Bi-2-naphthol Research Articles

Chiral catalyst optimization using both solid-phase and liquid-phase methods in asymmetric aza Diels-Alder reactions

[formula: see text] In the presence of 1-5 mol % of a chiral zirconium catalyst, aza Diels-Alder reactions of aldimines with Danishefsky's dienes proceeded smoothly to afford the corresponding piperidine derivatives in high yields with high enantioselectivities. For the catalyst optimization, solid-phase and liquid-phase methods were successfully used. In the solid-phase approach, polymer-supported (R)-1,1'-binaphthols (BINOLs) have been synthesized and rapid optimization using the solid-phase reactions has been achieved. On the other hand, novel chiral zirconium cyanides were developed as excellent catalysts using the liquid-phase approach.

Efficient Baylis–Hillman reactions promoted by mild cooperative catalysts and their application to catalytic asymmetric synthesis

Baylis–Hillman reactions were promoted by mild cooperative catalysts of tributylphosphine with phenols such as (±)-1,1′-bi-2-naphthol (BINOL) in THF to give α-methylene-β-hydroxyalkanones in high yield. The reactions proceeded much faster in the presence of 1,1′-bi-2-naphthol than in its absence. The 1H NMR studies suggested that 1,1′-bi-2-naphthol functions as a Brønsted acid to activate the carbonyl group of an aldehyde and a polarized alkene. Application of the reactions to catalytic asymmetric synthesis was examined by using cooperative catalysts of tributylphosphine with the calcium chiral catalyst to give the desired product with fairly good % ee in fairly good yield.

Hexyltrimethylammonium Bromide Inclusion Complex With Rac-1,1′-Bi-2-Naphthol

The crystal structure of 1:1 inclusion complex of hexyltrimethylammonium bromide (6TAB) and rac-1, 1′-bi-2-naphthol (BNP) was analysed by the X-ray diffraction method. It was shown that the bromide anion participates in a hydrogen bond with one of the OH groups of BNP (Ol···Br, 3.22(1)Å). The bromide anion also plays a role as the hydrogen acceptor of the OH group of the water molecule (OW···Br, 3.21(3)Å). A strong hydrogen bond was found between the other OH group of BNP and oxygen of the water molecule (O2···OW, 2.63(3)Å). The short C-H···C distances between hydrogen atoms of the alkyl chain together with the methyl groups and carbon atoms of the aromatic rings suggested C-H···π interactions. The atomic distances shorter than the sum of the van der Waals radius (2.97Å) were C10···H6 2.85Å, C14···H9 2.83Å, and C16···H11 2.88Å. The X-ray powder diffraction studies on the complex suggested that the complex crystals can be obtained by crystallization from the solution and also by mixing powdered samples in a mortar.

The Molecular Complexes of Monoalkylammonium Bromide Salts with (R)-(+)-1,1′-Bi-2-Naphthol and Rac-1,1′-Bi-2-Naphthol

The crystal structures of hexyltrimethylammonium bromide (6TAB) adduct of (R)-(+)-1,1′-bi-2-naphthol (RBNP) and decyltrimethylammonium bromide (10TAB) adduct of rac-1,1′-bi-2-naphthol (BNP) have been determined by the X-ray diffraction method. The molecules of the 6TAB/RBNP complex are held in their aggregates by O1…Br [3.228(4)Å], O2…Br [3.225(6)Å] intermolecular hydrogen bonds and C-H…π interactions between the alkyl chain, methyl groups and aromatic rings of the naphthol moieties. It was observed in the crystal structure of 10TAB adduct of BNP that the crystal structure formation was mainly stabilized by the intermolecular hydrogen bonds between the bromide anion and OH group of BNP (01…Brl [3.241(4)Å], O2…Br2 [3.172(3)Å]). In both complexes, the packing arrangement of the monoalkylammonium bromide salts with non-planar aromatic molecules are different from those observed in complexes of monoalkylammonium bromide salts with planar aromatic guest molecules. X-ray powder diffraction studies on both complexes showed that the crystals complex can be obtained by crystallization from solution and also by mixing powdered samples in a mortar. This study has shown that a non-chiral host amphiphile can form a complex with either a chiral or racemic aromatic guest compound.

Twisted Nematics: Conformation of Chiral Dopants

The conformational properties of binaphthol (BN) derivatives dissolved in a pentylcyanobiphenyl liquid crystalline (LC) matrix were determined by molecular dynamics (MD) simulation. Due to the influence of intermolecular interactions between the molecules of the LC matrix and the BN molecules, the conformations of the BN molecules in LC phase are found to change in the direction from transoid to cisoid on heating that results in decrease of observed helical twisting power (HTP). The changes of molecular conformation are mainly connected with orienting potential acting on solute molecule.

