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Search for "phase transfer catalysts" in Full Text gives 32 result(s) in Beilstein Journal of Organic Chemistry.
Synthesis of the reported structure of piperazirum using a nitro-Mannich reaction as the key stereochemical determining step
- James C. Anderson,
- Andreas S. Kalogirou,
- Michael J. Porter and
- Graham J. Tizzard
Beilstein J. Org. Chem. 2013, 9, 1737–1744, doi:10.3762/bjoc.9.200
- . Enantioselective reactions have been controlled by asymmetric metal-centred Lewis acids; chiral hydrogen bond donors, in particular by the use of asymmetric thiourea organocatalysts, chiral Brønsted acids, phase-transfer catalysts and Brønsted base catalysts [3][15][25][26][27][28][29][30][31][32][33][34][35][36
Graphical Abstract
Scheme 1: Schematic nitro-Mannich reaction.
Scheme 2: Retrosynthetic analysis of piperazirum.
Scheme 3: (a) iBuMgCl, Et2O, −78 °C; (b) KOH, EtOH/H2O, 100 °C; (c) (COCl)2.
Scheme 4: (a) Li(Et3BH), THF, rt then 14, CF3CO2H, −78 °C, dr 70:30; (b) (CF3CO)2O, Py, CH2Cl2, 0 °C to rt; (...
Scheme 5: (a) Li(Et3BH), CH2Cl2, rt then 19, CF3CO2H, −78 °C, dr >95:5; (b) Zn, 6 M HCl, EtOAc/EtOH, rt, sing...
Scheme 6: (a) (COCl)2, DMF, CH2Cl2, rt; (b) 21, Py, DMAP, CH2Cl2, rt; (c) EDC, HOBt, THF/CH2Cl2, rt; (d) H2 (...
Figure 1: X-ray crystal structure of 2·HCl.
Organocatalyzed enantioselective desymmetrization of aziridines and epoxides
- Ping-An Wang
Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192
- organocatalysts. Cinchona alkaloid derivatives The first organocatalytic enantioselective desymmetrization of meso-aziridines was discovered by Hou and co-workers in 2007 [40] with various arylthiols as nucleophiles in CCl4 at 0 °C in the presence of cinchonine-derived phase-transfer catalysts (PTCs, Figure 2, OC
- enantioselectivities. In the presence of some achiral phase-transfer catalysts or phosphines such as TBAB and P(t-Bu)3, the vicinal chlorohydrins were obtained in high yields. Up to now, three classes of organocatalysts including chiral phosphoramides, chiral phosphine oxides, and chiral pyridine N-oxides were used in
Graphical Abstract
Figure 1: The catalyzed enantioselective desymmetrization.
Figure 2: Cinchona alkaloid-derived catalysts OC-1 to OC-11.
Scheme 1: The enantioselective desymmetrization of meso-aziridines in the presence of selected Cinchona alkal...
Figure 3: Cinchona alkaloid-derived catalysts OC-12 to OC-19.
Scheme 2: The enantioselective ring-opening of aziridines in the presence of OC-16.
Scheme 3: OC-16 catalyzed enantioselective ring-opening of aziridines.
Figure 4: The chiral phosphoric acids catalysts OC-20 and OC-21.
Scheme 4: OC-20 and OC-21 catalyzed enantioselective desymmetrization of meso-aziridines.
Figure 5: The proposed mechanism for chiral phosphorous acid-induced enantioselctive desymmetrization of meso...
Scheme 5: OC-21 catalyzed enantioselective desymmetrization of meso-aziridines by Me3SiSPh.
Scheme 6: OC-21 catalyzed the enantioselective desymmetrization of meso-aziridines by Me3SiSePh/PhSeH.
Figure 6: L-Proline and its derivatives OC-22 to OC-27.
Scheme 7: OC-23 catalyzed enantioselective desymmetrization of meso-aziridines.
Figure 7: Proposed bifunctional mode of action of OC-23.
Figure 8: The chiral thioureas OC-28 to OC-44 for the desymmetrization of meso-aziridines.
Scheme 8: Desymmetrization of meso-aziridines with OC-41.
Figure 9: The chiral guanidines (OC-45 to OC-48).
Scheme 9: OC-46 catalyzed desymmetrization of meso-aziridines by arylthiols.
