Lithium 2,2,6,6-tetramethylpiperidide transmetalation

Acyclic bis(seleno)acetals 426 (R = H) must be deprotonated with LDA at —78 °C, because w-BuLi produces lithium-selenium exchange8,13,635 639. a-Lithioselenoacetals can also be prepared by this transmetallation from selenoorthoesters 427 (R = SeMe) with n-BuLi638,639. a-Alkyl substituted selenoacetals 426 (R = alkyl) can be deprotonated with LDA or lithium tetramethylpiperidide in the presence of HMPA at — 30 °C640. 

Although (64) is produced by treatment of the corresponding allyl selenide with LDA or lithium 2,2,6,6-tetramethylpiperidide (LITMP) in THF, treatment with n-butyl- or methyl-lithium leads to rapid transmetallation at-78 C, giving the allyllithium and alkyl phenyl selenides. ... 

Aluminum enolates can be obtained also by transmetallation of lithium enolates (Scheme 31 ). 3 Diethylaluminum enolates can be produced regiospecifically through reaction of diethylaluminum chloride and zinc dust with a-bromo ketones and esters (Scheme 32). Obviously zinc is involved in this reaction, but the mild conditions are in sharp contrast to the Refoimatsky reaction and support the existence of an aluminum enolate in this process. The same type of enolate can be obtained from r-butyi acetates and diethylaluminum 2,2,6,6-tetramethylpiperidide (DATMP), which is generated in situ from diethylaluminum chloride and LITMP (Scheme 33). ... 

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