Synthesis
The general procedure for the synthesis of 4-methoxybenzenesulfonyl hydrazide from p-methoxybenzenesulfonyl chloride is as follows: Hydrazine hydrate (2.5 eq.) was added slowly and dropwise to a solution of tetrahydrofuran (THF, 0.2 M) of p-methoxybenzenesulfonyl chloride (1.0 eq.) at 0 °C. The reaction mixture was stirred continuously at 0 °C until thin layer chromatography (TLC) analysis showed complete reaction. Subsequently, the reaction mixture was diluted with ethyl acetate (EtOAc), washed sequentially with saturated brine, dried over anhydrous sodium sulfate (Na2SO4), and concentrated under reduced pressure to remove the solvent to give the crude p-methoxybenzenesulfonyl hydrazide. The p-methoxybenzenesulfonyl hydrazide (1.0 eq.) was dissolved in methanol (MeOH, 0.5 M) and the corresponding ketone (1.0 eq.) was added. The reaction mixture was stirred at room temperature until TLC monitoring showed that the reaction was complete. The solvent was removed under reduced pressure to give p-methoxybenzenesulfonylhydrazone. The p-methoxybenzenesulfonylhydrazone (0.5 mmol, 1.0 eq.), boric acid (0.75 mmol, 1.5 eq.), and cesium carbonate (0.75 mmol, 1.5 eq.) were placed in a reaction tube that had been pre-dried in an oven and evacuated, and kept for 30 minutes. Subsequently, the reaction tube was filled with argon for protection and dry and degassed 1,4-dioxane (2 mL, 0.25 M) was added. The reaction tube was sealed and the reaction was heated at 110°C for 18 hours. Upon completion of the reaction, the reaction was cooled to room temperature, quenched with saturated aqueous sodium bicarbonate (NaHCO3) (2 mL) and extracted with dichloromethane (CH2Cl2, 3 x 5 mL). The organic phases were combined, dried with anhydrous magnesium sulfate (MgSO4) and concentrated under reduced pressure to give the crude product. Finally, the target product 4-methoxybenzenesulfonyl hydrazide was purified by fast column chromatography (eluent: 10% to 30% ethyl acetate/hexane gradient elution).
References
[1] Marine Drugs, 2016, vol. 14, # 5,
[2] RSC Advances, 2016, vol. 6, # 96, p. 93476 - 93485
[3] Tetrahedron, 2017, vol. 73, # 49, p. 6871 - 6879
[4] Journal of Organic Chemistry, 2014, vol. 79, # 1, p. 328 - 338
[5] Bioorganic and Medicinal Chemistry, 2014, vol. 22, # 17, p. 4629 - 4636
