Organolithium compounds heteroatom-stabilized

Some heteroatom-substituted or chelate-stabilized organolithium compounds, on the other hand, can be sufficiently stable toward racemization to enable their use in stereoselective reactions with electrophiles [223, 225, 271, 531, 543, 552-554] (Scheme 5.75). This increased configurational stability of a-heteroatom-substituted carbanions might be due to the stronger pyramidalization of such carbanions [261,555] and fixation of the metal by chelate formation. 

Stabilized organolithium compounds, such as lithium enolate intermediates [5], a-organolithium compounds bearing electron-withdrawing groups (RSO, RSOj, CN, NOj, etc.) and heteroatoms such as sulfur [6], selenium and phosphorus as well as functionalized aryllithium compounds will not be consider in depth in this chapter due to the limited length of this review. 

Arylsilver compounds ArAg, where the aryl group carries one or two substituents containing a heteroatom, have been obtained by transmetallation reactions of silver bromide with the corresponding organolithium compounds 2-[(dimethylamino)methyl]phenyl silver (17)70, (2,6-dimethoxyphenyl)silver (18)70 71 and (2,4,6-trimethoxyphenyl)silver (19)70. The compounds show an enhanced thermal stability with decomposition temperatures well above 150 °C. 

Reports on organolithium compounds with internal heteroatom stabilization and their reactions with alkylating agents7 12 -14 are informative for stereoselective protonations and deuter-ations. 

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