Solvent and Metal-Free Synthesis of 3-(organochalcogenyl)-2H-indazoles by Direct Chalcogenation of 2H-indazoles Using I₂/DMSO as Catalytic System

Indazoles are fused azaheterocycles with wide applicability in the medical field. In the last decades, the pharmacology interest in this nucleus has increased due to a variety of compounds that show biological activities. Among them are antipyretic, analgesic, anti-inflammatory, antimicrobial, anti-HIV, anti-hypertensive, anti-tumour, anti-fungal and lately is used as an inhibitor of bacterial β-gyrase and a selective estrogen receptor. In addition, organochalcogen compounds have been widely explored due to their possible use as biologically active agents, or as key intermediates and catalysts in organic synthesis.

Based on this and due to our continuous interest in the preparation of nitrogen-functionalized organochalcogen compounds, we describe herein our results on the synthesis of 3-(arylselanyl)- and (arylsulfenyl)-2H-indazoles by molecular iodine-catalyzed. Through the reaction of 2H-indazoles and a diverse range of diorganyl diselenides and diorganyl disulfates using catalytic amount of I₂ (5 mol%) in DMSO (3.0 equiv.) as oxidant at 100 °C. This protocol proved to be simple, efficient and highly chalcogenated regioselectively at the C3 position to furnish a range of corresponding products selectively substituted 3-(organochalcogenyl)-2H-indazoles. A total of 15 examples were synthesized in good to excellent yields (36 to 98 % ). The products were obtained through a solvent and metal free methodology under mild conditions.