Shapiro Reaction and Mechanism

Shapiro Reaction and Mechanism

Shapiro Reaction and Mechanism


Shapiro reaction is also known as tosylhydrazone decomposition reaction. The reaction in which a ketone or aldehyde is converted to an alkene through an intermediate hydrazone in the presence of 2 equivalents of organolithium reagent is called Shapiro Reaction.

Shapiro Reaction or Tosylhydrazone Decomposition Reaction

In case of unsymmetrical ketones, least substituted alkenes (kinetic products) predominates.
Shapiro reaction of unsymmetrical ketones


Tosyl Hydrazone Formation

Tosyl Hydrozone is formed by the Nucleophilic addition between aldehyde or ketone and Tosyl hydrazide (p-Toluenesulfonyl hydrazide).
Tosyl Hydrazone Formation


Mechanism of Shapiro Reaction

Mechanism of Shapiro reaction starts with deprotonation of Tosyl hydrazone with a strong base to form Hydrazone aza enolate followed by elimination of aryl sulfenate gives an unstable anion then loss of Nitrogen leads to vinyl anion which can be trapped by number various electrophiles. Mechanism of Shapiro Reaction or Tosylhydrazone Decomposition Reaction


The source of electrophiles(E+) in shapiro reaction may be H2O, CO2, DMF, RX, H-CHO, D2O, Me3SiCl etc.
Electrophiles used in Shapiro Reaction


Examples of Shapiro Reaction

Electrophiles used in Shapiro Reaction


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