Chlorosilanes rearrangement

Hydrosilation of alkylcyclohexenes illustrates the ability of active catalytic complexes to isomerize olefins and the tendency chlorosilanes have to form primary alkyl adducts even if this requires a skeletal rearrange-... 

The Claisen rearrangement of lactonic enolates provides a new route to cycloalkenes. Cyclocitral was converted to the lactone (642) through a multistep sequence, the lactone deprotonated with LDA in THF at -78 °C, and the enolate quenched with f-butyldimethyl-chlorosilane (80JA6889, 6891). The crude ketene acetal (643) was heated at 110 °C for 10 h, and the product treated with fluoride ion to afford a single acid. Replacement of the quaternary carboxyl group by hydroxyl was accomplished through use of the carboxy inversion reaction (Scheme 147). The product (645) of this last reaction was identical with an authentic sample of widdrol in all respects excluding its optical rotation. 

As shown earlier (Figure 13.22), silyl ketene acetals can be prepared at -78 °C by the reaction of ester enolates with chlorosilanes. O-Allyl-O-silyl ketene acetals (A in Figure 14.48) are formed in this reaction if one employs allyl esters. Silyl ketene acetals of type A undergo [3,3]-rearrangements rapidly upon warming to room temperature. This variation of the Claisen rearrangement is referred to as the Ireland-Claisen rearrangement. 

The C vs P reactivity of phosphinomethanides towards silicon centers may be turned by the substitution pattern of both, the phosphinomethanide and the chlorosilane. Novel heterocycles, skeleton rearrangements and high coordinations numbers may be achieved. 9 and 14 potentially be precursors for a specific type of unsaturated silicon compounds, adding to the growing class of compoimds at the interface between organophosphorus and organosilicon chemistry. 

Summary The reaction of two equivalents of lithium phosphinomethanides with di- or trifunctional chlorosilanes yields novel five- and six-membered heterocycles by multistep rearrangements or transmetallation reactions. Silaethene intermediates and hypervalent intermediates are likely to be involved. The reaction of one or two equivalents of lithium phosphinomethanide Li[C(PMe2)2(SiMe2Ph)] TMEDA with pTolSiCb and ci QHbcii iCb yields novel penta- and hexacoordinated silicon complexes. Both are the first examples of truly hypervalent organosilicon species with phosphorus donors characterized by X-ray structure determination. 

The reactions with oxygen and MesSiCl, on the other hand, occurred without allylic rearrangement it is noteworthy that the presence of ether prevented any reaction of 67 with the chlorosilane (27). 

The hydridosilanes 5 offer the possibility of further derivatizations and rearrangements of the resultant products. Thus, chlorination of these compounds with carbon tetrachloride is expected to lead to the chlorosilanes 9. This, actually, was found for 5a,d,e,f>g (Scheme 1). The chlorosilanes 9 proved to be rather labile. After prolonged standing of 9 in CCI4 solution at room temperature a MesSiO/Cl interconversion occurred to give 10. In the case of the reaction of 5b,c with CCI4 no chlorosilanes 9b,c were found, but the chloroalkyldisiloxanes 10b,c were obtained directly. Obviously, the conversion of 9b,c, which probably act as intermediates in the formation of 10b,c, proceeds very fast, so that their isolation failed. 

C-Glycosides from glycosides and chlorosilanes Stereospecific conversion via rearrangement of O -silylglycosides... 

Chlorosilanes are reported to react with j8-ketostannanes to give in most cases the siloxyalkenes (95, 101), whereas chlorogermanes yield only the j8-ketogermane (95). On the other hand, j3-ketogermanes react with silyl iodides (chlorides are less reactive) to give rearranged siloxyalkenes (95). 

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