Bi-2-naphthol Research Articles

Two‐Photon Absorption Circular Dichroism: A New Twist in Nonlinear Spectroscopy

Herein we report on the full experimental measurement of the two-photon absorption circular dichroism spectra of (S)-(-)-1,1'-bi(2-naphthol) and (R)-(+)-1,1'-bi(2-naphthol), their analysis, and theoretical support. The finding of new nonlinear optical fingerprints in chiral molecules offers new opportunities in the recognition and understanding of optically active systems in regions where CD could present strong limitations.

Chiral Phosphoric Acids as Versatile Catalysts for Enantioselective Carbon–Carbon Bond Forming Reactions

Abstract An inventive approach to the development of chiral Brønsted acid catalysis, to enable catalysts which possess strong acid functionalities, has been accomplished. Among the various organic Brønsted acids surveyed, phosphoric acids have become the focus of our attention as potential chiral Brønsted acid catalysts because of their unique structural and chemical features. The desirable features of phosphoric acids as chiral Brønsted acid catalysts are summarized as follows. 1) Phosphoric acids are expected to have relatively strong yet appropriate acidity. 2) The phosphoryl oxygen would function as a Brønsted basic site and hence it is anticipated that it would convey acid/base dual function even to monofunctional phosphoric acid catalysts. 3) An acidic functionality is available even with the introduction of a ring system which effectively restricts the conformational flexibility of the chiral backbone. 4) Substituents can be introduced to the ring system to provide an efficient chiral environment for enantioselective transformations. It is anticipated that an efficient substrate recognition site would be constructed around the activation site due to the acid/base dual function and the steric and electronic influence of the substituents introduced at the ring system. In this context, we developed 1,1′-bi-2-naphthol (BINOL)-derived monophosphoric acids as chiral Brønsted acid catalysts. The chiral phosphoric acids thus developed functioned as efficient enantioselective catalysts for a variety of carbon–carbon bond forming reactions via activation of a series of functionalities, affording enantioenriched products in excellent selectivities. In this article, we review our recent achievements in developing enantioselective reactions using the chiral phosphoric acid catalysts. The contents are arranged according to the type of functionality, including imines, hemiaminal ethers, aldehydes, and electron-rich double bonds, followed by specific reaction types.

Synthesis and Application of Modular Phosphine–Phosphoramidite Ligands in Asymmetric Hydroformylation: Structure–Selectivity Relationship

A series of hybrid phosphine-phosphoramidite ligands has been designed and synthesized in moderate yields from chiral BINOL (1,1'-bi-2-naphthol) or NOBIN (2-amino-2'-hydroxy-1,1'-binaphthyl). They have achieved highly regio- and enantioselectivities in Rh-catalyzed asymmetric hydroformylations of styrene derivatives (branched/linear ratio up to 56.6, ee up to 99 %), vinyl acetate derivatives (up to 98 % ee), and allyl cyanide (up to 96 % ee). Systematic variation of ligand structure showed that the steric factor on the phsophoramidite moiety determined the performance of the ligand. With the increased hindrance, the branched/linear ratio rose, while the ee value dropped in the hydroformylation of styrene. However, the N-substituents did not influence the selectivities much.

Two‐photon absorption circular‐linear dichroism on axial enantiomers

We report on the experimental-theoretical analysis of degenerated two-photon absorption circular-linear dichroism (2PA-CLD) in (S)-(-)-1,1'-bi(2-naphthol) and (R)-(+)-1,1'-bi(2-naphthol) dissolved in THF. 2PA-CLD reveals similarities and differences between optical polarization states for the different enantiomers. These results unveil the potential applications of 2PA-CLD for the study and identification of chiral molecules with active and pivotal role in biological systems and the systematic design of chiral photonic structures.

