Alkenyl-, Vinyl-, and Allyl-silanes

Pyrolysis of phenylaminocarbonyl esters of j3-hydroxysilanes (prepared from ketones and Me3SiCH2MgBr) leads to mixtures of allyl- and vinyl-silanes, and may be of some preparative significance. Compound (94) is converted into other types of vinylsilanes (95) by successive treatment with Bu Li and an electrophile such as Bu Br, CO2, 

Fluoride ion, an effective nucleophile towards Si, enhances the nucleophilicity of alkynylsilanes towards carbonyl compounds, so that Bu 4NF is a useful catalyst in the synthesis of propargylic alcohols by this method. Similarly, Me NF is useful for generation of a vinylidenecarbene (98) from an a-chlorovinylsilane (99) the carbene is useful for synthesis of alkylidenecyclopropanes.  

Fluoride ion displaces McjSiF from compounds of type (102), and on quenching with water the Si-free oxiranes are obtained in good yield. Application of the reaction to derivatives of type (103) gives access to the allene oxide (104).  

Pyrolysis of epoxysilanes gives silyl enol ethers, though often as a mixture of isomers.Another route to silyl enol ethers involves direct silylation of ketones, and Me3SiCH3C02Et, with Bu NF as catalyst, is a useful reagent in this respect. 

The same reagent is also useful for other silylationsT Carbonyl compounds devoid of acidic hydrogen atoms undergo a Reformatsky-type reaction with the intermediate BuSN+ CHjCOjEt formed in the reaction of MCiSiCHjCO Et with Bu2NF. 

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Silicon.—Alkenyl, Vinyl-, and Allyl-silanes. Hydroboration of alkynylsilanes proceeds stereospecifically, subsequent carbodeboronation leading to stereochemically defined vinylsilanes (Scheme 26). A similar route using hydroalumination can also be employed, but the stereochemistry is dependent upon the conditions of the hydroalumination step (product of cw-hydroalumination in ether-hexane, transin hexane alone). ... 

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