Synthesis of constrained analogues of tryptophan

• Elisabetta Rossi,
• Valentina Pirovano,
• Marco Negrato,
• Giorgio Abbiati and
• Monica Dell’Acqua

Beilstein J. Org. Chem. 2015, 11, 1997–2006, doi:10.3762/bjoc.11.216

• results are summarized in Table 1. The reaction was ineffective under thermal conditions (Table 1, entry 1). As a consequence we tested simple Lewis acids as potential promoters for the transformation. Magnesium perchlorate, scandium and copper triflate and boron trifluoride failed to give the desired

Polythiophene and oligothiophene systems modified by TTF electroactive units for organic electronics

• Alexander L. Kanibolotsky,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2015, 11, 1749–1766, doi:10.3762/bjoc.11.191

• units into a conjugated network is a standard way to narrow the HOMO/LUMO band gap and examples of such units include dioxopyrrolopyrrole (DPP) [17][18][19], benzodifuranone [20] and boron-dipyrromethene (BODIPY) [21][22]. As a different class of electroactive materials, TTF derivatives are well-known

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

• Louis P. Sandjo,
• Victor Kuete and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2015, 11, 1667–1699, doi:10.3762/bjoc.11.183

• indole catalyzed by potassium fluoride in alumina and a sufficient amount of 18-crown-6. The product obtained from this reaction was decarboxylated by copper chromite and quinolone to yield arnoamine B. This latter was then demethylated with boron tribromide to afford arnoamine A (40, Scheme 5) [63

Pyridine-promoted dediazoniation of aryldiazonium tetrafluoroborates: Application to the synthesis of SF₅-substituted phenylboronic esters and iodobenzenes

• George Iakobson,
• Junyi Du,
• Alexandra M. Z. Slawin and
• Petr Beier

Beilstein J. Org. Chem. 2015, 11, 1494–1502, doi:10.3762/bjoc.11.162

• -science [6][18][33][34][35][36][37][38], and material sciences [5][19][38][39] are emerging. Arylboronic acids and arylboronates represent versatile building blocks in organic synthesis [40]. They have found wide applications in transition metal-catalyzed cross-coupling reactions [41][42]. These boron

Synthesis of novel N-cyclopentenyl-lactams using the Aubé reaction

• Madhuri V. Shinde,
• Rohini S. Ople,
• Ekta Sangtani,
• Rajesh Gonnade and
• D. Srinivasa Reddy

Beilstein J. Org. Chem. 2015, 11, 1060–1067, doi:10.3762/bjoc.11.119

• ·OEt2 Boron trifluoride etherate (0.07 mL, 0.71 mmol) was added to a solution of azido alcohol 3 (0.10 g, 0.71 mmol) and ketones (2.0 mmol, 3 equiv) in HFIP (0.2 mL) cooled to 0 °C. The mixture was warmed to room temperature and stirred for 2–5 h. Upon completion, the reaction was quenched with 15% aq

Design, synthesis and photochemical properties of the first examples of iminosugar clusters based on fluorescent cores

• Mathieu L. Lepage,
• Antoine Mirloup,
• Manon Ripoll,
• Fabien Stauffert,
• Anne Bodlenner,
• Raymond Ziessel and
• Philippe Compain

Beilstein J. Org. Chem. 2015, 11, 659–667, doi:10.3762/bjoc.11.74

• insights into the multivalent effect observed in CFTR correcting activity. The originality of our approach relies on the fact that, in the structures designed, this is the scaffold itself [29][30], based on a pyrene or a boron-dipyrromethene (F-BODIPY) dye, which has fluorescence activity. Results and

• . Difluoroboradiaza-s-indacenes, commonly named boron-dipyrromethene dyes (F-BODIPY), were logically selected for the construction of the probes. These compounds indeed combine high fluorescence quantum yields and high molar extinction coefficients, strong chemical and photochemical stability in solution and in solid

