CuCl/bpy-promoted unusual Z-stereoselective synthesis of trichloroacetic acid phenyl ester for Hirshfeld surface analysis and DFT study

Abstract A trichloromethyl ester devoid of suitably substituted C C bond, any leaving group or a H-atom at the β-position to the radical, which are otherwise known for ATRA/ATRC, 1,2-rearrangement/fragmentation or simple 1,2-H shift respectively, in a reaction of trichloro-acetic acid phenyl ester with 2 mol equiv CuCl/bpy in reflux DCE or benzene under inert N 2 condition resulted to stereoselective synthesis of Z-2,3-dichloro-but-2-enedioic acid diphenyl ester and/or formation of reductive de-chlorination side product. The Z-stereochemistry of the product was confirmed by X-ray diffraction spectroscopy of Z-2,3-dichloro-but-2-enedioic acid dinaphthalen-1-yl ester which crystalizes in monoclinic system of P21/c symmetry elements. Hirshfeld surface analysis of experimentally established structure of Z-2,3-dichloro-but-2-enedioic acid diphenyl ester unrevealed the intermolecular interactions showing both H-bonding and short contacts. The stereochemistry was also interpreted computationally using Density Functional Theory at B3LYP/6-311G(d,p) level of theory. The calculated energies, energy gap and balance between the electrostatic potential on the molecular surface were computed which revealed unusual formation of less stable Z-isomer.