org. Chem. 2016, 12, 2906–2915, doi:10.3762/bjoc.12.290

• selective Luche reduction [49][50] of the γ-ketophosphonate 2a using NaBH4 in the presence of CeCl3·6H2O in methanol at 0 °C. The TLC of the reaction mixture and analysis of 1H NMR and 31P NMR spectra showed the exclusive formation of the 1,2-adduct 5 (Scheme 5). The literature survey revealed that γ

O-Alkylated heavy atom carbohydrate probes for protein X-ray crystallography: Studies towards the synthesis of methyl 2-O-methyl-L-selenofucopyranoside

• Roman Sommer,
• Dirk Hauck,
• Annabelle Varrot,
• Anne Imberty,
• Markus Künzler and
• Alexander Titz

Beilstein J. Org. Chem. 2016, 12, 2828–2833, doi:10.3762/bjoc.12.282

• introduction of the methylseleno moiety was performed by nucleophilic substitution of the α-bromide in 5 with methylselenol obtained by in situ reduction of dimethyl diselenide with NaBH4 [23]. The obtained crude methyl β-selenofucoside was anomerized under Lewis acid catalysis to give the anomeric mixture in

• -methylation in position 2 could solve the phase problem for Lb-Tec2 structure determination. Synthesis of 3 through initial introduction of the seleno aglycon and subsequent O-methylation. Reagents and conditions: (a) NaOAc, Ac2O, 140 °C, 3 h; (b) TMSBr, CH2Cl2, 0 °C–rt, 6 h; (c) Me2Se2, NaBH4, MeCN, 90 °C

• ) PdCl2, CH2Cl2, MeOH, rt, 24 h; (f) NaOAc, Ac2O, 90 °C, 1.5 h; (g) TMSBr, CH2Cl2, 0 °C, 2.5 h; (h) (Me2Se2, NaBH4, MeCN, 90 °C, 1 h), CH2Cl2, 90 °C 15 min–1 h; (i) NaOMe, MeOH, rt, 30 min–2 h; (j) Ac2O, pyridine, 0 °C to rt, 3 h; (k) Ac2O, BF3·OEt2, 0 °C to rt, 17 h; (l) BF3·OEt2, CH2Cl2, rt, 20 h

Useful access to enantiomerically pure protected inositols from carbohydrates: the aldohexos-5-uloses route

• Felicia D’Andrea,
• Giorgio Catelani,
• Lorenzo Guazzelli and
• Venerando Pistarà

Beilstein J. Org. Chem. 2016, 12, 2343–2350, doi:10.3762/bjoc.12.227

• aqueous NaOH followed by NaBH4 reduction of the crude inosose mixture. Although these pioneering results were not of synthetic significance, they elucidated for the first time the biosynthetic correlation between D-glucose and myo-inositol through the intermediate formation of D-xylo-hexos-5-ulose. A more

• anti reduction using NaBH4 as a reducing reagent in an alcoholic solvent (condition A). In particular, it has been proven that the axial OH group β to the keto function plays a fundamental role in directing the nucleophilic attack [45][46][47]. It has also to be mentioned that by changing the

Experimental and theoretical investigations into the stability of cyclic aminals

• Edgar Sawatzky,
• Antonios Drakopoulos,
• Martin Rölz,
• Christoph Sotriffer,
• Bernd Engels and
• Michael Decker

Beilstein J. Org. Chem. 2016, 12, 2280–2292, doi:10.3762/bjoc.12.221

• ] (Scheme 2). Furthermore, copper-catalysed reactions or oxidation with sodium hypochlorite were also described to yield the aromatic quinazoline core [26][29][30] (Scheme 2). Besides all the oxidation reactions described, also reductive conditions applying NaBH4 onto the tetrahydroquinazoline-based aminal

• tetrahydroquinazoline core (Scheme 4b). Thus, anthranilic acid was alkylated by reductive amination with acetone and NaBH4 in two steps to yield the isopropyl-substituted derivative 14. The derivative 14 and the commercially available N-phenylanthranilic acid were converted to amides 15a,b under standard conditions

