Vinyl lithium analog

When the enamine is in conjugation with a carbonyl function, as in a-aminomethylene aldehydes (528,529), ketones (530), or esters (531), a Michael addition is found in vinylogous analogy to the reactions of amides. An application to syntheses in the vitamin A series employed a vinyl lithium compound (532). 

Shortly thereafter, Veith and coworkers reported the synthesis of the same dendrimers, but they were able to synthesize dendrimers up to the fourth generation143. The larger dendrimers were obtained by the use of potassium bis(vinyldimethylsilyl)amide as nucleophilic reagent, which is more reactive than the lithium analog. The fourth generation vinyl-terminated dendrimer was obtained in 74% yield. Methyl and phenyl groups were also used as terminal groups. 

Treatment of vinyl Sn, B, or Al compounds with BuLi results in effective addition of Bu to the metal to form a hypervalent anion such as 154. These are often referred to as ate complexes. The analogy is with the names of anions such as sulfate or carbonate. You are already familiar with the copper analogues, usually called cuprates. Lithium now replaces tin at the vinyl group 155 to form a vinyl-lithium derivative -156. The reaction is an electrophilic substitution at carbon - the lithium atom attacks the C-Sn bond and does so with retention of configuration. 

In contrast to the small effects of added lithium alkoxide observed for diene miaostmcture, the addition of other alkali metal alkoxides increases the amount of vinyl miaostmcture analogous to the microstmcture obtained with the corresponding alkali metal counterion. Thus, the maximum vinyl contents (%) were 67, 48, 55, and 53 for the sodium, potassium, mbidium, and cesium alkoxides, respec-... 

It is possible to treat ketones with allyl alcohol and an acid catalyst to give y,5-unsaturated ketones directly, presumably by initial formation of the vinylic ethers, and then Claisen rearrangement.In an analogous procedure, the enolates (126) of allylic esters [formed by treatment of the esters with lithium isopropylcyclohex-... 

Lithium aluminum hydride (LAH) does not, as a rule, react with ethers,but does reduce ortho esters to acetals (equation 2). 2-Vinyl-l,3-dioxolane (5) is reduced to a vinyl ether with double-bond rearrangement (equation 3), but the cinnamyl analog (6) is only reduced at the double bond (equation 4). 

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