Sakurai allylation reaction

The Sakurai reaction can be defined as the allylation of a carbonyl compound, or equivalent thereof, performed with an allylsilane and promoted by a Lewis acid. 

This book chapter is limited to Lewis acid-mediated reactions, and does not discuss the important field of Lewis base-mediated allylations, nor does it describe the reactions of allylsilanes with other electrophiles such as epoxides, imines, and allyl-X (X = -Cl, -OR, -OAc). The SaJcurai reaction has been covered under different forms in reviews focusing on The Stereochemistry of the Sakurai reaction , Intramolecular Addition Reactions of Allylic and Propargylic Silanes , Selective Reactions Using Allylic Metals , Catalytic Enantioselective Addition of Allylic Organometallic Reagents to Aldehydes and Ketones , and Modem Carbonyl Chemistry .  

The Sakurai reaction is most commonly performed in dichloromethane at -78 °C with one equivalent of Lewis acid. Diethyl ether and tetrahydrofuran are rarely used as solvents, because they sequester the Lewis acid as ethereal complexes. 

The most popular promoters are BF3 OEt2, TiCU, and SnCU. They are followed, arguably, by AICI3, AlC Et, and TMSOTf. Protic acids are used more rarely since they tend to cause an unwanted protodesilylation. BF3, TiCU, and SnCL have somewhat different properties. BF3 does not react with allylsilanes directly, and has only one coordination site. TiCU is also inert towards allylsilanes, even at room temperature, and has two coordination sites. TiCU forms 1 1 or 1 2 adducts with aldehydes, depending on the stoichiometry of the reagents. It can also form chelates with a- and P-alkoxyaldehydes, which influences the stereochemistry of the reaction (chelation control). TiCU is best used at low temperatures (-78 °C) to prevent the formation of unwanted chlorination products that appear at room temperature. The major characteristic of SnCU is that, in the presence of an allylsilane, it undergoes a transmetallation within minutes at -80 °C. Hence, 

Allylsilanes can be prepared by a wide array of methods, including (1) the reaction of allyl metals with ClSiRs, (2) the reaction of silylanions (MSiRs) with allylic substrates, (3) the Kumada coupling of Me3SiCH2MgBr with vinyl halides, catalyzed by Pd or Ni species, (4) the Wittig reaction of P-silylated Wittig reagents, (5) the cross-metathesis of olefins with allylsilanes, and (6) the reductive silylation of unsaturated compounds.  

Lewis acid-mediated addition of allylsilanes to carbon nucleophiles. Also known as the Hosomi-Sakurai reaction. The allylsilane will add to the carbonyl compound directly if the electrophile (carbonyl group) is not part of an a,p-unsatuiated system (Example 2), giving rise to an alcohol. 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 241, Springer International Publishing Switzerland 2014 

Hosomi, A. Sakurai, H. Tetrahedron Lett. 1976, 1295-1298. Hideki Sakurai was a professor at Tohuko University in Japan. This reaction is also known as the Hosomi-Sakurai reaction. 

Bonini, B. F. Comes-Franchini, M. Fochi, M. Mazzanti, G. Ricci, A. Varchi, G. 

Makino, C. Hisazumi, K. Sono, M. Nakashhna, K. Tetrahedron Asymmetry TDOl, 12, 301. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 226, Springer-Verlag Berlin Heidelberg 2009 

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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. 

Bismuth Triflate-Catalyzed Sakurai Allylation Reaction. 71... 

In the laboratory of B.M. Trost, a modular approach toward the total syntheses of furaquinocins was developed. To introduce the homoallylic side chain in a diastereoselective fashion, they utilized the Sakurai allylation reaction. During their studies they found that the highest diastereoselectivity can be achieved using 1 equivalent of TiCU at room temperature. Application of other Lewis acids such as BF3 OEt2 gave the product with lower selectivity. Attempts to perform the allylation using catalytic amounts of Lewis acids such as FeCIs or Sc(OTf)s led to no conversion. The resulting homoallylic alcohol served as a common intermediate toward the syntheses of both furaquinocin A and B. 

Sakurai allylation Reaction of allylsilanes with a variety of aldehydes and ketones in the presence of a Lewis acid. 392... 

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. 

Since the discovery of the Hosomi-Sakurai allylation reaction [332] much attention... 

Sakurai allylation reaction (Hosomi-Sakurai reaction)... 

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