• , 70 °C, 1–3 h. Reagents and conditions: (a) (i) MeNH3Cl, Et3N, DMF, 70 °C, 3 h; (ii) AcOH, 70 °C, 4 h; (iii) n-PrBr, t-BuOK, DMF, 110 °C, 16 h; (iv) LiAlH4, THF, 70 °C, 2–3 h; (b) (v) 1) acetone, MeOH, 80 °C, 5 h; 2) NaBH4, rt, 3 h; (vi) MeNH3Cl, Et3N, EDCI, HOBt, DMF, 70 °C, 8–14 h. Calculated

A new and expeditious synthesis of all enantiomerically pure stereoisomers of rosaprostol, an antiulcer drug

• Wiesława Perlikowska,
• Remigiusz Żurawiński and
• Marian Mikołajczyk

Beilstein J. Org. Chem. 2016, 12, 2234–2239, doi:10.3762/bjoc.12.215

• cyclopentanone 3. Reagents and conditions: (a) Al2O3, SiO2, MS 5 Å, DCM, rt, 5 d; (b) cation exchanger Dowex 50WX4, MeOH/H2O 5:1, rt, 3 N HCl (drops), column chromatography. Synthesis of rosaprostol stereoisomers 1a and 1c. Reagents and conditions: (a) KOH/Al2O3, OHC(CH2)5CO2Me, C6H6, 3 h rt; (b) Te, NaBH4, EtOH

• , 6 h, rt; (c) 1 N NaOH, EtOH, 3 h, 45 °C; (d) L-Selectride, THF, −75 °C, 4 h. Conversion of methyl ester (+)-6 into rosaprostol (−)-1a. Reagents and conditions: (a) L-Selectride, THF, −45 °C, 3 h; (b) O2 (air), Pd/C, NaBH4, KOH, H2O/MeOH 2:1. Synthesis of rosaprostol stereoisomers 1b and 1d. Reagents

A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis

• Mariano Goldberg,
• Denis Sartakov,
• Jan W. Bats,
• Michael Bolte and
• Michael W. Göbel

Beilstein J. Org. Chem. 2016, 12, 1870–1876, doi:10.3762/bjoc.12.176

• equiv NaBH4, 1.2 equiv I2, THF, 66 °C, 18 h, 86%; (e) 1 equiv Boc2O, 1.2 equiv triethylamine, CH2Cl2, 0 °C, 3 h, 100%; (f) 1.1 equiv MsCl, 1.1 equiv triethylamine, CH2Cl2, 0 °C, 3 h, 79%; (g) 3 equiv NaN3, DMF, 24 °C, 120 h, 96%; (h) 2 equiv SO3*Py, 2.3 equiv pyridine, 4.1 equiv triethylamine, DMSO

• , CH2Cl2, 0 °C, 10 min, 24 °C, 2 h, 87%; (i) H2, Pd/C, MeOH, overnight, 84%; (k) 1 equiv 17, THF, 48 h, 2 equiv NaBH4; MeOH, 96 h, 58%; (l) 10 equiv TFA, CH2Cl2, 40 °C, 24 h, 100%; (m) 1.3 equiv dimethyl trithiocarbonate, MeNO2, 101 °C, 2 h, 4 equiv AcOH, 2 equiv MeI, 101 °C, 3 h, 67% as iodide salt 10a

Experimental and theoretical insights in the alkene–arene intramolecular π-stacking interaction

• Valeria Corne,
• Ariel M. Sarotti,
• Carmen Ramirez de Arellano,
• Rolando A. Spanevello and
• Alejandra G. Suárez

Beilstein J. Org. Chem. 2016, 12, 1616–1623, doi:10.3762/bjoc.12.158

• chemical transformations under microwave irradiation [17], affording the cycloadducts 3a,b in very good yields (76–81%) after irradiating a THF solution of 1 and 2 at 150 °C during 4 hours. The reduction of the ketone group in 3 with NaBH4 produced alcohols 4 and 5 in excellent yields and a ratio of about

Synthesis of a deuterated probe for the confocal Raman microscopy imaging of squalenoyl nanomedicines

