Highly substrate selective nucleophilic amination of nitro-substituted 4-(2-hydroxyethylamino)phthalazin-1(2H)-ones

An unexpected selectivity was observed in the aromatic displacement reaction of 4-(2-hydroxyethylamino)phthalazinones 1-3 and 7, 8 differently substituted with the leaving nitro group on the condensed benzene ring. On treatment with a series of amine and hydrazine nucleophiles, the 8-nitro isomers 1-3 were readily transformed into the corresponding aromatic amine (4-6), while the substrates carrying the nitro group at position 6 or 7 (7 and 8) remained unchanged on prolonged treatment with any of the reagents used. Application of pyridine or DMF as a solvent proved to be indispensable to successful conversions even of the 8-nitro derivatives 1-3.