Bi-2-naphthol Research Articles

Reversal of Elution Order between Enantiomers of Binaphthol on an Immobilized Polysaccharide-Based Chiral Stationary Phase

Enantioseparation of 1,1′-bi-2-naphthol (BINOL) was performed on an immobilized polysaccharide-based chiral stationary phase (CSP), Chiralpak IA, in the normal-phase mode. The effects of polar modifier in the mobile phase and column temperature on retention, enantioseparation, and elution order were investigated. An interesting reversal of elution order for BINOL was observed. When ethanol was used as a polar modifier, R-BINOL was eluted first with marginal enantioseparation. Excellent enantioseparation was obtained when ethanol was replaced by 1-propanol, and S-BINOL was eluted first, this effect being retained with 2-butanol, 1-butanol, 1-pentanol or 1-hexanol as the modifier. When isoamyl alcohol was used, reversal of elution order was again observed, i.e., R-BINOL eluted first with marginal enantioseparation, similar to the case of ethanol. When cyclohexanol and cyclopentanol were used, R-BINOL was still eluted first, but enantioseparation was as good as with 1-propanol as the modifier. This is the first report of large enantioseparation obtained in both elution orders for a given selector/selectant system. A retention model based on stoichiometric displacement theory for retention (SDT-R) was investigated to fit the chromatographic data. The reason for solvent-induced reversal of elution order was elucidated based on a derivation of the retention model. Reversal of elution order for BINOL induced by the content of isoamyl alcohol was also predicted based on the model and confirmed by experiment.

Ab initio study of excited state electronic circular dichroism. Two prototype cases: Methyl oxirane and R-(+)-1,1′-bi(2-naphthol)

A computational approach to the calculation of excited state electronic circular dichroism (ESECD) spectra of chiral molecules is discussed. Frequency dependent quadratic response theory is employed to compute the rotatory strength for transitions between excited electronic states, by employing both a magnetic gauge dependent and a (velocity-based) magnetic gauge independent approach. Application is made to the lowest excited states of two prototypical chiral molecules, propylene oxide, also known as 1,2-epoxypropane or methyl oxirane, and R-(+)-1,1'-bi(2-naphthol), or BINOL. The dependence of the rotatory strength for transitions between the lowest three excited states of methyl oxirane upon the quality and extension of the basis set is analyzed, by employing a hierarchy of correlation consistent basis sets. Once established that basis sets of at least triple zeta quality, and at least doubly augmented, are sufficient to ensure sufficiently converged results, at least at the Hartree-Fock self-consistent field (HF-SCF) level, the rotatory strengths for all transitions between the lowest excited electronic states of methyl oxirane are computed and analyzed, employing HF-SCF, and density functional theory (DFT) electronic structure models. For DFT, both the popular B3LYP and its recently highly successful CAM-B3LYP extension are exploited. The strong dependence of the spectra upon electron correlation is highlighted. A HF-SCF and DFT study is carried out also for BINOL, a system where excited states show the typical pairing structure arising from the interaction of the two monomeric moieties, and whose conformational changes following photoexcitation were studied recently with via time-resolved CD.

Two-photon polarization dependent spectroscopy in chirality: a novel experimental-theoretical approach to study optically active systems.

