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Search for "chelation" in Full Text gives 109 result(s) in Beilstein Journal of Organic Chemistry.
Cross-metathesis of allylcarboranes with O-allylcyclodextrins
- Ivan Šnajdr,
- Zbyněk Janoušek,
- Jindřich Jindřich and
- Martin Kotora
Beilstein J. Org. Chem. 2010, 6, 1099–1105, doi:10.3762/bjoc.6.126
- reactions, which has also been observed in other metathetical reactions with alkenylcyclodextrins derivatives [27] and can be explained by several factors [28]. Firstly, by a chelation of the intermediate Ru-carbene complex to the oxygen atoms of the cyclodextrin which results in a conformationally rigid
Graphical Abstract
Figure 1: Starting allylcarboranes 1a–1c and O-allylcyclodextrins 2a–2c.
Scheme 1: Cross-metathesis of allylcarboranes 1 and O-allylcyclodextrins 2.
Halide exchanged Hoveyda-type complexes in olefin metathesis
- Julia Wappel,
- César A. Urbina-Blanco,
- Mudassar Abbas,
- Jörg H. Albering,
- Robert Saf,
- Steven P. Nolan and
- Christian Slugovc
Beilstein J. Org. Chem. 2010, 6, 1091–1098, doi:10.3762/bjoc.6.125
- : leaving group, e.g. phosphine or pyridine; olive: carbine substituents; and dashed lines symbolise possibilities of chelation). Three commercial and frequently used catalysts (G2: Grubbs 2nd generation catalyst; M2: Neolyst M2; and 1: Hoveyda 2nd generation catalyst). Details of the 1H NMR spectra
Graphical Abstract
Figure 1: General layout for modifications of ruthenium-based olefin metathesis catalysts (red: anionic ligan...
Scheme 1: Synthesis of 1, 2 and 3.
Figure 2: Details of the 1H NMR spectra acquired during the synthesis of 2 and the FD-MS spectrum of 2 isolat...
Figure 3: ORTEP drawing of 3. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms are omitt...
Figure 4: Polymerisation of 4 as a function of time, initiated by 1, 2 or 3, monitored by 1H NMR spectroscopy...
Figure 5: Polymerisations of 6 as a function of time, initiated by 1–3, monitored by 1H NMR spectroscopy (sol...
Figure 6: The RCM reaction of 7 as a function of time, catalysed by 1, 2 or 3, monitored by 1H NMR spectrosco...
Chromo- and fluorophoric water-soluble polymers and silica particles by nucleophilic substitution reaction of poly(vinyl amine)
- Katja Hofmann,
- Ingolf Kahle,
- Frank Simon and
- Stefan Spange
Beilstein J. Org. Chem. 2010, 6, No. 79, doi:10.3762/bjoc.6.79
- hydrolyzed PVFA contains ca. 5% of formamido groups and 95% of primary amino groups. The water-soluble PVAm copolymer has been widely applied for a number of purposes, e.g., in catalysis [7], chelation [8], treatment of waste water [9], paper making [10], recovery of oil [11] and as superabsorber [12
Graphical Abstract
Scheme 1: Synthesis of carbonitrile 1.
Scheme 2: Coupling of the β-DMCD-caged carbonitrile derivative 1-DMCD with PVAm to yield the fluorophore-func...
Figure 1: Solid state 13C-{1H}-CP-MAS NMR spectra of pure PVAm (a), functionalized PVAm 1-P (b) and the model...
Scheme 3: Synthesis of 1-Si by nucleophilic aromatic substitution of 1 adsorbed onto silica particles.
Figure 2: Wide-scan X-ray photoelectron spectra (left), C 1s and N 1s high-resolution spectra (right) of bare...
Figure 3: Pore-size distribution of bare silica, PVAm/silica and 1-Si.
Figure 4: UV–vis absorption and emission diffuse reflectance spectra of sample 1-Si.
Figure 5: Normalized absorption and emission spectra of 1-M (a) and 1-P (b).
Figure 6: Normalized emission spectra of 1-P in water at four different pH values and a sketch of the assumed...
