Abstract. Phthalimide protecting groups were removed from "benzene diamide AIB diphthalimide" in 32% yield by heating the starting material in neat excess ethanolamine for 1 h 15 min.
Procedure. "Diphthalimide" (0.2442 g, 0.453 mmol) was combined with ethanolamine (3 mL, 50.1 mmol) in a 35 mL round bottom flask equipped with a drying tube and magnetic stir bar, and warmed in an 80-100°C water bath for 1 hour and 15 minutes. The mixture was cooled to 50°C and ethanolamine was removed by vacuum distillation.
Dichloromethane (10 mL) and 3M HCl (10 mL) were added to the residue, the layers
were separated, and the organic layer was extracted with 3M HCl (10 mL). The
aqueous layers were combined, made basic (pH>10) with 10% aqueous NaOH (30
mL), and extracted with dichloromethane (40 mL). The solvent was evaporated
and the residue was briefly vacuum dried, then stored in a dessicator giving
a heterogeneous mixture of a white powder interspersed with a yellow oil. This
residue was dissolved in dichloromethane, the solvent was evaporated, giving
the "diamine" as a white
solid: 0.04g (31.9%); 1H NMR (DMSO-d6, 400 MHz) ppm: 1.35
(s, CH3), 7.17 (m, Ar-Ha), 7.61 (m, Ar-Hb) (KRR 21).