Advances in the Asymmetric Synthesis of BINOL Derivatives

A [3+3] Aldol-SNAr-Dehydration Approach to 2-Naphthol and 7-Hydroxyquinoline Derivatives

A one-pot [3+3] aldol-SNAr-dehydration annulation sequence was utilized to fuse hindered phenols onto aromatic substrates. The transformation joins doubly activated 1,3-disubstituted acetone derivatives (dinucleophiles) with C5-activated 2-fluorobenzaldehyde SNAr acceptors (dielectrophiles) in the presence of K2CO3 in DMF at 65-70 °C to form polysubstituted 2-naphthols and 7-hydroxyquinolines. The reaction is regioselective in adding the most stable anionic center to the aldehyde followed by SNAr closure of the less stabilized anion to the electron-deficient aromatic ring. Twenty-seven examples are reported, and a probable mechanism is presented. In two cases where SNAr activation on the acceptor ring was lower (a C5 trifluoromethyl group on the aromatic ring or a 2-fluoropyridine), diethyl 1,3-acetonedicarboxylate initiated an interesting Grob-type fragmentation to give cinnamate esters as the products.

BINOL-Based Chiral Macrocycles and Cages

Chirality, a fundamental principle in chemistry, biology, and medicine, is prevalent in nature and in organisms. Chiral molecules, such as DNA, RNA, and proteins, are crucial in biomolecular synthesis, as well as in the development of functional materials. Among these, 1,1'-binaphthyl-2,2'-diol (BINOL) stands out for its stable chiral configuration, versatile functionality, and commercial availability. BINOL is widely employed in asymmetric catalysis and chiral materials. This review mainly focuses on recent research over the past five years concerning the use of BINOL derivatives for constructing chiral macrocycles and cages. Their contributions to chiral luminescence, enantiomeric separation, transmembrane transport, and asymmetric catalysis were examined.

Chiral α-Aminophosphonates as Ligands in Copper-Catalyzed Asymmetric Oxidative Coupling of 2-Naphthols

Chiral α-aminophosphonates with adjacent carbon and phosphonate stereogenic centers have been employed as ligands in the copper-catalyzed oxidative coupling of 2-naphthols, resulting in the production of chiral BINOLs in favorable yields and moderate to good enantiomeric excess. This represents the first application of chiral P-based ligands to enable such a transformation. The synthesis of these chiral α-aminophosphonate ligands offers a significant advantage over approaches that typically necessitate elaborate synthetic processes for chiral ligand production.

Structure and Chiroptical Properties of Anthra[1,2-a]anthracene-1-yl Dimers as New Biaryls

Dimers of anthra[1,2-a]anthracene-1-yl units and its mesityl derivative were synthesized by Ni(0)-mediated coupling of the corresponding chloro derivatives as new biaryls. The X-ray analysis and DFT calculations revealed that two polycyclic aromatic units with nonplanar deformations took a twisted conformation about the single bond as a chiral axis. Enantiomers of the nonsubstituted compound were resolved by chiral HPLC, and the enantiopure samples showed intense Cotton effects at 321 nm in the circular dichroism (CD) spectra and emission bands at 449 nm in the circularly polarized luminescence (CPL) spectra with dissymmetry factor of |glum| 3.6×10-3. The absolute stereochemistry of this biaryl was determined by the theoretical calculation of CD spectrum by the time-dependent DFT method. The barrier to enantiomerization was determined to be 108 kJ mol-1 at 298 K. The dynamic process proceeded via a stepwise mechanism involving the helical inversion of each aromatic unit and the rotation about the biaryl axis as analyzed by the DFT calculations.

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.

Kinetic resolution of 1,1'-binaphthyl-2,2'-diamine derivatives by chiral calcium phosphate-catalyzed acylation

1,1'-Binaphthyl-2,2'-diamine (BINAM) is a useful axially chiral compound. The kinetic resolution of BINAM is one of the most crucial methods for synthesizing chiral BINAM. We have developed a chiral calcium phosphate-catalyzed kinetic resolution of BINAM by utilizing an acylation reaction to produce a mono-amide. The kinetic resolution of BINAM derivatives was achieved by using isobutyric anhydride in the presence of chiral calcium phosphate and 4-morpholinopyridine with up to s = 127. 6,6'-Substituted BINAM derivatives were also applicable for this reaction. The resulting mono-acylated BINAM could be transformed into BINAM by hydrolysis under acidic conditions.

Decarboxylative Iodination and Suzuki-Miyaura Coupling Reactions to Access Chiral 3,3'-Diaryl-1,1'-bi-2-naphthols

An efficient synthesis of the enantiomerically pure 3,3'-bis-arylated BINOLs is accomplished through decarboxylative iodination of the dimethyl ether derivative of BINOL-3,3'-dicarboxylic acid followed by Suzuki-Miyaura coupling using a one-pot protocol. The decarboxylative iodination is effected with the dimethyl ether derivative of BINOL-3,3'-dicarboxylic acid using iodine as a terminal oxidant and the cheaply available K3PO4 as a base under neat conditions. This protocol facilitated the introduction of the aryl group at the 3,3'-position on the binaphthyl system using aryl boronic acid through a palladium-catalyzed Suzuki-Miyaura coupling reaction.

Luminescent Behavior of Zn(II) and Mn(II) Halide Derivatives of 4-Phenyldinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine 4-Oxide and Single-Crystal X-ray Structure Determination of the Ligand

The two enantiomers of chiral phosphonate 4-phenyldinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine 4-oxide, O=PPh(BINOL), were synthesized from the proper 1,1'-bi-2-naphtol (BINOL) enantiomer and characterized. The structure of the (S)-enantiomer was elucidated by means of single-crystal X-ray diffraction. The reaction with anhydrous ZnBr2 afforded complexes having the general formula [ZnBr2{O=PPh(BINOL)}2] that showed intense fluorescence centered in the near-UV region rationalized on the basis of TD-DFT calculations. The corresponding Mn(II) complexes with the general formula [MnX2{O=PPh(BINOL)}2] (X = Cl, Br) exhibited dual emission upon excitation with UV light, with the relative intensity of the bands dependent upon the choice of the halide. The highest energy transition is comparable with that of the Zn(II) complex, while the lowest energy emission falls in the red region of the spectrum and is characterized by lifetimes in the hundreds of microseconds range. Although the emission at lower energy can also be achieved by direct excitation of the metal center, the luminescence decay curves suggest that the band in the red range is possibly derived from BINOL-centered excited states populated by intersystem crossing.