Sakurai-Hosomi reaction

Allylation of aldehydes or ketones using allylsilanes, known as the Hosomi-Sakurai reaction, is a useful method for obtaining homoallylic alcohols. TiIV compounds have been successfully applied to this reaction (Scheme 21) 80 Besides aldehydes and ketones, acylsilanes, 0,0-acetals, and A-,(7-acetals can be employed.81-83 1,4-Addition of an allyl group to an a,/ -unsaturated ketone has been also reported.84... 

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 it is not part of an a,P-unsaturated system (Example 2), giving rise to an alcohol. 

The introduction of the allylic silane moiety required for the intermolec-ular Hosomi-Sakurai reaction is depicted in Scheme 16. Following the formation of the enol triflate 97, a Stille coupling provided excess to the allylic alcohol 98 [51]. The allylic alcohol (98) was endowed with a phosphate leaving group for the subsequent allylic substitution. Utilizing a trimethylsilyl cuprate as nucleophile for the 5 2 reaction, the allylic phosphate was converted into the allylic silane 89. A useful substrate-induced diastereoselectivity in favour of (14i )-89 was encountered at small scale but decreased significantly upon up-scaling. 

The dihydropyran 88 served as the precursor for an oxocarbenium ion that was utilized as the acceptor for the intermolecular Hosomi-Sakurai reaction [53, 54]. Utilizing a second Hosomi-Sakurai reaction, pyran 88 was synthesized as outlined in Scheme 17 [53, 54]. Easy accessible MOM protect-... 

Scheme 18 Hosomi-Sakurai reaction and McMurry-type coupling as key transformations toward the completion of the (-l-)-deoxyneodolabellane (50) synthesis...

Hosomi-Sakurai reaction, allylsilations, 9, 305 Host complexes calixarenes as, 12, 799 crown-ethers as, 12, 813... 

The Hosomi Sakurai Reaction involves the Lewis acid-promoted allylation of various electrophiles with allyltrimethysilane. Activation by Lewis acids is critical for an efficient allylation to take place. 

A one-pot synthesis of 2,3>S-trisubstituted tetrahydrofurans by a double Hosomi-Sakurai reaction has been described. The product was obtained without the contamination of any regio- or stereoisomers. This remarkable selectivity has been explained by the difference in reactivity between the allylic starting material and the allylic silane formed in situ and between that of the two aldehydes employed (Scheme 80) <2004AGE1417>. 

Benzo[/][l,2]oxasilepines, which are available by RCM, have been employed in the synthesis of as- and trans-dihydrobenzoMfuran neolignans (Equation 145) <2005SL3011>. A mechanistic proposal for the stereochemical outcome of this variant of the Hosomi-Sakurai reaction has been given <2007CEJ557>. 

HOSOMI-SAKURAI REACTION Tita-nium(IV) chloride. 

Shing, T K M, Li, L H, Asymmetric Hosomi-Sakurai reaction of allylsilanes containing arabinose-derived alcohols as chiral auxiliaries, J. Org. Chem., 62, 1230-1233, 1997. 

In 1976 we reported that aldehydes and ketones are efficiently allylated with allyl-trimethylsilane in the presence of a substoichiometric amount of I iLf, [332]. Subsequently, BU4NF, a fluoride ion source, was found to be an effective catalyst of this allylation reaction [333]. After these initial reports of the Hosomi-Sakurai reaction, several allylsilanes, including highly functionalized compounds, were used for regio- and stereoselective allylation of a variety of carbon electrophiles [6, 13, 14, 334]. In the nineteen-eighties, some Lewis acids (TMSOTf [335], TMSI [336]... 

The Hosomi-Sakurai reaction of in situ-generated iminium salts were extensively... 

The Hosomi-Sakurai reaction is a powerful method for conjugate allylation of a,fi-unsaturated ketones [425], In the presence of TiCl4 the allylation occurs smoothly at the y-position of allylsilanes and the / -position of a, -unsaturated ketones. This highly regioselective process has been widely used for introduction of functionalized carbon chains and construction of carbocycles in natural product synthesis [6, 426]. When TBAF is used as catalyst, both conjugate addition and 1,2-addition occur competitively [333]. The fluoride ion-catalyzed procedure is, however, effec-... 

The intramolecular version of the Lewis-acid-promoted conjugate addition of allylsilanes to a,/ -unsaturated ketones (Hosomi-Sakurai reaction) has... 

For the synthesis of clerodane diterpenoids, Tokoroyama and co-workers examined another version of the intramolecular Hosomi-Sakurai reaction (108). Substrates 55.1 and 55.4 were cyclized to yield adducts 55.2-55.3 and 55.5-55.6, respectively (Scheme 55). 

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

Compound 12 was first subjected to the Hosomi-Sakurai reaction [6] to give 17, which was converted to 18 via m-chloroperbenzoic acid (MCPBA) oxidation etc. [7a, b]. The lithium salt of 19, derived from 1-0-benzylbutane-1,2(1 ), 4-triol, was added to 18 in tetrahydrofuran to give the adduct. Oxidation, desulfonylation, and removal of the benzylidene and ethoxyethyl groups gave the triol (20), which was readily converted to the aldehyde (segment B 16) [7b]. 

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. 

The 5-lactols and their acetylated derivatives (2, 8) are activated by acid to form oxonium cation intermediates (3, 9), which are attacked by nucleophiles to provide the substituted tetrahydropyrans with good stereoselectivity (Scheme 3) [13]. As the nucleophiles, allylsilane 4 (Hosomi-Sakurai reaction), silyl enol ethers 5 (Mukaiyama aldol) and EtaSiH (reduction) have frequently been used. Since the axial attack of the nucleophiles determines the product s... 

The acid-promoted Prins reaction between a homoaUyhc alcohol and an aldehyde is a weU-estabhshed synthesis of tetrahydropyrans (Scheme 4) [ 14,15]. While substituted tetrahydropyrans are often assembled by cyclizations forming a C - O bond, the Prins reaction undergoes cyclization by C - C bond formation. The Prins reaction of the silyl-modified substrates [16], which can be regarded as the intramolecular Hosomi-Sakurai reaction, is effectively activated by the allylsilane unit. The stereochemistry of the 2,6-cfs-form produced in the case of the exo-allylsilane unit is elucidated by the 6-membered transition state model, hi the cyclization of the ewdo-aUylsilane substrates, since the silyl group would be fixed on the axial position of the 6-membered transition states, the tetrahydropyrans with both 2,6-cis and fraws-forms can be synthesized (Panek Sect. 3.3.9). This type of cychzation was also... 

---