My watch list
my.chemeurope.com  
Login  

Shapiro reaction



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.[1][2][3]

Additional recommended knowledge

Contents

Reaction mechanism

In a prelude to the actual Shapiro reaction a ketone or an aldehyde is reacted with p-toluenesulfonylhydrazide[4] 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.

Scope

Although many secondary reactions exist for this functional group, in the Shapiro reaction in particular water is added resulting in hydrolysis to the alkene.[5] Other reactions of vinyllithium compounds include alkylation reactions with for instance alkyl halides.[6] 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.

See also

References

  1. ^ Shapiro, R.H.; Lipton, M.F.; Kolonko, K.J.; Buswell, R.L.; Capuano, L.A. Tetrahedron Lett., 1975, 1811.
  2. ^ Shapiro, R. H. Org. React., 1976, 23, 405. (Review)
  3. ^ Adlington, R.M.; Barret, A.G.M. Acct. Chem. Res., 1983, 16, 55. (Review)
  4. ^ Organic Syntheses Coll. Vol. 5, p.1055 (1973); Vol. 40, p.93 (1960) (Article)
  5. ^ Shapiro, R. H.; Duncan, J. H. Organic Syntheses Coll. Vol. 6, p.172 (1988); Vol. 51, p.66 (1971). (Article)
  6. ^ Organic Syntheses Coll. Vol. 7, p.77 (1990); Vol. 61, p.141 (1983). (Article)
 
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.
Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE