Steric Effects of Silyl Groups

Hwu, R. Jih‐Ru; Tsay, Shwu‐Chen; Cheng, Buh‐Luen

doi:10.1002/0470857250.ch8

Cited by 6 publications

(3 citation statements)

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“…Steric Factors. Steric effects on silicon have been well documented and exploited . Indeed, the size of various silicon substituents has been used to control the reactivity of a neighboring group and the rate of nucleophilic substitution at the silicon.…”

Section: Discussionmentioning

confidence: 99%

A Qualitative Examination of the Effects of Silicon Substituents on the Efficiency of Cross-Coupling Reactions

et al. 2006

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A qualitative study of the effects of various substituents on the silicon atom in cross-coupling reactions of alkenylsilanes has been carried out. In intermolecular competition experiments, the influence of carbon-based groups (methyl, ethyl, isopropyl, tert-butyl, phenyl, and 3,3,3-trifluoropropyl) and alkoxy groups (monoethoxydimethyl-, diethoxymethyl-, and triethoxy) on the silicon have been evaluated under activation by two different methods, fluoride (TBAF) and silanolate (TMSOK). The influence of the substituents was highly dependent on the method of activation. In the presence of TBAF, there was only a modest steric effect (except for tert-butyl substituents), and the efficiency decreased slightly with increasing numbers of alkoxy groups. In the presence of TMSOK, a significant steric effect was noted, but the number of alkoxy groups had almost no influence. These trends were interpreted in terms of the divergent mechanisms for the cross-coupling process.

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Section: Discussionmentioning

confidence: 99%

A Qualitative Examination of the Effects of Silicon Substituents on the Efficiency of Cross-Coupling Reactions

et al. 2006

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“…Furthermore, replacement of the SiMe 3 group at position C-3 with a bulkier silyl group, , including SiMe 2 Ph, SiMePh 2 , and SiPh 3 , gave the corresponding 3-silyl-2-cyclohexen-1-ones 13 − 15 in 31%, 15%, and 0% yields, respectively. These results indicate that a smaller C-3 silyl group in the substrate provided a greater yield; the SiMe 3 group was the most effective one among various silyl groups tested.…”

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confidence: 99%

“…As first control experiments, we applied the same oxygenation conditions to 3-(isopropyl)-1-cyclohexenyl acetate ( 10 ) and the parent cyclohexenyl acetate ( 11 ). Although the isopropyl group in 10 and the trimethylsilyl group in 4 might exert a similar steric effect, the smooth oxidation of 10 with molecular dioxygen occurred to a negligible extent, as for the unsuccessful oxygenation of 11 . The thermal oxidation shown in Table was therefore induced by a silicon atom through its electronic effect.…”

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confidence: 99%

Silicon-Induced Ene-Type Reaction in the Thermal Conversion of Enolates to β-Silyl Enones with Molecular Dioxygen

et al. 2008

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Reaction of alkyl, acetoxy, and silyl enol ethers of 3-(organosilyl)cyclohexanone with molecular dioxygen in toluene at 110 degrees C produced the corresponding conjugated enones in yields up to 88% yield. The reaction of the same type failed on replacement of the silyl group at the C-3 position with an isopropyl group. These results indicate the existence of an unprecedented silicon-induced ene-type reaction. Its reaction mechanism, generality, limitations, and exceptions are discussed.

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