Hosomi-Sakurai allylation

What is Hosomi-Sakurai allylation?

In 1976, Hosomi and Sakurai reported a reaction that involves the Lewis acid or fluoride-promoted allylation of various carbon electrophiles, such as aldehydes, ketones, aldmines, alkenes, imines, α,β-unsaturated carbonyl compounds, and acetals, using allyltrimethylsilane.

Sakurai reaction - Hosomi-Sakurai reaction - Hosomi-Sakurai allylation - Sakurai allylation - general reaction scheme
Hosomi-Sakurai allylation
  • R1 = alkyl, aryl
  • R2 = H, alkyl, aryl
Sakurai reaction - Hosomi-Sakurai reaction - Hosomi-Sakurai allylation - Sakurai allylation - general reaction scheme
Hosomi-Sakurai allylation
  • R1, R2 = H, alkyl, aryl
Sakurai reaction - Hosomi-Sakurai reaction - Hosomi-Sakurai allylation - Sakurai allylation - general reaction scheme
Hosomi-Sakurai allylation
  • R1, R2R3 = alkyl, aryl
Sakurai reaction - Hosomi-Sakurai reaction - Hosomi-Sakurai allylation - Sakurai allylation - general reaction scheme
Hosomi-Sakurai allylation
  • R1, R3 = alkyl
  • R2 = alkyl, alkylsilyl

This reaction is also known as the Homosi-Sakurai reaction, Sakurai-Hosomi allylation, Sakurai allylation, and Sakurai addition.

The reaction leads to the regiospecific transposition of allylic moiety and the generation of new chiral center(s). When the electrophiles are acetals, the reaction may occur in the presence of a catalytic amount of Lewis acid, such as FeCl3. Other Lewis acids, including TiCl4, BF3·Et2O, SnCl4, AlCl3, TMSI, TMSOTf, TMSNTf2, Sc(OTf)3, Bi(OTf)3, and trityl perchlorate, have also been used as promoters or catalysts for the allylation of acetals (see list of acronyms). For electrophiles of aldehydes, even the use of an excess amount of Lewis acid (BF3·Et2O) does not significantly increase the yield of homoallylic alcohol, but a catalytic amount of FeCl3 can promote the allylation of aliphatic aldehydes.

In contrast, the allylation of alkylsilyl mixed acetals leads to the replacement of either an alkoxyl or an alkylsiloxyl group, depending on the Lewis acids applied. For the allylation of aldehydes with substituted allylsilane, such as crotylsilane, the syn-homoallylic alcohols form predominantly from either cis-crotylsilane or trans-crotylsilane. The allylation of aldehydes also results in the formation of ether. This reaction has been improved to occur in the presence of a catalytic amount of Lewis acids using allylsilyl chlorides instead of allyltrimethylsilane.”

References

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