Benzylamine → 1-benzyl-3-bromo-2,5-dihydro-1H-pyrrole-2,5-dione

A solution of bromomaleic anhydride (1 g, 5.7 mmol) and benzyl amine (0.7 mL, 6.8 mmol) in acetic acid (15 mL) was warmed to 50° C. and stirred overnight. The reaction was then cooled to room temperature, diluted with CH2Cl2 (50 mL) and washed with NaHCO3 (3×25 mL) and brine (25 mL). The organic layer was then dried (MgSO4), filtered and the solvent removed under reduced pressure. The residue was purified using gradient flash chromatography (0-100% ethyl acetate in pet ether) to provide 1-benzyl-3-bromo-1H-pyrrole-2,5-dione (18). 1H NMR (400 MHz, CDCl3) δ 4.71 (s, 2H), 6.87 (s, 2H), 7.26-7.37 (m, 5H). A stirred solution of 1-benzyl-3-bromo-1H-pyrrole-2,5-dione (0.26 g, 1.0 mmol) and p-tolylboronic acid (0.16 g, 1.2 mmol) in dioxane (10 mL) was degassed with a stream of nitrogen for 10 minutes before being treated with CsF (0.39 g, 2.6 mmol) and C12Pd(dppf).CH2Cl2 (0.05 g, 0.06 mmol). The reaction was stirred at room temperature for 1 h then warmed to 40° C. for 1 h. The mixture was then cooled, diluted with CH2Cl2 (30 mL) and filtered through a pad of celite. The filtrate was concentrated under reduced pressure and purified using gradient flash chromatography (0-10% ethyl acetate in pet ether) to provide the title compound 15.