Recent advances in carbocupration of α-heterosubstituted alkynes
- Ahmad Basheer and
- Ilan Marek
Beilstein J. Org. Chem. 2010, 6, No. 77, doi:10.3762/bjoc.6.77
- species resulting from the addition of 1 equivalent of alkylmagnesium bromide [R1 = primary, secondary and benzyl groups] to 1 equivalent of copper salt leads, after reaction with electrophiles, to the unique formation of the linear adducts 11 in excellent isolated yields. The intramolecular chelation of
- (−40 instead of −78 °C), which can be attributed to a slow copper to magnesium contrathermodynamic transmetalation reaction, probably due to a strong intramolecular chelation of the sp2 organometallic derivative by the carbamate moiety. N-substituted alkynes Nitrogen-substituted alkynes (ynamine
- (branched/linear: 82/18), again showing that the chelation effect plays a major role in the regiochemistry of the carbometalation. The carbometalation of enantiomerically enriched cyclic ynamide 20 was recently used in a single-pot operation as a new entry to aldol products 21 possessing quaternary
Graphical Abstract
Scheme 1: General scheme for the carbocupration reaction.
Scheme 2: Regioselectivity in the carbocupration reaction.
Scheme 3: Carbocupration of α-alkoxyalkynes.
Scheme 4: Carbocupration of substituted α-alkoxyalkynes.
Scheme 5: Formation of the branched isomer.
Scheme 6: Formation of the linear isomer.
Scheme 7: Carbocupration of O-alkynyl carbamates.
Scheme 8: Carbocupration of ynamines.
Scheme 9: Carbocupration of ynamide.
Scheme 10: Formation of aldol products possessing stereogenic quaternary carbon centers.
Scheme 11: Carbocupration of alkynyl sulfonamide.
Scheme 12: Tandem carbocupration-sigmatropic rearrangement.
Scheme 13: Silylcupration of alkynyl sulfonamides.
Scheme 14: Carbocupration of P-substituted alkynes.
Scheme 15: Carbocupration of alkynylphosphonates.
Scheme 16: Carbocupration of thioalkynes.
Scheme 17: Tandem carbocupration-1,2-metalate rearrangement.
Scheme 18: Carbocupration with functionalized organocopper species.
Scheme 19: Carbocupration of alkynyl sulfoxides.
Scheme 20: Carbocupration of alkynyl sulfones.
Scheme 21: Carbocupration of alkynyl sulfoximines.
Scheme 22: Carbocupration of alkynylsilanes.
Scheme 23: Carbocupration of functionalized alkynylsilanes.
Scheme 24: Silyl- and stannyl cupration of silyl- and stannylalkynes.
Anion receptors containing thiazine-1,1-dioxide heterocycles as hydrogen bond donors
- Hong-Bo Wang,
- James A. Wisner and
- Michael C. Jennings
Beilstein J. Org. Chem. 2010, 6, No. 50, doi:10.3762/bjoc.6.50
- , occlude this central cleft like those of 1 and 2. Rather, they form a divergent “V”-shaped geometry upon chelation of anionic species by the two NH groups of 3, regardless of whether coplanarity is maintained with the central benzene ring. The ortho-protons of these terminal rings (Hc) are certainly too
Graphical Abstract
Figure 1: Structures of thiazine-1,1-dioxide heterocycle (A) and sulfonamide function (B).
Figure 2: Structures of anion receptors 1–4.
Scheme 1: Syntheses of 1 and 2. Reaction conditions: (a) (X = CH) NBS, TsOH, CH3CN, reflux or (X = N) Br2, Al...
Figure 3: Stick representations of the X-ray crystal structures of (a) receptor 1 and (b) receptor 2. Non-aci...
