Search results
Search for "dipole moment" in Full Text gives 108 result(s) in Beilstein Journal of Organic Chemistry.
The C–F bond as a conformational tool in organic and biological chemistry
- Luke Hunter
Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38
- -fluorocarbonyl compounds, but the effect decreases with the decreasing dipole moment of the carbonyl group (4–6, Figure 1a) [2]. As well as stabilising certain conformations, dipole–dipole interactions can also be responsible for destabilising other conformations. For example, in 1,3-difluoroalkanes (e.g. 7
- liquid crystals. A liquid crystal is a fluid phase in which there is some orientational ordering of the molecules. Liquid crystal display (LCD) technology requires rod-shaped molecules that have a dipole moment perpendicular to the long axis of the molecule, and this is often achieved by incorporating
- molecular conformation as well as the molecular dipole moment. The difluoro compound 60 (Figure 15) can be viewed as a conceptual progression from the axially fluorinated liquid crystal 58. NMR and modelling data show that the fluoroalkyl chain of 60 adopts a zigzag conformation in which the two C–F bonds
Graphical Abstract
Figure 1: Conformational effects associated with C–F bonds.
Figure 2: HIV protease inhibitor Indinavir (17) and fluorinated analogues 18 and 19. In analogue 18 the gauche...
Figure 3: Cholesteryl ester transfer protein inhibitors 20 and 21. In the fluorinated analogue 21, nO→σ*CF hy...
Figure 4: HIV reverse transcriptase inhibitor 22 and acid-stable fluorinated analogues 23–25. The F–C–C–O gau...
Figure 5: Dihydroquinidine (26) and fluorinated analogues 27 and 28. Newman projections along the C9–C8 bonds...
Figure 6: The neurotransmitter GABA (29) and fluorinated analogues (R)-30 and (S)-30. Newman projections of (R...
Figure 7: The insect pheromone 31 and fluorinated analogues (S)-32 and (R)-32. The proposed bioactive conform...
Figure 8: Capsaicin (33) and fluorinated analogues (R)-34 and (S)-34.
Figure 9: Asymmetric epoxidation reaction catalysed by pyrrolidine 35. Inset: the geometry of the activated i...
Figure 10: The asymmetric transannular aldol reaction catalysed by trans-4-fluoroproline (41), and its applica...
Figure 11: The asymmetric Stetter reaction catalysed by chiral NHC catalysts 49–52. The ring conformations of ...
Figure 12: A multi-vicinal fluoroalkane.
Figure 13: X-ray crystal structures of diastereoisomeric multi-vicinal fluoroalkanes 55 and 56. The different ...
Figure 14: Examples of fluorinated liquid crystal molecules. Arrows indicate the orientation of the molecular ...
Figure 15: Di-, tri- and tetra-fluoro liquid crystal molecules 60–62.
Figure 16: Collagen mimics of general formula (Pro-Yaa-Gly)10 where Yaa is either 4(R)-hydroxyproline (63) or ...
Figure 17: Enkephalin-related peptide 64 and the fluorinated analogue 65. The electron-withdrawing trifluorome...
Figure 18: The C–F bond influences the conformation of β-peptides. β-Heptapeptide 66 adopts a helical conforma...
Figure 19: The conformations of pseudopeptides 69 and 70 are influenced by the α-fluoroamide effect and the fl...
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...
Ring-alkyl connecting group effect on mesogenic properties of p-carborane derivatives and their hydrocarbon analogues
- Aleksandra Jankowiak,
- Piotr Kaszynski,
- William R. Tilford,
- Kiminori Ohta,
- Adam Januszko,
- Takashi Nagamine and
- Yasuyuki Endo
Beilstein J. Org. Chem. 2009, 5, No. 83, doi:10.3762/bjoc.5.83
- angle θ between the ring and substituent increases in the series 25, 28 < 27 < 26 or –OR, –C(O)OR < –OOCR < –CH2R. Further analysis of the computational results demonstrates that molecular dipole moment μ increases in the following order: 26 < 25 < 27 < 28. The quadrupole moment tensor Qxx perpendicular
- molecular dipole moment in phase stabilization. Since p-carboranes are moderately electron withdrawing substituents, the alkoxy derivatives have a larger dipole moment than the alkyl derivatives [16]. Alternatively, the effect can be due to higher rigidity of 1-4, which attenuates the effect as compared to
- : ethoxybenzene (25), propylbenzene (26), phenyl acetate (27), and methyl benzoate (28) and pertinent molecular parameters: dihedral angle θ, dipole moment μ, and quadrupole moment tensor QXX perpendicular to the ring plane. Preparation of diesters 16[n]. Preparation of esters 18–20. Preparation of phenol 24
Graphical Abstract
Figure 1: The molecular structures of 1,12-dicarba-closo-dodecaborane (12-vertex p-carborane, A) and 1,10-dic...
Figure 2: The molecular structures of derivatives 1–20.
Scheme 1: Preparation of diesters 16[n].
Scheme 2: Preparation of esters 18–20.
Scheme 3: Preparation of phenol 24.
