Binaphthyl Scaffold Research Articles

Stereocontrol via Propeller Chirality in FLP-Catalyzed Asymmetric Hydrogenation.

Utilization of chiral frustrated Lewis pairs as catalysts in enantioselective hydrogenation of unsaturated molecules represents a promising approach in asymmetric synthesis. In our effort to improve our current understanding of the factors governing the stereoselectivity in these catalytic processes, herein we examined the mechanism of direct hydrogenation of aromatic enamines catalyzed by a binaphthyl-based chiral amino-borane. Our computational analysis reveals that only one particular conformer of the key borohydride reaction intermediate can be regarded as a reactive form of this species. This borohydride conformer has a well-defined chiral propeller shape, which induces facial selectivity in the hydride transfer to pro-chiral iminium intermediates. The propeller chirality of the reactive borohydride conformer is generated by the axially chiral binaphthyl scaffold of the amino-borane catalyst through stabilizing π-π stacking interactions. This new computational insight can be readily used to interpret the high degree of stereoinduction observed for these reactions. We expect that the concept of chirality relay could be further exploited in catalyst design endeavors.

Binaphthyl Scaffold: A Class of Versatile Structure in Asymmetric C–H Functionalization

Binaphthyl Scaffold: A Class of Versatile Structure in Asymmetric C–H Functionalization

Exploration of chromophores for a VCD couplet in a spectrally transparent infrared region for biomolecules.

Interactions of two chromophores such as carbonyl groups yield a strong VCD couplet that reflects the molecular structures. The use of VCD couplets for biomacromolecular structural studies has been hampered by severe signal overlap caused by numerous functional groups that originally exist in biomacromolecules. Nitrile, isonitrile, alkyne, and azido groups show characteristic IR absorption in the 2300-2000 cm-1 region, where biomolecules do not strongly absorb. We herein examined the usefulness of these functional groups as chromophores to observe a strong VCD couplet that can be readily interpreted using theoretical calculations. Studies on a chiral binaphthyl scaffold possessing two identical chromophores showed that nitrile and isonitrile groups generate moderately-strong but complex VCD signals due to anharmonic contributions. The nature of their anharmonic VCD patterns is discussed by comparison with the VCD spectrum of a mono-chromophoric molecule and by anharmonic DFT calculations. On the other hand, through studies on diazido binaphthyl and diazido monosaccharide, we demonstrated that the azido group is more promising for structural analysis of larger molecules due to its simple, strong VCD couplet whose spectral patterns are readily predicted by harmonic DFT calculations.

Circularly Polarized Luminescence of a Stereogenic Curved Paraphenylene Anchoring a Chiral Binaphthyl in Solution and Solid State.

Invited for the cover of this issue are Masashi Hasegawa, Yoshitane Imai, Yasuhiro Mazaki and co-workers at Kitasato University, Kindai University and Osaka University. The image depicts a stereogenic twisted cycloparaphenylene that exhibits circularly polarized luminescence in a polymethyl methacrylate thin film. Read the full text of the article at 10.1002/chem.202004283.

Circularly Polarized Luminescence of a Stereogenic Curved Paraphenylene Anchoring a Chiral Binaphthyl in Solution and Solid State.

A curved stereogenic [6]paraphenylene ([6]PP), anchoring a chiral binaphthyl scaffold at 7,7'-positions, was prepared and investigated for its properties as a solid-state circularly polarized luminescence (CPL) dye. X-ray analysis revealed a helically twisted structure of PP units induced by axial chirality of binaphthyl framework. The curved [6]PP exhibits fluorescence in powder and polymethyl methacrylate (PMMA) film as well as solution. A significant increase in quantum yield was observed for a non-fluid PMMA film owing the suppression of the molecular motion. The gCPL values of the dye in solution and as PMMA film were almost the same (4.3-4.4×10-3 ) and lager than that in powder. TD-DFT calculations in the excited state suggest that the exciton can be delocalized into a twisted PP unit to produce a larger magnetic transition dipole moment.

Diastereoselective Synthesis of P-Chirogenic and Atropisomeric 2,2'-Bisphosphino-1,1'-binaphthyls Enabled by Internal Phosphine Oxide Directing Groups.