Anthracene coupled adenine for the selective sensing of copper ions
- Kumaresh Ghosh and
- Tanushree Sen
Beilstein J. Org. Chem. 2010, 6, No. 44, doi:10.3762/bjoc.6.44
- presumably occur by the chelation enhanced anthracene → Cu2+ π-cation interactions, the paramagnetic effect of Cu2+ [34][35][36]. To understand the selective sensing of Cu2+ by both 1 and 2, we recorded the emission spectra of the receptors with the addition of 10 equivalents of Cu2+ to the receptor
Graphical Abstract
Scheme 1: Adenine-based receptors 1 and 2.
Scheme 2: Syntheses of receptors 1 and 2.
Figure 1: Design principle for 1 and 2.
Figure 2: AM1 optimized geometries of 1 (E = −162.48 au) of 2 (E = −139.59 au).
Figure 3: a) Fluorescence ratio (I-I0/I0) of receptor 1 (c = 5.09 × 10−5 M) at 413 nm upon addition of 20 equ...
Figure 4: Emission spectra of receptor 1 (c = 5.09 × 10−5 M) during titration with Cu2+ ion (c = 1.4 × 10−3 M...
Figure 5: a) Emission spectra of receptor 2 (c = 1.48 × 10−5 M) during titration with Cu2+ ion (c = 4.4 × 10−4...
Figure 6: Stern–Volmer plot of receptor 2 (c = 1.48 × 10−5 M) at 413 nm upon addition of 20 equiv of a partic...
Figure 7: Change in emission of 1 (c = 8.66 × 10−5 M) (a) and 2 (c = 1.29 × 10−4 M) (b) upon addition of 10 e...
Figure 8: a) Binding constant curve for 1 with Cu2+ ion; b) binding constant curve for 2 with Cu2+ ion.
Figure 9: a) Absorption spectra of receptor 1 (c = 5.09 × 10−5 M) upon gradual addition of Cu2+ ion (c = 1.4 ...
Figure 10: a) Absorption spectra of receptor 2 (c = 1.48 × 10−5 M) upon gradual addition of Ag+ ion (c = 4.4 ×...
Figure 11: Absorption spectra of anthracene (c = 2.39 × 10−5 M) upon gradual addition of Cu2+ ion (c = 1.20 × ...
Molecular recognition of organic ammonium ions in solution using synthetic receptors
- Andreas Späth and
- Burkhard König
Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32
Graphical Abstract
Figure 1: Biologically important amines and quaternary ammonium salts: histamine (1), dopamine (2) and acetyl...
Figure 2: Crown ether 18-crown-6.
Figure 3: Conformations of 18-crown-6 (4) in solvents of different polarity.
Figure 4: Binding topologies of the ammonium ion depending on the crown ring size.
Figure 5: A “pseudorotaxane” structure consisting of 24-crown-8 and a secondary ammonium ion (5); R = Ph.
Figure 6: Typical examples of azacrown ethers, cryptands and related aza macrocycles.
Figure 7: Binding of ammonium to azacrown ethers and cryptands [111-113].
Figure 8: A 19-crown-6-ether with decalino blocking groups (11) and a thiazole-dibenzo-18-crown-6-ether (12).
Figure 9: 1,3-Bis(6-oxopyridazin-1-yl)propane derivatives 13 and 14 by Campayo et al.
Figure 10: Fluorescent azacrown-PET-sensors based on coumarin.
Figure 11: Two different pyridino-cryptands (17 and 18) compared to a pyridino-crown (19); chiral ammonium ion...
Figure 12: Pyridino-18-crown-6 ligand (21), a similar acridino-18-crown-6 ligand (22) and a structurally relat...
Figure 13: Ciral pyridine-azacrown ether receptors 24.
Figure 14: Chiral 15-crown-5 receptors 26 and an analogue 18-crown-6 ligand 27 derived from amino alcohols.
Figure 15: C2-symmetric chiral 18-crown-6 amino alcohol derivatives 28 and related macrocycles.
Figure 16: Macrocycles with diamide-diester groups (30).
Figure 17: C2-symmetric chiral aza-18-crown-6 ethers (31) with phenethylamine residues.
Figure 18: Chiral C-pivot p-methoxy-phenoxy-lariat ethers.
Figure 19: Chiral lariat crown ether 34.
Figure 20: Sucrose-based chiral crown ether receptors 36.
