Síntese de 3-Calcogenil-indóis empregando peróxido de hidrogênio-ureia (UHP) como agente oxidante

Abstract

The present work presents a new proposal for a synthetic route to obtain 3-Chalcogenyl-indoles. The methodology developed has as its main characteristics the use of urea-hydrogen peroxide (UHP) as an oxidizing agent. The addition of this reagent provides an anhydrous reaction medium, in addition to greater safety to the manipulator, therefore being environmentally friendly and of low toxicity. Thus, the proposed methodology for the preparation of both 3-selenyl- and 3-sulphenyl-indoles was based on the reaction of diorganoyl dichalcogenides (0.25 mmol) with indoles (0.5 mmol), in a medium containing potassium iodide (1 equivalent) or molecular iodine (10 mol%) as iodine sources, UHP (1 equivalent) as oxidizing agent and acetonitrile (1 mL) as solvent. The reactions for the synthesis of 3-selenyl-indoles occurred at a temperature of 80 °C in the presence of KI, while the 3-sulphenyl-indoles could be prepared at room temperature using I2. With this, a total of 17 compounds were prepared, with yields from 39 to 97%, among which groups with the most diverse characteristics could be tested. The methodology could also be used for a scale up test quite satisfactorily, demonstrating its industrial applicability. In addition, it was possible to carry out the variation of the nucleophile, testing 2-methoxy-naphthalene and 2-naphthol to react with diphenyl dichalcogenides, obtaining very satisfactory yields. Finally, additional studies were carried out in order to verify the effect that the presence of water could exert on the formation of the products in order to demonstrate the importance of the anhydrous medium. The results confirmed that the presence of an aqueous medium exerts a negative influence on the formation of 3-selenyl-indoles.