Reactions between azolium anions and electrophilic reagents. Part II. Direct thiation of 1,2-disubstituted pyrazolium anions with sulphur

Abstract

Pyrazolium salts (1) afford Δ³-pyrazoline-5-thiones (2) in good yields when treated with sulphur and sodium hydride in dimethylformamide. Pyrazolium salts (1a) with two different N-substituents produce two isomeric Δ³-pyrazoline-5-thiones (2a and b) in a ratio reflected by the ratio between the deuterium exchange rates of H-3 and H-5 in the starting material (1a).