The condensation reaction was carried out by reacting methyl 3,4-diaminobenzoate and diethyl oxalate (8.0 eq.) in toluene (10 v/v) under reflux conditions for 88 hours. After the reaction was complete, the reaction mixture was concentrated to dryness and the resulting residue was washed with methyl tert-butyl ether (MTBE). After drying, Intermediate 184 was obtained in 90% yield.
