Sakurai reaction mechanism

Sakurai M, Miyake N, Tsutsumi A, Yoshida K (1996) Analysis of a reaction mechanism in the UT-3... 

LiC104 was shown to be a more compatible Lewis acid for chelation in an ethereal solvent—when TiCU, a typical chelation agent for a-alkoxyaldehydes, was used in EtaO for alkylation of 79, moderate diastereoselectivity (68 32) was obtained. Rapid injection NMR studies of the TiCU-promoted chelation-controlled Mukaiyama aldol reaction and the Sakurai reaction show that an acyclic transition state must be involved in which the silyl groups never reach the carbonyl oxygen atom. In LPDE-mediated enolsilane additions silylated products predominate. Obviously, the mechanism is different—it is a group-transfer aldol reaction [107]. 

The Sakurai reaction involves the conjugate addition of an allylsilane to an a, -unsaturated ketone in the presence of a Lewis acid. Suggest a mechanism for the following intramolecular Sakurai reaction ... 

SCHEME 12.12 General mechanism for Hosomi-Sakurai reaction. 

The undefined mechanism of the aldol-type Mukaiyama and Sakurai allylation reactions arose the discussion and interest in mechanistic studies [143-145]. The proposed mechanism was proved to proceed through the catalytic activation of the aldehyde and its interaction with the silyl ketene acetal or allylsilane producing the intermediate. From that point the investigation is complicated with two possible pathways that lead either to the release of TMS triflate salt and its electrophihc attack on the trityl group in the intermediate or to the intramolecular transfer of the TMS group to the aldolate position resulting in the evolution of the trityl catalyst and the formation of the product (Scheme 51). On this divergence, series of experimental and spectroscopic studies were conducted. 

Sakurai and coworkers75 generated the five-membered silene 44 by a photochemical 1,3-silyl shift in the cyclic divinyldisilane 45 (Scheme 13). Since the silene 44 is constrained to be planar, no bond rotation is possible during the reaction. Contrary to the previous observations i.e. a simple two-step or a concerted four-centered mechanism, alcohols add to 44 nonstereospecifically, although in the cyclic silene bond rotation is prohibited. 

Bianchini, C., Glendenning, L. Homogeneous catalysis. Mechanisms of the catalytic Mukaiyama aldol and Sakurai allylation reactions. 

Hollis, T. K., Bosnich, B. Homogeneous Catalysis. Mechanisms of the Catalytic Mukaiyama Aldol and Sakurai Allylation Reactions. J. Am. Chem. Soc. 1995, 117, 4570-4581. 

Bianchini, C., Giendenning, L. Homogeneous cataiysis. Mechanisms of the cataiytic Mukaiyama aidoi and Sakurai aiiyiation reactions. Chemtracts Inorg. Chem. 1995, 7,107-111. 

Sakurai and coworkers have reported the interesting Si-Si bond-forming reaction in equation 109301. A mechanism for the reaction with the vinyldisilane was proposed to involve an >/3-silaallyl (Me2SiCHCH2) complex302,303. 

For mechanism a, there is no doubt that silylenes could add to alkynes to give silacyclopropenes. What is at issue is whether or not the dimerization of the silacyclopropene takes place. The evidence is as follows, (i) Stable silacyclopropenes have been recently prepared by Conlin and Gaspar from the reactions of SiMcj with 2-butyne, and by Seyferth and coworkers from the reactions of SiMcj with bis(trimethylsilyl)acetylene, and by Sakurai and coworkers from the photolysis of (pentamethyldisilanyl) phenylacetylene ... 

Ishitani O, Pac C, Sakurai H (1984) Redox-photosensitized reactions. 11. Ru(bpy)3 L photosensitized reactions of 1-benzyl-1,4-dihydronicotinamide with aryl-substituled enmies, derivatives of methyl cinnamate, and substituted cinnamonitriles electron-transfCT mechanism and structure-reactivity relationships. J Org Chem 49 26-34... 

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