Photochemical reactions of 2-bromotropone and 2,7-dibromotropone with 9,10-dicyanoanthracene

The photochemical reactions of 2-bromotropone and 2,7-dibromotropone with 9,10-dicyanoanthracene gave products with anthracene, anthracenone, and dihydroanthracene skeletons both in polar and non-polar solvents. These products were formed by attack of water contaminated in the solvent, by attack of the troponoid, and by attack of the solvent used in the reactions, respectively, on a reaction intermediate. In a mixed solvent of benzene and methanol, a benzaldehyde derivative with a tribenzo-2-oxabicyclo[3.2.2]nonane system was obtained. This result was informative about the reaction mechanism, and suggested the formation of an [8 + 4]pi cycloadduct with a tribenzo-2-oxabicyclo[3.2.2]nonane system between the troponoid as the 8 pi component and the 9,10-dicyanoanthracene as the 4 pi component. In non-polar benzene, a new tetrabromodihydroanthracene derivative was obtained together with anthracenone and anthracene derivatives. It was proved by the reaction in benzene-d6 that the new product was formed by attack of benzene-d6.