BINOL Complex Research Articles

The Chelate Effect Rationalizes Observed Rate Acceleration and Enantioselectivity in BINOL-Catalyzed Petasis Reactions.

Density functional theory (DFT) calculations afforded insight into the origin of the experimentally observed reaction rate acceleration (≥500 fold) and enantioselectivity (≥99 % ee) of 1,1'-bi-2-naphthol- (BINOL-) catalyzed three-component Petasis reactions . BINOL accelerates the rate determining step by forming a BIV chelate, which involves the loss of water from the hemiaminal moiety to generate an iminium intermediate. Subsequent vinyl group transfer from BIV to the iminium carbon affords the enantiomerically enriched product and a cyclic trigonal B(III)BINOL complex, which rapidly releases the BINOL allowing it to re-enter the catalytic cycle. In the transition state of the vinyl transfer step, C-H-O hydrogen bonding between the iminium C-H and O of (R)-BINOL directs the vinyl group addition to the Re-face of the iminium carbon. This mechanism explains both the rate acceleration and high enantioselectivity of the stereo determining step.

Strong Circularly Polarized Luminescence at 1550 nm from Enantiopure Molecular Erbium Complexes.

Circularly polarized luminescence (CPL) in two subregions of the near-infrared (NIR) has been achieved. By leveraging the rigidity and diminishing detrimental vibrations of the heterobimetallic binolate complexes of erbium [(Binol)3ErNa3], species exhibiting an exceptionally high dissymmetry factor (|glum |) of 0.47 at 1550 nm were obtained. These erbium complexes are the first reported examples of CPL observed beyond 1200 nm. Analogous complexes of ytterbium and neodymium also exhibited strong CPL (|glum| = 0.17, 0.05, respectively) in a higher energy NIR window (800-1200 nm). All complexes exhibit high quantum yields (Er: 0.58%, Yb: 17%, Nd: 9.3%) and high BCPL values (Er: 57 M-1 cm-1, Yb: 379 M-1 cm-1, Nd: 29 M-1 cm-1). Because of their strong CPL emission in the telecom band (1550 nm), biologically relevant NIR emission window (800-1100 nm), and synthetic versatility, the complexes reported here could permit further promising developments in quantum communication technologies and biologically relevant sensors.

Asymmetric synthesis of (S,R)- and (R,R)-methiin stereoisomers

An asymmetric synthesis of (+)- and (–)-methiine (S-methyl-(R)-cysteine sulfoxide) diastereomers has been developed. These natural sulfur compounds were isolated from a variety of Brassica vegetables. As the starting compound, (R)-cysteine was used, which was methylated to form (R)-S-methylcysteine. Then the oxidation of S-methylcysteine with tert-butyl hydroperoxide catalyzed by the chiral tetra(isopropylate)titanium/(S)- or (R)-Binol complex led to the formation of (1 R,2S)-(+)- or (1 R,2R)-(–)-methiin stereomers.

A Highly Stereoselective Synthesis of Tetrahydrofurans

The development of a direct and highly stereoselective synthesis of 2,3,5-substituted tetrahydrofurans has been accomplished through a combination of batch- and microchip-MS-experiments. This sequential transformation comprises a Lewis acid-mediated reaction of bis(silyl) dienediolate 1 and a broad range of aldehydes, furnishing products with three new σ-bonds and three stereogenic centers in a one-pot process with typically good yields and excellent stereoselectivity. Key steps which have been elucidated primarily with microchip-MS-experiments include a vinylogous aldol reaction and a Prins-type cyclization. Furthermore, a titanium BINOL complex is a powerful chiral catalyst for this process. The products were further converted into bi- and tricylic products by carbonyl-ene reactions, proceeding with excellent yields and diastereoselectivity.

A Highly Stereoselective Synthesis of Tetrahydrofurans

AbstractThe development of a direct and highly stereoselective synthesis of 2,3,5‐substituted tetrahydrofurans has been accomplished through a combination of batch‐ and microchip‐MS‐experiments. This sequential transformation comprises a Lewis acid‐mediated reaction of bis(silyl) dienediolate 1 and a broad range of aldehydes, furnishing products with three new σ‐bonds and three stereogenic centers in a one‐pot process with typically good yields and excellent stereoselectivity. Key steps which have been elucidated primarily with microchip‐MS‐experiments include a vinylogous aldol reaction and a Prins‐type cyclization. Furthermore, a titanium BINOL complex is a powerful chiral catalyst for this process. The products were further converted into bi‐ and tricylic products by carbonyl–ene reactions, proceeding with excellent yields and diastereoselectivity.

ChemInform Abstract: Synthesis of Enantioenriched Indolines by a Conjugate Addition/Asymmetric Protonation/Aza‐Prins Cascade Reaction.

