Intermediate 62 was ground as described by Yang et al. (see J. Am. Chem. Soc., 1996, 118:9557) and added in portions to a 50 mL conical flask containing 15 mL of concentrated sulfuric acid while maintaining stirring and maintaining the temperature at 90°C. Acetamide was added slowly, ensuring that the temperature of the reaction mixture did not exceed 105 °C. After addition, the purple-black solution was continued to be stirred at 90°C for 15 minutes, subsequently cooled to 60°C and poured into a beaker containing 15 g of crushed ice. Ice was continued to be added until the outside of the beaker was cold to the touch. The orange-brown precipitate was collected by filtration and dried overnight under vacuum to afford dihydroindole-2,3-dione (Intermediate 63, 0.77 g, 27% yield) of sufficient purity for use in the next step. Intermediate 63 was also recrystallized from ethanol to give a pure orange-red needle product.1H NMR (400 MHz, DMSO-d6) δ 1.14 (t, J = 7.5 Hz, 3H), 2.56 (q, J = 7.6 Hz, 2H), 7.03 (t, J = 7.5 Hz, 1H), 7.35 (d, J = 7.3 Hz, 1H), 7.46 (d , J = 7.6 Hz, 1H), 11.11 (s, 1H).
