Optically active distorted cyclic triptycenes: chiral stationary phases for HPLC

Preparation of Optically Active Biphenyl Compounds via an Albumin- Mediated Asymmetric Nitroaldol Reaction

Abstract:

Human serum albumin (HSA) was found to catalyze the asymmetric nitroaldol reaction of biphenyl aldehydes with nitromethane to afford the corresponding optically active 2-nitro alcohols. Careful optimization of the conditions for the reaction of 4-phenylbenzaldehyde with nitromethane in water at a neutral pH improved both the reactivity and the enantioselectivity. Finally, the reaction of 4-phenylbenzaldehyde (56 mg, 0.30 mmol) in nitromethane (2.8 mL) and water (1.1 mL) using HSA (68 mg) at 5 °C for 240 h gave (R)-1-([1,1'-biphenyl]-4-yl)-2-nitroethanol in 71% yield (52 mg), with an ee up to 85% ee. Subsequent recrystallization improved the ee up to 95%. The reaction was useful in a preparative-scale operation, and the biocatalyst could be reused several times. The procedure was also applicable to other substrates with different substitution patterns. Although the nitroaldol reaction of 2-phenylbenzaldehyde with nitromethane proceeded with low enantioselectivity to afford the corresponding (R)-2-nitroalcohols (35% ee), the reactions of the substrates bearing Br, Me, OMe, or CN group at the 4'-position of the benzene ring gave the corresponding optically active compounds with high enantioselectivities (80-88% ee).

Triptycene Derivatives: From Their Synthesis to Their Unique Properties

Since the first preparation of triptycene, great progress has been made with respect to its synthesis and the understanding of its properties. Interest in triptycene-based systems is intense; in recent years, advances in the synthetic methodology and properties of new triptycenes have been reported by researchers from various fields of science. Here, an account of these new developments is given and placed in reference to earlier pivotal works that underpin the field. First, we discuss new approaches to the synthesis of new triptycenes. Progress in the regioselective synthesis of sterically demanding systems is discussed. The application of triptycenes in catalysis is also presented. Next, progress in the understanding of the relations between triptycene structures and their properties is discussed. The unique properties of triptycenes in the liquid and solid states are elaborated. Unique interactions, which involve triptycene molecular scaffolds, are presented. Molecular interactions within a triptycene unit, as well as between triptycenes or triptycenes and other molecules, are also evaluated. In particular, the summary of the synthesis and useful features will be helpful to researchers who are using triptycenes as building blocks in the chemical and materials sciences.

Chiral Triptycenes: Concepts, Progress and Prospects

Triptycenes have been established as unique scaffolds because of their backbone π-structure with a propeller-like shape and saddle-like cavities. They are some of the key organic molecules that have been extensively studied in polymer chemistry, in supramolecular chemistry and in material science. Triptycenes become chiral molecules when substituents are unsymmetrically attached in at least two of their different aromatic rings. This Minireview highlights the chirality of triptycenes from basics to an advanced stage for the development of functional molecules.

A Triptycene-Based Enantiopure Bis(Diazadibenzoanthracene) by a Chirality-Assisted Synthesis Approach

By applying a chirality-assisted synthesis (CAS) approach enantiopure diaminodibromotriptycenes were converted to rigid chiral helical diazadibenzoanthracenes, which show besides pronounced Cotton effects in circular dichroism spectra higher photoluminescence quantum yields as comparable carbacyclic analogues. For the enantiopure building blocks, a protocol was developed allowing the large scale synthesis without the necessity of separation via HPLC.

Anthranoxides as Highly Reactive Arynophiles for the Synthesis of Triptycenes

We report herein an efficient method to synthesize triptycenes by the reaction of benzynes and anthranoxides, which are electron-rich and readily prepared from the corresponding anthrones. Using this method, 1,9-syn-substituted triptycenes were regioselectively obtained employing 3-methoxybenzynes. This method was also applied to synthesize pentiptycenes. A DFT study revealed that the cycloaddition of lithium anthranoxide and benzyne proceeds stepwise.

Triptycene-based stationary phases for gas chromatographic separations of positional isomers

This work presents the investigation of two triptycene-based materials (TP-3OB and TP-3Im) as the stationary phases for gas chromatographic (GC) separations. The TP-3OB and TP-3Im capillary columns fabricated by static coating exhibited column efficiency of 3000-3500 plates/m for n-dodecane at 120 °C. Also, their McReynolds constants and Abraham system constants were determined to characterize their polarity and molecular interactions with analytes. On the basis of the unique 3D TP architecture, the TP-3OB and TP-3Im stationary phases exhibited complementary high-resolution performance for analytes of a wide ranging polarity, including alkylbenzenes, alkylnaphthalenes, halobenzenes, phenols and anilines, respectively. Moreover, the TP-based columns exhibited good repeatability and reproducibility on the retention times of analytes with the relative standard deviation (RSD) values in the range of 0.01-0.14% for run-to-run, 0.11-0.47% for day-to-day and 0.68-4.7% for column-to-column, respectively. Additionally, their applications for the determination of isomer impurities in the commercial reagents of o-dichlorobenzene, p-/m-diethylbenzene, o-toluidine and 2,3-/3,5-xylidine proved their good potential for practical analysis. This work demonstrates the promising future of the triptycene-based stationary phases for chromatographic separations.

Optically active triptycenes containing hexa-peri-hexabenzocoronene units

We have successfully generated both left- and right-handed circularly polarized light using crystals prepared from a racemic triptycene containing hexa-peri-hexabenzocoronene units.