Enantioselective addition of diethylzinc to aldehydes catalyzed by 3,3?-bis(2-oxazolyl)-1,1?-bi-2-naphthol (BINOL-Box) ligands derived from 1,1?-bi-2-naphthol

With 3,3'-bis(2-oxazolyl)-1,1'-bi-2-naphthols (BINOL-Box) synthesized from 1,1'-bi-2-naphthol (BINOL), the enantioselective addition of diethylzinc to aryl aldehydes proceeded smoothly to give secondary aryl alcohols in good yield with good enantioselectivity. Interestingly, the yields and enantioselectivities were affected by the mixing sequence of the reactants. Furthermore, the synthesis of both enantiomers of the addition products has been achieved using the same ligands by choosing achiral additives, Ti(O-iPr) 4 and 4A molecular sieves.

Polymer-supported BINOL ligand for the titanium-catalyzed diethylzinc addition to aldehydes: A remarkable positive influence of the support on the enantioselectivity of the catalyst

A new polymer-supported BINOL (1,1'-Bi-2-naphthol) was synthesized by coupling of aminomethyl polystyrene resin and (S)-2, 2'-dihydroxy-1,1'-binaphthyl-3,3'-dicarboxylic acid. This new ligand was found to be more enantioselective for the asymmetric addition of diethylzinc to aldehydes than its "free" analog [Ti(BINOL)(i)PrO(2)]. A range of 57-99% ee's as well as 78-97% yields was obtained, and the electronic properties of the enantioselectivity were also observed.

Substituent Effects of Ligands on Asymmetric Induction in a Prototypical Palladium-Catalyzed Allylation Reaction: Making Both Enantiomers of a Product in High Optical Purity Using the Same Source of Chirality

The substituent effects of the ligands 1 through 8 play a crucial role in determining the enantioselectivity in the palladium-catalyzed asymmetric allylation reaction between 1,3-diphenylprop-2-en-1-yl acetate and the sodium salt of diethyl malonate. For a given chirality of the backbone, electron-deficient and electron-rich ligands generally gave opposite enantiomers, while sterically hindered ligands had the same enantioselectivity as electron-rich ligands. In the case of flexible backbones with ligands of comparable size, a variation of the enantioselectivity with the electronic properties of the ligand is predictable. In ligands with rigid backbones, the steric effects of the substituents appear to play a more decisive role, and caution should be exercised in interpreting the role of electronic effects in such cases. Examples are provided for maximizing both the chemical yield and the enantioselectivity of the allylation reaction through the tuning of the electronic properties of the ligands. In selected cases, the major sense of the asymmetric induction could be reversed solely by changing the electronic properties of the ligands. Bisphosphinites from (R)-(+)-1,1‘-bi-2-naphthol (BINOL) can be tuned to produce both (R)- and (S)-products in 80 and 87% ee, respectively. Stoichiometric reaction of complexes 10e* and 10j* with the sodium salt of diethyl malonate gave malonate adducts with enantiomeric excesses in agreement with those obtained under the catalytic conditions. Also reported are the details of an NMR study of the Pd(η3-1,3-diphenylallyl)bis-diphenylphosphinite and the corresponding bis-dicyclohexylphosphinite complexes 10e* and 10j*.

Allylation of Unactivated Ketones by Tetraallyltin Accelerated by Phenol. Application to Asymmetric Allylation Using a Tetraallyltin-BINOL System

Abstract The tetraallyltin-phenol system was mild and effective for allylation of unactivated ketones, giving tertiary alcohols in high yields. The asymmetric allylation was achieved by a tetraallyltin-homochiral BINOL (1,1′-bi-2-naphthol) system. The addition of methanol raised the enantioselectivity to afford the tertiary homoallylic alcohol up to 60% ee.

Diphosphonites as highly efficient ligands for enantioselective rhodium-catalyzed hydrogenation

Chiral ligands with achiral backbones such as ethano- or ferroceno-bridges linking two phosphonites derived from chiral diols such as binaphthol (BINOL) have been prepared; the corresponding Rh complexes are excellent catalysts in the hydrogenation of prochiral olefins such as itaconic acid dimethyl ester or 2-acetamido methyl acrylate, the ee values being 90–99.5%.

Asymmetric activation of chiral BINOL-zirconium catalysts: Effect of a product-like activator

The asymmetric activation of binaphthol (BINOL)-zirconium catalysts is described on the enantioselective allylation of benzaldehyde with allyltin reagents. This model reaction has been used with the intention of establishing a protocol for a zirconium-based catalyst system, to be followed by structural studies. Initial results are reported that characterise a number of interesting features, namely the influence of an induction period and a high level of asymmetric activation obtained after addition of a product-like activator. Chirality 10:717–721, 1998. © 1998 Wiley-Liss, Inc.

