A Rhodamine-B Catalyzed Visible-Light-Mediated Benign Synthetic Route for 4,5-Dihydro-1H-pyrazoles

Herein, an apposite and straightforward methodology has been established for the synthesis of 4,5-dihydro-1H-pyrazole and its derivatives by using Chalcones and Hydrazines as substrates in EtOH under 20W CFL irradiation at room temperature. The distinctive trait of this protocol is the utilization of an efficient, green, highly water soluble organophotoredox catalyst “Rhodamine B”, a simple red xanthene dye, to create C–N bonds via formation of free radicals and eventually terminating with intramolecular cyclization. Short reaction time, environmentally benign approach, cost effectiveness, feasibility and adaptability with respect to a wide range of substrates and good to excellent yield of the product supplements the synthesis.