Preparation of Novel Fluoroalkyl End-Capped Trimethoxyvinylsilane Oligomeric Nanoparticle-Encapsulated Binaphthol: Encapsulated Binaphthol Remaining Thermally Stable Even at 800 °C

Abstract Novel cross-linked fluoroalkyl end-capped trimethoxyvinylsilane oligomeric nanoparticles [RF–(VM-SiO2)n–RF]-encapsulated 1,1′-bi(2-naphthol) (BINOL) were prepared by the hydrolysis of fluoroalkyl end-capped trimethoxyvinylsilane oligomer in the presence of BINOL under alkaline conditions. RF–(VM-SiO2)n–RF-encapsulated BINOL nanocomposite thus obtained afforded no weight loss corresponding to the presence of BINOL in the composite at 800 °C. Interestingly, RF–(VM-SiO2)n–RF/BINOL nanocomposite did not show absorption peaks before calcination however this nanocomposite was found to exhibit similar absorption and fluorescence peaks to those of the parent BINOL after calcination at 800 °C. More interestingly, RF–(VM-SiO2)n–RF/BINOL nanocomposite after calcination exhibited a releasing characteristic into methanol although before calcination this nanocomposite showed no such characteristic at all. In particular, FT-IR spectra of the released molecules showed typical bands related to both the parent BINOL and silica gel, indicating that the released guest molecules should be thermally stable even at 800 °C through the architecture of rigid BINOL-containing silica gel matrices.

Highly enantioselective fluorescent sensor for chiral recognition of amino acid derivatives

A highly enantioselective fluorescent sensor, containing benzylaminomethyl groups at 3,3′-position of 1,1′-bi-2-naphthol (BINOL), has been used to conduct the chiral recognition of α-amino acid derivatives. It is observed that one enantiomer of N-Boc-proline can increase the fluorescence intensity of the binaphthyl fluorophores by over 57-fold, while the other enantiomer can cause only sixfold fluorescence enhancement. Such unusually highly enantioselective response demonstrates that this sensor is potentially useful in the enantioselective recognition of amino acid derivatives.

Enantioselective Rh-catalyzed hydrogenation of N-acyl dehydroamino esters and enamides with monodentate phosphoramidite ligands

Chiral monodentate phosphoramidite ligands were conveniently prepared from 1,1′-bi-2-naphthol (BINOL) and (S)-pyrrolidine in good yields, which were effective chiral ligands in the enantioselective rhodium-catalyzed hydrogenation of dehydroamino esters and enamides at low hydrogenation pressure. High conversion rate (up to 99% for dehydroamino esters and enamides) and good enantioselectivity (up to 96.3% ee for dehydroamino esters and 91.7% ee for enamides) were obtained.

Temperature-induced inversion of elution order in the chromatographic enantioseparation of 1,1′-bi-2-naphthol on an immobilized polysaccharide-based chiral stationary phase

In this work, the enantioseparations of 1,1′-bi-2-naphthol (BINOL) and its three derivatives were performed on an immobilized polysaccharide-based chiral stationary phase, Chiralpak IA, under normal-phase mode. The effects of the content of polar modifier in the mobile phase and the column temperature on the retention and enantioseparation were investigated in detail. Temperature-induced inversion of elution order for BINOL was observed directly when n-hexane/2-propanol (92/8, v/v) was used as mobile phase. The isoenantioselective temperature ( T iso) was calculated to be 31.4 °C. When n-hexane/2-propanol/THF (93/2/5, v/v/v) was used as mobile phase, the T iso value decreased to −8.2 °C. Entropically driven enantioseparation which had practical application was obtained successfully (separation factor being 1.189 and 1.332 at 25 °C and 50 °C, respectively). The corresponding thermodynamic parameters for other three binaphthyl compounds were compared with that for BINOL. Some inferences about chiral recognition mechanism were stressed.

Tunable Phosphoramidite Ligands for Asymmetric Hydrovinylation: Ligands par excellence for Generation of All-Carbon Quaternary Centers

1-Alkylstyrenes undergo efficient hydrovinylation (addition of ethylene) in the presence of a Ni-catalyst prepared from [(allyl)NiBr](2), Na(+) [BAr(4)](-) (Ar = 3,5-bis-trifluromethylphenyl), and a phosphoramidite ligand giving products in excellent yields and enantioselectivities. In many cases phosphoramidites derived from achiral 2,2'-biphenol are almost as good as ligands derived from the more expensive enantiopure 2,2'-binaphthols. The hydrovinylation products, which carry two versatile latent functionalities, an aryl and a vinyl group, are potentially useful for the synthesis of several important natural products containing benzylic all-carbon quaternary centers.

