Photodimerizations of 1,5- and 1,7-Azulenequinones: Solvent, Substituent, and Concentration Effects on the Product Distribution

Azulenequinones gave dimers when they were irradiated with a high-pressure mercury lamp. In polar solvents, head-to-head dimers were predominant, whereas head-to-tail dimers increased in less polar solvents. From 3-methoxy-1,5-azulenequinone, four products were obtained, while bromoazulenequinones and 1,5-azulenequinone gave a single dimer. The product distribution was dependent on the polarity of solvents, substituents, and concentrations.