Figure 3: Partial DSC trace for 16D[6]. Heating rate 5 K/min.
Figure 4: Optical textures of 16D[6] obtained for the same region of the sample upon cooling: (a) SmA growing...
Figure 5: The change in the clearing temperature ΔTc upon substitution –OCH2– → –CH2CH2– in selected pairs of...
Figure 6: The change in the clearing temperature ΔTc upon replacing of the –OCH2– connecting group with anoth...
Figure 7: Equilibrium ground state geometries (B3LYP/6-31G(d)) for benzene derivatives: ethoxybenzene (25), p...
Influence of spacer chain lengths and polar terminal groups on the mesomorphic properties of tethered 5-phenylpyrimidines
- Gundula F. Starkulla,
- Elisabeth Kapatsina,
- Angelika Baro,
- Frank Giesselmann,
- Stefan Tussetschläger,
- Martin Kaller and
- Sabine Laschat
Beilstein J. Org. Chem. 2009, 5, No. 63, doi:10.3762/bjoc.5.63
- twisted conformation with a dihedral angle of 43.1° [3]. The different conformations together with differences of the polarisation and dipole moment between 2- and 5-phenylpyrimidines also lead to different mesomorphic properties as was shown by Lemieux for phenylpyrimidines tethered to terminal
- nucleophilic substitution. Depending on the terminal group and the tether lengths the formation of smectic A mesophases was observed for the chloro-, bromo- and azido derivatives. Surprisingly, the strong latent dipole moment of hydroxy and cyano derivatives and the ability of hydroxy derivatives to form
Graphical Abstract
Scheme 1: Comparison of mesomorphic properties of 1a and 2a.
Scheme 2: Variation of spacer lengths and terminal group at 5-phenylpyrimidine.
Scheme 3: Synthesis of compounds 3–5, 9 and 11.
Scheme 4: Synthesis of compounds 6 and 7.
Figure 1: DSC curve of compound 3d (heating/cooling rate 10 K/min).
Figure 2: Fan-shaped texture of 3e under crossed polarizers upon cooling from the isotropic liquid (magnifica...
Figure 3: DSC curve of compound 4e (heating/cooling rate 5 K/min).
Figure 4: Fan-shaped texture of compound 4d at 45 °C upon cooling from the isotropic liquid (cooling rate 1 K...
Figure 5: DSC curve of compound 6c (heating/cooling rate 10 K/min).
Figure 6: Fan-shaped texture of compound 6e at 45 °C upon cooling from the isotropic liquid (cooling rate 10 ...
Figure 7: Comparison of the mesophase range ΔT for the different spacer lengths of compounds 3, 4 and 6: meso...
Figure 8: Comparison of the mesophase range ΔT for the different spacer lengths of compounds 3, 4 and 6: meso...
Figure 9: Proposed model for the layer structure.
Functional properties of metallomesogens modulated by molecular and supramolecular exotic arrangements
- Alessandra Crispini,
- Mauro Ghedini and
- Daniela Pucci
Beilstein J. Org. Chem. 2009, 5, No. 54, doi:10.3762/bjoc.5.54
- -mesogenic 4,4′-disubstituted 2,2′-bipyridine ligands with Pt(II) salts confirmed the role of coordination chemistry in the metal-mediated formation of liquid crystals. Indeed the induction of a dipole moment upon coordination with an MX2 moiety, allowed most of the half-disc shaped complexes [LnPtX2
- depend on the size of the X group and on the dipole moment associated with the Pt-X bond, with the sequence, for the clearing points Cl
Graphical Abstract
Figure 1: Molecular structure of NIRPAC: a Pd(II) complex based on Nile red and a curcumin derivative.
Figure 2: Molecular structure of Pd(II) complexes based on functionalised 2-phenylquinolines and β-diketonate...
Figure 3: Some unusual palladiomesogens based on 3,5-disubstituted-2,2′-pyridylpyrroles and β-diketonates.
Figure 4: Molecular structure of Pt(II) complexes based on 4,4′-disubstituted 2,2′-bipyridines.
Figure 5: Molecular structure of Zn(II) complexes based on polycatenar 4,4′-disubstituted 2,2′-bipyridines.
Figure 6: Molecular structure of a gallium(III) mesogen.
Acid- mediated reactions under microfluidic conditions: A new strategy for practical synthesis of biofunctional natural products
- Katsunori Tanaka and
- Koichi Fukase
Beilstein J. Org. Chem. 2009, 5, No. 40, doi:10.3762/bjoc.5.40
- reactive sialyl donors having C-5 cyclic imides (Table 1), especially N-phthalimide 1a, by virtue of the “fixed-dipole moment effects” (α-only, 92% on 50 mg scale) [41]. The scale-up in a batch process, however, significantly decreased the yield and selectivity. Thus, a 100 mg scale reaction of 1a gave
- alternative to the N-phthalyl function, we also employed the C-5 azide group in sialyl donor 1b because this azide group should direct similar “fixed-dipole moment effects”, but should be easier to convert to naturally occurring N-substituents of neuraminic acids, i.e., N-acetyl or N-glycolyl groups (see
Graphical Abstract
Figure 1: Synthetic strategy for asparagine-linked oligosaccharide on solid support and application of microf...