Development of Dinuclear Vanadium Catalysts for Enantioselective Coupling of 2-Naphthols via a Dual Activation Mechanism

This review describes our recent efforts in the development of chiral dinuclear vanadium complexes which work as dual activation catalysts for oxidative coupling of 2-naphthols. A chiral dinuclear vanadium(IV) complex (R(a),S,S)-1a possessing (S)-tert-leucine moieties at the 3,3'-positions of the (R)-binaphthyl skeleton was developed, and found to promote oxidative coupling of 2-naphthol to afford (S)-1,1'-bi-2-naphthol (BINOL) with 91% ee. To verify the dual activation mechanism, mononuclear vanadium(IV) complex (S)-10 was also prepared. Kinetic analysis revealed that the reaction rate of oxidative coupling of 2-naphthol promoted by (R(a),S,S)-1a is 48.3 times faster than that of (S)-10. In the coupling reaction, the two vanadium metals in the chiral complex activate two molecules of 2-naphthol simultaneously achieving a high reaction rate with high enantiocontrol. Since the dinuclear vanadium(IV) complex was found to be readily oxidized to afford a corresponding vanadium(V) species during preparation in air, a new synthetic procedure using VOCl3 and a convenient one-pot procedure using VOSO4 under O2 have been applied towards dinuclear vanadium(V) complexes (R(a),S,S)-2. The coupling of 2-naphthol was catalyzed by (R(a),S,S)-2 with reaction rates enhanced 2.3 times faster than that of (R(a),S,S)-1a, which is likely a precatalyst. To the best of our knowledge, (R(a),S,S)-1a, 2, and 3 show considerably higher catalytic activity than previously reported vanadium complexes for oxidative coupling of 2-naphthols.

複数の構成要素を持つ不斉触媒“Multicomponent Asymmetric Catalyst(MAC)”の固定化

Several methodologies for the immobilization of multicomponent asymmetric catalysts (MACs), which consist of two molecules of 1,1'-bi(2-naphthol)(BINOL) and two metals, have been developed. In the first place, Al-Li-bis(binaphthoxide)(ALB) and/or Ga-Na-bis(binaphthoxide)(GaSB) catalysts were introduced to the dendrimers and soluble polymers containing dendron units. Since these dendritic molecules require multi-step synthesis, efficient syntheses of the spherical particles that function like dendrimer-supported catalysts were realized by use of a micelle-derived polymer (MDP) and a monolayer-protected metal cluster (MPC). Secondly, a novel approach based on the use of “catalyst analogue” is found to be effective to position the ligands suitably on the polymer backbone. Thirdly, utilizing metal-bridged polymers, a simple and efficient method for immobilization without the need for a polymer support has also been realized. Heterogeneous ALB, GaSB and μ-oxodititanium complexes thus obtained have been used as catalysts for the asymmetric Michael addition and the asymmetric carbonyl-ene reactions, respectively. The catalysts displayed high activity, affording the corresponding products with high enantiomeric excesses. These catalysts could be recovered and reused.

Insight into the Mechanism of the Asymmetric Ring-Opening Aminolysis of 4,4-Dimethyl-3,5,8-trioxabicyclo[5.1.0]octane Catalyzed by Titanium/BINOLate/Water System: Evidence for the Ti(BINOLate)2-Bearing Active Catalyst Entities and the Role of Water

