New Computational and Experimental Evidence for the Mechanism of the Sakurai Reaction

Abstract

Reaction of aldehydes with allyltrimethylsilane promoted by BF3 (Sakurai reaction) affords fluorotrimethylsilane and a borylated homoallylic alcohol in a noncatalytic fashion. These reaction products have been identified through 13C NMR and 29Si NMR. A model system formed by acetaldehyde, allylsilane, and BH2F has been used to investigate the mechanism of this reaction at the DFT computational level. Four transition states, quite close in energy, have been found for the model reaction. These transition states, which explain the stereochemical features of the Sakurai reaction, correspond to eight-membered cyclic structures deriving from C−C (tight) and Si−F (loosen) bond formation and synclynal (gauche) disposition of the reacting double bonds. No antiperiplanar or six-membered cyclic transition structures have been located.

Catalytic Enantioselective Addition of Allylic Organometallic Reagents to Aldehydes and Ketones

“…40 On the basis of computational Scheme 8 studies, Bottoni proposed an eight-membered transition structure with one of the fluorine atoms coordinating to the silicon. In this picture, the formation of the C-C and Si-F bonds and the breaking of the Si-C and B-F bonds occurs in a highly asynchronous, concerted manner.…”

Diastereoselective Synthesis of 2‐Aryl‐3‐vinyl‐2,3‐dihydrobenzo[b]furans through a Sakurai Reaction: A Mechanistic Proposal

“…Bottoni et al have investigated the mechanism of the Sakurai reaction at the DFT computational level. [47] They found four transition states, quite close in energy, for a model reaction with acetaldehyde, allylsilane and BH 2 F, and predicted two of them (each one leading to a different diastereomer) to be associated to the most likely reaction channels in real systems. These are eight-membered cyclic structures, one resembling the boat-boat (BB, TS A) conformation of cyclooctane and the other a type of boat-chair (BC, TS B), in which one of the fluorine atoms from the BF 3 coordinated to the aldehyde approaches the silicon atom, while at the same time the C=C double bond adds to the carbonyl C=O (Scheme 5).…”

GaI3 Catalysed Nucleophilic Addition of Allyltrimethylsilane to Aldehydes

“…Some powerful Lewis acids such as TiCl 4 , BF 3 •Et 2 O, SnCl 4 have been employed to catalyze the reaction because the reactivity of allyltrimethylsilane is not high enough. [4][5][6] Metal triflates such as Sc(OTf) 3 have been found to be effective for this transformation, 7 and YbCl 3 has also been used in this reaction. 8 However, there are always some drawbacks with these procedures.…”