Studies of heteroaromaticity. Part LIX. Further investigations of the cycloaddition reactions of tropone with azo-dienophiles and the photochemical behaviour of the adducts

Abstract

The reactions of tropone with phthalazine-1,4-dione and 4,4-diethylpyrazoline-3,5-dione give the normal [4 + 2]π-cycloadducts (V) and (VII), in 38 and 18% yield, respectively. Irradiation of the adducts (V) and (VII) and the tropone–N-phenylmaleimide adduct (XIV) in protic solvents gives one photo-product in high yield in each case. These photoproducts are formed by addition of the solvents to the initially formed ketens, thus providing an efficient synthesis of heterotricyclic compounds.