Point-to-Axial Chirality Transmission: A Highly Sensitive Triaryl Chirality Probe for Stereochemical Assignments of Amines.

A readily available stereodynamic and the electronic circular dichroism (ECD)-silent 2,5-di(1-naphthyl)-terephthalaldehyde-based probe has been applied for chirality sensing of primary amines. The chiral amine (the inductor) forces a change in the structure of the chromophore system through the point-to-axial chirality transmission mechanism. As a result, efficient induction of optical activity in the chromophoric system is observed. The butterflylike structure of the probe, with the terminal aryl groups acting as changeable "wings", allowed for the generation of exciton Cotton effects in the region of 1Bb electronic transition in the naphthalene chromophores. The sign of the exciton couplets observed for inductor-reporter systems might be correlated with an absolute configuration of the inductor, whereas the linear relationship between amplitudes of the specific Cotton effect and enantiomeric excess of the parent amine gives potentiality for quantitative chirality sensing. Despite the structural simplicity, the probe turned out to be unprecedentedly highly sensitive to even subtle differences in the inductor structure (i.e., O vs CH2).

Optical Activity and Helicity Enhancement of Highly Sensitive Dinaphthylmethane-Based Stereodynamic Probes for Secondary Alcohols.

Chirality transfer from circular dichroism (CD)-silent secondary alcohol (inductor) to the stereodynamic bichromophoric di(1-naphthyl)methane probe (reporter) led to the generation of intense, induced exciton-type Cotton effects (CEs) in the ultraviolet-visible absorption region. The di(1-naphthyl)methane probe exhibits extraordinarily high sensitivity to even small structural variations of the alcohol skeleton, that is, the probe is able to distinguish between an oxygen atom and a methylene group in a 3-hydroxytetrahydrofurane skeleton. Signs and amplitudes of the exciton couplets of 1Bb electronic transition might be correlated with the type of stereo-differentiating parts of the molecule flanking the stereogenic center, however, not with the absolute configuration. The origin of the induced CEs was established by means of experimental and theoretical methods. As a result, a mechanism of chirality transfer from the permanent stereogenic center to the bichromophore is proposed.

Benzhydryl Ethers of Tartaric Acid Derivatives: Stereochemical Response of a Dynamically Chiral Propeller.

The benzhydryl (diphenylmethyl) group is a molecular propeller that can act as a chirality reporter if it is introduced nearby a stereogenic center by making an ether bond. The hydrophobic character of the benzhydryl group allows transformation of insoluble natural tartaric acid derivatives into soluble entities in a nonpolar environment. Electronic circular dichroism spectra, recorded within the short-wavelength region of the phenyl 1 B transitions (190-200 nm) shows strong bisignate Cotton effects. The signs and magnitudes of these Cotton effects are a function of absolute configuration and conformation of the molecule and do not primarily arise from exciton coupling of chiral benzhydryl chromophores. In crystals, the main-chain conformation is stabilized by intramolecular hydrogen bonds and CH-CO dipolar interactions. The number of the donor NH groups has a pronounced effect on the preferred conformations and inclusion properties of benzhydryl-(R,R)-tartaric acid diamides. Evidence is shown for the solvent dependency of the conformations of NH amides of tartaric acid diphenylmethyl ethers.