Figure 2: β-Mannosylation using an integrated microfluidic/batch system. Yield and β/α-ratio are analyzed by 1...
Scheme 1: Synthesis of pristane.
Figure 3: Process synthesis of pristane via microfluidic dehydration as a key step.
Scheme 2: Microfluidic dehydration.
Convenient method for preparing benzyl ethers and esters using 2-benzyloxypyridine
- Susana S. Lopez and
- Gregory B. Dudley
Beilstein J. Org. Chem. 2008, 4, No. 44, doi:10.3762/bjoc.4.44
- trifluorotoluene, but toluene has a lower dipole moment and also is subject to Friedel–Crafts benzylation under the reaction conditions [6][22]. Trifluorotoluene (also known as benzotrifluoride or BTF) is recommended as a “green” solvent alternative to dichloromethane [23]. Benzylation reactions of N-Boc-serine 3d
Graphical Abstract
Figure 1: Benzyl bromide, benzyl trichloroacetimidate, and 2-benzyloxy-1-methylpyridinium triflate (1).
Scheme 1: Published syntheses of benzyl esters from alcohols using neutral reagent 1; other benzylation proce...
Scheme 2: Preparation of 2-benzyloxypyridine (2).
Scheme 3: Synthesis of a benzyl ester from a carboxylic acid.
Scheme 4: Representative synthesis of a halobenzyl ether under neutral conditions.
The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives
- David O'Hagan,
- Henry S. Rzepa,
- Martin Schüler and
- Alexandra M. Z. Slawin
Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19
- free energy differences arising from vibrational terms) does not alter the relative energies of a and b, despite a having a zero dipole moment and b having a relatively large value (3.5D) [26]. Although the more polar b should perhaps gain more from electrostatic solvation, it has a smaller solvent
- and appears to be dominated by solvation of the trans relationship of the aryl rings and the zero dipole moment, although the smaller 3JHH coupling of 2.6 Hz and the slightly larger 3JHF coupling of 15 Hz in the NMR, measurement does suggest some contribution of conformer b in solution. The threo-13
- significantly smaller than the NMR estimate and may reflect a limitation of the solvation model. Taking all of the data together (theory, X-ray and NMR) conformer d appears to be the most favoured conformer for threo-13 with both the fluorine and the phenyl rings gauche, despite its larger dipole moment. 2,3
Graphical Abstract
Scheme 1: Synthesis of vicinal dimethyl difluorosuccinates. The conversion of the tartrates 1 with SF4 and HF ...
Scheme 2: Schlosser's route to vicinal erythro- or threo- difluoro alkanes 5 [13].
Scheme 3: Halofluorination of electron-rich alkenes with in situ fluoride displacement generates vicinal difl...
Scheme 4: Bromofluorination of stilbene [19].
Scheme 5: Treatment of anti-14 with base generated the E-fluorostilbene 15 by an anti elimination mechanism.
Scheme 6: Hypothesis for the predominent retention of configuration during fluoride substitution via phenoniu...
Scheme 7: Proposed C-C bond rotation during the preparation of 14 from cis-stilbene.
Figure 1: Crystal structure of erythro-13.
Figure 2: X-ray structure of threo-13.
Figure 3: Expanded regions of the second order AA'XX' spin systems in the 1H-NMR (left) and 19F-NMR spectra (...
Figure 4: NMR coupling constants and calculated relative energies (kcalmol-1) of the staggered conformers of ...
Scheme 8: Synthesis of erythro-19 via ozonolysis of erythro-13.
Figure 5: X-ray structure of erythro-19.
Figure 6: X-ray structure of threo-19.
Scheme 9: Strategy for the preparation of diastereoisomers of erythro- and threo- 20.
Figure 7: NMR (CDCl3, RT) coupling constants of erythro- and threo- 2,3-difluoro-3-phenylpropionates 21.
Figure 8: Newman projections showing the staggered conformations of erythro- and threo- 21.
Figure 9: X-ray structure of methyl threo- 21.
Figure 10: The preferred conformation of α-fluoroamides has the C-F and amide carbonyl anti-planar [29,30].
Scheme 10: The synthesis of stereoisomers of erythro- and threo- 22. These isomers could be separated by chrom...
Figure 11: X-ray structure of erythro-22.
Figure 12: Crystal packing of erythro-22 clearly indicating intermolecular hydrogen bonding.
Figure 13: X-ray structure of threo-22.
Figure 14: The conformations of erythro- and threo- 23 are very different as a consequence of each conformatio...
Figure 15: 3JHF and 3JHH coupling constants for the erythro (yellow) and threo (blue) diastereoisomers of the ...
Figure 16: Newman projections of the three staggered conformations of the erythro and threo stereoisomers of t...
Figure 17: The average coupling constant with no conformational bias. The limiting coupling constants Jg = 8 H...
Figure 18: The observed 3JHF coupling constants are an average over the rotational isomers.