• substitution at the boron has less influence on the spectroscopic properties of the dyes [42]. So far, major endeavors have been dedicated to the preparation of classical F-BODIPY structures and less common E-BODIPY (E for ethynyl) and the examination of their spectroscopic and salient physical properties [43

Weakly nucleophilic potassium aryltrifluoroborates in palladium-catalyzed Suzuki–Miyaura reactions: relative reactivity of K[4-RC₆F₄BF₃] and the role of silver-assistance in acceleration of transmetallation

• Vadim V. Bardin,
• Anton Yu. Shabalin and
• Nicolay Yu. Adonin

Beilstein J. Org. Chem. 2015, 11, 608–616, doi:10.3762/bjoc.11.68

• ability to transmetallation, to coordinate to the organoboronic acid with the three-coordinated boron atom to ArPdL2OH and subsequent transmetallation (Scheme 1). However, some experimental facts indicate the multilateral role of silver(I) compounds AgmY in the acceleration of the Suzuki–Miyaura cross

• the reaction and does not participate in the other steps [19][35]. The boron atom in K[4-RC6F4BF3] is coordinately saturated and transmetallation via transition state A (Scheme 1) is impossible. An alternative pathway is the polarization of the palladium–X bond by Ag+ and the generation of complex

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• of boron to α,β-unsaturated carbonyl compounds. Enantioenriched organoboron reagents are useful because they can be used in cross-coupling reactions [98][100] or they can be converted into the corresponding alcohol [101] while retaining the stereochemical information. Transition metals such as Cu

• [102][103][104][105][106][107][108][109][110][111][112], Rh [113][114][115], Ni [116][117], Pd [116][118] and Pt [119][120] have all been successfully used to catalyze the 1,4-additon of boron to α,β-unsaturated carbonyl compounds. Of the transition metals mentioned, copper is the most cost-effective

• and least toxic choice. Though there are many examples of copper-catalyzed 1,4-additions of boron, most of the reports use bis(pinacolato)diboron (B2pin2) as a source of boron. In 2013, Molander and co-workers reported the asymmetric 1,4-addition of bisboronic acid (BBA) and tetrakis(dimethylamino

Cathodic reductive coupling of methyl cinnamate on boron-doped diamond electrodes and synthesis of new neolignan-type products

• Taiki Kojima,
• Rika Obata,
• Tsuyoshi Saito,
• Yasuaki Einaga and
• Shigeru Nishiyama

Beilstein J. Org. Chem. 2015, 11, 200–203, doi:10.3762/bjoc.11.21

• methyl cinnamate on a boron-doped diamond (BDD) electrode was investigated. The hydrodimer, dimethyl 3,4-diphenylhexanedioate (racemate/meso = 74:26), was obtained in 85% yield as the major product, along with small amounts of cyclic methyl 5-oxo-2,3-diphenylcyclopentane-1-carboxylate. Two new neolignan

• -type products were synthesized from the hydrodimer. Keywords: boron-doped diamond (BDD) electrode; cathodic reduction; electrochemistry; electrosynthesis; neolignan; Introduction Numerous lignans and neolignans were found as secondary plant metabolites, and many of them are known to exhibit

• investigations. Several synthetic approaches, including electrochemical oxidative coupling reactions mimicking biosynthetic pathways, were reported to construct the backbones of these molecules [5]. Recently, boron-doped diamond (BDD) electrodes have attracted a great deal of attention for their wide potential

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

Efficient deprotection of F-BODIPY derivatives: removal of BF₂ using Brønsted acids

• Mingfeng Yu,
• Joseph K.-H. Wong,
• Cyril Tang,
• Peter Turner,
• Matthew H. Todd and
• Peter J. Rutledge

Beilstein J. Org. Chem. 2015, 11, 37–41, doi:10.3762/bjoc.11.6

• diversifying the F-BODIPY framework [9]. F-BODIPYs are readily prepared by condensing aldehydes, acyl chlorides or anhydrides with pyrroles and trapping the resulting dipyrrin in situ with boron trifluoride [9][10][11]. F-BODIPYs are generally stable and chemically robust, with photophysical properties that

