Sterics vs Electronics: Revisiting the Catalytic Regioselective Hydrodebromination of 2,3,5-Tribromothiophene

摘要

The application of sterically hindered palladium catalysts to the regioselective hydrodebromination of 2,3,5-tribromothiophene has been studied in detail, including the effects of catalyst choice, solvent, reaction time, and temperature, as well as the method of NaBH4 addition and the role of chelating additives to effect NaBH4 solubility. Ultimately it was determined that the background reaction between NaBH4 and bromothiophenes is too facile to allow both total conversion and high selectivity. Optimized conditions finally allowed a selectivity of ca. 16:1 with overall conversion of 100%. However, complications of over-debromination under these conditions still limit the yield of the desired 2,3-dibromothiophene to 65%.