Chemistry of 1,5-diketones: II. Specificity of transformations of polycyclic 1,5-diketones in acid media

2-(1,3-Diaryl-3-oxopropyl)cyclohexan-1-ones underwent carbo-and heterocyclization in a mixture of acetic acid with acetic anhydride in the presence of perchloric acid. The transformation of 2-(1,3-diaryl-3-oxopropyl)cyclohexan-1-ones into 2,4-diaryl-5,6,7,8-tetrahydrochromenylium salts was shown to involve intermediate 2,4-diarylbicyclo3.3.1]non-2-en-9-ones. The structure of 2,4-diaryl-substituted bicyclo3.3.1]non-2-en-9-ones and products of their reactions with halogens and hydroxylamine hydrochloride was confirmed by ¹H and ¹³C NMR spectroscopy.