INTRAMOLECULAR MICHAEL-TYPE ADDITION IN THE SOLID-STATE

Several substituted 2'-hydroxy-4',6'-dimethylchalcones undergo a solid state intramolecular Michael-type addition reaction to yield the corresponding flavanones, at temperatures significantly below the melting points of the reactants or products. Single crystal X-ray diffraction studies of the reactant and product phases have been carried out and indicate that these solid state reactions most likely proceed in a non-topochemical fashion. A similar conclusion is deduced from X-ray powder diffraction, differential scanning calorimetry and packing energy calculations. Reaction in the defect regions is probably important because considerable relaxation in the molecular conformation of the chalcone is required in the crystal before intramolecular ring-closure to the flavanone can occur.