Step 4: Synthesis of 6-methylphthalide
107 g (472 mmol) of 6-(bromomethyl)isobenzofuran-1(3H)-one was dissolved in 50 mL of methanol (dioxane may also be used as a solvent in some experiments). This solution was transferred to a Parr reaction flask containing 40 g (540 mmol) of calcium hydroxide and 2 g of 10% Pd/C. The suspension was subjected to a hydrogenation reaction under 40 psi hydrogen pressure until hydrogen uptake ceased. Upon completion of the reaction, all solids were removed by filtration and the filtrate was concentrated to give 67 g of brown solid product in 96% yield. The product was characterized by 1H NMR (CDCl3, 300 MHz): δ 2.53 (s, 3H), 5.30 (s, 2H), 7.49 (s, 1H), 7.54 (d, 3JHCCH = 7.9 Hz, 1H), 7.47 (d, 3JHCCH = 7.9 Hz, 1H).
