Silyl zincates

Conjugate Addition Reactions. The cuprate and zincate reagents lithium bis[dimethyl(phenyl)silyl]cuprate (75583-57-2) and lithium dimethyl[dimethyl(phenyl)silyl]-zincate (100112-20-7) are usually used in conjugate addition reactions, but PhMe2 SiLi can be used with catalytic amounts of dimethylzinc (eq More resistant substrates may employ the zincate produced in situ, with catalytic amounts of copper(I) additives, and aided by the cocatalyst Sc(OTf)3 (eq 18). ... 

Straightforward 5-lithiation results using -BuLi with ethyl 3-mcthoxy-l -methyl-17/-pyrazol-4-earboxy late and halides, zincates, or boronic acids can thus be produced <2002SL769>. A neat device allows 3-lithiation of indazole silylation at N(2) allows the desired 3-metallation (Scheme 60) <2006EJ02417>. 

Zinc Reagents. Negishi coupling of a-zincated vinyltrimethylsilanes with 2-bromopyridine yields 2-vinylpyridine functionalized by a silyl substituent at the a-carbon of the vinyl group 214 (Scheme 81). Similarly, the trifluoroethenyl group has been substituted into the 2-position in pyridine 215 nsing zincated trifluoroethene and 2-iodopyridine. ... 

Xerulinic acid (151) inhibited the biosynthesis of cholesterol in HeLa S3 cells by blocking HMG-CoA synthase. Bisstannane 147 was transmetallated to the zincate intermediate and was Negishi cross-coupled with butenolide 148 to give the all tra 5-polyene 149. The Stille reaction of 149 with enediyne 150 followed by deprotection of the silyl group with tetrabutylammonium fluoride afforded xerulinic acid (151). 

As an analog of alkyl zincate, 5i -zincate was synthesized as early as in 1985 by Oshima and co-workers, using ZnR2 and silyllithium instead of alkyllithium (Eq. 9) [35]. In 1999, Krief and co-workers reported the synthesis of 5n-zincates from stannyllithium in a similar way [36]. Such Si- and Sn-zincates undergo silylzincation or silyl/stannyl Michael addition to unsaturated compounds. The Michael addition employing zincates has been well reviewed elsewhere, so it will not be considered in detail here [8]. Another application of S/-zincate, silylzincation, will be discussed later. 

The 5 -zincate could not react directly with alkenes [89]. However, in the presence of TM catalyst, the silylzincation could also take place at terminal alkenes. The first such example was reported in 2005 by our group (Table 11) [90]. Catalyzed by Cp2TiCl2, SiSiNOL-zincate and terminal alkenes could be regio- and chemoselectively transformed into allylsilanes. It seemed that in the metalation, the silyl group was specifically introduced at the 1-position and the elimination at the 3-position was favored to form E- or Z-alkenes. Many active groups could be compatible with these reactions. 

Beside silylzincation, Michael addition using S/-zincate could also introduce silyl groups into C-C unsaturated bonds. l,4-Additi(Mi by using Sn-zincate was also reported. Since studies on Michael addition using (heteroelement)-zincates have been well summarized elsewhere [8], the reaction will not be ccmsidered in detail in this chapter. 

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