A conjugate addition/asymmetric protonation/aza-Prins cascade reaction has been developed for the enantioselective synthesis of fused polycyclic indolines. A catalyst system generated from ZrCl4 and 3,3'-dibromo-BINOL enables the synthesis of a range of polycyclic indolines in good yields and with high enantioselectivity. A key finding is the use of TMSCl and 2,6-dibromophenol as a stoichiometric source of HCl to facilitate catalyst turnover. This transformation is the first in which a ZrCl4 ⋅BINOL complex serves as a chiral Lewis-acid-assisted Bronsted acid.

Synthesis of Enantioenriched Indolines by a Conjugate Addition/Asymmetric Protonation/Aza‐Prins Cascade Reaction

AbstractA conjugate addition/asymmetric protonation/aza‐Prins cascade reaction has been developed for the enantioselective synthesis of fused polycyclic indolines. A catalyst system generated from ZrCl4 and 3,3′‐dibromo‐BINOL enables the synthesis of a range of polycyclic indolines in good yields and with high enantioselectivity. A key finding is the use of TMSCl and 2,6‐dibromophenol as a stoichiometric source of HCl to facilitate catalyst turnover. This transformation is the first in which a ZrCl4⋅BINOL complex serves as a chiral Lewis‐acid‐assisted Brønsted acid.

Synthesis of Enantioenriched Indolines by a Conjugate Addition/Asymmetric Protonation/Aza-Prins Cascade Reaction.

A conjugate addition/asymmetric protonation/aza-Prins cascade reaction has been developed for the enantioselective synthesis of fused polycyclic indolines. A catalyst system generated from ZrCl4 and 3,3'-dibromo-BINOL enables the synthesis of a range of polycyclic indolines in good yields and with high enantioselectivity. A key finding is the use of TMSCl and 2,6-dibromophenol as a stoichiometric source of HCl to facilitate catalyst turnover. This transformation is the first in which a ZrCl4 ⋅BINOL complex serves as a chiral Lewis-acid-assisted Brønsted acid.

Synthesis and Molecular Structures of BINOL Complexes: An STM Investigation of 2D Self-Assembly

Three new (R)-BINOL complexes have been prepared. 2D self-assembly has been observed in the system consisting of crystalline (R)-BINOL derivatives (guest) and 1,3,5-tris(10-carboxydecyloxy)-benzene (host) by means of the scanning tunneling microscopy (STM) technique. Density functional theory (DFT) calculations help to reveal the assembly on the HOPG surface.

ChemInform Abstract: Synthesis of Cyclic Carbonates from Epoxides Catalyzed by Metal‐BINOL Complexes.

Synthesis of cyclic carbonates from CO2 and terminal epoxides catalyzed by Mg, Ca and In BINOL complexes was achieved without organic solvents. Effects of temperature, CO2 pressure, reaction time and co-catalyst on the cycloaddition were investigated. Propylene carbonate was obtained under a CO2 pressure of 1.2 MPa within 10 hours in a yield of 98% catalyzed by Ca–BINOL at 120°C. The order of catalytic activity of the metal center is Ca > In > Mg. Copyright © 2014 John Wiley & Sons, Ltd.

ChemInform Abstract: Air‐ and Water‐Tolerant Rare Earth Guanidinium BINOLate Complexes as Practical Precatalysts in Multifunctional Asymmetric Catalysis.

AbstractThe usability of the title complexes is shown in several asymmetric and mechanistically diverse reactions including Michael additions, aza‐Michael additions, and direct Aldol reactions.

Synthesis of cyclic carbonates from epoxides catalyzed by metal–BINOL complexes

Synthesis of cyclic carbonates from CO2 and terminal epoxides catalyzed by Mg, Ca and In BINOL complexes was achieved without organic solvents. Effects of temperature, CO2 pressure, reaction time and co‐catalyst on the cycloaddition were investigated. Propylene carbonate was obtained under a CO2 pressure of 1.2 MPa within 10 hours in a yield of 98% catalyzed by Ca–BINOL at 120°C. The order of catalytic activity of the metal center is Ca > In > Mg. Copyright © 2014 John Wiley & Sons, Ltd.

Air- and water-tolerant rare earth guanidinium BINOLate complexes as practical precatalysts in multifunctional asymmetric catalysis.

Shibasaki's REMB catalysts (REMB; RE = Sc, Y, La-Lu; M = Li, Na, K; B = 1,1'-bi-2-naphtholate; RE/M/B = 1/3/3) are among the most enantioselective asymmetric catalysts across a broad range of mechanistically diverse reactions. However, their widespread use has been hampered by the challenges associated with their synthesis and manipulation. We report here the self-assembly of novel hydrogen-bonded rare earth metal BINOLate complexes that serve as bench-stable precatalysts for Shibasaki's REMB catalysts. Incorporation of hydrogen-bonded guanidinium cations in the secondary coordination sphere leads to unique properties, most notably, improved stability toward moisture in solution and in the solid state. We have exploited these properties to develop straightforward, high-yielding, and scalable open-air syntheses that provide rapid access to crystalline, nonhygroscopic complexes from inexpensive hydrated RE starting materials. These compounds can be used as precatalysts for Shibasaki's REMB frameworks, where we have demonstrated that our system performs with comparable or improved levels of stereoselectivity in several mechanistically diverse reactions including Michael additions, aza-Michael additions, and direct Aldol reactions.