The mechanism of the enantioselective ring-opening aminolysis of 4,4-dimethyl-3,5,8-trioxabicyclo[5.1.0]octane with benzylamine, catalyzed by the titanium-BINOLate species generated in situ from a mixture of enantiopure BINOL (1,1'-bi-2-naphthol), Ti(OiPr)4, and H2O in the presence of benzylamine in toluene, was investigated in detail using a combination of reaction profile measurements, nonlinear effect (NLE) studies, solution (1)H NMR analysis, electrospray ionization mass spectrometry (ESI-MS), as well as the results obtained from screening of dynamic catalyst library of complexes L(a)/Ti/L(b) (L(a) or L(b) = chiral diol ligands). The BINOL-to-titanium ratio and the presence or absence of water in the catalytic system were found to exert profound influences on both reactivity and enantioselectivity of the reaction. The NLE studies revealed that the titanium species involved in the catalysis should contain more than one BINOL unit, either within or at the periphery of the catalytic cycle. ESI-MS analysis of the catalytic systems provided strong support in favor of the mechanistic proposal that titanium complexes bearing the Ti(BINOLate)2 moiety should be the active species responsible for the catalysis, which was further confirmed by the observation of synergistic effect of the heteroligand combinations during screening of the dynamic catalyst library. ESI-MS analysis of the reaction system indicated that water does not take part in the catalyst generation, which is an unprecedented finding in contrast to the previous mechanistic understandings in the titanium catalytic chemistry involving the participation of water. Most probably, water functions as a proton shuttle in the catalysis, facilitating the proton transfer between the reactants. Furthermore, the origin of (+)-NLE observed in the present catalytic system is rationalized on the basis of the ESI-MS analysis of the catalyst system prepared from a 1:1 pseudoracemic mixture of (S)-BINOL and (R)-3,3',6,6'-D4-BINOL. Finally, the reactivity differences between several couples of epoxide/amine combinations were tentatively rationalized on the basis of the arguments on their relative coordination preferences, and several other aliphatic amines were also found to efficiently ring-open the titled epoxide in excellent enantioselectivities. The results from this study are expected to shed some light on the often elusive chemistry of Ti(IV)-based catalytic systems where water or molecular sieves (or alcohols, etc.) are found to play an important yet inexplicable role and may help the search for effective asymmetric Ti(IV) catalysts for other types of reactions.

Enantiomeric discrimination of 1,1′-binaphthol by room temperature phosphorimetry using γ-cyclodextrin as chiral selector

In the presence of a small amount of 1,2-dibromopropane (1,2-DBP), 1,1′-binaphthol (BINOL) displays strong room temperature phosphorescence in γ-cyclodextrin (γ-CD) solution without deoxygenation. The phosphorescence intensity as well as the phosphorescence lifetime of ( S)-BINOL is greater than that of ( R)-BINOL, indicating a distinct chiral discrimination of γ-CD toward this pair of enantiomers. Both ( R)-BINOL and ( S)-BINOL exhibit a double exponential phosphorescence decay with lifetimes of 5.89 ms and 17.3 ms for ( R)-BINOL and 7.58 ms and 23.6 ms for ( S)-BINOL, respectively. The association constant obtained for ( S)-BINOL/γ-CD/1,2-DBP ternary complex is larger than that for ( R)-BINOL/γ-CD/1,2-DBP complex. Thus, the observation of RTP lifetime differences between ( R)-BINOL and ( S)-BINOL can be attributed to their different ability to form complexes with chiral γ-CD, which is further supported by an analysis of the proton NMR chemical shift differences between ( R)-BINOL and ( S)-BINOL.

Synthesis, Characterization and Catalytic Properties of Chiral BINOL Functionalized Mesoporous Silicas for Enantioselective Morita-Baylis-Hillman Reaction

Several Chiral BINOL functionalized mesoporous silicas were prepared by post grafting of organosilane derivatives of (S)-BINOL (1,1′-bi-2-naphthol) on SBA-15 and characterized by 13C CP/MAS NMR, FT-IR, UV–visible absorption spectra, elemental analysis, powder XRD, nitrogen adsorption–desorption isotherms and TEM techniques. Their catalytic properties were demonstrated in enantioselective Morita-Baylis-Hillman reaction of 3-phenylpropanal and cyclohexenone. Among them, 3BSBA-15 linked through the 3 position of BINOL exhibit higher enantioselectivity (26% e.e.) and yield (88%) which are similar to the homogeneous catalyst (S)-BINOL (27% e.e. and 92% yield) as Bronsted acids catalyst, while complex of 3BSBA-15 and calcium 3BSBA-15-Ca show lower enantioselectivity (21% e.e.) than its homogeneous complex (S)-BINOL-Ca (32% e.e.) as ligand catalyst. 3BSBA-15 and 3BSBA-15-Ca can be reused with no significant decrease in enantioselectivity and yield.