Scheme 10: Desymmetrization of cis-aziridine-2,3-dicarboxylate.
Figure 10: The proposed activation mode of OC-46.
Scheme 11: The enantioselective desymmetrization of meso-aziridines by amine/CS2 in the presence of OC-46.
Figure 11: The chiral 1,2,3-triazolium chlorides OC-49 to OC-55.
Scheme 12: The enantioselective desymmetrization of meso-aziridines by Me3SiX (X = Cl or Br) in the presence o...
Figure 12: Early organocatalysts for enantioselective desymmetrization of meso-epoxides.
Scheme 13: Attempts of enantioselective desymmetrization of meso-epoxides in the presence of OC-58 or OC-60.
Scheme 14: The enantioselective desymmetrization of a meso-epoxide containing one P atom.
Figure 13: Some chiral phosphoramide and chiral phosphine oxides.
Scheme 15: OC-62 catalyzed enantioselective desymmetrization of meso-epoxides by SiCl4.
Figure 14: The proposed mechanism of the chiral HMPA-catalyzed desymmetrization of meso-epoxides.
Scheme 16: The enantioselective desymmetrization of meso-epoxides in the presence of OC-63.
Figure 15: The Chiral phosphine oxides (OC-70 to OC-77) based on an allene backbone.
Scheme 17: OC-73 catalyzed enantioselective desymmetrization of meso-epoxides by SiCl4.
Figure 16: Chiral pyridine N-oxides used in enantioselective desymmetrization of meso-epoxides.
Scheme 18: Catalyzed enantioselective desymmetrization of meso-epoxides in the presence of OC-80 or OC-82.
Figure 17: Chiral pyridine N-oxides OC-85 to OC-94.
Scheme 19: Enantioselective desymmetrization of cis-stilbene oxide by using OC-85 to OC-92 as catalysts.
Figure 18: A novel family of helical chiral pyridine N-oxides OC-95 to OC-97.
Scheme 20: Desymmetrization of meso-epoxides catalyzed by OC-95 to OC-97.
Scheme 21: OC-98 catalyzed enantioselective desymmetrization of meso-epoxides by SiCl4.
One-pot tandem cyclization of enantiopure asymmetric cis-2,5-disubstituted pyrrolidines: Facile access to chiral 10-heteroazatriquinanes
- Ping-An Wang,
- Sheng-Yong Zhang and
- Henri B. Kagan
Beilstein J. Org. Chem. 2013, 9, 265–269, doi:10.3762/bjoc.9.32
- , this 10-heteroazatriquinane 7b possesses a rigid bowl-like molecular scaffold with a quaternary nitrogen site (N2) at the bottom of the cavity. Recently, Denmark and colleagues [25][26] have synthesized a series of chiral phase-transfer catalysts (chiral PTCs) based on a 2-azatriquinane skeleton
Graphical Abstract
Figure 1: The structures of azatriquinanes and azatriquinacene.
Figure 2: The synthesis of 4 (previous work).
Scheme 1: The designed synthetic route to a hydroxy NHC from 4b.
Scheme 2: The reduction of amides 4 by LiAlH4 and BH3·THF.
Figure 3: X-ray crystal structure of compound 5a.
Scheme 3: One-pot tandem cyclization of 6 in the presence of HC(OCH3)3.
Figure 4: X-ray crystal structure of compound 7b.
Figure 5: The structural comparison of chiral ammonium salts such as 7 with the chiral PTCs of Denmark et al.
Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters
- Lukas Hintermann,
- Mauro Perseghini and
- Antonio Togni
Beilstein J. Org. Chem. 2011, 7, 1421–1435, doi:10.3762/bjoc.7.166
- -catalyzed asymmetric fluorinations were discovered by others and ourselves, based on complexes of Pd(II) [46], Cu(II) [47][48][49], Ni(II) [48][50] and Ru(II) [51] as catalysts [4][51]. In parallel, organocatalytic asymmetric electrophilic fluorination of carbonyl compounds by means of phase-transfer
- catalysts [52] and small-molecule chiral amine catalysts were introduced and explored with great success [53][54][55][56]. Here we present the full range of observations on titanium-catalyzed fluorinations of β-ketoesters. The focus is on the development of the reaction and the study of factors influencing
Graphical Abstract
Figure 1: Fluorinated substances of biomedical relevance.