Diphosphine ligands that merge both axial and P-centered chirality may exhibit superior or unique properties. Herein we report the diastereoselective introduction of P-centered chirality at the 2-position of the axially chiral 2'-(phosphine oxide)-1,1'-binaphthyl scaffold. A lithium-bromide exchange reaction of a 2-bromo-2'-(phosphine oxide)-1,1'-binaphthyl and treatment with dichlorophosphines followed by a nucleophilic organometallic reagent afforded unsymmetrical 2-phosphino-2'-(phosphine oxide)-1,1'-binaphthyls with binaphthyl axial chirality and one or two phosphorus stereocenters with a variety of P substituents. The final diastereomerically pure 2,2'-bisphosphino-1,1'-binaphthyls were obtained by reduction of the phosphine oxide directing group. Preliminary results demonstrated that a ligand with this hybrid chirality could induce higher stereoselectivity in the metal-complex-catalyzed asymmetric hydrogenation of a dialkyl ketone.

Diastereoselective Synthesis of P‐Chirogenic and Atropisomeric 2,2′‐Bisphosphino‐1,1′‐binaphthyls Enabled by Internal Phosphine Oxide Directing Groups

AbstractDiphosphine ligands that merge both axial and P‐centered chirality may exhibit superior or unique properties. Herein we report the diastereoselective introduction of P‐centered chirality at the 2‐position of the axially chiral 2′‐(phosphine oxide)‐1,1′‐binaphthyl scaffold. A lithium–bromide exchange reaction of a 2‐bromo‐2′‐(phosphine oxide)‐1,1′‐binaphthyl and treatment with dichlorophosphines followed by a nucleophilic organometallic reagent afforded unsymmetrical 2‐phosphino‐2′‐(phosphine oxide)‐1,1′‐binaphthyls with binaphthyl axial chirality and one or two phosphorus stereocenters with a variety of P substituents. The final diastereomerically pure 2,2′‐bisphosphino‐1,1′‐binaphthyls were obtained by reduction of the phosphine oxide directing group. Preliminary results demonstrated that a ligand with this hybrid chirality could induce higher stereoselectivity in the metal‐complex‐catalyzed asymmetric hydrogenation of a dialkyl ketone.

Sign Control of Circularly Polarized Luminescence Based on Geometric Arrangement of Fluorescent Pyrene Units in a Binaphthyl Scaffold

The signs of circularly polarized luminescence and circular dichroism of binaphthyl-pyrene fluorophores with the same axial chirality can be controlled by altering the bonding positions of the two ...

From Reactivity and Regioselectivity to Stereoselectivity: An Odyssey of Designing PIP Amine and Related Directing Groups for C—H Activation

AbstractImproving the reactivity and selectivity is a long pursuing goal in C—H functionalization reactions. In line with this goal, a well‐designed bidentate 2‐(pyridine‐yl)isopropyl amine (PIP amine) directing group was developed by our group to achieve the activation of unbiased methylene C(sp3)–H activation, which also found its broad applications in C—H activation reactions catalyzed by base metals, such as Cu, Ni, Co and Fe, to form various C—C and C—X bonds. Moreover, PIP amine has also been applied in the strategic step toward the total synthesis of aeruginosin marine natural products. Its highly tunable structure has triggered the design of a series of chiral auxiliaries for diastereoselective C—H activation. More recently, Pd(II)‐catalyzed enantioselective functionalization of unbiased methylene C(sp3)–H bonds enabled by the cooperative effects between PIP amine and chiral ligands with axially chiral binaphthyl scaffold has also been realized. In this account, we briefly summaries the journey of developing PIP amine for C—H activation, from controlling the reactivity and regioselectivity to stereoselectivity.

2,2'-Diamino-6,6'-diboryl-1,1'-binaphthyl: A Versatile Building Block for Temperature-Dependent Dual Fluorescence and Switchable Circularly Polarized Luminescence.