Enantiomeric Separations by Use of Calixarene Electrokinetic Chromatography

Chiral acylcalix[4]arene amino acid derivatives have been synthesized and used as pseudostationary phases in capillary electrophoresis (CE). Use of these calix[4]arene (CX4) derivatives with electrokinetic capillary chromatography (4-EKC) resulted in enantioseparation of three binaphthyl derivatives at pH values above 7. The structures of the CX4 derivatives, i.e., (N-l-alaninoacyl)calix[4]arene (CX4-l-Ala) and (N-l-valinoacyl)calix[4]arene (CX4-l-Val), and the buffer pH were found to be important factors in chiral separation. When CX4-l-Ala was used as a pseudostationary phase in the CE buffer, baseline resolution was achieved for 1,1‘-bi-2-naphthol (BINOL) and 1,1‘-binaphthyl-2,2‘-diamine (BNA). The addition of sodium dodecyl sulfate (SDS) to the CX4-l-Ala solution resulted in baseline resolution of the enantiomers of 1,1‘-binaphthyldiyl hydrogen phosphate (BNHP). In contrast, chiral separations of BNHP, BINOL, and BNA were successfully achieved in a single run with use of CX4-l-Val as a chiral selector...

Novel atropisomeric binaphthol containing comb‐shaped copolymers forming chiral nematic phases

AbstractNovel comb‐shaped liquid crystalline acrylic copolymers consisting of nematogenic methoxy‐phenylbenzoate acrylic monomers (A) together with novel chiral binaphthol (BN) methacrylic monomers (MB‐m) were synthesized in this study. The prepared copolymers differ in spacer lengths of MB‐m (m = 3, 5, 11) and in their compositions. The homopolymers of the three new chiral BN monomers MB‐m were also prepared. Copolymers with a low concentration of BN monomeric units (less than 16 mol %) display a cholesteric mesophase. The induced chirality in the polymers is due to atropisomerism (chirality due to hindered rotation around single bonds) of the BN molecules. The helical twisting power β (HTP) caused by the atropisomeric units in the synthesized copolymers was shown to decrease significantly on heating. The unusually high negative temperature coefficient of HTP observed above the glass transition temperature (Tg) could be explained in terms of conformational changes of the BN molecules in the copolymers.

Asymmetric Meerwein‐Ponndorf‐Verley reduction catalyzed by a new type of chiral binaphthol‐samarium complex

AbstractA new type of chiral 1,1′‐binaphthol(BINOL) derived samarium complex, prepared from (R)‐or (S)‐BINOL and SmCl3, serves as an enantioselective catalyst for the Meerwein‐Ponndorf‐Verley (MPV) reduction in the presence of Molecular Sieves 4Å(MS 4Å). Moderate enantioselectivity was obtained. Kinetic studies show slight decrease of the enantiomeric excess with the conversion.

New 6,6′-disubstituted-binaphthol derivatives as chiral dopants: Synthesis and temperature dependence of molecular conformations

Abstract A number of new chiral binaphthol (BN) derivatives with different substituents R,R′ in the 6,6′-positions in open (BN-diethylethers) and bridged forms (BN-acetals) have been synthesized. The syntheses of the chiral 6,6′-disubstituted-2,2′-diethoxy-1,1′-binaphthyls (R,R′ = -CH'CHCHO, -CH'CH-(p-BrPh), -CH'CH-(p-CHOPh)) and the chiral 9,14-disubstituted-dinaphtho [2,1-d:1′,2′-f][1,3] dioxepins with R,R′ = -CH'CH-(p-BrPh), -CH'CH-(p-CHOPh) are reported for the first time. The possible liquid crystalline properties and molar twisting powers (βM) in three different nematic liquid crystals (LCs) of the BN derivatives were investigated. Derivatives with spatially extended substituents in the 6,6′-positions (e.g. styryl or vinyl) show unusually high molar twisting power (up to 124.5μm−1). A direct correlation between the magnitude of βM and the length of the substituents was found. Bridged forms, in which the dihedral angle θ between the naphthyl moieties is ≊ 54°, show higher twisting power than the corr...

