To use all functions of this page, please activate cookies in your browser.
With an accout for my.chemeurope.com you can always see everything at a glance – and you can configure your own website and individual newsletter.
- My watch list
- My saved searches
- My saved topics
- My newsletter
The Shapiro reaction or tosylhydrazone decomposition is an organic reaction in which a ketone or aldehyde is converted to an alkene through an intermediate hydrazone in the presence of 2 equivalents of strong base.
Additional recommended knowledge
In a prelude to the actual Shapiro reaction a ketone or an aldehyde is reacted with p-toluenesulfonylhydrazide to a p-toluenesulfonylhydrazone (or tosyl hydrazone) which is an imine or hydrazone. Two equivalents of a strong base such as n-butyllithium then abstract first the hydrazone proton and then the less acidic α carbonyl proton leaving a carbanion. The carbanion proceeds in an elimination reaction creating the carbon to carbon double bond and converting the hydrazone group into a lithium diazonium group. This group expels nitrogen leaving a vinyllithium compound.
Although many secondary reactions exist for this functional group, in the Shapiro reaction in particular water is added resulting in hydrolysis to the alkene. Other reactions of vinyllithium compounds include alkylation reactions with for instance alkyl halides. In general the least substituted alkene is the preferred reaction product.
The Bamford-Stevens reaction is also a tosylhydrazone decomposition but in this reaction a much weaker base can only abstract the hydrazone proton and not the α carbonyl proton and the reaction mechanism now involves a carbene or in a protic solvent a carbocation.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Shapiro_reaction". A list of authors is available in Wikipedia.|