GENERAL STEPS: 3-Aminophenylacetic acid (12.4 g, 26.46 mmol, 1 equiv) was dissolved in a solvent mixture of dioxane (52 mL) and water (52 mL). An aqueous solution of sodium carbonate (2.8 g, 26.42 mmol, 1 equiv) was added to this solution (26 mL) under cooling in an ice bath. Subsequently, di-tert-butyl dicarbonate (Boc2O, 6.24 g, 28.59 mmol, 1.1 eq.) was added all at once and stirred continuously for 4 hours at room temperature. Upon completion of the reaction, the dioxane was removed by distillation under reduced pressure. The aqueous layer was cooled, covered with ethyl acetate and acidified with dilute KHSO4 solution to pH 4. The organic layer was extracted with ethyl acetate and purified by silica gel column chromatography (ethyl acetate was used as the eluent) to afford the target compound, N-Boc-3-aminophenylacetic acid (6.65 g, 85% yield), as a white solid.1H-NMR (300 MHz, CDCl3) data were as follows: δ 7.31 (d, 2H, J = 8.4 Hz), 7.20 (d, 2H, J = 8.4 Hz), 6.56 (br s, 1H), 3.59 (s, 2H), 1.50 (s, 9H).