Many phenomena, including life itself and its biochemical foundations are fundamentally rooted in chirality. Combinatorial methodologies for catalyst discovery and optimization remain an invaluable tool for gaining access to enantiomerically pure compounds in the development of pharmaceuticals, agrochemicals, and flavors. Some exotic metamaterials exhibiting negative refractive index at optical frequencies are based on chiral structures. Chiroptical activity is commonly quantified in terms of circular dichroism (CD) and optical rotatory dispersion (ORD). However, the linear nature of these effects limits their application in the far and near-UV region in highly absorbing and scattering biological systems. In order to surmount this barrier, in recent years we made important advancements on a novel non linear, low-scatter, long-wavelength CD approach called two-photon absorption circular dichroism (TPACD). Herein we present a descriptive analysis of the optics principles behind the experimental measurement of TPACD, i.e., the double L-scan technique, and its significance using pulsed lasers. We also make an instructive examination and discuss the reliability of our theoretical-computational approach, which uses modern analytical response theory, within a Time-Dependent Density Functional Theory (TD-DFT) approach. In order to illustrate the potential of this novel spectroscopic tool, we first present the experimental and theoretical results obtained in C2-symmetric, axially chiral R-(+)-1,1'-bi(2-naphthol), R-BINOL, a molecule studied at the beginning of our investigation in this field. Next, we reveal some preliminary results obtained for (R)-3,3′-diphenyl-2,2′-bi-1-naphthol, R-VANOL, and (R)-2,2′-diphenyl-3,3′-(4-biphenanthrol), R-VAPOL. This family of optically active compounds has been proven to be a suitable model for the structure-property relationship study of TPACD, because its members are highly conjugated yet photo-stable, and easily derivatized at the 5- and 6-positions. With the publication of these outcomes we hope to motivate more members of the scientist community to engage in state-of-the-art TPACD spectroscopy.

Enantioselective fluorescent recognition of mandelic acid by unsymmetrical salalen and salan sensors

As sensors with multiple chiral centers, salalen 1 and salan 2 composed of trans-cyclohexane-1,2-diamine (trans-DACH) and 1,1'-bi-2-naphthol (BINOL) units were designed and synthesized. Fluorescent recognition studies of resulting sensors towards mandelic acid (MA) reveal that salan 2a containing (R)-BINOL and (R,R)-DACH exhibits highly sensitive and enantioselective response towards MA. The relationship between the chirality combination and the enantioselectivity is discussed. Based on the studies of concentration and solvent effect on the recognition process of 2a, it was found that the sensitivity and enantioselectivity could be enhanced via changing the concentration of sensors or altering the polarity of solvents. To explain why higher enantioselectivity can be achieved in moderate polar solvent other than in nonpolar or polar solvent, a solvent-guest competition mechanism, which may shed a light on the enhancement of the enantioselectivity of chiral recognition and noncovalent asymmetric catalysis, has been proposed and validated.

Rational design of BINOL-based diimidazolyl ligands: homochiral channel-like mono-component organic frameworks by hydrogen-bond-directed self-assembly

We have developed a synthetic strategy to selectively incorporate the imidazole ring into the 1,1'-bi-2-naphthol (BINOL) skeleton at the different position. The resulting conformationally rigid BINOL-based diimidazolyl ligands bearing both hydrogen-bond-acceptors and -donators can self-assemble into homochiral channel-like mono-component organic frameworks via intermolecular O-H···N hydrogen bonds between the phenolic hydroxyl group and the N2 or N4 atom of the imidazole ring.

A fluorescence sensor based on chiral polymer for highly enantioselective recognition of phenylalaninol

The chiral polymer P-1 incorporating (S)-2,2′-binaphthol (BINOL) and (S)-2,2′-binaphthyldiamine (BINAM) moieties in the main chain of the polymer backbone was synthesized by the polymerization of (S)-6,6′-dibutyl-3,3′-diformyl-2,2′-binaphthol (S-M-1) with (S)-2,2′-binaphthyldiamine (S-M-2) via nucleophilic addition–elimination reaction, and the chiral polymer P-2 could be obtained by the reduction reaction of P-1 with NaBH4. The fluorescence intensity of the chiral polymer P-1 exhibits gradual enhancement upon addition of (d)- or (l)-phenylalaninol and keeps nearly a linear correlation with the concentration molar ratios of (d)- or (l)-phenylalaninol. The value of enantiomeric fluorescence difference ratio (ef) is 6.85 for the chiral polymer on (d)-phenylalaninol. On the contrary, the chiral polymer P-2 shows no obvious fluorescence response toward either (d)- or (l)-phenylalaninol.