Figure 21: Permethylated fructooligosaccharide 37 showing induced-fit chiral recognition.
Figure 22: Biphenanthryl-18-crown-6 derivative 38.
Figure 23: Chiral lariat crown ethers derived from binol by Fuji et al.
Figure 24: Chiral phenolic crown ether 41 with “aryl chiral barriers” and guest amines.
Figure 25: Chiral bis-crown receptor 43 with a meso-ternaphthalene backbone.
Figure 26: Chromogenic pH-dependent bis-crown chemosensor 44 for diamines.
Figure 27: Triamine guests for binding to receptor 44.
Figure 28: Chiral bis-crown phenolphthalein chemosensors 46.
Figure 29: Crown ether amino acid 47.
Figure 30: Luminescent receptor 48 for bis-alkylammonium guests.
Figure 31: Luminescent CEAA (49a), a bis-CEAA receptor for amino acids (49b) and the structure of lysine bindi...
Figure 32: Luminescent CEAA tripeptide for binding small peptides.
Figure 33: Bis crown ether 51a self assembles co-operatively with C60-ammonium ion 51b.
Figure 34: Triptycene-based macrotricyclic dibenzo-[24]-crown-8 ether host 52 and guests.
Figure 35: Copper imido diacetic acid azacrown receptor 53a and the suggested His-Lys binding motif; a copper ...
Figure 36: Urea (54) and thiourea (55) benzo crown receptor for transport and extraction of amino acids.
Figure 37: Crown pyryliums ion receptors 56 for amino acids.
Figure 38: Ditopic sulfonamide bridged crown ether receptor 57.
Figure 39: Luminescent peptide receptor 58.
Figure 40: Luminescent receptor 59 for the detection of D-glucosamine hydrochloride in water/ethanol and lumin...
Figure 41: Guanidinium azacrown receptor 61 for simple amino acids and ditopic receptor 62 with crown ether an...
Figure 42: Chiral bicyclic guanidinium azacrown receptor 63 and similar receptor 64 for the enantioselective t...
Figure 43: Receptors for zwitterionic species based on luminescent CEAAs.
Figure 44: 1,10-Azacrown ethers with sugar podand arms and the anticancer agent busulfan.
Figure 45: Benzo-18-crown-6 modified β-cyclodextrin 69 and β-cyclodextrin functionalized with diaza-18-crown-6...
Figure 46: Receptors for colorimetric detection of primary and secondary ammonium ions.
Figure 47: Porphyrine-crown-receptors 72.
Figure 48: Porphyrin-crown ether conjugate 73 and fullerene-ammonium ion guest 74.
Figure 49: Calix[4]arene (75a), homooxocalix[4]arene (75b) and resorcin[4]arene (75c) compared (R = H, alkyl c...
Figure 50: Calix[4]arene and ammonium ion guest (R = H, alkyl, OAcyl etc.), possible binding sites; A: co-ordi...
Figure 51: Typical guests for studies with calixarenes and related molecules.
Figure 52: Lower rim modified p-tert-butylcalix[5]arenes 82.
Figure 53: The first example of a water soluble calixarene.
Figure 54: Sulfonated water soluble calix[n]arenes that bind ammonium ions.
Figure 55: Displacement assay for acetylcholine (3) with a sulfonato-calix[6]arene (84b).
Figure 56: Amino acid inclusion in p-sulfonatocalix[4]arene (84a).
Figure 57: Calixarene receptor family 86 with upper and lower rim functionalization.
Figure 58: Calix[6]arenes 87 with one carboxylic acid functionality.
Figure 59: Sulfonated calix[n]arenes with mono-substitution at the lower rim systematically studied on their r...
Figure 60: Cyclotetrachromotropylene host (91) and its binding to lysine (81c).
Figure 61: Calixarenes 92 and 93 with phosphonic acids groups.
Figure 62: Calix[4]arene tetraphosphonic acid (94a) and a double bridged analogue (94b).
Figure 63: Calix[4]arene tetraphosphonic acid ester (92c) for surface recognition experiments.
