Sakurai coupling

Entries 4 and 5 are examples of use of the Sakurai reaction to couple major fragments in multistage synthesis. In Entry 4 an unusual catalyst, a chiral acyloxyboronate (see p. 126) was used to effect an enantioselective coupling. (See p. 847 for another application of this catalyst.) Entry 5 was used in the construction of amphidinolide P, a compound with anticancer activity. 

Sakurai, T., Amemiya, A, Ishii, M. el al. (1998). Orexins and orexin receptors a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior. Cell 92, 573-85. 

Silole incorporation was noted above in Section 3.11.4.1.l.(iii) where poly( 1,1 -silole)s synthesized by Tamao and co-workers via Wurtz-type coupling were described. The related silole-incorporated polysilanes bearing silole units on every fifth silicon in a regular sequence prepared by Sakurai and co-workers using anionic ROP were described in Section 3.11.4.1.4. 

Okazaki, H., Ishizaka, N., Sakurai, T., Kurokawa, K.., Goto, K., Kumada, M. and Takuwa, Y., 1993, Molecular cloning of a novel putative G protein-coupled receptor expressed in the cardiovascular system, Bioc/jem. Biophys. Res. Comm. 190 1104-1109. 

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. 

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

Allyl- and vinylsilane chemistry was one of the first areas of reagent synthesis impacted by CM methodology. Allylsilanes are commonly employed in nucleophilic additions to carbonyl compounds, epoxides, and Michael acceptors (the Sakurai reaction) vinylsilanes are useful reagents for palladium-coupling reactions. As the ubiquitous application of CM to this substrate class has recently been described in several excellent reviews, this topic will not be discussed in detail, with the exception of the use of silane moieties to direct CM stereoselectivity (previously discussed in Section 11.06.3.2). 

The ene reaction is the major side reaction in the Sakurai-Hosomi coupling reaction. Thus, treatment of 221 with carbonyl or with azo compounds in the presence of TiCl2(OPr-/)2 furnishes a mixture of ene-type product 222 and the Sakurai-Hosomi-type product 223 (equation 182)327. Allylsilylation of alkenes328 and alkynes329-330 proceeds regioselectively to give 224 (equation 183) and 225 (equation 184), respectively when aluminum catalysts are used. 

Sakurai T, Amemiya A, Ishii M, Matsuzaki I, Chemelli RM, Tanaka H, Williams SC, Richarson JA, Kozlowski GP, Wilson S, Arch JR, Buckingham RE, Haynes AC, Carr SA, Annan RS, McNulty DE, Liu WS, Terrett JA, Elshourbagy NA, Bergsma DJ, Yanagisawa M (1998) Orexin and orexin receptors a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behaviour. Cell 92 573-585. 

TiCl4 is used extensively as a Lewis acid in numerous organic transformations, forming adducts that mediate reactivity. Such reactions include Diels Alder, 54,355 hetero Diels Alder,356 cyclization of olefinic aldehydes,357 Flosomi Sakurai allylic coupling reactions,358 cyclopropanations,359 chal-cogen-Baylis Flillman,360 Mukaiyama Aldol reactions,36 363 reductions of ketones to alcohols 364 and stereoselective nucleophilic additions to aldehydes.365... 

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