Conducting polynaphthalenes from 1,1′-binaphthyl and 1,1′-bi-2-naphthol via electropolymerization

Polynaphthalene films with electrical conductivity of 10−3Scm−1 were successfully electrosynthesized by direct anodic oxidation of 1,1′-binaphthyl (BN) and 1,1′-bi-2-naphthol (BNO) in CH2Cl2 containing additional boron trifluoride diethyl etherate (BFEE). The introduction of BFEE greatly lowered the onset oxidation potentials of the monomers compared with other supporting electrolytes. The resulting poly(1,1′-binaphthyl) (PBN) films exhibited good redox activity and stability in different monomer-free electrolytes. Moreover, FT-IR spectra and quantum chemistry calculation results proved that PBN and poly(1,1′-bi-2-naphthol) (PBNO) were both synthesized mainly through the coupling of the monomers at α-positions of the naphthalene ring. Fluorescence spectral determination showed that the polymers were typical blue light-emitters with solution quantum yields of 0.17 and 0.13, respectively. The substitution of hydroxyl and naphthyl groups did not change the emission wavelength of polynaphthalene (about 417nm). Surface morphology determination revealed that regular particles with different sizes were orderly assembled on ITO electrode after electrochemical growth.

Pseudoenantiomeric Fluorescent Sensors in a Chiral Assay

Two enantioselective fluorescent sensors, namely, the 1,1'-binaphthol (BINOL)-amino alcohol (S)-1 and the H(8)BINOL-amino alcohol (R)-2, have been prepared as a pseudoenantiomeric pair. These two compounds have the opposite chiral configuration at both the axially chiral biaryl centers and the amino alcohol units. In methylene chloride solution, (R)-mandelic acid greatly enhances the emission of (S)-1 at λ(1) = 374 nm and (S)-mandelic acid greatly enhances the emission of (R)-2 at λ(2) = 330 nm. A 1:1 mixture of (S)-1 and (R)-2 was used to interact with mandelic acid at a variety of concentrations with various enantiomeric compositions. It was found that both the concentration of mandelic acid and its enantiomeric composition can be directly determined by measuring the sum and difference of the fluorescence intensities at λ(1) and λ(2).

Asymmetric Baeyer–Villiger Oxidation of 2,3‐ and 2,3,4‐Substituted Cyclobutanones Catalyzed by Chiral Phosphoric Acids with Aqueous H2O2 as the Oxidant

AbstractCatalytic asymmetric Baeyer–Villiger (B–V) oxidation of 2,3,4‐trisubstituted cyclobutanone (4) has been realized by the catalysis of a 1,1′‐bi‐2‐naphthol (BINOL)‐derived chiral phosphoric acid (1j), which contains bulky 2,4,6‐triisopropyl phenyl groups at the 3,3′‐positions of the BINOL backbone, using 30 % aqueous H2O2 as the oxidant, affording the corresponding γ‐lactone (5) in 99 % yield with 95 % ee. In a divergent kinetic resolution of racemic 2,3‐disubstituted bicyclic cyclobutanones (6) through asymmetric B–V oxidation, the chiral phosphoric acid 1p demonstrated excellent catalytic performance, giving a range of regioisomeric chiral lactones in a normal lactone (nl)/abnormal lactone (al) ratio of up to 2.1:1, with up to 99 % ee in the al product. It was found that fine tuning of the stereoelectronic properties of the backbone in chiral phosphoric acids is critically important for attaining high levels of enantioselectivity in the catalysis of B–V reactions of different type of cyclobutanones. The present work has provided a convenient approach to the synthesis of a variety of optically active chiral γ‐lactones.

One‐Pot Hydroxy Group Activation/Carbon‐Carbon Bond Forming Sequence Using a Brønsted Base/Brønsted Acid System

AbstractA new sequential two‐step multicatalytic strategy is presented consisting in the efficient DBU‐catalysed trichloroacetimidation of an alcohol followed by a ditriflylamine (Tf2NH)‐catalysed intermolecular alkylation by silicon‐based nucleophiles and CH nucleophiles. The distinct feature of the trichloroacetimidate group allows use of weaker acid catalysts such as 1,1′‐bi‐2‐naphthol (BINOL)‐derived phosphoric acid, pointing out the possible development of an enantioselective variant. This unprecedented sequential one‐pot Brønsted base‐Brønsted acid catalysis further expands the synthetic scope of the trichloroacetimidate group.

