Keck allylation

What is Keck allylation?

The Keck allylation is a chemical reaction that was first reported in 1982. It involves a three-carbon chain extension of alkyl halides or carbonyl compounds using allyl tri-n-butylstannane. The reaction can be initiated by either a radical initiator or a Lewis acid.

This reaction is also known as the Pereyre-Keck allylation, Keck reaction, or Keck radical coupling.

Keck allylation - general reaction scheme - Pereyre-Keck allylation - Keck reaction - Keck radical coupling
Keck allylation
  • R = alkyl, aryl
  • X = Cl, Br, I, etc.
Keck allylation - general reaction scheme - Pereyre-Keck allylation - Keck reaction - Keck radical coupling
Keck allylation
  • R = alkyl, aryl
  • X = Cl, Br, I, etc.
  • R’ = H, alkyl, aryl

When allyl tri-n-butylstannane reacts with α-hydroxyaldehyde, the stereoselectivity can be controlled to produce either erythro or threo products, depending on the order of addition of the reagent, solvent, and Lewis acid.

The threo product is formed under chelation control, whereas the erythro product predominates in the absence of Lewis acid. However, the stereochemistry can be reversed by using a strong electron-donating solvent.

Suitable Lewis acids for this reaction include BF3·OEt2, MgBr2, MgCl2, Mg(ClO4)2, ZnBr2, ZnI2, TiCl4, and AlMe3.

References

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