To a mixture of 5-bromophthalide (2.00 g, 9.39 mmol), tetrahydro-2-(2-propynyloxy)-2H-pyran (5.3 ml, 37.6 mmol), copper(I) iodide (0.645 g, 3.39 mmol), triethylamine (1.90 g, 18.8 mmol) in DMF (20 ml), was added tetrakis(triphenylphosphine)palladium (1.30 g, 1.13 mmol). The mixture was heated at 65° C. under argon for 16 hours, cooled to room temperature and diluted with diethyl ether (250 ml). The filtrate was washed with brine (4×100 ml), dried over anhydrous Na2SO4, and concentrated to give a dark-reddish residue. Purification of the residue mixture by silica gel column chromatography, eluted with a gradient of EtOAc, led to 5-[3-(tetrahydro-pyran-2-yloxy)-prop-1-ynyl]-3H-isobenzofuran-1-one as a white solid (2.23 g, 87%).