• Eric Buchy,
• Branko Vukosavljevic,
• Maike Windbergs,
• Dunja Sobot,
• Camille Dejean,
• Simona Mura,
• Patrick Couvreur and
• Didier Desmaële

Beilstein J. Org. Chem. 2016, 12, 1127–1135, doi:10.3762/bjoc.12.109

• synthetic pathway described above was reimplemented starting from tert-butyldiphenylsiloxysqualene 23 readily obtained in 85% yield from squalenaldehyde 10 by NaBH4 reduction followed by protection with tert-butyldiphenylsilyl chloride. Functionalisation of the opposite extremity of the polyisoprenoid chain

Modular synthesis of the pyrimidine core of the manzacidins by divergent Tsuji–Trost coupling

• Sebastian Bretzke,
• Stephan Scheeff,
• Felicitas Vollmeyer,
• Friederike Eberhagen,
• Frank Rominger and
• Dirk Menche

Beilstein J. Org. Chem. 2016, 12, 1111–1121, doi:10.3762/bjoc.12.107

• [56][57], and the resulting aldehydes (not shown) were reduced to the terminal alcohols with NaBH4, giving the desired pyrimidinones 3 and 4. These compounds represent key intermediates which may be transformed into the targeted natural products 1 and 2 following previously established protocols [6

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

• Bin Yu,
• Hui Xing,
• De-Quan Yu and
• Hong-Min Liu

Beilstein J. Org. Chem. 2016, 12, 1000–1039, doi:10.3762/bjoc.12.98

• oxidative coupling sequence (Scheme 48). Similarly, the tricyclic N-heterocyclic core in natural (+)-asperazine and idiospermuline was also efficiently synthesized in 71% overall yield. The oxindole was reduced to the lactol by NaBH4, which was then subjected to a camphorsulfonic acid (CSA)-promoted

Elucidation of a masked repeating structure of the O-specific polysaccharide of the halotolerant soil bacteria Azospirillum halopraeferens Au4

• Elena N. Sigida,
• Yuliya P. Fedonenko,
• Alexander S. Shashkov,
• Nikolay P. Arbatsky,
• Evelina L. Zdorovenko,
• Svetlana A. Konnova,
• Vladimir V. Ignatov and
• Yuriy A. Knirel

Beilstein J. Org. Chem. 2016, 12, 636–642, doi:10.3762/bjoc.12.62

• with NaBH4, desalted with an Amberlit IR-120 (H+-form) resin and fractionated by exclusion chromatography on TSK HW-40 (S) in 1% AcOH to yield a mixture of oligosaccharide (OS) 1 and OS 2 (7 mg) and a higher molecular mass material. The latter was fractionated by HPLC on a reverse-phase Zorbax C18

A selective and mild glycosylation method of natural phenolic alcohols

• Mária Mastihubová and
• Monika Poláková

Beilstein J. Org. Chem. 2016, 12, 524–530, doi:10.3762/bjoc.12.51

• reduced by NaBH4 at pH 7–8, which was kept constant by the continuous addition of 85% H3PO4 to avoid phenolic acetyl-group cleavage. The p-acetoxybenzyl alcohols 6a–c were isolated in 85–95% yields. p-Hydroxyphenylacetic acid (7) and ferulic acid (10) are also more readily available on the market than the

• carboxylic function with NaBH4–I2 in THF (Scheme 2). Due to the higher lability of the phenolic acetate under basic conditions, the method published by Kanth and Periasamy [32] was slightly modified. For this, the reagents were added at lower temperature, the reaction time was prolonged and a solution of

• protected and deprotected products. Reagents and conditions: a) Ac2O, pyridine, rt, 10 h, >98%; b) NaBH4, H3PO4, −5 °C, 85–95%. Reagents and conditions: a) Ac2O, H2SO4, 5 °C to rt, 30 min, >94%; b) 1. NaBH4, THF, 5 °C, 10 min, 2. I2, 5 °C, 15 min, rt, 3 h, 84% for 9, 69% for 12. General reaction scheme for

