Triphenylacetic Acid Amides: Molecular Propellers with Induced Chirality†

The combination of electronic circular dichroism spectroscopy (ECD), X-ray diffraction, and theoretical calculations permitted a detailed description of an unexpected chirality transfer in triphenylacetamides, which is achieved solely through weak intramolecular interactions. The observed phenomenon proceeds as a cascade process. The triphenylacetamide chromophore is sensitive to even small changes in the relative size of the substituent attached to the stereogenic center. Substitution at the stereogenic center influences helicity of the distal trityl chromophore but does not affect its propeller shape. Deformation of the propeller shape and consequent loss of its C3 symmetry results mainly from substitution of the amide hydrogen and is connected with an increase in steric hindrance. As an outcome of our studies, a model of optical activity of chiral triphenylacetamides is proposed. The performed X-ray studies revealed that this novel class of chiral compounds is likely to be of additional value due to the porosity of the crystals.