Abstract. Phthalimide protecting groups were removed from "benzene diamide AIB diphthalimide" in 41% yield by heating the starting material in neat excess ethanolamine for 30 min.
Procedure. "Diphthalimide" (0.5080g, 0.94 mmol) was combined with ethanolamine (3mL, 50.1 mmol) in a 35 mL round bottom flask equipped with a drying tube and magnetic stir bar, and warmed in an 80-90 °C water bath for 30 minutes. The mixture was cooled to room temperature and the ethanolamine was removed by vacuum distillation.
Dichloromethane (20 mL) was added to the residue, followed by 3M HCl (20 mL), and the layers were separated. The organic layer was extracted again with 3M HCl (20 mL). The aqueous layers were combined, and made basic (pH>10) with 10% aqueous NaOH (60 mL), and extracted with dichloromethane (80 mL). The solvent was evaporated and the product was stored in a dessicator for x days. This yielded a white powder interspersed with a yellow oil. This mixture was re-dissolved in dichloromethane, and the solvent was evaporated, giving the "diamine" as a white solid: 0.1067 g (41 %); mp 134-138 °C; 1H NMR (DMSO-d6, 400 MHz) ppm: 1.28 (s, CH3), 7.15 (m, Ar-Ha), 7.56 (m, Ar-Hb) (KRR 13b).