Green Conditions For Suzuki Cross-coupling Reaction And Synthesis Of Benzimidazoles

Reaction medium that is environmentally friendly is one of the most fundamental contents of green chemistry and water is an important green solvent. In this work, Suzuki cross-coupling reactions in water and the synthesis of 1,2-disubstituted benzimidazoles under catalyst-free condition were studied in detail.In part one, palladium-catalyzed Suzuki cross-coupling reaction in water was studied in detail. The results showed that stilbazo is an efficient promoter for the aqueous palladium-catalyzed Suzuki cross-coupling reaction. Under the optimized conditions—5 mol% Pd(OAc)2,5 mol% Stilbazo and 200 mol% K2CO3—the aqueous Suzuki reaction of aryl halides proceeds well with good functional group tolerance. We found that aryl bromides and iodides reacted with phenylboronic acid efficiently, giving the corresponding biaryls in good to excellent yields. Aryl iodides gave higher yields than the corresponding bromides.Aryl chlorides are unsuitable coupling partners in the Suzuki-Miyaura reaction.In part two, catalyst-free selective formations of 1,2-disubstituted benzimidazoles from aldehydes and o-phenylenediamine in 1,4-dioxane were studied in detail. The results showed that two equivalent aldehydes reacted with o-phenylenediamine at room temperature using dioxane as the solvent, and 1,2-disubstituted benzimidazoles were obtained selectively in high yields under mild conditions and good functional group tolerance.