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• , diastereoselective reduction of the cross-benzoin products with NaBH4 afforded valuable syn-diol products. Goodman and Johnson disclosed a dynamic kinetic resolution of β-halo-α-ketoesters via NHC-catalysed asymmetric cross-benzoin reaction. Here, the cross-benzoin reaction of aromatic aldehydes with β-stereogenic-α

Diastereoselective synthesis of new O-alkylated and C-branched inositols and their corresponding fluoro analogues

• Charlotte Collet,
• Françoise Chrétien,
• Yves Chapleur and
• Sandrine Lamandé-Langle

Beilstein J. Org. Chem. 2016, 12, 353–361, doi:10.3762/bjoc.12.39

• candidates for PET imaging experiments. Their potential use as radiotracers is under current investigation. Structures of targeted synthetic inositol derivatives. nOe correlations for C-alkenylated inositol intermediates. Synthesis of O-alkylated inositol derivatives 1. Reagents and conditions: a) NaBH4

Hydroquinone–pyrrole dyads with varied linkers

• Hao Huang,
• Christoffer Karlsson,
• Maria Strømme,
• Martin Sjödin and
• Adolf Gogoll

Beilstein J. Org. Chem. 2016, 12, 89–96, doi:10.3762/bjoc.12.10

• also investigated (vide infra), but did not produce satisfactory results. Settambolo et al. [20] reported a synthetic route starting from an acylation of pyrrole by phenylacetyl chloride via a Friedel–Crafts reaction, followed by reduction by NaBH4, and elimination to give the vinylpyrrole product

Selectively fluorinated cyclohexane building blocks: Derivatives of carbonylated all-cis-3-phenyl-1,2,4,5-tetrafluorocyclohexane

• Mohammed Salah Ayoup,
• David B. Cordes,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2015, 11, 2671–2676, doi:10.3762/bjoc.11.287

• –Smith method [13] as illustrated in Scheme 3. For further elaboration, aldehyde 15 was reduced with NaBH4 in good yield to generate the corresponding benzyl alcohol 19 [14]. Iodination of 19 to generate 20 with HI in chloroform [15] proved superior (95% yield) to the more classical Appel protocol which

• steps. iii. Zn, CH2I2, TiCl4, THF, 0 °C to 20 °C, 12 h; 79%. Reactions from aldehyde 15: i. NaBH4, THF, 20 °C, 1 h, 98%.; ii. HI (57%), CHCl3, 30 h, 95%; iii. Bu4NN3, acetone/H2O (4:1), 20 °C, 3 h, 94%; iv. MsCl, Et3N, DCM, −78 °C to 20 °C, 85%. Reactions of benzyl azide 21; i. 24, Cu(OAc)2, Na

• ascorbate, t-BuOH, H2O, 20 °C, 16 h, 72%; ii. HCl (6 M), 1,4-dioxane, 80 °C, 48 h, 96%; iii. Ph3P, THF/H2O (10:1), then HCl, rt, 1 h, 74%. Reactions of aldehyde 14: i. NaBH4, THF, rt, 1 h, 98%.; ii. HI (57%), CHCl3, 30 h, 94%; iii. Bu4NN3, acetone/H2O (4:1), rt, 3 h, 91%; iv. 24, Cu(OAc)2, Na ascorbate, t

A novel and practical asymmetric synthesis of dapoxetine hydrochloride

• Yijun Zhu,
• Zhenren Liu,
• Hongyan Li,
• Deyong Ye and
• Weicheng Zhou

Beilstein J. Org. Chem. 2015, 11, 2641–2645, doi:10.3762/bjoc.11.283

• screened and the results are presented in Table 1. Following a procedure reported in the literature [14], the reduction of 4 was carried out with NaBH4 in THF at 25 °C for 1 h (Table 1, entry 1). However, the main product was proven to be the denaphthalenyloxy compound 5’’ by 1H NMR and MS while the

• after reduction, the basicity resulting from NaBH4 might lead to the denaphthalenyloxylation. Therefore, AcOH was used as an additive in the reaction. The results showed that the denaphthalenyloxylation was almost negligible, but the diastereoselectivity was not good enough (Table 1, entry 5). Although