Scheme 2. Synthesis of Different Ortho-Substituted Para-Aminobenzoates.

Reagents and conditions: (a) (i) oxalyl dichloride, DMF (cat.), CH₂Cl₂, 0 °C to rt, 2 h; (ii) 3-aminopiperidine-2,6-dione hydrochloride, Et₃N, CH₂Cl₂, rt, 16 h, 80–83%; (b) EDC × HCl, HOBt, 3-aminopiperidine-2,6-dione hydrochloride, DIPEA, DMF, rt, 16 h, 35–74%; (c) Pd/C, H₂, DMF, rt, 18 h, 11–74%; (d) (2,4-dimethoxyphenyl)methanamine, DIPEA, DMSO, 90 °C, 16 h, 35%; (e) TFA, CH₂Cl₂, rt, 2 h, 77%.