Mono-oxygenated silanes

Oxygenated Silanes. Controlled introduction of oxygen substituents onto silicon is an interesting special case, since several syntheses are possible. For mono-oxygenated compounds, one can simply react a chloro-(chloromethyl)silane with two equivalents of triazole and then displace the labile silicon-bound triazole with water or an alcohol. However, a better alternative in practice is to introduce first an alcohol and then triazole. In this case, the hydroxy compound can be prepared by hydrolysis of the silyl ether with aqueous acid. Scheme II outlines these options. 

Structure-activity for oxygenated silanes is presented in Table II. Mono-oxy compounds were highly active, but those with two oxygens attached to silicon were less interesting. 

Alkyl silyl ethers are cleaved by a variety of reagents Whether the silicon-oxygen or the carbon-oxygen bond is cleaved depends on the nature of the reagent used Treatment of alkoxysilanes with electrophilic reagents like antimony tri-fluonde, 40% hydrofluonc acid, or a boron tnfluonde-ether complex results in the cleavage of the silicon-oxygen bond to form mono-, di-, and tnfluorosiloxanes or silanes [19, 20, 21) (equations 18-20)... 

The mono-alkoxy product from (+)-ethyl lactate and diisopropylsilane (le) is shown to be more reactive than la and If (Scheme 31). We can only speculate at this time that there may be some intramolecular interactions between the Lewis basic carbonyl oxygen of the (+)-ethyl lactate and the silicon atom, which may either, activate the silane towards oxidative addition to the metal catalyst or increase the rate at which the silane-metal complex is attacked by the nucleophilic alcohol. 

The low regioselectivity of the enc reaction of singlet oxygen with mono-alkenes can also be improved by incorporation of trialkylsilyl groups at a vinylic position. Thus, simple vinyl-silanes afforded, after photooxygenation and reduction, regioselectively, /1-silyl allylic alcohols35. The diastereoseleclivity of the titanium-catalyzed reaction of the /1-silyl allylic hydroperoxides is described in Section 4.9.4.2. 

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