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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.

[1] Patent: WO2017/60406, 2017, A1. Location in patent: Page/Page column 172
[2] Patent: WO2018/178280, 2018, A1. Location in patent: Page/Page column 78
[3] Patent: US2004/192698, 2004, A1. Location in patent: Page/Page column 18