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.
In case of unsymmetrical ketones, least substituted alkenes (kinetic products) predominates.
Tosyl Hydrazone Formation
Tosyl Hydrozone is formed by the Nucleophilic addition between aldehyde or ketone and Tosyl hydrazide (p-Toluenesulfonyl hydrazide).
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.
The source of electrophiles(E+) in shapiro reaction may be H2O, CO2, DMF, RX, H-CHO, D2O, Me3SiCl etc.
Examples of Shapiro Reaction
