Chain length dependent reactivity of 2-(ω-hydroxyalkyl)-4-(ω'-hydroxyalkylamino)phthalazin-1(2H)-ones in azeotropic hydrobromic acid

Article abstract of DOI:10.1016/S0040-4020(01)87114-3

In boiling 48% HBr conversions of title compounds (5a-f) resulted in 2-(ω-bromoalkyl)-4-(2-hydroxyethylamino)-phthalazinones 8a,c, angular tricycles 7a,c-f and the 14a tricyclic dione, respectively, depending on the lengths of the side chains and the reaction time applied. The large difference between the reactivities of 4-(2-hydroxyethylamino)- and 4-(3-hydroxypropylamino) homologues in the exchange OH → Br was interpreted on the basis of the relative OH-basicities in the N³-protonated molecules. The proposed mechanism for the conversion to 14a involving a Smiles-type rearrangement was supported by additional experiments with 4-amino-2-(ω-hydroxyalkyl)-phthalazinones 15a,b.