Temperature-dependent dual fluorescence and switchable circularly polarized luminescence (CPL) are two highly pursued but challenging properties for small organic molecules (SOMs). We herein disclose a triarylborane π-system based on a 2,2'-diamino-6,6'-diboryl-1,1'-binaphthyl scaffold that can serve as a versatile building block for achieving these two properties by simply choosing different amino groups. BNMe2 -BNaph with less bulky dimethylamino groups displays temperature-dependent dual fluorescence, and can thus be used as a highly sensitive ratiometric fluorescence thermometer. On the other hand, BNPh2 -BNaph with bulky diphenylamino groups exhibits intense fluorescence in both solution and in the solid state. A change of solvent from nonpolar cyclohexane to highly polar MeCN not only shifts the CPL position to much longer wavelength but also inverts the CPL sign. In addition, the complexation of BNPh2 -BNaph with fluoride greatly enhances the CPL intensity.

2,2′‐Diamino‐6,6′‐diboryl‐1,1′‐binaphthyl: A Versatile Building Block for Temperature‐Dependent Dual Fluorescence and Switchable Circularly Polarized Luminescence

AbstractTemperature‐dependent dual fluorescence and switchable circularly polarized luminescence (CPL) are two highly pursued but challenging properties for small organic molecules (SOMs). We herein disclose a triarylborane π‐system based on a 2,2′‐diamino‐6,6′‐diboryl‐1,1′‐binaphthyl scaffold that can serve as a versatile building block for achieving these two properties by simply choosing different amino groups. BNMe2‐BNaph with less bulky dimethylamino groups displays temperature‐dependent dual fluorescence, and can thus be used as a highly sensitive ratiometric fluorescence thermometer. On the other hand, BNPh2‐BNaph with bulky diphenylamino groups exhibits intense fluorescence in both solution and in the solid state. A change of solvent from nonpolar cyclohexane to highly polar MeCN not only shifts the CPL position to much longer wavelength but also inverts the CPL sign. In addition, the complexation of BNPh2‐BNaph with fluoride greatly enhances the CPL intensity.

Organocatalytic Asymmetric Decarboxylative Mannich Reaction of β-Keto Acids with Cyclic α-Ketiminophosphonates: Access to Quaternary α-Aminophosphonates.

An organocatalytic asymmetric decarboxylative Mannich reaction of β-keto acids with cyclic α-ketiminophosphonates has been developed. By using saccharide-derived bifunctional amine-thiourea catalysts bearing an axial chiral binaphthyl scaffold, a wide range of quaternary α-amino-γ-oxophosphonates were obtained in up to 93% yield and >99% ee. Furthermore, two interesting α-aminophosphonate derivatives were synthesized from the corresponding decarboxylative Mannich product via simple transformations.

Chiral Bifunctional Phosphine‐Carboxylate Ligands for Palladium(0)‐Catalyzed Enantioselective C−H Arylation

AbstractPrevious enantioselective Pd0‐catalyzed C−H activation reactions proceeding via the concerted metalation‐deprotonation mechanism employed either a chiral ancillary ligand, a chiral base, or a bimolecular mixture thereof. This study describes the development of new chiral bifunctional ligands based on a binaphthyl scaffold which incorporates both a phosphine and a carboxylic acid moiety. The optimal ligand provided high yields and enantioselectivities for a desymmetrizing C(sp2)−H arylation leading to 5,6‐dihydrophenanthridines, whereas the corresponding monofunctional ligands showed low enantioselectivities. The bifunctional system proved applicable to a range of substituted dihydrophenanthridines, and allowed the parallel kinetic resolution of racemic substrates.

Chiral Bifunctional Phosphine‐Carboxylate Ligands for Palladium(0)‐Catalyzed Enantioselective C−H Arylation

Previous enantioselective Pd0 -catalyzed C-H activation reactions proceeding via the concerted metalation-deprotonation mechanism employed either a chiral ancillary ligand, a chiral base, or a bimolecular mixture thereof. This study describes the development of new chiral bifunctional ligands based on a binaphthyl scaffold which incorporates both a phosphine and a carboxylic acid moiety. The optimal ligand provided high yields and enantioselectivities for a desymmetrizing C(sp2 )-H arylation leading to 5,6-dihydrophenanthridines, whereas the corresponding monofunctional ligands showed low enantioselectivities. The bifunctional system proved applicable to a range of substituted dihydrophenanthridines, and allowed the parallel kinetic resolution of racemic substrates.

