The regioselective synthesis of 1,2-dihydro-1-oxophthalazin-4-yl trifluoromethanesulfonate (3a) has been reported. The reaction of Tf₂O (2a) with phthalhydrazide (1a) provides a rapid access to 3a with an excellent yield and a high level of regioselectivity. The synthetic utility of this triflate is further enhanced by carrying out the successful Suzuki and Sonogashira coupling reactions for the first time on 3a, providing a simple access to a range of biologically significant 4-aryl/heteroaryl/alkynyl phthalazinones in good yields.