Synthesis and Structural Aspects of N‐Triflylphosphoramides and Their Calcium Salts—Highly Acidic and Effective Brønsted Acids

Recently, 1,1'-bi-2-naphthol (BINOL)-based N-triflylphosphoramides emerged as a new class of potent Brønsted acid catalysts. In this paper we describe the efficient synthesis of various BINOL-based N-triflylphosphoramides and their calcium salts. Furthermore, X-ray crystal structure analysis combined with energy-dispersive X-ray spectroscopy (EDX) measurements confirmed that the synthesised chiral N-triflylphosphoramides are highly acidic metal-free catalysts.

Chiral Resolution of Racemic (±)-1,1'Bi (2-Naphthol) by Use of Molecularly Imprinted Polymers

Polymers imprinted with (S)-(-)-1,1’-bi (2-naphthol) and (R)-(+)-1,1’-bi (2-naphthol) have been prepared by non-covalent imprinting. A combinational procedure was used to optimize the functional monomer and crosslinker. A copolymer of 2-vinylpyridine and divinylbenzene resulted in the best chiral recognition. The ratio of template to functional monomer and solvent in the pre-polymerization mixture were also optimized. The imprinted polymers were used as stationary phases in high-performance liquid chromatography (HPLC). The molecularly imprinted polymers (MIPs) were more selective when prepared using a less polar solvent. Effective separations of the enantiomers of racemic (±)-1, 1’-Bi (2-naphthol) were achieved by use of acetonitrile as mobile phase; no cross-selectivity was observed. Interactions between functional monomers and template were investigated by 1H NMR spectroscopy. The results suggest that hydrogen-bonding between the functional monomer and the template and π-π stacking interaction between the cross-linker and the template may contribute to chiral recognition.

ChemInform Abstract: Chiral Titanium Complex Catalyzed Carbonyl-Ene Reaction with Glyoxylate: Remarkable Positive Nonlinear Effect.

Abstract The enantioselective glyoxylate-ene reaction catalyzed by chiral titanium complex derived from partially resolved binaphthol (BINOL) is shown to exhibit a remarkable level of asymmetric amplification (positive nonlinear effect). Thus, the optical yield of the ene product significantly exceeds the enantio-purity of the chiral ligand (BINOL).

Highly efficient and stable blue-light-emitting binaphthol-fluorene copolymers: A joint experimental and theoretical study of the main-chain chirality

In a quest for the main-chain chiral and highly stable blue-light-emitting π-conjugated polymers, a novel series of soluble conjugated random and alternating copolymers (PF-BN) derived from fluorene and axially chiral 1,1'-binaphthol (BINOL) were successfully synthesized by Suzuki coupling polymerization. The polymer structures, optical properties, and their electrochemical properties were investigated by 1 H NMR, TGA/DSC, UV-Vis absorption, photoluminescence, cyclic voltammetry, circular dichroism spectroscopy, and DFT calculations. The blue-light-emitting BINOL-containing copolymers with proper content of BINOL show highly efficient photoluminescence and ultra highly stable light-emission with almost unchanged fluorescent spectra after annealing at 200 °C in air for 10 h. The joint experimental and theoretical study of the main-chain chirality reveals that (1) the chirality of BINOL can be transferred to the polymer backbone, (2) the effective conjugation length is about one BINOL and three fluorenes, (3) the main active chiral block in the copolymers is probably composed by one BINOL with the other two or three fluorenes, and (4) the dihedral angle in the PF-BN copolymers should be larger than 105°. The incorporation of BINOL into the polyfluorene backbone is an effective way to produce highly efficient and stable blue-light-emitting main-chain chiral conjugated polymer with interesting optoelectronic properties.