Figure 64: Calixarene receptors 95 with α-aminophosphonate groups.
Figure 65: A bridged homocalix[3]arene 95 and a distally bridged homocalix[4]crown 96.
Figure 66: Homocalix[3]arene ammonium ion receptor 97a and the Reichardt’s dye (97b) for colorimetric assays.
Figure 67: Chromogenic diazo-bridged calix[4]arene 98.
Figure 68: Calixarene receptor 99 by Huang et al.
Figure 69: Calixarenes 100 reported by Parisi et al.
Figure 70: Guest molecules for inclusion in calixarenes 100: DAP × 2 HCl (101a), APA (101b) and Lys-OMe × 2 HC...
Figure 71: Different N-linked peptido-calixarenes open and with glycol chain bridges.
Figure 72: (S)-1,1′-Bi-2-naphthol calixarene derivative 104 published by Kubo et al.
Figure 73: A chiral ammonium-ion receptor 105 based on the calix[4]arene skeleton.
Figure 74: R-/S-phenylalaninol functionalized calix[6]arenes 106a and 106b.
Figure 75: Capped homocalix[3]arene ammonium ion receptor 107.
Figure 76: Two C3 symmetric capped calix[6]arenes 108 and 109.
Figure 77: Phosphorous-containing rigidified calix[6]arene 110.
Figure 78: Calix[6]azacryptand 111.
Figure 79: Further substituted calix[6]azacryptands 112.
Figure 80: Resorcin[4]arene (75c) and the cavitands (113).
Figure 81: Tetrasulfonatomethylcalix[4]resorcinarene (114).
Figure 82: Resorcin[4]arenes (115a/b) and pyrogallo[4]arenes (115c, 116).
Figure 83: Displacement assay for acetylcholine (3) with tetracyanoresorcin[4]arene (117).
Figure 84: Tetramethoxy resorcinarene mono-crown-5 (118).
Figure 85: Components of a resorcinarene based displacement assay for ammonium ions.
Figure 86: Chiral basket resorcin[4]arenas 121.
Figure 87: Resorcinarenes with deeper cavitand structure (122).
Figure 88: Resorcinarene with partially open deeper cavitand structure (123).
Figure 89: Water-stabilized deep cavitands with partially structure (124, 125).
Figure 90: Charged cavitands 126 for tetralkylammonium ions.
Figure 91: Ditopic calix[4]arene receptor 127 capped with glycol chains.
Figure 92: A calix[5]arene dimer for diammonium salt recognition.
Figure 93: Calixarene parts 92c and 129 for the formation molecular capsules.
Figure 94: Encapsulation of a quaternary ammonium cation by two resorcin[4]arene molecules (NMe4+@[75c]2 × Cl−...
Figure 95: Encapsulation of a quaternary ammonium cation by six resorcin[4]arene molecules (NMe3D+@[130]6 × Cl−...
Figure 96: Structure and schematic of cucurbit[6]uril (CB[6], 131a).
Figure 97: Cyclohexanocucurbit[6]uril (CB′[6], 132) and the guest molecule spermine (133).
Figure 98: α,α,δ,δ-Tetramethylcucurbit[6]uril (134).
Figure 99: Structure of the cucurbituril-phthalhydrazide analogue 135.
Figure 100: Organic cavities for the displacement assay for amine differentiation.
Figure 101: Displacement assay methodology for diammonium- and related guests involving cucurbiturils and some ...
Figure 102: Nor-seco-Cucurbituril (±)-bis-ns-CB[6] (140) and guest molecules.
Figure 103: The cucurbit[6]uril based complexes 141 for chiral discrimination.
Figure 104: Cucurbit[7]uril (131c) and its ferrocene guests (142) opposed.
Figure 105: Cucurbit[7]uril (131c) guest inclusion and representative guests.
Figure 106: Cucurbit[7]uril (131c) binding to succinylcholine (145) and different bis-ammonium and bis-phosphon...
Figure 107: Paraquat-cucurbit[8]uril complex 149.
