Sakurai reaction

Sakurai the reaction ( more correctly called Hosomi - Sakurai reaction) is the reaction of an electrophilic compound, such as a carbonyl compound with a nucleophilic allylic silane, wherein a substituted β -allyl alcohol formed. The reaction is similar to the Grignard reaction, but operates only when the presence of strong Lewis acids such as titanium ( IV) chloride, boron (III ) fluoride or tin ( II) chloride as catalyst.

The reaction is named after the Japanese chemists Akira Hosomi and Hideki Sakurai, who in 1976 published the first time.

Analogous to the Grignard reaction is determined by the type of carbonyl compound employed, whether a primary ( of formaldehyde, R1 = R2 = H), secondary ( from other aldehydes, R1 = H, R2 = any group ≠ H) or tertiary ( from ketones R1, R2 are any residues ≠ H) alcohol is produced. Also α -keto- alkenes, imines, acetals, epoxides and carboxylic acid halides can be used.

Mechanism

The Lewis acid enhances the reactivity of the electrophile by increasing the partial positive charge. This is the nucleophilic addition, which is the rate-determining step allows you to:

The trimethylsilyl group does not behave as a Lewis acid. For this reason, a ring-shaped transition state is excluded. In reactions of substituted aldehydes can allylene with an antiperiplanar arrangement be adopted at the transition state: