Allyl selenides lithiation

The reaction of the lithiated allylic carbanion derived from prenyl selenide with hexamethyldistannane did not lead to the mono a-stannylated allylic selenide but to a bis-stannylated compound. A consecutive Se/Sn exchange, without allylic isomerization, occurred [5] (Scheme 4). The reaction involves a selenophilic attack by Mej SnLi formed in the media. 

Allylic sulfoxides and sulfones are completely metallated in liquid ammonia by all alkali amides [1]. For metallation in organic solvents, LDA and BuLi are usually applied. The lithiation of allyltrimethylsilane can be conveniently achieved with BuLi TMEDA (or HMPT) or f-BuLi TMEDA (or HMPT) in THF-alkane mixtures [3], As in the case of the sulfur compounds, extension of the unsaturated system leads to an increased acidity. Thus H2C=CHCH=CHCH2SiMe3 can be metallated with the less strongly basic LDA in THF [4], For the metallation of allylic selenides, LDA seems to be the reagent of choice. Butyllithium will presumably attack on selenium. 

Lithiated allyl sulfides (in common with allyl sulfoxides and selenides, but in contrast with allyl ethers and allyl amine derivatives) tend to react with alkyl halides at the a position, adjacent to S.1 The best a-selectivities are obtained with lithium-coordinating S-substituents such as pyridyl (114),85 imidazolyl (115), and dimethylaminocarbonyl (116).1... 

Organolithiums. Allylic and benzylic alcohols undergo deoxygenative lithiation by treatment of their lithium alkoxides or phenyldimethylsilyl ethers with LDTBB. Alkyl phenyl selenides are also cleaved to give organolithium species that can react with aldehydes and allyl bromide. Some special alkyllithiums have been prepared from (2-pyridylthio)alkanes, which are available from carboxylic acids. ... 

Lithiated allylic sulfoxides may be a-alkylated and the resulting products subjected to [2,3]-sigmatropic rearrangement induced by a thiophile to give allylic alcohols (eq 43). In contrast, alkenyl aryl sulfoxides produce a-lithiated species which are alkylated with Mel or PhCHO in good yields (eq 44). LDA has also been used to metalate allylic and propargylic selenides as weU as aryl vinyl selenides. ... 

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