Dimeric Rare‐Earth BINOLate Complexes: Activation of 1,4‐Benzoquinone through Lewis Acid Promoted Potential Shifts

Reaction of p-benzoquinone (BQ) with a series of rare-earth metal/alkali metal/1,1'-BINOLate (REMB) complexes (RE: La, Ce, Pr, Nd; M: Li) results in the largest recorded shift in reduction potential observed for BQ upon complexation. In the case of cerium, the formation of a 2:1 Ce/BQ complex shifts the two-electron reduction of BQ by greater than or equal to 1.6 V to a more favorable potential. Reactivity investigations were extended to other RE(III) (RE = La, Pr, Nd) complexes where the resulting highly electron-deficient quinone ligands afforded isolation of the first lanthanide quinhydrone-type charge-transfer complexes. The large reduction-potential shift associated with the formation of 2:1 Ce/BQ complexes illustrate the potential of Ce complexes to function both as a Lewis acid and an electron source in redox chemistry and organic-substrate activation.

Uranium(IV) BINOLate Heterobimetallics: Synthesis and Reactivity in an Asymmetric Diels–Alder Reaction

The first heterobimetallic BINOLate complexes incorporating uranium were prepared, and their reactivity in an asymmetric Diels–Alder reaction was investigated. The contributions of both the Li+ and UIV cations to the reaction selectivity were addressed through control of the two different Lewis acidic centers. The presence of an anionic ligand in the seventh coordination site of the central uranium cation resulted in enhanced selectivity compared to the RE(III) catalyst with the same alkali metal cation and represents the highest enantioselectivities obtained with a uranium-based catalyst to date. Additionally, we describe a simple workup procedure to obtain organic products free of the trace radioactivity present in the reaction mixtures.

ChemInform Abstract: Enantioselective Addition of Terminal Alkynes to N‐(Diphenylphosphinoyl)imines Catalyzed by Zn—BINOL Complexes.

Abstract Chiral nonracemic N-(diphenylphosphinoyl)-protected propargylic amines have been prepared by addition of terminal alkynes to N-(diphenylphosphinoyl)aldimines in the presence of dimethylzinc and 3,3′-dibromo-BINOL as catalyst. The reaction works with a variety of aromatic and heteroaromatic aldimines and with different alkynes, providing the expected products in generally good yields and enantiomeric excesses (up to 96%).

Enantioselective Synthesis of 2,2-Disubstituted Terminal Epoxides via Catalytic Asymmetric Corey-Chaykovsky Epoxidation of Ketones

Catalytic asymmetric Corey-Chaykovsky epoxidation of various ketones with dimethyloxosulfonium methylide using a heterobimetallic La-Li3-BINOL complex (LLB) is described. The reaction proceeded smoothly at room temperature in the presence of achiral phosphine oxide additives, and 2,2-disubstituted terminal epoxides were obtained in high enantioselectivity (97%–91% ee) and yield (>99%–88%) from a broad range of methyl ketones with 1-5 mol% catalyst loading. Enantioselectivity was strongly dependent on the steric hindrance, and other ketones, such as ethyl ketones and propyl ketones resulted in slightly lower enantioselectivity (88%–67% ee).

Enantioselective addition of terminal alkynes to N-(diphenylphosphinoyl)imines catalyzed by Zn–BINOL complexes

Chiral nonracemic N-(diphenylphosphinoyl)-protected propargylic amines have been prepared by addition of terminal alkynes to N-(diphenylphosphinoyl)aldimines in the presence of dimethylzinc and 3,3′-dibromo-BINOL as catalyst. The reaction works with a variety of aromatic and heteroaromatic aldimines and with different alkynes, providing the expected products in generally good yields and enantiomeric excesses (up to 96%).

Total synthesis of racemic and ( R) and ( S)-4-methoxyalkanoic acids and their antifungal activity

The total synthesis of 4-methoxydecanoic acid and 4-methoxyundecanoic acid in racemic and stereoselective [( R) and ( S)] forms has been accomplished. For stereoselective synthesis of the compounds ( S) and ( R)-BINOL complexes have been used to generate the required chiral centres. The antifungal activity of these compounds has been studied against different organisms and the results were found to be impressive. The activity of the compounds in racemic and in stereoselective forms was compared. ( R)-4-Methoxydecanoic acid was found to be most potent (MIC: 0.019 mg/mL against Candida albicans MTCC 227, C. albicans MTCC 4748, Aspergillus brasiliensis ( niger) MTCC 281 and Issatchenkia orientalis MTCC 3020).

ChemInform Abstract: Catalytic Enantioselective 1,3‐Dipolar Cycloaddition of C,N‐Cyclic Azomethine Imines with α,β‐Unsaturated Aldehydes.

AbstractA titanium/(S)‐BINOL complex catalyzes the title reaction of azomethine imines (I) to give a variety of pharmaceutically attractive chiral pyrazolo‐fused tetrahydroisoquinolines.