Chiral epoxysilanes

The cyclohexyloxy(dimethyl)silyl unit in 8 serves as a hydroxy surrogate and is converted into an alcohol via the Tamao oxidation after the allylboration reaction. The allylsilane products of asymmetric allylboration reactions of the dimethylphenylsilyl reagent 7 are readily converted into optically active 2-butene-l, 4-diols via epoxidation with dimethyl dioxirane followed by acid-catalyzed Peterson elimination of the intermediate epoxysilane. Although several chiral (Z)-y-alkoxyallylboron reagents were described in Section 1.3.3.3.3.1.4., relatively few applications in double asymmetric reactions with chiral aldehydes have been reported. One notable example involves the matched double asymmetric reaction of the diisopinocampheyl [(Z)-methoxy-2-propenyl]boron reagent with a chiral x/ -dialkoxyaldehyde87. 

A carbanion generated at the y-position of a,p-epoxysilanes via a process such as deprotonation can cause (3-ring opening to provide a-silyl alkoxides fScheme 6.4. Eq. 5). Taking into consideration the ready availability of enantiomerically pure epoxides, this method opens the possibility for using epoxides as a source of chiral carbanions via Brook rearrangement. 

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