A simple synthetic approach to homochiral 6- and 6′-substituted 1,1′-binaphthyl derivatives

Regioselective Substitution of BINOL

1,1'-Bi-2-naphthol (BINOL) has been extensively used as the chirality source in the fields of molecular recognition, asymmetric synthesis, and materials science. The direct electrophilic substitution at the aromatic rings of the optically active BINOL has been developed as one of the most convenient strategies to structurally modify BINOL for diverse applications. High regioselectivity has been achieved for the reaction of BINOL with electrophiles. Depending upon the reaction conditions and substitution patterns, various functional groups can be introduced to the specific positions, such as the 6-, 5-, 4-, and 3-positions, of BINOL. Ortho-lithiation at the 3-position directed by the functional groups at the 2-position of BINOL have been extensively used to prepare the 3- and 3,3'-substituted BINOLs. The use of transition metal-catalyzed C-H activation has also been explored to functionalize BINOL at the 3-, 4-, 5-, 6-, and 7-positions. These regioselective substitutions of BINOL have allowed the construction of tremendous amount of BINOL derivatives with fascinating structures and properties as reviewed in this article. Examples for the applications of the optically active BINOLs with varying substitutions in asymmetric catalysis, molecular recognition, chiral sensing and materials are also provided.

Synthesis of a Novel Chiral Stationary Phase by (R)-1,1′-Binaphthol and the Study on Mechanism of Chiral Recognition

(R)-6-Acrylic-BINOL CSP, a novel chiral stationary phase was prepared by (R)-Binaphthol (R-BINOL) by introducing the acrylic group into the 6-position of (R)-BINOL before bonding it to the surface of silica gel. The structure of the CSP was characterized by IR, SEM, and element analysis. This new material was tested for its potential as a CSP for HPLC under normal phase conditions, especially for conjugated compounds. Six solutes were chosen to evaluate the chiral separation ability of the novel CSP. The effects of the mobile phase and temperature on enantioseparation were studied, and the chiral recognition mechanism was also discussed. The results showed that the space adaptability and π-π stacking between the solutes and the CSP affected the retention and enantioseparation. The Van’t Hoff curve indicated that under the experimental conditions, the separation mechanism of six solutes did not change, which were all enthalpy driven.

CAr-O Rotamers in 3,3'-Disubstituted BINOL Esters

Rotamers around the C_Ar-O bond were disclosed in 3,3'-disubstituted BINOL esters by NMR spectroscopy. A bulky R¹ group increased the rotational barrier. The pivalate showed two rotamers at 2 °C, and broad signals were observed close to room temperature when R² = Ph. The highest rotational barrier was recorded for the (tetracyanocyclopentadienyl)carboxylate, and C-O rotamers were present at room temperature. DFT calculations indicated the presence of repulsion between R¹ and R² during rotation of the C_Ar-O bond.

Practical Synthesis of Axially Chiral Dicarboxylates via Pd-Catalyzed External-CO-Free Carbonylation

We have developed a safe and practical synthetic method for preparing axially chiral diphenyl dicarboxylates using Pd-catalyzed external-CO-free carbonylation with phenyl formate as a CO surrogate. Optimized conditions consisted of axially chiral [1,1'-binaphthalene]-2,2'-diyl ditriflate and its congeners, each easily prepared from commercially available enantiomerically pure diols, Pd(OAc)₂, 1,3-bis(diphenylphosphino)propane, ethyldiisopropylamine, and no solvent. To demonstrate the potential utility of these products, this method was conducted on gram-scale and the phenyl ester products were converted to other useful compounds, and both processes were carried out without difficulty.

Enantioselective total synthesis of (-)-blennolide A

Blennolide A can be synthesized through an enantioselective domino-Wacker/carbonylation/methoxylation reaction of 7a with 96 % ee and an enantioselective Wacker oxidation of 7b with 89 % ee. Further transformations led to the α,β-unsaturated ester (E)-17, which was subjected to a highly selective Michael addition, introducing a methyl group to give 18a. After a threefold oxidation and an intramolecular acylation, the tetrahydroxanthenone 4 was obtained, which could be transformed into (-)-blennolide A (ent-1) in a few steps.

(R)-Di-tert-butyl 1,1'-binaphthyl-2,2'-dicarboxyl-ate

The crystal structure of the title compound, C₃₀H₃₀O₄, comprises two crystallographically independent half-mol­ecules which are completed by crystallographic twofold symmetry. The dihedral angles between the naphthalene ring planes are 85.83 (3) and 83.69 (3)° for the two molecules. The atoms of the tert-butyl group of one mol­ecule are disordered over two sets of sites with occupancies of 0.60:0.40. The crystal packing is achieved via π–π stacking inter­actions between the naphthyl groups of adjacent mol­ecules, with a separation of 3.790 (1) Å between the centroids of the rings.

DNA-based phosphane ligands

In order to expand the repertoire of DNA sequences specifically interacting with transition metals, we report here the first examples of DNA sequences carrying mono- and bidentate phosphane ligands as well as P,N-ligands. Aminoalkyl-modified oligonucleotides have been reacted at predetermined internal sites with carboxylate derivatives of pyrphos, BINAP and phosphinooxazoline (PHOX) 2 b-d. Carbodiimide coupling in the presence of N-hydroxysuccinimide provided the DNA-ligand conjugates in 38-78 % yield. Phosphane-containing oligonucleotides and their phosphane sulfide analogues were characterized by mass spectrometry (MALDI-TOF and FT-ICR-ESI) and their stability after purification and isolation was systematically investigated. While DNA-appended pyrphos ligand was quickly oxidized, BINAP and PHOX conjugates showed high stabilities, making them useful precursors for incorporation of transition metals into DNA.

Asymmetric allylic substitution of cycloalkenyl esters in water with an amphiphilic resin-supported chiral palladium complex

A novel homochiral phosphine ligand, (3R,9aS)[2-aryl-3-(2-diphenylphosphino)phenyl]tetrahydro-1H-imidazo[1,5-a]indole-1-one, was designed, prepared, and anchored onto an amphiphilic polystyrene-poly(ethylene glycol) copolymer (PS-PEG) resin. Catalytic asymmetric substitution of a racemic mixture of cycloalkenyl esters with carbon, nitrogen, and oxygen nucleophiles was achieved in water as the single reaction medium under heterogeneous conditions by using the PS-PEG resin-supported palladium-imidazoindole phosphine complex to give optically active substituted cycloalkenes with up to 99 % ee.