Regioselective Synthesis of Substituted 4-Alkylamino and 4-Arylaminophthalazin-1(2H)-ones.

An efficient regioselective synthesis of substituted 4-alkylamino and 4-arylaminophthalazin-1(1H)-ones 5 is described. This new method features the formation of substituted phthalazin-1(1H)-ones 3 by the reaction of 2-formylbenzoic acids 1 or 3-hydroxyisobenzofuran-1(3H)-ones 2 with hydrazine to generate phthalazin-1(2H)-ones 3. Subsequent regioselective bromination of phthalazin-1(2H)-ones 3 with benzyltrimethylammonium tribromide (BTMA-Br3) followed by mixed copper–copper oxide-catalyzed amination of 4-bromophthalazin-1(2H)-ones 4 with primary amines generates aminophthalazin-1(2H)-ones in good overall yields.