Study On Synthesis Of2-amine-substituted Aryl Sulfides With Benzothiazole In Aqueous Media

Since Migita and coworkers firstly reported palladium-catalyzed C-Scross-coupling reaction, much research had been putted on the carbon-sulfur bondforming reaction. The construction of amine-substituted aryl sulfides is an importanttool in biological, pharmaceutical and material aspects. For example, various sorts ofamine-substituted aryl sulfides are used in different kinds of pharmaceuticalcompounds which have been shown to exhibit anti-inflammatory, antitumor,antiprotozoal, antipsychotic, and antidepressant agent properties. These methods havebecome common and reliable methods in application, but still have some limitations,including harsh conditions, multi-step reactions, and expensive raw materials. So thedesign of a “green” chemical protocol is necessary. In the past few decades theenvironmentally-benign and economic chemical processes have attracted broadattentions, both the use of ligand-free catalytic systems and water as solvent are stillthe perfect target. Because this solvent has many valuable features, such asnon-toxicity, low cost, availability and greater chemoselectivity compared withorganic solvents. In this paper, we research the C-S coupling reaction based on usingwater as solvent.A novel synthetic method for2-aminophenyl sulphide derivatives ofbenzothiazole with aryl iodides was reported for the first time. The reactions werecatalyzed by a combination of ligand-free copper salt and tetrabutylammoniumhydroxide (acting as the base) using water as the solvent at50oC for12h. A varietyof aryl iodides underwent the C-S Cross-Coupling reaction with benzothiazolesmoothly to afford the corresponding products in good yield. This demonstrated thatthe universality of the reaction were very broad. Unfortunately, ArBr, ArCl and ArFcouldn’t react with benzothiazole in spite of doing many attempts. Only poor amountof the products were obtained for the aryl bromides with electron-withdrawingsubstituents. Both1-Methyl-1H-benzo[d]-imidazole and benzo[d]oxazole, which hassimilar chemical properties with benzothiazole, couldn’t react with aryl iodides in thiscatalyst system. In addition, we also research and state the possible mechanism of thereaction. The2-aminophenyl sulpho salts which enters the catalytic cycle was gotafter deprotonation of benzothiazole, ring-opened and hydrolysis process. The catalytic cycle is ordinary oxidative addition and reductive elimination process. Ofcourse, the mechanism and the further application of the reaction still needs furtherstudy.