Photoluminescence and Crystal Structures of Chiro-Optical 1,1′-Bi-2-naphthol Crystals and Their Inclusion Compounds with Dimethyl Sulfoxide

Crystal structures of (R)-(+)-1,1′-bi-2-naphthol (BINOL), (R,S)-(±)-BINOL, (S)-(−)-BINOL, (R,S)-(±)-BINOL·DMSO, (R)-(+)-BINOL·2DMSO, (R,S)-(±)-BINOL·2DMSO, and (S)-(−)-BINOL·2DMSO (DMSO = dimethyl sulfoxide) were determined and related to their photoluminescence measurements systematically. The intensities of both excitation and emission bands of BINOL tended to rise as the average distance between BINOL molecules increased. The polarity of DMSO in the inclusion compounds with DMSO probably induced a different magnitude of the Davydov splitting and the degree of shifting of the levels of BINOL molecules. The stabilization of the excited state and the lowering of its energy led to a red-shifted emission. It was proven that photoluminescence of lumophore molecules in the solid state was able to be fine-tuned through supramolecular organization and the host−guest interaction by crystallization of a racemic compound (i.e., co-crystallization of R and S enantiomers), by formation of an enantiomorph, and by sol...

ChemInform Abstract: 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)iPrO2]. 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.

ChemInform Abstract: Efficient Baylis-Hillman Reactions Promoted by Mild Cooperative Catalysts and Their Application to Catalytic Asymmetric Synthesis.

Abstract 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 Bronsted 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.

ChemInform Abstract: 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.

Enantioseparation of 1,1′-bi-2-naphthol benzoates using high performance liquid chromatography

The enantioseparations of 2'-hydroxy-1,1'-binaphthyl-2-yl benzoate (HBNB), 1,1'-binaphthyl-2,2'-diyl dibenzoate (BNDB) and 2'-methoxy-1,1'-binaphthyl-2-yl benzoate (MBNB) were studied on Chirex (S)-LEU & (S)-NEA, cellulose tris (3,5-dimethylphenylcarbamate) (Chiralcel OD-H) and amylose tris (3,5-dimethylphenyl-carbamate) (Chiralpak AD-H) columns, respectively, using high performance liquid chromatography. The effects of mobile phase, column temperature and compound structures on the enantioseparations were discussed. The Chiralpak AD-H exhibited stronger capability of enantioseparation in comparison with those of Chirex (S)-LEU & (S)-NEA and Chiralcel OD-H for 1,1'-bi-2-naphthol benzoates. When using the mobile phase of n-hexane/2-propanol (40/60, v/v), the chiral selectivities of HBNB, BNDB and MBNB were 1.76, 1.74, and 1.40, respectively. Moreover, in comparison with that of 1,1'-bi-2-naphthol (BN), the mechanisms of the enantioseparation of 1,1'-bi-2-naphthol benzoates, related to the substituted groups at 2-position, the elution orders and thermodynamic parameters were also discussed.

Solvent effect in the chromatographic enantioseparation of 1,1′-bi-2-naphthol on a polysaccharide-based chiral stationary phase

Enantioseparation of 1,1′-bi-2-naphthol (BINOL) was performed on a polysaccharide-based chiral stationary phase, Chiralcel OD-H, under normal-phase mode. The effects of polar modifier in the mobile phase on the retention, enantioseparation and elution order were investigated in detail. Solvent-induced reversal of elution order for BINOL was observed. When linear alcohols were adopted, R-BINOL was always eluted first. S-BINOL was eluted first when 2-propanol was used as a polar modifier. Enantioseparation could not be obtained when sec-butyl alcohol or tert-butyl alcohol was used as a polar modifier. When isoamyl alcohol or cyclohexanol was used as a polar modifier, favorable enantioseparation was obtained as with 1-pentanol or 1-hexanol; also, R-BINOL was the first-eluted enantiomer. It is worth emphasizing that significantly better enantioseparation was obtained when higher alcohols were used as polar modifier of the mobile phase. A nonlinear characteristic for the ln α against 1/ T plots was universally observed in this study though the ln k against 1/ T plots exhibited a linear feature. Associated with the obtained thermodynamic parameters, some interesting inferences about chiral recognition mechanism were proposed.