Figure 108: Gluconuril-based ammonium receptors 150.
Figure 109: Examples of clefts (151a), tweezers (151b, 151c, 151d) and clips (151e).
Figure 110: Kemp’s triacid (152a), on example of Rebek’s receptors (152b) and guests.
Figure 111: Amino acid receptor (154) by Rebek et al.
Figure 112: Hexagonal lattice designed hosts by Bell et al.
Figure 113: Bell’s amidinium receptor (156) and the amidinium ion (157).
Figure 114: Aromatic phosphonic acids.
Figure 115: Xylene phosphonates 159 and 160a/b for recognition of amines and amino alcohols.
Figure 116: Bisphosphonate recognition motif 161 for a colorimetric assay with alizarin complexone (163) for ca...
Figure 117: Bisphosphonate/phosphate clip 164 and bisphosphonate cleft 165.
Figure 118: N-Methylpyrazine 166a, N-methylnicotinamide iodide (166b) and NAD+ (166c).
Figure 119: Bisphosphate cavitands.
Figure 120: Bisphosphonate 167 of Schrader and Finocchiaro.
Figure 121: Tweezer 168 for noradrenaline (80b).
Figure 122: Different tripods and heparin (170).
Figure 123: Squaramide based receptors 172.
Figure 124: Cage like NH4+ receptor 173 of Kim et al.
Figure 125: Ammonium receptors 174 of Chin et al.
Figure 126: 2-Oxazolin-based ammonium receptors 175a–d and 176 by Ahn et al.
Figure 127: Racemic guest molecules 177.
Figure 128: Tripods based on a imidazole containing macrocycle (178) and the guest molecules employed in the st...
Figure 129: Ammonium ion receptor 180.
Figure 130: Tetraoxa[3.3.3.3]paracyclophanes 181 and a cyclophanic tetraester (182).
Figure 131: Peptidic bridged paraquat-cyclophane.
Figure 132: Shape-selective noradrenaline host.
Figure 133: Receptor 185 for binding of noradrenaline on surface layers from Schrader et al.
Figure 134: Tetraphosphonate receptor for binding of noradrenaline.
Figure 135: Tetraphosphonate 187 of Schrader and Finocchiaro.
Figure 136: Zinc-Porphyrin ammonium-ion receptors 188 and 189 of Mizutani et al.
Figure 137: Zinc porphyrin receptor 190.
Figure 138: Zinc porphyrin receptors 191 capable of amino acid binding.
Figure 139: Zinc-porphyrins with amino acid side chains for stereoinduction.
Figure 140: Bis-zinc-bis-porphyrin based on Tröger’s base 193.
Figure 141: BINAP-zinc-prophyrin derivative 194 and it’s guests.
Figure 142: Bisaryl-linked-zinc-porphyrin receptors.
Figure 143: Bis-zinc-porphyrin 199 for diamine recognition and guests.
Figure 144: Bis-zinc-porphyrin crown ether 201.
Figure 145: Bis-zinc-porphyrin 202 for stereodiscrimination (L = large substituent; S = small substituent).
Figure 146: Bis-zinc-porphyrin[3]rotaxane and its copper complex and guests.
Figure 147: Dien-bipyridyl ligand 206 for co-ordination of two metal atoms.
Figure 148: The ligand and corresponding tetradentate co-complex 207 serving as enantioselective receptor for a...
Figure 149: Bis(oxazoline)–copper(II) complex 208 for the recognition of amino acids in aqueous solution.
Figure 150: Zinc-salen-complexes 209 for the recognition tertiary amines.
Figure 151: Bis(oxazoline)–copper(II) 211 for the recognition of amino acids in aqueous solution.
Figure 152: Zn(II)-complex of a C2 terpyridine crown ether.
Figure 153: Displacement assay and receptor for aspartate over glutamate.
Figure 154: Chiral complex 214 for a colorimetric displacement assay for amino acids.
Figure 155: Metal complex receptor 215 with tripeptide side arms.
Figure 156: A sandwich complex 216 and its displaceable dye 217.