Scheme 1: Enantioselective electrophilic fluorination catalyzed by TADDOLates K1, K2. TADDOL = α,α,α',α'-tetr...
Scheme 2: Halogenation of β-ketocarbonyl compounds: Importance of enolization and the potential role of a met...
Figure 2: Model substrates for catalytic fluorinations, with the degree of enolization determined by 1H NMR m...
Figure 3: 1H NMR (250 MHz) spectra of fluorination reaction mixtures diluted with CDCl3 and filtered. a) Full...
Scheme 3: Qualitative ordering of catalytic activity of several Lewis acids in the fluorination 1→1-F.
Scheme 4: Catalysis of the “neutral” fluorination of β-ketoesters with F–TEDA by Lewis acidic titanium comple...
Figure 4: Structure of the chiral ansa-metallocene [(EBTHI)Ti(OTf)2].
Figure 5: Electrophilic fluorinating reagents of the N–F-type. F–TEDA [27]; NFTh = 1-fluoro-4-hydroxy-1,4-diazoni...
Scheme 5: Synthesis of trifluoromethyl-substituted TADDOL ligands.
Scheme 6: Correlation experiments for the assignment of absolute configuration to fluorination products 11-F, ...
Scheme 7: Mechanistic scheme proposed, based on visual and spectroscopic observations. L = solvent, counterio...
Figure 6: 1H NMR spectra of a species of the type A, generated in CD3CN solution from K1 by ionization in the...
Figure 7: Steric model explaining the face selectivity observed in the titanium–TADDOLate complex catalyzed f...
Figure 8: Excerpt from the X-ray structure of a catalyst/substrate complex [Ti(1-naphthyl-TADDOLato)(β-ketoen...
Synthesis of cationic dibenzosemibullvalene-based phase-transfer catalysts by di-π-methane rearrangements of pyrrolinium-annelated dibenzobarrelene derivatives
- Heiko Ihmels and
- Jia Luo
Beilstein J. Org. Chem. 2011, 7, 119–126, doi:10.3762/bjoc.7.17
- and its derivatives is a synthetically useful reaction, because it allows the preparation of polycyclic structures which are relatively difficult to obtain by ground-state transformations [8]. During our attempts to develop novel ammonium-based phase-transfer catalysts [9][10][11] that are embedded
- dibenzosemibullvalene derivatives are accessable by the photoinduced di-π-methane rearrangement of appropriately substituted dibenzobarrelene substrates. With one representative example, it was demonstrated that these compounds may act as phase-transfer catalysts in alkylation reactions with comparable or even better
- performance than the commonly employed tetrabutylammonium salts. It is therefore concluded that this class of chiral compounds may be used as a promising platform for the development of versatile phase-transfer catalysts. Experimental General remarks: NMR spectra were recorded on a Bruker Avance 400 (1H NMR
Graphical Abstract
Scheme 1: Photorearrangements of dibenzobarrelene (DBB).
Figure 1: General structure of pyrrolidinium-annelated dibenzosemibullvalenes (pyDBS).
Scheme 2: Synthesis of dibenzobarrelene derivatives 2a–g.
Scheme 3: Di-π-methane rearrangements of dibenzobarrelene derivatives 2a–f (counter ions omitted for clarity)....
Scheme 4: Di-π-methane rearrangement of dibenzobarrelene derivative 2g.
Scheme 5: Synthesis and solid-state photoreactivity of the sulfonate salt 2b-4.
Scheme 6: Phase-transfer catalyzed alkylation reactions (see Table 1 for details).
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...
Enantioselective nucleophilic difluoromethylation of aromatic aldehydes with Me3SiCF2SO2Ph and PhSO2CF2H reagents catalyzed by chiral quaternary ammonium salts
- Chuanfa Ni,
- Fang Wang and
- Jinbo Hu
Beilstein J. Org. Chem. 2008, 4, No. 21, doi:10.3762/bjoc.4.21
- RbOH (Table 2, entries 8 and 9). Encouraged by these results, we further examined the influence of substituents on the chiral phase transfer catalysts. As shown in Table 2, the different substituents showed some influence on the enantioselectivity. The electron-withdrawing group CF3 at C-4 position of
Graphical Abstract
Scheme 1: Structure of chiral quaternary ammonium salts.
Scheme 2: Determination of the absolute configuration of (+)-3a.
