Study On Copper-Catalyzed C-S And C-Se Coupling Reactions

The formations of C-S and C-Se bonds play a key role in the synthesis of diaryl sulfides and diaryl selenides, so the C-S and C-Se cross-coupling reactions have significance in modern organic chemistry.Transition-metal-catalyzed C-S and C-Se cross-coupling reactions have been widely investigated. Copper-catalyzed cross-coupling reactions are always hot topic as copper is low-cost and easy to obtain compared to other catalysts such as Pd and Ni. But these metal-catalyzed reactions require readily oxidizable, foul-smelling, expensive, and less available arene chalcogens. The use of easily available chalcogen sources as coupling partners is of great interest as a means to develop cost-efficient coupling procedures. However, only a few methods are involved in the selective synthesis of symmetrical and unsymmetrical diaryl chalcogenides.We report a protocol for selective synthesis of diaryl chalcogenides using easily available chalcogen sources under ligand-free conditions.After optimizing the reaction conditions, we found the effective reaction conditions for symmetrical diaryl chalcogenides:aryl iodide (1mmol), Na2S-9H2O (Se)(0.6mmol), Cul (0.1mmol), K2CO3(1mmol) and DMF (DMSO)(2mL) stirred at120℃for18h under argon. Reaction conditions for unsymmetrical diaryl sulfides:1) iodobenzene (0.5mmol), Na2S-9H2O (1equiv.), S (1equiv.), Cul (0.1equiv.) and DMF (1mL) stirred at100℃for15h under argon.2)1-iodo-4-methoxybenzene, K2CO3(1mmol), Fe powder (0.3mmol) and DMSO (2mL) stirred at120℃for18h under argon.To explore the scope of substrates to synthesize symmetrical diaryl chalcogenides and unsymmetrical diaryl sulfides, various aryl iodides were investigated under the optimized conditions. Steric hindrance seemed to have little effect on these reactions and also this system has an exceptional functional group tolerance and high chemoselectivity.Encouraged by the above research subject, we synthesize2-phenylbenzo[b]selenophenes with o-bromoarylyne and selenides through closed-loop reaction of addition and coupling without catalyst.