Alkenyllithium intermediates, Shapiro reaction

Alkenyllithium compounds are intermediates in the Shapiro reaction, which is discussed in Section 5.7.2. The reaction can be run in such a way that the organolithium compound is generated in high yield and subsequently allowed to react with a variety of electrophiles.64 This method provides a route to vinyllithium compounds starting from a ketone. 

The Shapiro reaction is a nonconnective procedure for interconversion of a keto group and its a-methylene moiety into an alkene, providing a powerful method for the preparation of alkenyllithiums that are not readily available by current methodologies. Further elaboration of the intermediate alkenyllithiums leads to a variety of structurally diverse alkenes. 

The Shapiro reaction1 is the conversion of arylsulfonylhydrazones to alkenes via treatment with alkyllithium reagents or alkali metal amides.2,3,4,5 The reactions proceed via alkenyllithium intermediates, which can be transformed to the alkene upon protonation or can be captured with other electrophilic reagents. For example, the tosylhydrazone 1 derived from 2-methylcyclohexanone was converted to 3-methylcyclohexene (2) in 98% yield upon treatment with two equivalents of butyllithium.1... 

---