• recent reports have deployed Lewis acids to achieve this transformation: Thompson and co-workers used boron trihalides in dichloromethane under anhydrous conditions, followed by treatment with acetone/water (10:1) to achieve quantitative removal of the BF2 moiety [18]; Ravikanth and co-workers screened a

• range of metal-based Lewis acids (ZrCl4, TiCl4, AlCl3, Sc(OTf)3, SnCl4) and reported yields up to 96% using ZrCl4 in refluxing methanol/acetonitrile [19]. Related efforts have wrought substitution at boron in F-BODIPY analogues without removing it from the dipyrrin. For example, Lundrigan et al. have

Redox active dendronized polystyrenes equipped with peripheral triarylamines

• Toshiki Nokami,
• Naoki Musya,
• Tatsuya Morofuji,
• Keiji Takeda,
• Masahiro Takumi,
• Akihiro Shimizu and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2014, 10, 3097–3103, doi:10.3762/bjoc.10.326

•  2. Di(p-bromophenyl)carbinol (1) was treated with SOCl2 to obtain di(p-bromophenyl)methyl chloride (2) in quantitative yield. A Friedel–Crafts-type alkylation [29] of diphenylsilane 3 with 2 in the presence of boron trifluoride etherate as a Lewis acid gave 4 in 86% yield. The oxidation potential of

Synthesis and properties of novel star-shaped oligofluorene conjugated systems with BODIPY cores

• Clara Orofino-Pena,
• Diego Cortizo-Lacalle,
• Joseph Cameron,
• Muhammad T. Sajjad,
• Pavlos P. Manousiadis,
• Neil J. Findlay,
• Alexander L. Kanibolotsky,
• Dimali Amarasinghe,
• Peter J. Skabara,
• Tell Tuttle,
• Graham A. Turnbull and
• Ifor D. W. Samuel

Beilstein J. Org. Chem. 2014, 10, 2704–2714, doi:10.3762/bjoc.10.285

• these two families were studied in order to determine their suitability as emissive materials in photonic applications. Keywords: absorption spectroscopy; BODIPY; cyclic voltammetry; photoluminescence; star-shaped oligofluorene; Introduction The boron-dipyrromethene (BODIPY) or 4,4-difluoro-4-bora-3a

Solution processable diketopyrrolopyrrole (DPP) cored small molecules with BODIPY end groups as novel donors for organic solar cells

• Diego Cortizo-Lacalle,
• Calvyn T. Howells,
• Upendra K. Pandey,
• Joseph Cameron,
• Neil J. Findlay,
• Anto Regis Inigo,
• Tell Tuttle,
• Peter J. Skabara and
• Ifor D. W. Samuel

Beilstein J. Org. Chem. 2014, 10, 2683–2695, doi:10.3762/bjoc.10.283

• ). Compound 6 was prepared by acid-catalysed condensation of 5-bromothiophene-2-carbaldehyde with 3-ethyl-2,4-dimethylpyrrole, followed by oxidation with DDQ. Deprotonation with triethylamine and subsequent treatment with boron trifluoride diethyl etherate yielded 6. The entire synthesis was carried out as a

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids

• Roman Matthessen,
• Jan Fransaer,
• Koen Binnemans and
• Dirk E. De Vos

Beilstein J. Org. Chem. 2014, 10, 2484–2500, doi:10.3762/bjoc.10.260

• prepared using cyanides. In the proposed setup for the electrocatalytic preparation of MHA, a boron-doped diamond coated permeable cathode and Pt coated permeable anode rest directly on the cation exchange membrane to decrease ohmic resistance by the membrane, minimizing the required voltage. Hydrogen

A small azide-modified thiazole-based reporter molecule for fluorescence and mass spectrometric detection

