Hosomi Sakurai reaction

The Sakurai reaction (more correctly called the Hosomi-Sakurai reaction ) is the reaction of an electrophilic compound, such as a carbonyl compound , with a nucleophilic allylic silane , producing a substituted β-allyl alcohol. The reaction is comparable to the Grignard reaction , but only runs in the presence of strong Lewis acids such as titanium (IV) chloride , boron (III) fluoride , tin (II) chloride or AlCl (C ₂ H ₅ ) ₂ as Catalyst off.

The reaction is named after the Japanese chemists Akira Hosomi and Hideki Sakurai , who first published it in 1976. Analogous to the Grignard reaction, the type of carbonyl compound used determines whether a primary (from formaldehyde , R ¹ = R ² = H), secondary (from all other aldehydes , R ¹ = H, R ² = any radical ≠ H) or tertiary (from ketones , R ¹ , R ² any radicals ≠ H) alcohol is formed:

Also imines , acetals , epoxides and acyl halides can be used.

In the case of α, β-unsaturated ketones (R ¹ = e.g. alkyl), a 1,4 addition takes place:

mechanism

The Lewis acid increases the reactivity of the electrophile by increasing the positive partial charge. This enables nucleophilic addition, which is the rate-limiting step:

The trimethylsilyl group does not behave like a Lewis acid. For this reason, an annular transition state can be ruled out. In reactions of substituted allyls with aldehydes, an antiperiplanar arrangement can be assumed for the transition state:

Individual evidence

1. ↑ ^{a b} Akíra Hosomi, Hideki Sakurai: Syntheses of γ, δ- unsaturated alcohols from allylsilanes and carbonyl compounds in the presence of titanium tetrachloride . In: Tetrahedron Letters . tape 17 , no. April 16 , 1976, p. 1295-1298 , doi : 10.1016 / S0040-4039 (00) 78044-0 .
2. ↑ Portal for Organic Chemistry: Hosomi-Sakurai Reaction .
3. ↑ Portal for Organic Chemistry: Hosomi-Sakurai Reaction .
4. ↑ Portal for Organic Chemistry: Hosomi-Sakurai Reaction .