Vinyllithium compounds Shapiro reaction

Removal of the carbonate ring from 7 (Scheme 1) and further functional group manipulations lead to allylic alcohol 8 which can be dissected, as shown, via a retro-Shapiro reaction to give vinyl-lithium 9 and aldehyde 10 as precursors. Vinyllithium 9 can be derived from sulfonyl hydrazone 11, which in turn can be traced back to unsaturated compounds 13 and 14 via a retro-Diels-Alder reaction. In keeping with the Diels-Alder theme, the cyclohexene aldehyde 10 can be traced to compounds 16 and 17 via sequential retrosynthetic manipulations which defined compounds 12 and 15 as possible key intermediates. In both Diels-Alder reactions, the regiochemical outcome is important, and special considerations had to be taken into account for the desired outcome to. prevail. These and other regio- and stereochemical issues will be discussed in more detail in the following section. 

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 reaction of a tosylhydrazone with at least 2 equiv. of an alkyllithium reagent in ether or hexane generates the dianion (Shapiro reaction) this gives, after loss of Ts" and N2, the vinyllithium compound, which can be trapped by a variety of electrophiles, e.g. H", CO2, DMF (Scheme 27). The less-substituted alkene is formed predominantly under these conditions. 

Another fragmentation reaction especially useful for the synthesis of vinyllithium compounds is the well-known Shapiro reaction We were successful in preparing 2,3-dilithio-l,3-butadiene 166 by a double Shapiro reaction although in 12% yield only The main reaction product was 2-butyne. 

Alpha alkylation of hydrazones and Shapiro reaction in a one-pot process provides a versatile route to tetrasubstituted alkenes. The addition of 2 equiv of butyllithium to a trisyUiydrazone generates a dianion, which may be trapped at low temperature with different electrophiles such as methyl iodide. An additional equivalent of butyllithium generates a dianion species that decomposes at room temperature to yield the vinyllithium intermediate of the Shapiro reaction. This t)q)e of compound can react with different electrophiles as commented before. In this example, the final addition of paraformaldehyde gave rise to the tetrasubstituted alkene represented in eq 22. ... 

The first vinyllithium carbolithiation reaction was reported by Chamberlin and Bloom15, who showed that Shapiro-derived organolithium 10 cyclized onto a terminal alkene giving stereoselectively (>50 1) bicyclic compounds 11, after treatment with electrophiles (Scheme 4). The intermediate alkyllithiums 12 are generated via a 5-exo-trig cyclization reaction from 10, which undergo the carbolithiation reaction at approximately the same rate as reported by Bailey for the simple parent compound 5-hexenylIithium, i.e. with a half-life of a few minutes at 0 °C. 

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