• Stefanie Wolfram,
• Hendryk Würfel,
• Stefanie H. Habenicht,
• Christine Lembke,
• Phillipp Richter,
• Eckhard Birckner,
• Rainer Beckert and
• Georg Pohnert

Beilstein J. Org. Chem. 2014, 10, 2470–2479, doi:10.3762/bjoc.10.258

• unproblematic toxicology they have almost completely replaced radioactive tags. Widely used representatives include dansyl chloride, fluoresceins, rhodamines and boron-dipyrromethenes (BODIPYs) [1]. Dansyl chloride, with a maximum UV–vis absorption at 369 nm, is one of the first extrinsic fluorescent dyes

Automated solid-phase peptide synthesis to obtain therapeutic peptides

• Veronika Mäde,
• Sylvia Els-Heindl and
• Annette G. Beck-Sickinger

Beilstein J. Org. Chem. 2014, 10, 1197–1212, doi:10.3762/bjoc.10.118

• -histidinyl acetyl (NαHis-ac) chelator (Figure 5) was attached to lysine side chains or the N-terminus of the peptide by manual coupling, whereas the chelation with 99mTc occurred in solution [133]. The incorporation of carbaboranes that can be used for boron neutron capture therapy demonstrated the potential

Amino acid motifs in natural products: synthesis of O-acylated derivatives of (2S,3S)-3-hydroxyleucine

• Oliver Ries,
• Martin Büschleb,
• Markus Granitzka,
• Dietmar Stalke and
• Christian Ducho

Beilstein J. Org. Chem. 2014, 10, 1135–1142, doi:10.3762/bjoc.10.113

• to introduce an N,O-acetal moiety by transformation of 7 into the dimethyloxazolidine 8, a reaction which required careful optimization though (Scheme 2, Table 1). Using boron trifluoride and 2,2-dimethoxypropane (2,2-DiMP), as known from the synthesis of the structurally related Garner's aldehyde

Synthesis of zearalenone-16-β,D-glucoside and zearalenone-16-sulfate: A tale of protecting resorcylic acid lactones for regiocontrolled conjugation

• Hannes Mikula,
• Julia Weber,
• Dennis Svatunek,
• Philipp Skrinjar,
• Gerhard Adam,
• Rudolf Krska,
• Christian Hametner and
• Johannes Fröhlich

Beilstein J. Org. Chem. 2014, 10, 1129–1134, doi:10.3762/bjoc.10.112

• rather harsh unfavorable demethylation with boron tribromide in the last step [26]. Without structure verification and characterization ZEN-16-β,D-glucoside (7, Figure 2B) was tentatively identified as a byproduct of the Königs–Knorr glucosylation of ZEN for preparation of ZEN-14-glucoside [27]. In the

Palladium-catalysed cross-coupling reaction of ultra-stabilised 2-aryl-1,3-dihydro-1H-benzo[d]1,3,2-diazaborole compounds with aryl bromides: A direct protocol for the preparation of unsymmetrical biaryls

• Siphamandla Sithebe and
• Ross S. Robinson

Beilstein J. Org. Chem. 2014, 10, 1107–1113, doi:10.3762/bjoc.10.109

• π-conjugated organic molecules containing a three-coordinate boron moiety such as trimesitylborane (4), arylalkynyldimesitylborane 5 and 2-aryl-1,3-diethyl-1H-benzo[d]1,3,2-diazaborole 6 (Figure 2) are well known and have received considerable attention due to their interesting luminescence

• characteristics, fluoride ion sensing abilities, emissive as well as electron-transporting properties [8][9][10][11]. Three-coordinate boron compounds are electron-poor and strong π-electron acceptors owing to the empty boron pz-orbital, which is capable of significant delocalisation when attached to an organic π

• -system [11]. These compounds exhibit an unusual stability because of the bulky aryl groups, such as mesityl (2,4,6-trimethylphenyl) groups, which provide steric conjunction around the empty boron pz-orbital thereby blocking the incoming nucleophile (Figure 2, compounds 4 and 5) [12]. Alternatively, three

