Spherical Amides with C3 Symmetry: Improved Synthetic Approach and Structural/Optical Analysis

A spherical amide with <i>C</i>₃ symmetry was synthesized by a one-step cyclization reaction using triphenylphosphine and hexachloroethane as coupling reagents. This method enabled synthesis of <i>N</i>-benzyl and <i>N</i>-allyl derivatives, which could not be obtained by the previously reported method. The optical resolution of each compound was measured, and their electronic circular dichroism spectra revealed that they were mirror images. The high structural symmetry resulted in a higher Δε (molar absorption difference against right or left circular polarization: <i>ε_L</i> - <i>ε_R</i> value compared to that of another structural isomer synthesized previously. The absolute structure of the enantiopure crystal of the <i>N</i>-benzyl derivative was determined using the Flack parameter obtained by X-ray crystallographic analysis.