Synthesis of Medium and Large Ring Compounds, XLIII. Synthesis and Isomerization of 8,9-Dimethyl[6]paracyclophane and Its Bridged Dewar Isomer

An improved sonochemical procedure for the synthesis of dimethyl [6]paracyclophane‐8,9‐dicarboxylate (2a) on a 10‐g scale is described. The title compound 2d was synthesized from 2a in three steps. Irradiation of 2d yielded the Dewar isomer 3. In solution, the reaction enthalpy for the thermal isomerization of 3 to 2d was determined to be ‐162 ± 16 kJ · mol‐1, while the activation energy for this reaction was found to be 123 ± 12 kJ · mol‐1. Synthesis of Medium and Large Ring Compounds, XLIII. — Synthesis and Isomerization of 8,9‐Dimethyl[6]paracyclophane and Its Bridged Dewar Isomer