A selective synthesis of 4-bromo-2-furancarboxaldehyde and its pinacolborane derivative

A selective synthesis of ethylene acetal of 4-bromo-2-furancarboxaldehyde (4) and its pinacolborane derivative (5) is described. The synthesis was carried out using 2-furancarboxaldehyde (1) that was brominated to 4,5-dibromo-2- furancarboxaldehyde (2) in an emulsion of aluminum chloride and methylene chloride. The product was isolated, protected as ethylene acetal, and selectively debrominated to the ethylene acetal of 4-bromo-2-furancarboxaldehyde (4) in one step. This moiety was reacted with pinacolborane to give a reactive reagent of Suzuki coupling.