Synthesis of 4-Functionalized Pyrazoles via Oxidative Thio/selenocyanation Mediated by PhICl₂ and NH₄SCN/KSeCN

A series of 4-thio/selenocyanated pyrazoles were conveniently synthesized from 4-unsubstituted pyrazoles using NH4SCN/KSeCN as thio/selenocyanogen sources and PhICl2 as the hypervalent iodine oxidant. This metal-free approach was postulated to involve the in situ generation of the reactive thiocyanogen chloride (Cl-SCN/SeCN) from the reaction of PhICl2 and NH4SCN/KSeCN, followed by an electrophilic thio/selenocyanation of pyrazole skeleton.