Shapiro reaction vinyllithium generation

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. 

A complementary approach, developed by Paquette, - uses substituted acryloyl chlorides as addends in reaction with structii ly embellished vinylsilanes. A general route to the vinylsilanes (87) was found in the silylation of vinyllithiums generated by the Shapiro reaction.The acylation with acryloyl chlorides takes place readily with aluminum trichloride to afford the divinyl ketones which are subsequently cyclized with tin tetrachloride. The Nazarov cyclization products were formed as a mixture of double tend isomers (equation 47). The best results were obtained with p,p-dimethylacryloyl chloride. Crotonyl chloride could be employed, but acryloyl chloride proved impractical. This metl owes much of its utility to the regiocontroUed synthesis of Ae vinylsilmes, thereby clearly establishing the loci of cyclopentannulation. 

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. 

Most Shapiro reactions of acyclic sulfonylhydrazones or cyclic sulfonylhydra-zones derived from larger rings proceed with selectivity for the formation of the E-vinyllithium reagent. For example, the trisylhydrazone generated from 4-heptanone (12)... 

The two modifications described above have allowed for the efficient capture of vinyllithium intermediates generated in Shapiro reactions with a wide variety of electrophiles. For example, the alkyllithium reagent 20 prepared from treatment of trisylhydrazone 18 with n-BuLi was effectively trapped with benzaldehyde (62% yield, 21), 1 -bromobutane (58% yield, 22), and bromine from 1,2-dibromoethane (43% yield, 23)." Similarly, formation of 20 from tosylhydrazone 19 followed by trapping with CO2 afforded 24 (52% yield). The reaction of intermediate 20 (generated from 19) with cyclohexenone provided 25, the product of 1,2-addition, in 61% yield.13... 

The Shapiro reaction has been utilized in the functionalization of phenanthroline to obtain chiral ligands. The vinyllithium generated with 2 equiv of s-BuLi was trapped with phenanthroline. 

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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