Synthesis of Biaryls and Polyaryls by Ligand-Free Suzuki Reaction in Aqueous Phase

A highly efficient palladium acetate-catalyzed ligand-free Suzuki reaction in aqueous phase was developed in short reaction times (0.5−1 h) at 35 °C in air. The key for such a successful catalytic system was the use of a suitable amount of cosolvents in the aqueous phase. The method could be extended to the consecutive multi-Suzuki coupling, and polyaryls were prepared in a single one-pot step in high selectivity and excellent yield under mild reaction conditions (60 °C)

Phosphine-Free Palladium Acetate Catalyzed Suzuki Reaction in Water

Pd(OAc)2 in a mixture of water and poly(ethylene glycol) (PEG) is shown to be an extremely active catalyst for the Suzuki reaction of aryl iodides and bromides. The reaction can be conducted under mild conditions (50 °C) without the use of a microwave or phosphine ligand in high yields. The isolation of the products is readily performed by the extraction of diethyl ether, and the Pd(OAc)2−PEG can be reused without significant loss in activity

Copper-Catalyzed Alkyne−Aryne and Alkyne−Alkene−Aryne Coupling Reactions

The efficient copper-catalyzed two-component coupling reaction of alkynes with arynes and the three-component coupling reaction of alkynes with allylic chlorides and arynes have been developed. Copper acetylide was postulated as a transient intermediate for the initiation of the coupling reactions

Palladium-Catalyzed Homocoupling and Cross-Coupling Reactions of Aryl Halides in Poly(ethylene glycol)

The direct coupling of aryl halides to prepare symmetrical and unsymmetrical biaryls were performed successfully in poly(ethylene glycol) (PEG) using Pd(OAc)2 as the catalyst in the absence of other additives or reductants. The selectivity toward biaryl depended on the amount of PEG used. Excessive PEGs induce the increase of hydrodehalogenation product, and the best selectivity to biaryl is obtained when the concentration of the hydroxyl group in PEG achieves 100 mol % relative to aryl halides. The catalyst system could be recycled and reused up to five times with no loss of catalytic activity

[Bmim]PF₆‑Promoted Ligandless Suzuki–Miyaura Coupling Reaction of Potassium Aryltrifluoroborates in Water

The Suzuki–Miyaura coupling reactions of potassium aryltrifluoroborates with aryl bromides in water are promoted by the addition of [bmim]­PF₆ using Pd­(OAc)₂ as a catalyst and Na₂CO₃ as a base under air. The quantity of [bmim]­PF₆ used is crucial to the efficiency of the catalytic system. A wide range of biaryls and polyaryls can be easily prepared in good to excellent yields