An environmentally benign and efficient synthesis of 4-Selanylpyrazoles catalyzed by haloid salts in water

An environmentally benign procedure is developed for the preparation of 4-selanylpyrazoles from pyrazoles and diselenides. Using haloid salts as catalysts and H2O2 as oxidant, this catalytic protocol is convenient in water at room temperature under open-air condition, and is suitable for a wide variety of starting materials and provides a series of 4-selanylpyrazoles in good yields. A plausible catalytic electrophilic substitution mechanism is hypothesized.