Synthesis of New Chiral Disubstituted Binaphthol Derivatives and their use as the Chiral Dopants

AbstractA number of new chiral binaphthol (BN) derivatives with different substituents in the 6,6'-positions in open and bridged forms have been synthesized. Their possible liquid crystalline properties and their helical twisting power (B) of three different nematic liquid crystals (LCs) were investigated. Derivatives with spatially extended substituents in the 6,6'-positions (e.g. styryl or vinil) show unusual high helical twisting power (up to 120 μm–1). A direct correlation between the magnitude of β and the length of the substituents was found.From the different temperature dependence of β of the open and bridged BNs, a molecular model was developed relating the molecular conformation and twisting power

Novel Chiral Bis-dipolar 6,6‘-Disubstituted Binaphthol Derivatives for Second-Order Nonlinear Optics: Synthesis and Linear and Nonlinear Optical Properties

A number of thermally and optically stable, bis-dipolar chiral molecules based on two geometries of the binaphthol (BN) system with different acceptors/substituents have been synthesized for the first time, and the synthetic routes are reported: optically pure 6,6‘-disubstituted 2,2‘-diethoxy-1,1‘-binaphthyls {R, R‘= −Br, −CHO, −CHC(CN)(COOEt), −CHC(CN)2, −CHCHCN, −CHCH(p-NO2Ph)} and optically pure 9,14-disubstituted dinaphtho[2,1-d:1‘,2‘-f][1,3]dioxepins {R, R‘ = −Br, −CHO, −CH=C(CN)(COOEt), −CHC(CN)2, −CHCHCN, −CHCHSO2CH3, −CHCHCHO, −CHCHCHC(CN)2}. All molecules possess two equal donor−acceptor systems linked together to give a bis-dipolar system. Two mono-dipolar 6-substituted 2-butoxynaphthalene (R = −CHC(CN)2, −CHC(CN)(COOEt)) donor−acceptor systems were prepared as references. The linear optical properties including solvatochromic shifts of absorption and fluorescence revealed strong charge transfer excitations in the new dipolar systems. The molecules show a high first hyperpolarizability β (up to (344−364) × 10-30 esu) as measured by electric-field-induced second-harmonic generation (EFISHG) and hyper-Rayleigh scattering (HRS). A model is developed to express the first hyperpolarizability of the bis-dipolar molecules in terms of the molecular geometry and the β of the monomeric donor−acceptor units. The tensor components were determined experimentally using this model and data from HRS and EFISHG. These techniques probe different combinations of the components of the molecular hyperpolarizability tensor. The results obtained are found to be in excellent mutual agreement.

Asymmetric [2 + 1] Cycloaddition Reactions of 1-Seleno-2-silylethene.

The reaction of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene (1) and vinyl ketones 2a-d in the presence of a chiral Lewis acid prepared from TiCl(4), Ti(O(i)Pr)(4), (R)- or (S)-1,1'-binaphthol (BINOL), and MS4A gave enantiomerically enriched cis cyclopropane products 3a-d. The enantiomeric excess and chemical yield varied depending on the ratio of TiCl(4) and Ti(O(i)Pr)(4) to 1. Reproducible results (43-47% ee/33-41% yields) for cis-1-acetyl-2-[(phenylseleno)(trimethylsilyl)methyl]cyclopropane (3a) were obtained using 1.1 equiv of TiCl(4), 0.54-0.65 equiv of Ti(O(i)Pr)(4), and 1.65 equiv of BINOL. The observed enantioselectivity was explained by consideration of the structure of the postulated intermediates, alkoxy titanium-carbonyl complexes, via ab initio MO calculations.

Asymmetric calysis of carbonyl-ene reactions and related carbon-carbon bond forming reactions

Abstract

Chromatographic resolution of enantiomers on a chiral stationary phase physically anchored to porous graphitic carbon

A chrysene–tartramide derived chiral stationary phase (CSP) was prepared and adsorbed onto the surface of porous graphitic carbon (Hypercarb). The stereoselective properties of the carbon-based chiral stationary phase was evaluated in a pre-packed high-performance liquid chromatography column. The carbon-based CSP was found to be capable of separating the enantiomers of a range of compounds including 1,1′-bi(2-naphthol),2,2-diaminobinaphthalene, 1,5-hexadiene-3,4-diol, benzoin, 1,4-di-O-benzylthreitol, 1,1′-binaphthalene-2,2′-diylhydrogenphosphate, propranolol, nadolol and labetolol using a non-aqueous mobile phase. The addition of ammonium acetate to the mobile phase was found to improve the resolution of enantiomers for 1,1′-binaphthalene-2,2′-diylhydrogenphosphate, propranolol, nadolol and labetolol. The amount of chrysene–tartramide adsorbed on porous graphitic carbon was calculated from the cycling process and the value corresponded to 2.6% by mass of porous graphitic carbon.