Poly(N-phenylmaleimides) bearing chiral oxazolinyl pendant: Supramolecular aggregation and enantioselectivity in fluorescence response

N-Phenylmaleimide derivatives bearing a chiral oxazoline substituent at the benzene ring (N-[o-(4,5-dihydro-1,3-oxazol-2-yl)phenyl]maleimides, OPMIs) were polymerized using a binary initiating system composed of Et2Zn and n-BuLi to in situ produce the zinc complexes of optically active poly(OPMI)s. The significant changes in chiroptical and fluorescent properties were observed for these polymers upon complexation with metal ions due to the formation of supramolecular structure, evidenced by circular dichroism, fluorescence spectrum and atomic force microscopy. The fluorescence spectra of poly(OPMI)/ZnII complexes in the presence of (R)/(S)-1,1′-bi-2-naphthol (BINOL) and (R)/(S)-2-amino-1-propanol were studied in THF media. It was found that the fluorescence intensity of the complexes responded differently to both enantiomers of BINOL and the amino alcohol in a quenching and enhancement fashion, respectively. Furthermore, the enantioselective fluorescence response was strongly dependent on the amount of incorporated zinc in polymer matrices.

Synthesis and optical activity analysis of chiral titanium(IV) sec-butoxide and its group IV analogues

The complete series of chiral group IV sec-butoxides has been obtained by the treatment of M(NMe 2) 4 (M = Ti, Zr, Hf) with resolved ( R)-(−)- or ( S)-(+)-2-butanol. These complexes were analyzed by polarimetry, revealing a decreasing trend in molar rotation down the group, from titanium to hafnium. Catalysis screenings showed that the resolved titanium sec-butoxides, in conjunction with the resolved BINOL (BINOL = 1,1′-bi-2-naphthol) of the opposite configuration designation, catalyzed the addition of dimethyl zinc to benzaldehyde with higher enanteoselectivity than that observed for resolved BINOL with titanium(IV) isopropoxide or with the titanium(IV) sec-butoxide of the same configuration designation.

Monolayers of Twisted Binaphthyls for Aromatic Crystallization at Low Nucleation Densities and High Growth Rates

Monolayers of 1,1'-bi-2-naphthol (BN) derivatives, of which the two naphthalene rings are twisted along the carbon(1)-carbon(1') single bond, were studied for their conformational effect on the growth of pentacene crystals on their monolayer surface. BN monolayers with H and Br at 6,6'-positions (H-BN and Br-BN) were prepared by immersion-coating in toluene solution of the corresponding BNSiCl2. Pentacene was thermally evaporated onto the H-BN and Br-BN monolayers, silica, octadecylsilyl (ODTS) SAM, and a micropattern of H-BN and ODTS SAM. Pentacene crystals were also grown on the SAMs of 1-naphthylsilyl(NPh), phenylsilyl(Ph), and diphenylsilyl (DPh) groups, which are aromatic and have contact angle values similar to those of the the BN monolayers. AFM images of the crystals at the early stage of growth indicated that the BN monolayers suppressed the nucleation while facilitating the growth of nuclei to larger crystals. The low nucleation density and high growth rate are accounted for by the amorphous nature of the twisted BN monolayer surface where the intermolecular interaction between neighboring adsorbates is likely to be suppressed. The results offer new insights into designing surfaces for controlling the crystallization kinetics of organic materials.

Photochemistry of 1,1′-bi-2-naphthol (BINOL) — ESIPT is responsible for photoracemization and photocyclization

The photochemistry of 1,1′-bi-2-naphthol (BINOL, 5) has been studied in aqueous solution and found to undergo rapid deuterium incorporation at the 4 and 5 positions (in D2O-CH3CN). All data is consistent with exchange arising via a formal excited state intramolecular proton transfer (ESIPT) from the naphtholic OH to the 4 and 5 positions of the other ring to give quinine methides (QMs) 8 and 9, respectively, both of which subsequently revert to starting material. Photolysis of enantiomerically pure (+)-5 in D2O-CH3CN resulted in racemization concurrent with deuterium incorporation. This is strong evidence to indicate that photoracemization of BINOL is a direct result of ESIPT, in keeping with the invocation of planar QM intermediates. Prolonged irradiation also gave a ring-closed product that is assigned as dihydrobenzoxanthene 7, based on NMR and UV–vis data, and in analogy to known reactions of similar biaryl systems initiated by ESIPT. The formation of 7 is believed to arise via initial ESIPT from the naphtholic OH to the 7 position of the other naphthol ring generating an o-quinone methide intermediate that subsequently undergoes exclusive electrocyclic ring closure to give 7. The deuterium exchange and photocyclization reach maximum quantum efficiency at ~8 mol/L water (in CH3CN). A “water relay” mechanism for ESIPT is proposed that is consistent with the need for water in the photochemical deuterium exchange, racemization, and formation of 7. The photostability and photoracemization of other related BINOL asymmetric catalysts in water should be a concern based on the reported results herein.Key words: BINOL, ESIPT, photoprotonation, photoracemization, photocyclization, quinone methide.

