Silyl Grignard reagents reactions with

In 1999, Sekiguchi et al. prepared the first silyl acetylene dendrimers 255 and 256 with up to 22 Si atoms and 21 acetylene units (Schemes 35 and 36).358 The preparation of 255 and 256 has been achieved by the reaction of the triple Grignard reagent 257 with the trisila diyne 258 and the heptasila hexayne 259, respectively. 

Reactions of a-Silylated Grignard Reagents with Alkenyl Halides... 

Vinyl Grignard reagent reacts with the aldehyde function in the open-chain form of compound 6. leading initially to diol 25 with a diastereoselectivity of 71 2 antr.syn). The diasteromeric alcohols atn be separated after silylation to 7, but this is unnecessary since both isomers lead to the same product in the subsequent reaction. 

The formation of chiral silyllithium and silyl-Grignard reagents was also observed in the reactions of an optically active silyl-cobalt carbonyl complex93,94. Treatment of the chiral cobalt complex with methyllithium produced optically active silyllithium which hydrolysed to the corresponding hydrosilane (equation 26). 

The optical purity of the recovered hydrosilane indicated 70% retention of configuration in the overall process. In a similar way the reaction of methylmagnesium bromide with the silyl-cobalt complex afforded a chiral silyl-Grignard reagent (equation 27). 

This reaction is extended to the intramolecular ring closure of the intermediate radical 224 with olefinic or trimethylsilylacetylenic side chains [121]. Cu(BF4)2 is also effective as an oxidant (Scheme 89) [122]. Conjugate addition of Grignard reagents to 2-eyclopenten-l-one followed by cyclopropanation of the resulting silyl enol ethers gives the substituted cyclopropyl silyl ethers, which are oxidized to 4-substituted-2-cyclohexen-l-ones according to the above-mentioned method [123]. (Scheme 88 and 89)... 

This work was initiated in 1988 when Villacorta et al.71a reported the asymmetric conjugate addition of a Grignard reagent to 2-cyclohexenone. This study showed that 1,4-adducts with 4-14% ee were obtained in the presence of aminotroponeimine copper complex.713 Enhanced results (74% ee) were obtained by adding HMPA or silyl halides.71b Several other copper complexes were also used for inducing asymmetric conjugate addition reactions. Moderate results were obtained in most cases when THF was used as the solvent and HMPA as the additive. 

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