New [4 + 4] photodimerization of 5-chloro-2-pyridone to the meso-cis-syn dimmer as an inclusion complex with 1,2,4,5-benzenetetracarboxylic acid

As the first example of the [4 + 4] cis-syn dimer of 2-pyridone, the meso-cis-syn dimer of 5-chloro-2-pyridone was prepared by photoirradiation of a 1:4 inclusion complex of a 1,2,4,5-benzenetetracarboxylic acid host and 5-chloro-2-pyridone in the solid state, and the steric course of the reaction was studied by X-ray analysis.