Regioselective Synthesis of -Aryl Pyrazoles from Alkenyl Sulfoxonium Ylides and Aryl Diazonium Salts.

A convenient and practical method has been developed for synthesizing various -aryl pyrazoles from vinyl sulfoxonium ylides and diazonium salts. When using 1,3-disubstituted vinyl sulfoxonium ylides, the reaction selectively yields 1,3,5-trisubstituted pyrazoles. On the other hand, employing 2,3-disubstituted vinyl sulfoxonium ylides results in the formation of 1,3,4-trisubstituted pyrazoles. The reaction proceeds through the novel aryl diazene-derived vinyl sulfoxonium ylide. Furthermore, this method efficiently produces pyrazoles from aniline derivatives in a one-pot transformation. The reaction takes place under transition metal-free, mild conditions using easily accessible starting materials, making it a practical approach for generating pyrazoles in pharmaceutical chemistry.