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• , we propose mechanisms for the stereospecific isomerization. The isomerization process is initiated by BF3 complexation. Boron trifluoride may complex silybin through a coordinate bond, in which the two electrons originate from the oxygen atoms of silybin. Silybin and BF3 are hard bases (η = 4.8 eV in

• (compared to O-9) by 4 kcal·mol−1. The coordination with boron initiates isomerization at C-2, C-3 and C-10, C-11 by charge rearrangements (e.g., proton release and formation of IIb in Scheme 5). The mechanisms related to both sites can be considered separately, as both moieties are electronically

N-Alkylated dinitrones from isosorbide as cross-linkers for unsaturated bio-based polyesters

• Oliver Goerz and
• Helmut Ritter

Beilstein J. Org. Chem. 2014, 10, 902–909, doi:10.3762/bjoc.10.88

• acid yielding isosorbide diacrylate (9a) and isosorbide dicrotonate (9b), which were reacted with benzaldehyde oxime in the presence of zinc(II) iodide and boron triflouride etherate as catalysts to obtain N-alkylated dinitrones 10a/b. Poly(isosorbide itaconite -co- succinate) 13 as a bio-based

• -toluenesulfonic acid, phenothiazine (98%), zinc iodide (98%), and boron trifluoride diethyl etherate (46%) were purchased from Sigma-Aldrich and used as received. Isosorbide (98%) and E-benzaldoxime (97%) were purchased from Alfa Aesar, and isosorbide was recrystallized from acetone/ethyl acetate. All used

• methyl 3-[benzylidene(oxido)amino]propanoate (3a): Methyl acrylate (2a, 0.86 g, 10 mmol) and benzaldoxime (1, 2.42 g, 20 mmol) were placed in a 100 mL round bottom flask and dissolved in 20 mL toluene. Zinc iodide (0.32 g, 1 mmol) and boron triflouride diethyl etherate (0.30 g, 1 mmol) were added. The

Clean and fast cross-coupling of aryl halides in one-pot

• Valerica Pandarus,
• Geneviève Gingras,
• François Béland,
• Rosaria Ciriminna and
• Mario Pagliaro

Beilstein J. Org. Chem. 2014, 10, 897–901, doi:10.3762/bjoc.10.87

• involves a boron-containing nucleophile (a variety of aryl and heteroaryl boronic acids, esters, Ar-BBN, trifluoroborate and other boron species) and vinyl- or aryl halides as the electrophilic species. The use of the Suzuki–Miyaura reaction became routine both in industry and in research laboratories

Molecular recognition of isomeric protonated amino acid esters monitored by ESI-mass spectrometry

• Andrea Liesenfeld and
• Arne Lützen

Beilstein J. Org. Chem. 2014, 10, 825–831, doi:10.3762/bjoc.10.78

• Grignard reagent which was reacted with 9-fluorenone to afford tertiary alcohol 4 in 55% yield. Adopting a protocol of Tour et al. [16] led to 2-methoxy-9,9'-spirobifluorene (5) in 95% yield via acidic condensation of 4. Next, the methoxy group was cleaved quantitatively by reaction with boron tribromide

• , followed by hydrolysis to afford phenol 6 which was finally transferred into the corresponding triflate 7 in 64% yield (Scheme 1). Triflate 7 was then subjected to a Sonogashira cross-coupling reaction and a Suzuki cross-coupling reaction followed by treatment with boron tribromide to obtain the

Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines

• Jian-bo Xie,
• Jian Luo,
• Timothy R. Winn,
• David B. Cordes and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 746–751, doi:10.3762/bjoc.10.69

• hexanes. The solid product was collected and dried in vacuo. The yield was calculated from the starting amide 1. The dr value and purity were checked by 31P NMR and 1H NMR. ORTEP diagram of (S,S,R)-3a (left, most of the hydrogen atoms were omitted except the one on the chiral center connected to boron