Sakurai reaction Allyltrimethylsilane

Lithium diallylcuprate, 11 Lithium dibutylcuprate, 61 Lithium dimethylcuprate, 63, 258 Sakurai reaction Alkylaluminum halides, 5 Allyltrimethylsilane, 11, 305 Titanium(IV) chloride, 304 with other organometallic agents (IS, 2S) -2-Amino-3-methoxy-1 -pheny 1-1-propanol, 17... 

Another type of convertible nucleoside phosphoramidite, a derivative of (5 S)-5 -C-(5-bromo-2-penten-l-yl)-2 -deoxyribosylfuranosyl thymidine (49), has been reported. The synthesis of this phosphoramidite was stereoselective and involved a Sakurai reaction between 5 -C-thymidine aldehyde and allyltrimethylsilane. Seela has reported the synthesis of the ribosyl-phosphoramidite derivatives of 7-bromo- and 7-iodo-8-aza-7-deazapurine-2,6-diamine (50a,b) from advanced synthetic precursors and of the bromo- and iodo-derivatives at the 5-position of uracyl phosphoramidite (51a,b). He further described the effect on base-pair stability due to their incorporation into oligonucleotide duplexes. ... 

An example of attaching a carbon nucleophile to an o, j8-unsaturated ketone is the Sakurai reaction. This involves the reaction of allyltrimethylsilane with an a,fi-unsaturated ketone to form a -unsaturated ketone in the presence of a Lewis acid. Howarth used indium(iii) chloride to catalyze this reaction in the ionic liquids [BMIM][BF4] and [BMIM][PF6] [207]. An example ofthis is shovm in Scheme 5.2-83. 

Modified Sakurai reaction.- The original reaction involved the TiCU-catalyzed addition of allyltrimethylsilane to aldehydes and ketones or the acetals and ketals to form homoallylic alcohols or ethers (7,370-371). Marko et al. have extended this reaction to a synthesis of homoallylic ethers by a Lewis acid catalyzed reaction of allyltrimethylsilane with a carbonyl compound and a trimethylsilyl ether. 

Another short synthesis of ( )-9a-ep(-quinolizidine 195C (rat-2318), by Mann and coworkers, is worth mentioning in view of its use of a Hnear hydroformylation of a homoallylamine (cyclohydrocarbonylation) to constmct the piperidine ring (Scheme 296). ° A three-component aza-Hosomi—Sakurai reaction between allyltrimethylsilane, butanal, and O-benzylurethane catalyzed by boron trifluoride was used to form the protected homoallylamine ( )-2319. The cyclohydrocarbonylation was then performed with a biphephos/rhodium(I) catalytic system in methanol, yielding the piperidine-containing hemiaminal 2320 in 84% yield. This... 

The reaction of 179 with allyltrimethylsilane and TiCU illustrates the limit of the Sakurai reaction in the presence of acid-sensitive protecting groups (Boc, trityl, acetonide). Ikota obtained a remarkable 21% yield (it could have been worse) by quenching the reaction at -78 °C with NaOH. The Sakurai reaction was not an optimal choice in this case. The reaction proceeded better using allylmagnesium chloride (180 60%, 181 24%) or allyllithium (180 68%, 181 13%) in THF at -78 °C. The interest of the experimental procedure is the work-up that minimizes the unwanted deprotections. 

Conjugate addition to acyclic Michael acceptors. Sakurai and Hosomi (9, 445-446) reported one example of the fluoride ion-catalyzed reaction of allyltrimethylsilane with an acyclic enone. In that case (reaction with C6H5CH=CHCOCH,). 1.2- and 1,4-adducts are obtained in the ratio 2 1.1,4-Addition is enhanced by use of DMF and HMPT as solvent and by increase in the size of the group adjacent to the carbonyl group. 1,4-Addition is the main or predominant reaction with a,3-unsaturated esters or nitriles. In this case, it is superior to or competitive with allylation with lithium diallylcuprate. Yields in 1,4-additions to a,p-enones can compare favorably with those obtained with reactions catalyzed by TiC. ... 

The use of C2-symmetric 1,2- and 1,3-diols as chiral auxiliaries is a reliable method for asymmetric allylation of acetals [382]. Acyclic acetals derived from homochiral 1-phenylethanol undergo the Hosomi-Sakurai allylation with high diastereoselectivity [383]. Tietze et al. have, on the other hand, reported that the TMSOTf-catalyzed successive acetalization-allylation reaction of aliphatic aldehydes with homochiral silyl ethers 123 and allyltrimethylsilane gives the corresponding homoallyl ethers with complete diastereocontrol these ethers can be readily converted into enantiomerically pure homoallyl alcohols without epimerization (Scheme 10.135) [384]. This method is applicable to asymmetric allylation of methyl ketones [385]. 

Sabitha et al. [81] developed a simple and efficient one-pot synthetic strategy for the synthesis of symmetrical 4-amido tetrahydropyrans 56 via the Sakurai-Prins-Ritter reaction sequence using molecular iodine as the catalyst by the reaction of aldehyde and allyltrimethylsilane in acetonitrile at room temperature (Scheme 10.38). 

The InCl3-TMSCl catalytic pair was found to be effective in the catalysis of the conjugate addition of allyltrimethylsilanes to enones, a variation of the Sakurai-Hosomi reaction, in a report by Lee et al [58] (Figure 8.32). The authors had also demonstrated the superiority of this catalyst pair over various other In(III) catalysts, AICI3, and TiCU. A similar work using the InCU-TMSCl catalytic pair (20 mol% of InCl3 and 4 equivalents of TMSCl) was also reported to work in ionic liquids by Howarth et al with comparable yields [59]. 

In the pioneering works by Hosomi and Sakurai, a stoichiometric or substoichio-metric amount of TiCU, a conventional Lewis acid, was used for the carbonyl allylation with allylsilanes [106]. Davis and coworkers found that TMS borates such as Me3Si[BX(OTf)3] (X = OTf, Cl) enables an efficient, catalytic Hosomi-Sakurai allylation of aldehydes although (la) and Me3SiI show low catalytic activities (Scheme 9.41) [18, 107]. Ishihara and Yamamoto have demonstrated the utility of (lb) as Lewis acid catalyst of the carbonyl allylation as well as the Mukaiyama aldol reaction [15]. The silicon Lewis acid (lb), generated in situ by the reaction of allyltrimethylsilane with HNTf2, efficiently promotes the allylation of aldehydes and ketones with a loading of 0.5 mol% (Scheme 9.41). 

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