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

The benzhydryl (diphenylmethyl) group is a molecular propeller that can acts as a chirality reporter when it is introduced nearby the stereogenic center by making the ether bond. Hydrophobic character of the benzhydryl group allows transformation of insoluble in non-polar environment natural tartaric acid derivatives into soluble entities. Electronic circular dichroism spectra, recorded within the short wavelength region of the phenyl 1B transitions (190-200 nm) showed strong bisignate Cotton effects. The signs and magnitudes of these Cotton effects are a function of absolute configuration and conformation of the molecule and primarily are not due to 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 conformational preferences and inclusion properties of benzhydryl-(R,R)-tartrdiamides. Helicity of the benzhydryl chromophores is overwhelmingly P,P in tartrates and predominantly P,M in tartramides. We show the evidence for solvent dependent conformation of NH amides of tartaric acid diphenylmethyl ethers.