One-pot synthesis of 2H-phenanthro[9,10-c]pyrazoles from isoflavones by two dehydration processes

An environmentally friendly and efficient method was developed for one-pot synthesis of a series of 2H-phenanthro[9,10-c]pyrazoles in EtOH by two dehydration processes. Firstly, 3,4-diaryl-1H-pyrazoles were synthesized by the cyclocondensation of isoflavones and hydrazine hydrate in refluxing EtOH. Secondly, the final target products 2H-phenanthro[9,10-c]pyrazoles were given by photocyclization and dehydration of 3,4-diaryl-1H-pyrazoles in 1 : 1 (v/v) EtOH–H₂O. The advantages of this method are catalyst-free, short synthetic routes, mild reaction conditions and easy work-up. In addition, the fluorescence properties of 2H-phenanthro[9,10-c]pyrazoles were determined.