Reduction of Carbonyl Compounds to Alkenes

Ketone p-toluenesulfonylhydrazones are converted to alkenes on treatment with strong bases such as an alkyllithium or lithium dialkylamide.286 Known as the Shapiro reaction,2 7 this proceeds through the anion of a vinyldiimide, which decomposes to a vinyllithium reagent. Treatment of this intermediate with a proton source gives the alkene. 

The Shapiro reaction has been particularly useful for cyclic ketones, but its scope includes acyclic systems as well. In the case of unsymmetrical acyclic ketones, 

Reduction of Carbon-Carbon Multiple Bonds, Carbonyl Groups, and Other Functional Groups 

This regiospecificity has been shown to depend on the stereochemistry of the C=N bond in the starting hydrazone. There is evidently a strong preference for abstracting the proton syn to the arenesulfonyl group, probably because this permits chelation with the lithium ion. 

The vinyl lithium reagents generated in the Shapiro reaction can be used in tandem reactions. In the reaction shown below, a hydroxymethyl group was added by formylation followed by reduction. 

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Reduction of carbonyl compounds to alkenes. In Sundberg RJ, Carey FA (eds) Advanced organic chemistry part B, 5th edn. Springer Science, Business Media, LLC... 

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