The Mechanism of the Wolff‐Kishner Reduction, Elimination, and Isomerization Reactions

The mechanism of the Wolff‐Kishner reaction is discussed in the light of accumulated information about the kinetics, thermodynamics, and solvent effects of the process. Wolff‐Kishner reduction under normal conditions is thought to involve the trans hydrazone anion, which, in the rate‐determining step, exhibits a more or less concerted proton capture at the carbanion terminal and undergoes a solvent‐induced proton loss at the nitrogen terminal. The stereochemistry of the Wolff‐Kishner reduction is believed to be affected by the presence of “ortho” substituents and by a change to a nonpolar, aprotic reaction medium. The mechanism elaborated for the Wolff‐Kishner reduction is extended to the Wolff‐Kishner elimination and isomerization reactions. Conformational analysis of the intermediates permits correlation of the competitive reduction and elimination processes with the structures of acyclic systems.