Single diastereomers of unsymmetrical tris‐spirocyclic cyclotriphosphazenes based on 1,1′‐bi‐2‐naphthol—Synthesis and structures

Diastereoselective synthesis and characterization of chiral unsymmetrical tris-spirocyclic cyclotriphosphazenes based on chiral 1,1'-bi-2-naphthol (BINOL) are reported. Specifically, the chiral compounds (-)N(3)P(3)[1,1'-O(2)(C(10)H(6))(2)](O-2,2'C(6)H(4)-C(6)H(4)O)Cl(2) [(-)-4] and (-)N(3)P(3)[1,1'-O(2)(C(10)H(6))(2)](OCH(2)CH(2)NMe)(2) [(-)-5] are prepared by starting with the chiral mono-spiro compound (-)N(3)P(3)[1,1'-O(2)(C(10)H(6))(2)]Cl(4) [(-)-3]. Synthesis of four other chiral spirocyclics, N(3)P(3)[1,1'-O(2)(C(10)H(6))(2)](OCH(2)CH(2) NMe)(O-2,2'C(6)H(4)-C(6)H(4)O)[(-)-6 and (+)-6], N(3)P(3)[1,1'-O(2)(C(10)H(6))(2)](NMe(2))(4) [(-)-7], N(3)P(3)[1,1'-O(2)(C(10)H(6))(2)](O-2,2'C(6)H(4)-C(6)H(4)O)(NMeCH(2)CH(2)OH)(2) [(-)-8 and (+)-8], and N(3)P(3)[1,1'-O(2)(C(10)H(6))(2)](O-2,2'C(6)H(4)-C(6)H(4)O)[NHCH(2)CH(2)CH(2)Si(OEt)(3)](2) (9) is also reported herein. Compounds 4-6 are obtained in the solid state diastereoselectively and their X-ray structures have been determined and discussed. The diastereoselectivity is also shown by structural characterization of two distinct isomers in the case of 6 [(-)-6 and (+)-6, respectively] by starting with precursor of 3 having (R) or (S)-BINOL residue. The (1)H NMR spectra of 7 and 8 exhibit doublets with virtual coupling for the methyl protons, consistent with the chiral nature of the binaphthoxy residue. The potential of 9, which hydrolyzes readily in CDCl(3) solution, as a useful precursor for chiral polymer applications is highlighted.

Optical Recognition of Chirality at Surfaces by Vibrational Sum Frequency Generation Spectroscopy

Two-dimensional chirality has attracted interest as an approach to develop novel chiral catalysts and sensors. However, there is no standard tool to distinguish and evaluate the chirality at surfaces and interfaces, since the number of chiral molecules or chiral sites are limited in the two-dimensional system. Linear chiroptical spectroscopy, such as circular dichroism (CD) and Raman optical activity (ROA), cannot be applied to the two dimensional system, because these methods are basing on the optical transition forbidden under the electric dipole approximation and, then, the chiral responses becomes much weak. Recently, one of the nonlinear spectroscopy, infrared-visible sum frequency generation (VSFG) has been established as a novel chiroptical tool to investigate the molecular and surface chirality. In the present study, this optical technique was applied to recognize the chirality at chiral molecules-modified surfaces under the nonelectronic resonant condition. For polycrystalline films of bi-naphthol (BINOL), chiral VSFG signal reached around 50% of achiral SFG signal and the chirality of the thin film could be successfully recognized. On the other hand, for submonolayer of binaphthyl molecules on Au, there was a limitation in the sensitivity and it was desired to introduce the doubly resonant VSFG enhancement for in situ monitoring of chiral recognition processes.