Chiral Bidentate NHC Ligands Based on the 1,1'-Binaphthyl Scaffold: Synthesis and Application in Transition-Metal-Catalyzed Asymmetric Reactions.

The use of the chiral 1,1'-binaphthyl scaffold to construct chiral ligands can be traced back for a long time. However, the development of bidentate NHC ligands based on the same backbone has only appeared recently. In this account, we describe the design and synthesis of a new family of chiral NHC ligands based on the 1,1'-binaphthyl scaffold and demonstrate the applications of these chiral NHC-metal complexes in the catalyzed oxidative kinetic resolution of secondary alcohols, asymmetric carbon-carbon bond formations, hydrosilylations, and cyclizations of 1,6-enynes. The chiral NHC ligands containing the 1,1'-binaphthyl backbone can be synthesized in good yields from enantiomerically pure 1,1'-binaphthyl-2,2'-diamine. These transition metals coordinated with chiral bidentate NHC ligands exhibit high catalytic activities and good enantioselectivities for a wide range of metal-catalyzed asymmetric reactions.

ChemInform Abstract: Phosphine‐Catalyzed Asymmetric [4 + 1] Annulation of Activated α,β‐Unsaturated Ketones with Morita—Baylis—Hillman Carbonates: Enantioselective Synthesis of Spirooxindoles Containing Two Adjacent Quaternary Stereocenters.

AbstractThe title reaction is promoted by a bifunctional thiourea‐phosphine catalyst derived from an axially chiral binaphthyl scaffold affording spirooxindoles (III) with high enantioselectivities but only moderate diastereoselectivities.

Phosphine-catalyzed asymmetric [4+1] annulation of activated α,β-unsaturated ketones with Morita–Baylis–Hillman carbonates: enantioselective synthesis of spirooxindoles containing two adjacent quaternary stereocenters

The asymmetric [4+1] annulation of activated α,β-unsaturated ketones with MBH carbonates catalyzed by bifunctional thiourea-phosphine catalysts derived from an axially chiral binaphthyl scaffold has been developed, giving spirooxindoles with two adjacent quaternary stereocenters in good yields with high enantioselectivities and moderate diastereoselectivities under mild conditions.

Phosphine-Catalyzed [3 + 2] Cycloaddition of 4,4-Dicyano-2-methylenebut-3-enoates with Benzyl Buta-2,3-dienoate and Penta-3,4-dien-2-one

4,4-Dicyano-2-methylenebut-3-enoates are employed in the phosphine-catalyzed [3 + 2] cycloaddition with allenoates for the first time, affording regiospecific [3 + 2]-annulation products in moderate to good yields. The multifunctional chiral thiourea-phosphines having an axially chiral binaphthyl scaffold are effective catalysts for the asymmetric variant of this reaction, giving the α-regioisomers in good yields and moderate enantioselectivities.

A Selective, Colorimetric, and Fluorescent Chemodosimeter for Relay Recognition of Fluoride and Cyanide Anions Based on 1,1′-Binaphthyl Scaffold

The reaction-based relay recognition of fluoride and cyanide anions was demonstrated for the first time, with rapid response and unique triple (fluorescence color, intensity and absorption band) output modes in either of two sequential sensing events. Ratiometric determination of these two anions by fluorescence and/or absorbance spectra is also achieved.

Enantioselective Conjugate Addition of Anthrone to Nitroalkenes Catalyzed by Binaphthyl-Modified Organocatalyst

We envisioned that the assembly of a structurally well-defined chiral 1,2-diamine and binaphthyl scaffold with athiourea or squaramide motif could constitute a new class ofbifunctional organocatalyst. In this communication, we wish todescribe the direct enantioselective conjugate addition reactionof anthrone with nitroalkenes catalyzed by binaphthyl-modifiedorganocatalysts bearing both central and axial chiralelements. In an attempt to validate the feasibility of the organocatalyticenantioselective conjugate addition reaction of anthrone, weinitially investigated the reaction system with anthrone 1 and