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General procedure for the synthesis of methyl 4-hydroxy-3,5-diiodobenzoate from methyl nipagin: Potassium iodide (2.1 eq.) was added to a 50% (v/v) aqueous solution under stirring conditions. Subsequently, a solution of acetic acid (1.0 M) containing phenol derivative S5 and sodium percarbonate (SPC) (3.8 eq.) was slowly added over 30 min. The reaction mixture was stirred continuously at 50 °C for 2.0 h under a reflux condenser. Upon completion of the reaction, the reaction mixture was cooled and slowly poured into a vigorously stirred two-phase mixture consisting of dichloromethane and saturated aqueous sodium sulfite solution. The aqueous layer was separated and extracted twice with dichloromethane. The organic layer was combined and washed with saturated aqueous sodium chloride solution. The organic layer was dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure. The crude product was purified by column chromatography to afford the target product methyl 4-hydroxy-3,5-diiodobenzoate (23).

[1] Angewandte Chemie - International Edition, 2010, vol. 49, # 32, p. 5563 - 5566
[2] Tetrahedron, 2013, vol. 69, # 21, p. 4338 - 4352
[3] Patent: CN106632180, 2017, A. Location in patent: Paragraph 0054-0058
[4] Patent: CN106478619, 2017, A. Location in patent: Paragraph 0097; 0098
[5] Chemistry Letters, 1987, p. 2109 - 2112