Figure 157: Lanthanide complexes 218–220 for amino acid recognition.
Figure 158: Nonactin (221), valinomycin (222) and vancomycin (223).
Figure 159: Monesin (224a) and a chiral analogue for enantiodiscrimination of ammonium guests (224b).
Figure 160: Chiral podands (226) compared to pentaglyme-dimethylether (225) and 18-crown-6 (4).
Figure 161: Lasalocid A (228).
Figure 162: Lasalocid derivatives (230) of Sessler et al.
Figure 163: The Coporphyrin I tetraanion (231).
Figure 164: Linear and cyclic peptides for ammonium ion recognition.
Figure 165: Cyclic and bicyclic depsipeptides for ammonium ion recognition.
Figure 166: α-Cyclodextrin (136a) and novocaine (236).
Figure 167: Helical diol receptor 237 by Reetz and Sostmann.
Figure 168: Ammonium binding spherand by Cram et al. (238a) and the cyclic[6]metaphenylacetylene 238b in compar...
Figure 169: Receptor for peptide backbone and ammonium binding (239).
Figure 170: Anion sensor principle with 3-hydroxy-2-naphthanilide of Jiang et al.
Figure 171: 7-bromo-3-hydroxy-N-(2-hydroxyphenyl)naphthalene 2-carboxamide (241) and its amine binding.
Figure 172: Naturally occurring catechins with affinity to quaternary ammonium ions.
Figure 173: Spiropyran (244) and merocyanine form (244a) of the amino acid receptors of Fuji et al.
Figure 174: Coumarin aldehyde (245) and its iminium species with amino acid bound (245a) by Glass et al.
Figure 175: Coumarin aldehyde appended with boronic acid.
Figure 176: Quinolone aldehyde dimers by Glass et al.
Figure 177: Chromogenic ammonium ion receptors with trifluoroacetophenone recognition motifs.
Figure 178: Chromogenic ammonium ion receptor with trifluoroacetophenone recognition motif bound on different m...
An efficient partial synthesis of 4′-O-methylquercetin via regioselective protection and alkylation of quercetin
- Nian-Guang Li,
- Zhi-Hao Shi,
- Yu-Ping Tang,
- Jian-Ping Yang and
- Jin-Ao Duan
Beilstein J. Org. Chem. 2009, 5, No. 60, doi:10.3762/bjoc.5.60
- groups at position 3′ and 4′ in quercetin may be protected after chelation with borax [21]. However, the Wender group [22] and the Rolando group [23] reported that under these conditions quercetin methylation gave a complex mixture with at least three non-identified partially methylated quercetin ethers
Graphical Abstract
Figure 1: Structures of quercetin and methylated metabolites.
Scheme 1: Synthesis of 4′-O-methylquercetin (2, tamarixetin). a) Ph2CCl2, Ph2O, 175 °C, 30 min, 86%; b) MOMCl...
Figure 2: ROESY correlations of compound 2.
The role of an aromatic group in remote chiral induction during conjugate addition of α-sulfonylallylic carbanions to ethyl crotonate
- Shlomo Levinger,
- Ranjeet Nair and
- Alfred Hassner
Beilstein J. Org. Chem. 2008, 4, No. 32, doi:10.3762/bjoc.4.32
- geometry of the aromatic ring during chelation with the lithiated species is as yet unknown, it evidently plays an important role in determining the approach of the carbanion to the conjugate acceptor and thus the stereoselectivity of the conjugate addition. Preliminary ab initio calculations [17] for the
Graphical Abstract
Scheme 1: Transmission of asymmetry in the conjugate addition of allyl sulfones to ethyl crotonate depending ...
Scheme 2: Preparation of donor precursors for conjugate addition (1), bearing a remote stereogenic center.
Scheme 3: Borch reductive amination of acetophenones.
Scheme 4: Preparation of [(9-anthryl)alkyl]- and (mesitylalkyl)amines 6h and 6j from nitriles via imines 8.
Figure 1: Calculated minimum energy conformation of lithiated amino-substituted sulfone 1a showing π-interact...
